down integrate to svn

78 files changed, 9061 insertions, 1998 deletions

diff --git a/src/google/protobuf/compiler/code_generator.cc b/src/google/protobuf/compiler/code_generator.cc
index 455c239a..bc4800a6 100644
--- a/src/google/protobuf/compiler/code_generator.cc
+++ b/src/google/protobuf/compiler/code_generator.cc
@@ -44,6 +44,11 @@ namespace compiler {
 CodeGenerator::~CodeGenerator() {}
 GeneratorContext::~GeneratorContext() {}
 
+io::ZeroCopyOutputStream*
+GeneratorContext::OpenForAppend(const string& filename) {
+  return NULL;
+}
+
 io::ZeroCopyOutputStream* GeneratorContext::OpenForInsert(
     const string& filename, const string& insertion_point) {
   GOOGLE_LOG(FATAL) << "This GeneratorContext does not support insertion.";
@@ -58,8 +63,7 @@ void GeneratorContext::ListParsedFiles(
 // Parses a set of comma-delimited name/value pairs.
 void ParseGeneratorParameter(const string& text,
                              vector<pair<string, string> >* output) {
-  vector<string> parts;
-  SplitStringUsing(text, ",", &parts);
+  vector<string> parts = Split(text, ",", true);
 
   for (int i = 0; i < parts.size(); i++) {
     string::size_type equals_pos = parts[i].find_first_of('=');
diff --git a/src/google/protobuf/compiler/code_generator.h b/src/google/protobuf/compiler/code_generator.h
index 252f68d1..541f784c 100644
--- a/src/google/protobuf/compiler/code_generator.h
+++ b/src/google/protobuf/compiler/code_generator.h
@@ -104,6 +104,9 @@ class LIBPROTOC_EXPORT GeneratorContext {
   // contain "." or ".." components.
   virtual io::ZeroCopyOutputStream* Open(const string& filename) = 0;
 
+  // Similar to Open() but the output will be appended to the file if exists
+  virtual io::ZeroCopyOutputStream* OpenForAppend(const string& filename);
+
   // Creates a ZeroCopyOutputStream which will insert code into the given file
   // at the given insertion point.  See plugin.proto (plugin.pb.h) for more
   // information on insertion points.  The default implementation
diff --git a/src/google/protobuf/compiler/command_line_interface.cc b/src/google/protobuf/compiler/command_line_interface.cc
index b9293c97..358d6462 100644
--- a/src/google/protobuf/compiler/command_line_interface.cc
+++ b/src/google/protobuf/compiler/command_line_interface.cc
@@ -49,8 +49,10 @@
 #include <ctype.h>
 
 #include <google/protobuf/stubs/hash.h>
+#include <memory>
 
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/stubs/stringprintf.h>
 #include <google/protobuf/compiler/importer.h>
 #include <google/protobuf/compiler/code_generator.h>
 #include <google/protobuf/compiler/plugin.pb.h>
@@ -64,7 +66,7 @@
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
-#include <google/protobuf/stubs/map-util.h>
+#include <google/protobuf/stubs/map_util.h>
 #include <google/protobuf/stubs/stl_util.h>
 
 
@@ -160,8 +162,7 @@ bool VerifyDirectoryExists(const string& path) {
 // directories listed in |filename|.
 bool TryCreateParentDirectory(const string& prefix, const string& filename) {
   // Recursively create parent directories to the output file.
-  vector<string> parts;
-  SplitStringUsing(filename, "/", &parts);
+  vector<string> parts = Split(filename, "/", true);
   string path_so_far = prefix;
   for (int i = 0; i < parts.size() - 1; i++) {
     path_so_far += parts[i];
@@ -252,6 +253,7 @@ class CommandLineInterface::GeneratorContextImpl : public GeneratorContext {
 
   // implements GeneratorContext --------------------------------------
   io::ZeroCopyOutputStream* Open(const string& filename);
+  io::ZeroCopyOutputStream* OpenForAppend(const string& filename);
   io::ZeroCopyOutputStream* OpenForInsert(
       const string& filename, const string& insertion_point);
   void ListParsedFiles(vector<const FileDescriptor*>* output) {
@@ -271,7 +273,8 @@ class CommandLineInterface::GeneratorContextImpl : public GeneratorContext {
 class CommandLineInterface::MemoryOutputStream
     : public io::ZeroCopyOutputStream {
  public:
-  MemoryOutputStream(GeneratorContextImpl* directory, const string& filename);
+  MemoryOutputStream(GeneratorContextImpl* directory, const string& filename,
+                     bool append_mode);
   MemoryOutputStream(GeneratorContextImpl* directory, const string& filename,
                      const string& insertion_point);
   virtual ~MemoryOutputStream();
@@ -290,6 +293,9 @@ class CommandLineInterface::MemoryOutputStream
   // The string we're building.
   string data_;
 
+  // Whether we should append the output stream to the existing file.
+  bool append_mode_;
+
   // StringOutputStream writing to data_.
   scoped_ptr<io::StringOutputStream> inner_;
 };
@@ -434,7 +440,13 @@ void CommandLineInterface::GeneratorContextImpl::AddJarManifest() {
 
 io::ZeroCopyOutputStream* CommandLineInterface::GeneratorContextImpl::Open(
     const string& filename) {
-  return new MemoryOutputStream(this, filename);
+  return new MemoryOutputStream(this, filename, false);
+}
+
+io::ZeroCopyOutputStream*
+CommandLineInterface::GeneratorContextImpl::OpenForAppend(
+    const string& filename) {
+  return new MemoryOutputStream(this, filename, true);
 }
 
 io::ZeroCopyOutputStream*
@@ -446,9 +458,10 @@ CommandLineInterface::GeneratorContextImpl::OpenForInsert(
 // -------------------------------------------------------------------
 
 CommandLineInterface::MemoryOutputStream::MemoryOutputStream(
-    GeneratorContextImpl* directory, const string& filename)
+    GeneratorContextImpl* directory, const string& filename, bool append_mode)
     : directory_(directory),
       filename_(filename),
+      append_mode_(append_mode),
       inner_(new io::StringOutputStream(&data_)) {
 }
 
@@ -471,8 +484,12 @@ CommandLineInterface::MemoryOutputStream::~MemoryOutputStream() {
   if (insertion_point_.empty()) {
     // This was just a regular Open().
     if (*map_slot != NULL) {
-      cerr << filename_ << ": Tried to write the same file twice." << endl;
-      directory_->had_error_ = true;
+      if (append_mode_) {
+        (*map_slot)->append(data_);
+      } else {
+        cerr << filename_ << ": Tried to write the same file twice." << endl;
+        directory_->had_error_ = true;
+      }
       return;
     }
 
@@ -565,6 +582,7 @@ CommandLineInterface::MemoryOutputStream::~MemoryOutputStream() {
 
 CommandLineInterface::CommandLineInterface()
   : mode_(MODE_COMPILE),
+    print_mode_(PRINT_NONE),
     error_format_(ERROR_FORMAT_GCC),
     imports_in_descriptor_set_(false),
     source_info_in_descriptor_set_(false),
@@ -632,7 +650,9 @@ int CommandLineInterface::Run(int argc, const char* const argv[]) {
   // Parse each file.
   for (int i = 0; i < input_files_.size(); i++) {
     // Import the file.
+    importer.AddUnusedImportTrackFile(input_files_[i]);
     const FileDescriptor* parsed_file = importer.Import(input_files_[i]);
+    importer.ClearUnusedImportTrackFiles();
     if (parsed_file == NULL) return 1;
     parsed_files.push_back(parsed_file);
 
@@ -721,6 +741,25 @@ int CommandLineInterface::Run(int argc, const char* const argv[]) {
     }
   }
 
+  if (mode_ == MODE_PRINT) {
+    switch (print_mode_) {
+      case PRINT_FREE_FIELDS:
+        for (int i = 0; i < parsed_files.size(); ++i) {
+          const FileDescriptor* fd = parsed_files[i];
+          for (int j = 0; j < fd->message_type_count(); ++j) {
+            PrintFreeFieldNumbers(fd->message_type(j));
+          }
+        }
+        break;
+      case PRINT_NONE:
+        GOOGLE_LOG(ERROR) << "If the code reaches here, it usually means a bug of "
+                     "flag parsing in the CommonadLineInterface.";
+        return 1;
+
+      // Do not add a default case.
+    }
+  }
+
   return 0;
 }
 
@@ -735,6 +774,7 @@ void CommandLineInterface::Clear() {
   descriptor_set_name_.clear();
 
   mode_ = MODE_COMPILE;
+  print_mode_ = PRINT_NONE;
   imports_in_descriptor_set_ = false;
   source_info_in_descriptor_set_ = false;
   disallow_services_ = false;
@@ -889,7 +929,8 @@ bool CommandLineInterface::ParseArgument(const char* arg,
       *name == "--include_imports" ||
       *name == "--include_source_info" ||
       *name == "--version" ||
-      *name == "--decode_raw") {
+      *name == "--decode_raw" ||
+      *name == "--print_free_field_numbers") {
     // HACK:  These are the only flags that don't take a value.
     //   They probably should not be hard-coded like this but for now it's
     //   not worth doing better.
@@ -919,8 +960,8 @@ CommandLineInterface::InterpretArgument(const string& name,
     // Java's -classpath (and some other languages) delimits path components
     // with colons.  Let's accept that syntax too just to make things more
     // intuitive.
-    vector<string> parts;
-    SplitStringUsing(value, kPathSeparator, &parts);
+    vector<string> parts = Split(
+        value, kPathSeparator, true);
 
     for (int i = 0; i < parts.size(); i++) {
       string virtual_path;
@@ -1061,6 +1102,19 @@ CommandLineInterface::InterpretArgument(const string& name,
 
     plugins_[plugin_name] = path;
 
+  } else if (name == "--print_free_field_numbers") {
+    if (mode_ != MODE_COMPILE) {
+      cerr << "Cannot use " << name << " and use --encode, --decode or print "
+           << "other info at the same time." << endl;
+      return PARSE_ARGUMENT_FAIL;
+    }
+    if (!output_directives_.empty() || !descriptor_set_name_.empty()) {
+      cerr << "Cannot use " << name
+           << " and generate code or descriptors at the same time." << endl;
+      return PARSE_ARGUMENT_FAIL;
+    }
+    mode_ = MODE_PRINT;
+    print_mode_ = PRINT_FREE_FIELDS;
   } else {
     // Some other flag.  Look it up in the generators list.
     const GeneratorInfo* generator_info =
@@ -1082,8 +1136,8 @@ CommandLineInterface::InterpretArgument(const string& name,
     } else {
       // It's an output flag.  Add it to the output directives.
       if (mode_ != MODE_COMPILE) {
-        cerr << "Cannot use --encode or --decode and generate code at the "
-                "same time." << endl;
+        cerr << "Cannot use --encode, --decode or print .proto info and "
+                "generate code at the same time." << endl;
         return PARSE_ARGUMENT_FAIL;
       }
 
@@ -1151,7 +1205,12 @@ void CommandLineInterface::PrintHelpText() {
 "                              well as surrounding comments.\n"
 "  --error_format=FORMAT       Set the format in which to print errors.\n"
 "                              FORMAT may be 'gcc' (the default) or 'msvs'\n"
-"                              (Microsoft Visual Studio format)." << endl;
+"                              (Microsoft Visual Studio format).\n"
+"  --print_free_field_numbers  Print the free field numbers of the messages\n"
+"                              defined in the given proto files. Groups share\n"
+"                              the same field number space with the parent \n"
+"                              message. Extension ranges are counted as \n"
+"                              occupied fields numbers."  << endl;
   if (!plugin_prefix_.empty()) {
     cerr <<
 "  --plugin=EXECUTABLE         Specifies a plugin executable to use.\n"
@@ -1431,6 +1490,113 @@ void CommandLineInterface::GetTransitiveDependencies(
   }
 }
 
+namespace {
+
+// Utility function for PrintFreeFieldNumbers.
+// Stores occupied ranges into the ranges parameter, and next level of sub
+// message types into the nested_messages parameter.  The FieldRange is left
+// inclusive, right exclusive. i.e. [a, b).
+//
+// Nested Messages:
+// Note that it only stores the nested message type, iff the nested type is
+// either a direct child of the given descriptor, or the nested type is a
+// decendent of the given descriptor and all the nodes between the
+// nested type and the given descriptor are group types. e.g.
+//
+// message Foo {
+//   message Bar {
+//     message NestedBar {}
+//   }
+//   group Baz = 1 {
+//     group NestedBazGroup = 2 {
+//       message Quz {
+//         message NestedQuz {}
+//       }
+//     }
+//     message NestedBaz {}
+//   }
+// }
+//
+// In this case, Bar, Quz and NestedBaz will be added into the nested types.
+// Since free field numbers of group types will not be printed, this makes sure
+// the nested message types in groups will not be dropped. The nested_messages
+// parameter will contain the direct children (when groups are ignored in the
+// tree) of the given descriptor for the caller to traverse. The declaration
+// order of the nested messages is also preserved.
+typedef pair<int, int> FieldRange;
+void GatherOccupiedFieldRanges(const Descriptor* descriptor,
+                               set<FieldRange>* ranges,
+                               vector<const Descriptor*>* nested_messages) {
+  set<const Descriptor*> groups;
+  for (int i = 0; i < descriptor->field_count(); ++i) {
+    const FieldDescriptor* fd = descriptor->field(i);
+    ranges->insert(FieldRange(fd->number(), fd->number() + 1));
+    if (fd->type() == FieldDescriptor::TYPE_GROUP) {
+      groups.insert(fd->message_type());
+    }
+  }
+  for (int i = 0; i < descriptor->extension_range_count(); ++i) {
+    ranges->insert(FieldRange(descriptor->extension_range(i)->start,
+                              descriptor->extension_range(i)->end));
+  }
+  // Handle the nested messages/groups in declaration order to make it
+  // post-order strict.
+  for (int i = 0; i < descriptor->nested_type_count(); ++i) {
+    const Descriptor* nested_desc = descriptor->nested_type(i);
+    if (groups.find(nested_desc) != groups.end()) {
+      GatherOccupiedFieldRanges(nested_desc, ranges, nested_messages);
+    } else {
+      nested_messages->push_back(nested_desc);
+    }
+  }
+}
+
+// Utility function for PrintFreeFieldNumbers.
+// Actually prints the formatted free field numbers for given message name and
+// occupied ranges.
+void FormatFreeFieldNumbers(const string& name,
+                            const set<FieldRange>& ranges) {
+  string output;
+  StringAppendF(&output, "%-35s free:", name.c_str());
+  int next_free_number = 1;
+  for (set<FieldRange>::iterator i = ranges.begin();
+       i != ranges.end(); ++i) {
+    // This happens when groups re-use parent field numbers, in which
+    // case we skip the FieldRange entirely.
+    if (next_free_number >= i->second) continue;
+
+    if (next_free_number < i->first) {
+      if (next_free_number + 1 == i->first) {
+        // Singleton
+        StringAppendF(&output, " %d", next_free_number);
+      } else {
+        // Range
+        StringAppendF(&output, " %d-%d", next_free_number, i->first - 1);
+      }
+    }
+    next_free_number = i->second;
+  }
+  if (next_free_number <= FieldDescriptor::kMaxNumber) {
+    StringAppendF(&output, " %d-INF", next_free_number);
+  }
+  cout << output << endl;
+}
+
+}  // namespace
+
+void CommandLineInterface::PrintFreeFieldNumbers(
+    const Descriptor* descriptor) {
+  set<FieldRange> ranges;
+  vector<const Descriptor*> nested_messages;
+  GatherOccupiedFieldRanges(descriptor, &ranges, &nested_messages);
+
+  for (int i = 0; i < nested_messages.size(); ++i) {
+    PrintFreeFieldNumbers(nested_messages[i]);
+  }
+  FormatFreeFieldNumbers(descriptor->full_name(), ranges);
+}
+
+
 
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/command_line_interface.h b/src/google/protobuf/compiler/command_line_interface.h
index 86ea9bde..3b734150 100644
--- a/src/google/protobuf/compiler/command_line_interface.h
+++ b/src/google/protobuf/compiler/command_line_interface.h
@@ -48,8 +48,9 @@
 namespace google {
 namespace protobuf {
 
-class FileDescriptor;        // descriptor.h
+class Descriptor;            // descriptor.h
 class DescriptorPool;        // descriptor.h
+class FileDescriptor;        // descriptor.h
 class FileDescriptorProto;   // descriptor.pb.h
 template<typename T> class RepeatedPtrField;  // repeated_field.h
 
@@ -259,6 +260,22 @@ class LIBPROTOC_EXPORT CommandLineInterface {
       set<const FileDescriptor*>* already_seen,
       RepeatedPtrField<FileDescriptorProto>* output);
 
+  // Implements the --print_free_field_numbers. This function prints free field
+  // numbers into stdout for the message and it's nested message types in
+  // post-order, i.e. nested types first. Printed range are left-right
+  // inclusive, i.e. [a, b].
+  //
+  // Groups:
+  // For historical reasons, groups are considered to share the same
+  // field number space with the parent message, thus it will not print free
+  // field numbers for groups. The field numbers used in the groups are
+  // excluded in the free field numbers of the parent message.
+  //
+  // Extension Ranges:
+  // Extension ranges are considered ocuppied field numbers and they will not be
+  // listed as free numbers in the output.
+  void PrintFreeFieldNumbers(const Descriptor* descriptor);
+
   // -----------------------------------------------------------------
 
   // The name of the executable as invoked (i.e. argv[0]).
@@ -295,11 +312,19 @@ class LIBPROTOC_EXPORT CommandLineInterface {
   enum Mode {
     MODE_COMPILE,  // Normal mode:  parse .proto files and compile them.
     MODE_ENCODE,   // --encode:  read text from stdin, write binary to stdout.
-    MODE_DECODE    // --decode:  read binary from stdin, write text to stdout.
+    MODE_DECODE,   // --decode:  read binary from stdin, write text to stdout.
+    MODE_PRINT,    // Print mode: print info of the given .proto files and exit.
   };
 
   Mode mode_;
 
+  enum PrintMode {
+    PRINT_NONE,               // Not in MODE_PRINT
+    PRINT_FREE_FIELDS,        // --print_free_fields
+  };
+
+  PrintMode print_mode_;
+
   enum ErrorFormat {
     ERROR_FORMAT_GCC,   // GCC error output format (default).
     ERROR_FORMAT_MSVS   // Visual Studio output (--error_format=msvs).
diff --git a/src/google/protobuf/compiler/command_line_interface_unittest.cc b/src/google/protobuf/compiler/command_line_interface_unittest.cc
index 16559923..9e244da3 100644
--- a/src/google/protobuf/compiler/command_line_interface_unittest.cc
+++ b/src/google/protobuf/compiler/command_line_interface_unittest.cc
@@ -40,6 +40,7 @@
 #else
 #include <unistd.h>
 #endif
+#include <memory>
 #include <vector>
 
 #include <google/protobuf/descriptor.pb.h>
@@ -126,6 +127,9 @@ class CommandLineInterfaceTest : public testing::Test {
   void ExpectErrorSubstringWithZeroReturnCode(
       const string& expected_substring);
 
+  // Checks that the captured stdout is the same as the expected_text.
+  void ExpectCapturedStdout(const string& expected_text);
+
   // Returns true if ExpectErrorSubstring(expected_substring) would pass, but
   // does not fail otherwise.
   bool HasAlternateErrorSubstring(const string& expected_substring);
@@ -182,6 +186,9 @@ class CommandLineInterfaceTest : public testing::Test {
   // The captured stderr output.
   string error_text_;
 
+  // The captured stdout.
+  string captured_stdout_;
+
   // Pointers which need to be deleted later.
   vector<CodeGenerator*> mock_generators_to_delete_;
 
@@ -224,7 +231,7 @@ void CommandLineInterfaceTest::SetUp() {
   }
 
   // Create the temp directory.
-  GOOGLE_CHECK(File::CreateDir(temp_directory_.c_str(), DEFAULT_FILE_MODE));
+  GOOGLE_CHECK_OK(File::CreateDir(temp_directory_, 0777));
 
   // Register generators.
   CodeGenerator* generator = new MockCodeGenerator("test_generator");
@@ -255,8 +262,7 @@ void CommandLineInterfaceTest::TearDown() {
 }
 
 void CommandLineInterfaceTest::Run(const string& command) {
-  vector<string> args;
-  SplitStringUsing(command, " ", &args);
+  vector<string> args = Split(command, " ", true);
 
   if (!disallow_plugins_) {
     cli_.AllowPlugins("prefix-");
@@ -295,18 +301,20 @@ void CommandLineInterfaceTest::Run(const string& command) {
     }
   }
 
-  scoped_array<const char*> argv(new const char*[args.size()]);
+  scoped_array<const char*> argv(new const char* [args.size()]);
 
   for (int i = 0; i < args.size(); i++) {
     args[i] = StringReplace(args[i], "$tmpdir", temp_directory_, true);
     argv[i] = args[i].c_str();
   }
 
+  CaptureTestStdout();
   CaptureTestStderr();
 
   return_code_ = cli_.Run(args.size(), argv.get());
 
   error_text_ = GetCapturedTestStderr();
+  captured_stdout_ = GetCapturedTestStdout();
 }
 
 // -------------------------------------------------------------------
@@ -318,16 +326,20 @@ void CommandLineInterfaceTest::CreateTempFile(
   string::size_type slash_pos = name.find_last_of('/');
   if (slash_pos != string::npos) {
     string dir = name.substr(0, slash_pos);
-    File::RecursivelyCreateDir(temp_directory_ + "/" + dir, 0777);
+    if (!File::Exists(temp_directory_ + "/" + dir)) {
+      GOOGLE_CHECK_OK(File::RecursivelyCreateDir(temp_directory_ + "/" + dir,
+                                          0777));
+    }
   }
 
   // Write file.
   string full_name = temp_directory_ + "/" + name;
-  File::WriteStringToFileOrDie(contents, full_name);
+  GOOGLE_CHECK_OK(File::SetContents(full_name, contents, true));
 }
 
 void CommandLineInterfaceTest::CreateTempDir(const string& name) {
-  File::RecursivelyCreateDir(temp_directory_ + "/" + name, 0777);
+  GOOGLE_CHECK_OK(File::RecursivelyCreateDir(temp_directory_ + "/" + name,
+                                      0777));
 }
 
 // -------------------------------------------------------------------
@@ -414,14 +426,18 @@ void CommandLineInterfaceTest::ReadDescriptorSet(
     const string& filename, FileDescriptorSet* descriptor_set) {
   string path = temp_directory_ + "/" + filename;
   string file_contents;
-  if (!File::ReadFileToString(path, &file_contents)) {
-    FAIL() << "File not found: " << path;
-  }
+  GOOGLE_CHECK_OK(File::GetContents(path, &file_contents, true));
+
   if (!descriptor_set->ParseFromString(file_contents)) {
     FAIL() << "Could not parse file contents: " << path;
   }
 }
 
+void CommandLineInterfaceTest::ExpectCapturedStdout(
+    const string& expected_text) {
+  EXPECT_EQ(expected_text, captured_stdout_);
+}
+
 // ===================================================================
 
 TEST_F(CommandLineInterfaceTest, BasicOutput) {
@@ -813,7 +829,7 @@ TEST_F(CommandLineInterfaceTest, WriteDescriptorSet) {
   FileDescriptorSet descriptor_set;
   ReadDescriptorSet("descriptor_set", &descriptor_set);
   if (HasFatalFailure()) return;
-  ASSERT_EQ(1, descriptor_set.file_size());
+  EXPECT_EQ(1, descriptor_set.file_size());
   EXPECT_EQ("bar.proto", descriptor_set.file(0).name());
   // Descriptor set should not have source code info.
   EXPECT_FALSE(descriptor_set.file(0).has_source_code_info());
@@ -838,7 +854,7 @@ TEST_F(CommandLineInterfaceTest, WriteDescriptorSetWithSourceInfo) {
   FileDescriptorSet descriptor_set;
   ReadDescriptorSet("descriptor_set", &descriptor_set);
   if (HasFatalFailure()) return;
-  ASSERT_EQ(1, descriptor_set.file_size());
+  EXPECT_EQ(1, descriptor_set.file_size());
   EXPECT_EQ("bar.proto", descriptor_set.file(0).name());
   // Source code info included.
   EXPECT_TRUE(descriptor_set.file(0).has_source_code_info());
@@ -863,7 +879,7 @@ TEST_F(CommandLineInterfaceTest, WriteTransitiveDescriptorSet) {
   FileDescriptorSet descriptor_set;
   ReadDescriptorSet("descriptor_set", &descriptor_set);
   if (HasFatalFailure()) return;
-  ASSERT_EQ(2, descriptor_set.file_size());
+  EXPECT_EQ(2, descriptor_set.file_size());
   if (descriptor_set.file(0).name() == "bar.proto") {
     std::swap(descriptor_set.mutable_file()->mutable_data()[0],
               descriptor_set.mutable_file()->mutable_data()[1]);
@@ -894,7 +910,7 @@ TEST_F(CommandLineInterfaceTest, WriteTransitiveDescriptorSetWithSourceInfo) {
   FileDescriptorSet descriptor_set;
   ReadDescriptorSet("descriptor_set", &descriptor_set);
   if (HasFatalFailure()) return;
-  ASSERT_EQ(2, descriptor_set.file_size());
+  EXPECT_EQ(2, descriptor_set.file_size());
   if (descriptor_set.file(0).name() == "bar.proto") {
     std::swap(descriptor_set.mutable_file()->mutable_data()[0],
               descriptor_set.mutable_file()->mutable_data()[1]);
@@ -1393,6 +1409,70 @@ TEST_F(CommandLineInterfaceTest, MissingValueAtEndError) {
   ExpectErrorText("Missing value for flag: --test_out\n");
 }
 
+TEST_F(CommandLineInterfaceTest, PrintFreeFieldNumbers) {
+  CreateTempFile(
+      "foo.proto",
+      "syntax = \"proto2\";\n"
+      "package foo;\n"
+      "message Foo {\n"
+      "  optional int32 a = 2;\n"
+      "  optional string b = 4;\n"
+      "  optional string c = 5;\n"
+      "  optional int64 d = 8;\n"
+      "  optional double e = 10;\n"
+      "}\n");
+  CreateTempFile(
+      "bar.proto",
+      "syntax = \"proto2\";\n"
+      "message Bar {\n"
+      "  optional int32 a = 2;\n"
+      "  extensions 4 to 5;\n"
+      "  optional int64 d = 8;\n"
+      "  extensions 10;\n"
+      "}\n");
+  CreateTempFile(
+      "baz.proto",
+      "syntax = \"proto2\";\n"
+      "message Baz {\n"
+      "  optional int32 a = 2;\n"
+      "  optional int64 d = 8;\n"
+      "  extensions 15 to max;\n"  // unordered.
+      "  extensions 13;\n"
+      "  extensions 10 to 12;\n"
+      "  extensions 5;\n"
+      "  extensions 4;\n"
+      "}\n");
+  CreateTempFile(
+      "quz.proto",
+      "syntax = \"proto2\";\n"
+      "message Quz {\n"
+      "  message Foo {}\n"  // nested message
+      "  optional int32 a = 2;\n"
+      "  optional group C = 4 {\n"
+      "    optional int32 d = 5;\n"
+      "  }\n"
+      "  extensions 8 to 10;\n"
+      "  optional group E = 11 {\n"
+      "    optional int32 f = 9;\n"    // explicitly reuse extension range 8-10
+      "    optional group G = 15 {\n"  // nested group
+      "      message Foo {}\n"         // nested message inside nested group
+      "    }\n"
+      "  }\n"
+      "}\n");
+
+  Run("protocol_compiler --print_free_field_numbers --proto_path=$tmpdir "
+      "foo.proto bar.proto baz.proto quz.proto");
+
+  ExpectNoErrors();
+  ExpectCapturedStdout(
+      "foo.Foo                             free: 1 3 6-7 9 11-INF\n"
+      "Bar                                 free: 1 3 6-7 9 11-INF\n"
+      "Baz                                 free: 1 3 6-7 9 14\n"
+      "Quz.Foo                             free: 1-INF\n"
+      "Quz.E.G.Foo                         free: 1-INF\n"
+      "Quz                                 free: 1 3 6-7 12-14 16-INF\n");
+}
+
 // ===================================================================
 
 // Test for --encode and --decode.  Note that it would be easier to do this
@@ -1412,7 +1492,7 @@ class EncodeDecodeTest : public testing::Test {
 
   void RedirectStdinFromText(const string& input) {
     string filename = TestTempDir() + "/test_stdin";
-    File::WriteStringToFileOrDie(input, filename);
+    GOOGLE_CHECK_OK(File::SetContents(filename, input, true));
     GOOGLE_CHECK(RedirectStdinFromFile(filename));
   }
 
@@ -1446,7 +1526,7 @@ class EncodeDecodeTest : public testing::Test {
     SplitStringUsing(command, " ", &args);
     args.push_back("--proto_path=" + TestSourceDir());
 
-    scoped_array<const char*> argv(new const char*[args.size()]);
+    scoped_array<const char*> argv(new const char* [args.size()]);
     for (int i = 0; i < args.size(); i++) {
       argv[i] = args[i].c_str();
     }
@@ -1467,7 +1547,7 @@ class EncodeDecodeTest : public testing::Test {
 
   void ExpectStdoutMatchesBinaryFile(const string& filename) {
     string expected_output;
-    ASSERT_TRUE(File::ReadFileToString(filename, &expected_output));
+    GOOGLE_CHECK_OK(File::GetContents(filename, &expected_output, true));
 
     // Don't use EXPECT_EQ because we don't want to print raw binary data to
     // stdout on failure.
@@ -1476,7 +1556,7 @@ class EncodeDecodeTest : public testing::Test {
 
   void ExpectStdoutMatchesTextFile(const string& filename) {
     string expected_output;
-    ASSERT_TRUE(File::ReadFileToString(filename, &expected_output));
+    GOOGLE_CHECK_OK(File::GetContents(filename, &expected_output, true));
 
     ExpectStdoutMatchesText(expected_output);
   }
@@ -1496,22 +1576,23 @@ class EncodeDecodeTest : public testing::Test {
 };
 
 TEST_F(EncodeDecodeTest, Encode) {
-  RedirectStdinFromFile(TestSourceDir() +
-    "/google/protobuf/testdata/text_format_unittest_data.txt");
+  RedirectStdinFromFile(TestSourceDir() + "/google/protobuf/"
+    "testdata/text_format_unittest_data_oneof_implemented.txt");
   EXPECT_TRUE(Run("google/protobuf/unittest.proto "
                   "--encode=protobuf_unittest.TestAllTypes"));
   ExpectStdoutMatchesBinaryFile(TestSourceDir() +
-    "/google/protobuf/testdata/golden_message");
+    "/google/protobuf/testdata/golden_message_oneof_implemented");
   ExpectStderrMatchesText("");
 }
 
 TEST_F(EncodeDecodeTest, Decode) {
   RedirectStdinFromFile(TestSourceDir() +
-    "/google/protobuf/testdata/golden_message");
+    "/google/protobuf/testdata/golden_message_oneof_implemented");
   EXPECT_TRUE(Run("google/protobuf/unittest.proto "
                   "--decode=protobuf_unittest.TestAllTypes"));
   ExpectStdoutMatchesTextFile(TestSourceDir() +
-    "/google/protobuf/testdata/text_format_unittest_data.txt");
+    "/google/protobuf/"
+    "testdata/text_format_unittest_data_oneof_implemented.txt");
   ExpectStderrMatchesText("");
 }
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_bootstrap_unittest.cc b/src/google/protobuf/compiler/cpp/cpp_bootstrap_unittest.cc
index b7c1766b..48da534c 100644
--- a/src/google/protobuf/compiler/cpp/cpp_bootstrap_unittest.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_bootstrap_unittest.cc
@@ -48,7 +48,7 @@
 #include <google/protobuf/compiler/importer.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
-#include <google/protobuf/stubs/map-util.h>
+#include <google/protobuf/stubs/map_util.h>
 #include <google/protobuf/stubs/stl_util.h>
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
@@ -93,9 +93,9 @@ class MockGeneratorContext : public GeneratorContext {
       << "Generator failed to generate file: " << virtual_filename;
 
     string actual_contents;
-    File::ReadFileToStringOrDie(
-      TestSourceDir() + "/" + physical_filename,
-      &actual_contents);
+    GOOGLE_CHECK_OK(
+        File::GetContents(TestSourceDir() + "/" + physical_filename,
+                          &actual_contents, true));
     EXPECT_TRUE(actual_contents == *expected_contents)
       << physical_filename << " needs to be regenerated.  Please run "
          "generate_descriptor_proto.sh and add this file "
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum.cc b/src/google/protobuf/compiler/cpp/cpp_enum.cc
index 67c12d7a..0c4796f6 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_enum.cc
@@ -45,11 +45,27 @@ namespace protobuf {
 namespace compiler {
 namespace cpp {
 
+namespace {
+// The GOOGLE_ARRAYSIZE constant is the max enum value plus 1. If the max enum value
+// is kint32max, GOOGLE_ARRAYSIZE will overflow. In such cases we should omit the
+// generation of the GOOGLE_ARRAYSIZE constant.
+bool ShouldGenerateArraySize(const EnumDescriptor* descriptor) {
+  int32 max_value = descriptor->value(0)->number();
+  for (int i = 0; i < descriptor->value_count(); i++) {
+    if (descriptor->value(i)->number() > max_value) {
+      max_value = descriptor->value(i)->number();
+    }
+  }
+  return max_value != kint32max;
+}
+}  // namespace
+
 EnumGenerator::EnumGenerator(const EnumDescriptor* descriptor,
                              const Options& options)
   : descriptor_(descriptor),
     classname_(ClassName(descriptor, false)),
-    options_(options) {
+    options_(options),
+    generate_array_size_(ShouldGenerateArraySize(descriptor)) {
 }
 
 EnumGenerator::~EnumGenerator() {}
@@ -67,7 +83,10 @@ void EnumGenerator::GenerateDefinition(io::Printer* printer) {
 
   for (int i = 0; i < descriptor_->value_count(); i++) {
     vars["name"] = descriptor_->value(i)->name();
-    vars["number"] = SimpleItoa(descriptor_->value(i)->number());
+    // In C++, an value of -2147483648 gets interpreted as the negative of
+    // 2147483648, and since 2147483648 can't fit in an integer, this produces a
+    // compiler warning.  This works around that issue.
+    vars["number"] = Int32ToString(descriptor_->value(i)->number());
     vars["prefix"] = (descriptor_->containing_type() == NULL) ?
       "" : classname_ + "_";
 
@@ -97,9 +116,13 @@ void EnumGenerator::GenerateDefinition(io::Printer* printer) {
   printer->Print(vars,
     "$dllexport$bool $classname$_IsValid(int value);\n"
     "const $classname$ $prefix$$short_name$_MIN = $prefix$$min_name$;\n"
-    "const $classname$ $prefix$$short_name$_MAX = $prefix$$max_name$;\n"
-    "const int $prefix$$short_name$_ARRAYSIZE = $prefix$$short_name$_MAX + 1;\n"
-    "\n");
+    "const $classname$ $prefix$$short_name$_MAX = $prefix$$max_name$;\n");
+
+  if (generate_array_size_) {
+    printer->Print(vars,
+      "const int $prefix$$short_name$_ARRAYSIZE = "
+      "$prefix$$short_name$_MAX + 1;\n\n");
+  }
 
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(vars,
@@ -123,6 +146,7 @@ void EnumGenerator::
 GenerateGetEnumDescriptorSpecializations(io::Printer* printer) {
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(
+      "template <> struct is_proto_enum< $classname$> : ::google::protobuf::internal::true_type {};\n"
       "template <>\n"
       "inline const EnumDescriptor* GetEnumDescriptor< $classname$>() {\n"
       "  return $classname$_descriptor();\n"
@@ -150,9 +174,12 @@ void EnumGenerator::GenerateSymbolImports(io::Printer* printer) {
     "static const $nested_name$ $nested_name$_MIN =\n"
     "  $classname$_$nested_name$_MIN;\n"
     "static const $nested_name$ $nested_name$_MAX =\n"
-    "  $classname$_$nested_name$_MAX;\n"
-    "static const int $nested_name$_ARRAYSIZE =\n"
-    "  $classname$_$nested_name$_ARRAYSIZE;\n");
+    "  $classname$_$nested_name$_MAX;\n");
+  if (generate_array_size_) {
+    printer->Print(vars,
+      "static const int $nested_name$_ARRAYSIZE =\n"
+      "  $classname$_$nested_name$_ARRAYSIZE;\n");
+  }
 
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(vars,
@@ -218,7 +245,7 @@ void EnumGenerator::GenerateMethods(io::Printer* printer) {
        iter != numbers.end(); ++iter) {
     printer->Print(
       "    case $number$:\n",
-      "number", SimpleItoa(*iter));
+      "number", Int32ToString(*iter));
   }
 
   printer->Print(vars,
@@ -245,8 +272,11 @@ void EnumGenerator::GenerateMethods(io::Printer* printer) {
     }
     printer->Print(vars,
       "const $classname$ $parent$::$nested_name$_MIN;\n"
-      "const $classname$ $parent$::$nested_name$_MAX;\n"
-      "const int $parent$::$nested_name$_ARRAYSIZE;\n");
+      "const $classname$ $parent$::$nested_name$_MAX;\n");
+    if (generate_array_size_) {
+      printer->Print(vars,
+        "const int $parent$::$nested_name$_ARRAYSIZE;\n");
+    }
 
     printer->Print("#endif  // _MSC_VER\n");
   }
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum.h b/src/google/protobuf/compiler/cpp/cpp_enum.h
index 2e85a0bd..98cbdf69 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum.h
+++ b/src/google/protobuf/compiler/cpp/cpp_enum.h
@@ -89,6 +89,8 @@ class EnumGenerator {
   const EnumDescriptor* descriptor_;
   string classname_;
   Options options_;
+  // whether to generate the *_ARRAYSIZE constant.
+  bool generate_array_size_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(EnumGenerator);
 };
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
index 6e1620d4..2723c04a 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
@@ -51,7 +51,8 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
   SetCommonFieldVariables(descriptor, variables, options);
   const EnumValueDescriptor* default_value = descriptor->default_value_enum();
   (*variables)["type"] = ClassName(descriptor->enum_type(), true);
-  (*variables)["default"] = SimpleItoa(default_value->number());
+  (*variables)["default"] = Int32ToString(default_value->number());
+  (*variables)["full_name"] = descriptor->full_name();
 }
 
 }  // namespace
@@ -83,12 +84,14 @@ void EnumFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return static_cast< $type$ >($name$_);\n"
     "}\n"
     "inline void $classname$::set_$name$($type$ value) {\n"
     "  assert($type$_IsValid(value));\n"
     "  set_has_$name$();\n"
     "  $name$_ = value;\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
 }
 
@@ -121,10 +124,15 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
     "       input, &value)));\n"
     "if ($type$_IsValid(value)) {\n"
     "  set_$name$(static_cast< $type$ >(value));\n");
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(variables_,
       "} else {\n"
       "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+  } else {
+    printer->Print(
+      "} else {\n"
+      "  unknown_fields_stream.WriteVarint32(tag);\n"
+      "  unknown_fields_stream.WriteVarint32(value);\n");
   }
   printer->Print(variables_,
     "}\n");
@@ -153,6 +161,52 @@ GenerateByteSize(io::Printer* printer) const {
 
 // ===================================================================
 
+EnumOneofFieldGenerator::
+EnumOneofFieldGenerator(const FieldDescriptor* descriptor,
+                        const Options& options)
+  : EnumFieldGenerator(descriptor, options) {
+  SetCommonOneofFieldVariables(descriptor, &variables_);
+}
+
+EnumOneofFieldGenerator::~EnumOneofFieldGenerator() {}
+
+void EnumOneofFieldGenerator::
+GenerateInlineAccessorDefinitions(io::Printer* printer) const {
+  printer->Print(variables_,
+    "inline $type$ $classname$::$name$() const {\n"
+    "  if (has_$name$()) {\n"
+    "    return static_cast< $type$ >($oneof_prefix$$name$_);\n"
+    "  }\n"
+    "  return static_cast< $type$ >($default$);\n"
+    "}\n"
+    "inline void $classname$::set_$name$($type$ value) {\n"
+    "  assert($type$_IsValid(value));\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "  }\n"
+    "  $oneof_prefix$$name$_ = value;\n"
+    "}\n");
+}
+
+void EnumOneofFieldGenerator::
+GenerateClearingCode(io::Printer* printer) const {
+  printer->Print(variables_, "$oneof_prefix$$name$_ = $default$;\n");
+}
+
+void EnumOneofFieldGenerator::
+GenerateSwappingCode(io::Printer* printer) const {
+  // Don't print any swapping code. Swapping the union will swap this field.
+}
+
+void EnumOneofFieldGenerator::
+GenerateConstructorCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "  $classname$_default_oneof_instance_->$name$_ = $default$;\n");
+}
+
+// ===================================================================
+
 RepeatedEnumFieldGenerator::
 RepeatedEnumFieldGenerator(const FieldDescriptor* descriptor,
                            const Options& options)
@@ -166,7 +220,8 @@ void RepeatedEnumFieldGenerator::
 GeneratePrivateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "::google::protobuf::RepeatedField<int> $name$_;\n");
-  if (descriptor_->options().packed() && HasGeneratedMethods(descriptor_->file())) {
+  if (descriptor_->options().packed()
+      && HasGeneratedMethods(descriptor_->file())) {
     printer->Print(variables_,
       "mutable int _$name$_cached_byte_size_;\n");
   }
@@ -187,23 +242,28 @@ void RepeatedEnumFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$(int index) const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return static_cast< $type$ >($name$_.Get(index));\n"
     "}\n"
     "inline void $classname$::set_$name$(int index, $type$ value) {\n"
     "  assert($type$_IsValid(value));\n"
     "  $name$_.Set(index, value);\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n"
     "inline void $classname$::add_$name$($type$ value) {\n"
     "  assert($type$_IsValid(value));\n"
     "  $name$_.Add(value);\n"
+    "  // @@protoc_insertion_point(field_add:$full_name$)\n"
     "}\n");
   printer->Print(variables_,
     "inline const ::google::protobuf::RepeatedField<int>&\n"
     "$classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_list:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
     "inline ::google::protobuf::RepeatedField<int>*\n"
     "$classname$::mutable_$name$() {\n"
+    "  // @@protoc_insertion_point(field_mutable_list:$full_name$)\n"
     "  return &$name$_;\n"
     "}\n");
 }
@@ -238,10 +298,15 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
     "       input, &value)));\n"
     "if ($type$_IsValid(value)) {\n"
     "  add_$name$(static_cast< $type$ >(value));\n");
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(variables_,
       "} else {\n"
       "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+  } else {
+    printer->Print(
+      "} else {\n"
+      "  unknown_fields_stream.WriteVarint32(tag);\n"
+      "  unknown_fields_stream.WriteVarint32(value);\n");
   }
   printer->Print("}\n");
 }
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum_field.h b/src/google/protobuf/compiler/cpp/cpp_enum_field.h
index 65770083..1da1623a 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_enum_field.h
@@ -63,13 +63,30 @@ class EnumFieldGenerator : public FieldGenerator {
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const;
   void GenerateByteSize(io::Printer* printer) const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
 
+ private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(EnumFieldGenerator);
 };
 
+class EnumOneofFieldGenerator : public EnumFieldGenerator {
+ public:
+  explicit EnumOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                   const Options& options);
+  ~EnumOneofFieldGenerator();
+
+  // implements FieldGenerator ---------------------------------------
+  void GenerateInlineAccessorDefinitions(io::Printer* printer) const;
+  void GenerateClearingCode(io::Printer* printer) const;
+  void GenerateSwappingCode(io::Printer* printer) const;
+  void GenerateConstructorCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(EnumOneofFieldGenerator);
+};
+
 class RepeatedEnumFieldGenerator : public FieldGenerator {
  public:
   explicit RepeatedEnumFieldGenerator(const FieldDescriptor* descriptor,
diff --git a/src/google/protobuf/compiler/cpp/cpp_field.cc b/src/google/protobuf/compiler/cpp/cpp_field.cc
index 0786176b..beea8bac 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_field.cc
@@ -33,6 +33,8 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/cpp/cpp_field.h>
+#include <memory>
+
 #include <google/protobuf/compiler/cpp/cpp_helpers.h>
 #include <google/protobuf/compiler/cpp/cpp_primitive_field.h>
 #include <google/protobuf/compiler/cpp/cpp_string_field.h>
@@ -68,6 +70,12 @@ void SetCommonFieldVariables(const FieldDescriptor* descriptor,
   (*variables)["cppget"] = "Get";
 }
 
+void SetCommonOneofFieldVariables(const FieldDescriptor* descriptor,
+                                  map<string, string>* variables) {
+  (*variables)["oneof_prefix"] = descriptor->containing_oneof()->name() + "_.";
+  (*variables)["oneof_name"] = descriptor->containing_oneof()->name();
+}
+
 FieldGenerator::~FieldGenerator() {}
 
 void FieldGenerator::
@@ -84,8 +92,9 @@ GenerateMergeFromCodedStreamWithPacking(io::Printer* printer) const {
 
 FieldGeneratorMap::FieldGeneratorMap(const Descriptor* descriptor,
                                      const Options& options)
-  : descriptor_(descriptor),
-    field_generators_(new scoped_ptr<FieldGenerator>[descriptor->field_count()]) {
+    : descriptor_(descriptor),
+      field_generators_(
+          new scoped_ptr<FieldGenerator>[descriptor->field_count()]) {
   // Construct all the FieldGenerators.
   for (int i = 0; i < descriptor->field_count(); i++) {
     field_generators_[i].reset(MakeGenerator(descriptor->field(i), options));
@@ -109,6 +118,21 @@ FieldGenerator* FieldGeneratorMap::MakeGenerator(const FieldDescriptor* field,
       default:
         return new RepeatedPrimitiveFieldGenerator(field, options);
     }
+  } else if (field->containing_oneof()) {
+    switch (field->cpp_type()) {
+      case FieldDescriptor::CPPTYPE_MESSAGE:
+        return new MessageOneofFieldGenerator(field, options);
+      case FieldDescriptor::CPPTYPE_STRING:
+        switch (field->options().ctype()) {
+          default:  // StringOneofFieldGenerator handles unknown ctypes.
+          case FieldOptions::STRING:
+            return new StringOneofFieldGenerator(field, options);
+        }
+      case FieldDescriptor::CPPTYPE_ENUM:
+        return new EnumOneofFieldGenerator(field, options);
+      default:
+        return new PrimitiveOneofFieldGenerator(field, options);
+    }
   } else {
     switch (field->cpp_type()) {
       case FieldDescriptor::CPPTYPE_MESSAGE:
diff --git a/src/google/protobuf/compiler/cpp/cpp_field.h b/src/google/protobuf/compiler/cpp/cpp_field.h
index f7d99b15..e4340672 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_field.h
@@ -36,9 +36,9 @@
 #define GOOGLE_PROTOBUF_COMPILER_CPP_FIELD_H__
 
 #include <map>
+#include <memory>
 #include <string>
 
-#include <google/protobuf/stubs/common.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/compiler/cpp/cpp_options.h>
 
@@ -61,6 +61,9 @@ void SetCommonFieldVariables(const FieldDescriptor* descriptor,
                              map<string, string>* variables,
                              const Options& options);
 
+void SetCommonOneofFieldVariables(const FieldDescriptor* descriptor,
+                                  map<string, string>* variables);
+
 class FieldGenerator {
  public:
   FieldGenerator() {}
@@ -71,6 +74,11 @@ class FieldGenerator {
   // class.
   virtual void GeneratePrivateMembers(io::Printer* printer) const = 0;
 
+  // Generate static default variable for this field. These are placed inside
+  // the message class. Most field types don't need this, so the default
+  // implementation is empty.
+  virtual void GenerateStaticMembers(io::Printer* printer) const {}
+
   // Generate prototypes for all of the accessor functions related to this
   // field.  These are placed inside the class definition.
   virtual void GenerateAccessorDeclarations(io::Printer* printer) const = 0;
diff --git a/src/google/protobuf/compiler/cpp/cpp_file.cc b/src/google/protobuf/compiler/cpp/cpp_file.cc
index 3d869a37..f7f2cdda 100644
--- a/src/google/protobuf/compiler/cpp/cpp_file.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_file.cc
@@ -33,6 +33,9 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/cpp/cpp_file.h>
+#include <memory>
+#include <set>
+
 #include <google/protobuf/compiler/cpp/cpp_enum.h>
 #include <google/protobuf/compiler/cpp/cpp_service.h>
 #include <google/protobuf/compiler/cpp/cpp_extension.h>
@@ -50,18 +53,17 @@ namespace cpp {
 
 // ===================================================================
 
-FileGenerator::FileGenerator(const FileDescriptor* file,
-                             const Options& options)
-  : file_(file),
-    message_generators_(
-      new scoped_ptr<MessageGenerator>[file->message_type_count()]),
-    enum_generators_(
-      new scoped_ptr<EnumGenerator>[file->enum_type_count()]),
-    service_generators_(
-      new scoped_ptr<ServiceGenerator>[file->service_count()]),
-    extension_generators_(
-      new scoped_ptr<ExtensionGenerator>[file->extension_count()]),
-    options_(options) {
+FileGenerator::FileGenerator(const FileDescriptor* file, const Options& options)
+    : file_(file),
+      message_generators_(
+          new scoped_ptr<MessageGenerator>[file->message_type_count()]),
+      enum_generators_(
+          new scoped_ptr<EnumGenerator>[file->enum_type_count()]),
+      service_generators_(
+          new scoped_ptr<ServiceGenerator>[file->service_count()]),
+      extension_generators_(
+          new scoped_ptr<ExtensionGenerator>[file->extension_count()]),
+      options_(options) {
 
   for (int i = 0; i < file->message_type_count(); i++) {
     message_generators_[i].reset(
@@ -153,19 +155,28 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
       "#include <google/protobuf/service.h>\n");
   }
 
-  if (HasUnknownFields(file_) && file_->message_type_count() > 0) {
+  if (UseUnknownFieldSet(file_) && file_->message_type_count() > 0) {
     printer->Print(
       "#include <google/protobuf/unknown_field_set.h>\n");
   }
 
 
+  set<string> public_import_names;
+  for (int i = 0; i < file_->public_dependency_count(); i++) {
+    public_import_names.insert(file_->public_dependency(i)->name());
+  }
+
   for (int i = 0; i < file_->dependency_count(); i++) {
+    const string& name = file_->dependency(i)->name();
+    bool public_import = (public_import_names.count(name) != 0);
+
+
     printer->Print(
-      "#include \"$dependency$.pb.h\"\n",
-      "dependency", StripProto(file_->dependency(i)->name()));
+      "#include \"$dependency$.pb.h\"$iwyu$\n",
+      "dependency", StripProto(name),
+      "iwyu", (public_import) ? "  // IWYU pragma: export" : "");
   }
 
-
   printer->Print(
     "// @@protoc_insertion_point(includes)\n");
 
@@ -248,6 +259,7 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
   printer->Print(kThickSeparator);
   printer->Print("\n");
 
+
   // Generate class inline methods.
   for (int i = 0; i < file_->message_type_count(); i++) {
     if (i > 0) {
@@ -317,6 +329,12 @@ void FileGenerator::GenerateSource(io::Printer* printer) {
     "filename", file_->name(),
     "basename", StripProto(file_->name()));
 
+  // Unknown fields implementation in lite mode uses StringOutputStream
+  if (!UseUnknownFieldSet(file_) && file_->message_type_count() > 0) {
+    printer->Print(
+      "#include <google/protobuf/io/zero_copy_stream_impl_lite.h>\n");
+  }
+
   if (HasDescriptorMethods(file_)) {
     printer->Print(
       "#include <google/protobuf/descriptor.h>\n"
@@ -542,17 +560,12 @@ void FileGenerator::GenerateBuildDescriptors(io::Printer* printer) {
   for (int i = 0; i < file_->dependency_count(); i++) {
     const FileDescriptor* dependency = file_->dependency(i);
     // Print the namespace prefix for the dependency.
-    vector<string> dependency_package_parts;
-    SplitStringUsing(dependency->package(), ".", &dependency_package_parts);
-    printer->Print("::");
-    for (int j = 0; j < dependency_package_parts.size(); j++) {
-      printer->Print("$name$::",
-                     "name", dependency_package_parts[j]);
-    }
+    string add_desc_name = QualifiedFileLevelSymbol(
+        dependency->package(), GlobalAddDescriptorsName(dependency->name()));
     // Call its AddDescriptors function.
     printer->Print(
       "$name$();\n",
-      "name", GlobalAddDescriptorsName(dependency->name()));
+      "name", add_desc_name);
   }
 
   if (HasDescriptorMethods(file_)) {
diff --git a/src/google/protobuf/compiler/cpp/cpp_file.h b/src/google/protobuf/compiler/cpp/cpp_file.h
index 2deefaa8..07970971 100644
--- a/src/google/protobuf/compiler/cpp/cpp_file.h
+++ b/src/google/protobuf/compiler/cpp/cpp_file.h
@@ -35,6 +35,7 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_CPP_FILE_H__
 #define GOOGLE_PROTOBUF_COMPILER_CPP_FILE_H__
 
+#include <memory>
 #include <string>
 #include <vector>
 #include <google/protobuf/stubs/common.h>
@@ -85,7 +86,6 @@ class FileGenerator {
 
   // E.g. if the package is foo.bar, package_parts_ is {"foo", "bar"}.
   vector<string> package_parts_;
-
   const Options options_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FileGenerator);
diff --git a/src/google/protobuf/compiler/cpp/cpp_generator.cc b/src/google/protobuf/compiler/cpp/cpp_generator.cc
index 1813510b..a43e993b 100644
--- a/src/google/protobuf/compiler/cpp/cpp_generator.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_generator.cc
@@ -35,6 +35,7 @@
 #include <google/protobuf/compiler/cpp/cpp_generator.h>
 
 #include <vector>
+#include <memory>
 #include <utility>
 
 #include <google/protobuf/compiler/cpp/cpp_file.h>
@@ -102,7 +103,7 @@ bool CppGenerator::Generate(const FileDescriptor* file,
   // Generate header.
   {
     scoped_ptr<io::ZeroCopyOutputStream> output(
-      generator_context->Open(basename + ".h"));
+        generator_context->Open(basename + ".h"));
     io::Printer printer(output.get(), '$');
     file_generator.GenerateHeader(&printer);
   }
@@ -110,7 +111,7 @@ bool CppGenerator::Generate(const FileDescriptor* file,
   // Generate cc file.
   {
     scoped_ptr<io::ZeroCopyOutputStream> output(
-      generator_context->Open(basename + ".cc"));
+        generator_context->Open(basename + ".cc"));
     io::Printer printer(output.get(), '$');
     file_generator.GenerateSource(&printer);
   }
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.cc b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
index 28911ab0..2c94b3a9 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
@@ -82,6 +82,22 @@ hash_set<string> MakeKeywordsMap() {
 
 hash_set<string> kKeywords = MakeKeywordsMap();
 
+// Returns whether the provided descriptor has an extension. This includes its
+// nested types.
+bool HasExtension(const Descriptor* descriptor) {
+  if (descriptor->extension_count() > 0) {
+    return true;
+  }
+  for (int i = 0; i < descriptor->nested_type_count(); ++i) {
+    if (HasExtension(descriptor->nested_type(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
 string UnderscoresToCamelCase(const string& input, bool cap_next_letter) {
   string result;
   // Note:  I distrust ctype.h due to locales.
@@ -107,22 +123,6 @@ string UnderscoresToCamelCase(const string& input, bool cap_next_letter) {
   return result;
 }
 
-// Returns whether the provided descriptor has an extension. This includes its
-// nested types.
-bool HasExtension(const Descriptor* descriptor) {
-  if (descriptor->extension_count() > 0) {
-    return true;
-  }
-  for (int i = 0; i < descriptor->nested_type_count(); ++i) {
-    if (HasExtension(descriptor->nested_type(i))) {
-      return true;
-    }
-  }
-  return false;
-}
-
-}  // namespace
-
 const char kThickSeparator[] =
   "// ===================================================================\n";
 const char kThinSeparator[] =
@@ -256,27 +256,35 @@ const char* DeclaredTypeMethodName(FieldDescriptor::Type type) {
   return "";
 }
 
+string Int32ToString(int number) {
+  // gcc rejects the decimal form of kint32min.
+  if (number == kint32min) {
+    GOOGLE_COMPILE_ASSERT(kint32min == (~0x7fffffff), kint32min_value_error);
+    return "(~0x7fffffff)";
+  } else {
+    return SimpleItoa(number);
+  }
+}
+
+string Int64ToString(int64 number) {
+  // gcc rejects the decimal form of kint64min
+  if (number == kint64min) {
+    // Make sure we are in a 2's complement system.
+    GOOGLE_COMPILE_ASSERT(kint64min == GOOGLE_LONGLONG(-0x8000000000000000),
+                   kint64min_value_error);
+    return "GOOGLE_LONGLONG(-0x8000000000000000)";
+  }
+  return "GOOGLE_LONGLONG(" + SimpleItoa(number) + ")";
+}
+
 string DefaultValue(const FieldDescriptor* field) {
   switch (field->cpp_type()) {
     case FieldDescriptor::CPPTYPE_INT32:
-      // gcc rejects the decimal form of kint32min and kint64min.
-      if (field->default_value_int32() == kint32min) {
-        // Make sure we are in a 2's complement system.
-        GOOGLE_COMPILE_ASSERT(kint32min == -0x80000000, kint32min_value_error);
-        return "-0x80000000";
-      }
-      return SimpleItoa(field->default_value_int32());
+      return Int32ToString(field->default_value_int32());
     case FieldDescriptor::CPPTYPE_UINT32:
       return SimpleItoa(field->default_value_uint32()) + "u";
     case FieldDescriptor::CPPTYPE_INT64:
-      // See the comments for CPPTYPE_INT32.
-      if (field->default_value_int64() == kint64min) {
-        // Make sure we are in a 2's complement system.
-        GOOGLE_COMPILE_ASSERT(kint64min == GOOGLE_LONGLONG(-0x8000000000000000),
-                       kint64min_value_error);
-        return "GOOGLE_LONGLONG(-0x8000000000000000)";
-      }
-      return "GOOGLE_LONGLONG(" + SimpleItoa(field->default_value_int64()) + ")";
+      return Int64ToString(field->default_value_int64());
     case FieldDescriptor::CPPTYPE_UINT64:
       return "GOOGLE_ULONGLONG(" + SimpleItoa(field->default_value_uint64())+ ")";
     case FieldDescriptor::CPPTYPE_DOUBLE: {
@@ -319,7 +327,7 @@ string DefaultValue(const FieldDescriptor* field) {
       return strings::Substitute(
           "static_cast< $0 >($1)",
           ClassName(field->enum_type(), true),
-          field->default_value_enum()->number());
+          Int32ToString(field->default_value_enum()->number()));
     case FieldDescriptor::CPPTYPE_STRING:
       return "\"" + EscapeTrigraphs(
         CEscape(field->default_value_string())) +
@@ -366,11 +374,39 @@ string GlobalShutdownFileName(const string& filename) {
   return "protobuf_ShutdownFile_" + FilenameIdentifier(filename);
 }
 
+// Return the qualified C++ name for a file level symbol.
+string QualifiedFileLevelSymbol(const string& package, const string& name) {
+  if (package.empty()) {
+    return StrCat("::", name);
+  }
+  return StrCat("::", DotsToColons(package), "::", name);
+}
+
 // Escape C++ trigraphs by escaping question marks to \?
 string EscapeTrigraphs(const string& to_escape) {
   return StringReplace(to_escape, "?", "\\?", true);
 }
 
+// Escaped function name to eliminate naming conflict.
+string SafeFunctionName(const Descriptor* descriptor,
+                        const FieldDescriptor* field,
+                        const string& prefix) {
+  // Do not use FieldName() since it will escape keywords.
+  string name = field->name();
+  LowerString(&name);
+  string function_name = prefix + name;
+  if (descriptor->FindFieldByName(function_name)) {
+    // Single underscore will also make it conflicting with the private data
+    // member. We use double underscore to escape function names.
+    function_name.append("__");
+  } else if (kKeywords.count(name) > 0) {
+    // If the field name is a keyword, we append the underscore back to keep it
+    // consistent with other function names.
+    function_name.append("_");
+  }
+  return function_name;
+}
+
 bool StaticInitializersForced(const FileDescriptor* file) {
   if (HasDescriptorMethods(file) || file->extension_count() > 0) {
     return true;
@@ -432,6 +468,26 @@ bool HasEnumDefinitions(const FileDescriptor* file) {
   return false;
 }
 
+bool IsStringOrMessage(const FieldDescriptor* field) {
+  switch (field->cpp_type()) {
+    case FieldDescriptor::CPPTYPE_INT32:
+    case FieldDescriptor::CPPTYPE_INT64:
+    case FieldDescriptor::CPPTYPE_UINT32:
+    case FieldDescriptor::CPPTYPE_UINT64:
+    case FieldDescriptor::CPPTYPE_DOUBLE:
+    case FieldDescriptor::CPPTYPE_FLOAT:
+    case FieldDescriptor::CPPTYPE_BOOL:
+    case FieldDescriptor::CPPTYPE_ENUM:
+      return false;
+    case FieldDescriptor::CPPTYPE_STRING:
+    case FieldDescriptor::CPPTYPE_MESSAGE:
+      return true;
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return false;
+}
+
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.h b/src/google/protobuf/compiler/cpp/cpp_helpers.h
index 526e19cc..27444d5a 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.h
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.h
@@ -103,6 +103,12 @@ const char* PrimitiveTypeName(FieldDescriptor::CppType type);
 // methods of WireFormat.  For example, TYPE_INT32 becomes "Int32".
 const char* DeclaredTypeMethodName(FieldDescriptor::Type type);
 
+// Return the code that evaluates to the number when compiled.
+string Int32ToString(int number);
+
+// Return the code that evaluates to the number when compiled.
+string Int64ToString(int64 number);
+
 // Get code that evaluates to the field's default value.
 string DefaultValue(const FieldDescriptor* field);
 
@@ -115,14 +121,23 @@ string GlobalAddDescriptorsName(const string& filename);
 // Return the name of the AssignDescriptors() function for a given file.
 string GlobalAssignDescriptorsName(const string& filename);
 
+// Return the qualified C++ name for a file level symbol.
+string QualifiedFileLevelSymbol(const string& package, const string& name);
+
 // Return the name of the ShutdownFile() function for a given file.
 string GlobalShutdownFileName(const string& filename);
 
 // Escape C++ trigraphs by escaping question marks to \?
 string EscapeTrigraphs(const string& to_escape);
 
-// Do message classes in this file keep track of unknown fields?
-inline bool HasUnknownFields(const FileDescriptor* file) {
+// Escaped function name to eliminate naming conflict.
+string SafeFunctionName(const Descriptor* descriptor,
+                        const FieldDescriptor* field,
+                        const string& prefix);
+
+// Do message classes in this file use UnknownFieldSet?
+// Otherwise, messages will store unknown fields in a string
+inline bool UseUnknownFieldSet(const FileDescriptor* file) {
   return file->options().optimize_for() != FileOptions::LITE_RUNTIME;
 }
 
@@ -178,6 +193,11 @@ void PrintHandlingOptionalStaticInitializers(
     const char* without_static_init);
 
 
+// Returns true if the field's CPPTYPE is string or message.
+bool IsStringOrMessage(const FieldDescriptor* field);
+
+string UnderscoresToCamelCase(const string& input, bool cap_next_letter);
+
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.cc b/src/google/protobuf/compiler/cpp/cpp_message.cc
index 1ea4f13d..962ff535 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message.cc
@@ -35,6 +35,8 @@
 #include <algorithm>
 #include <google/protobuf/stubs/hash.h>
 #include <map>
+#include <memory>
+#include <set>
 #include <utility>
 #include <vector>
 #include <google/protobuf/compiler/cpp/cpp_message.h>
@@ -74,15 +76,6 @@ struct FieldOrderingByNumber {
   }
 };
 
-const char* kWireTypeNames[] = {
-  "VARINT",
-  "FIXED64",
-  "LENGTH_DELIMITED",
-  "START_GROUP",
-  "END_GROUP",
-  "FIXED32",
-};
-
 // Sort the fields of the given Descriptor by number into a new[]'d array
 // and return it.
 const FieldDescriptor** SortFieldsByNumber(const Descriptor* descriptor) {
@@ -255,8 +248,9 @@ void OptimizePadding(vector<const FieldDescriptor*>* fields) {
     aligned_to_4.push_back(field_group);
   }
   // Sort by preferred location to keep fields as close to their original
-  // location as possible.
-  sort(aligned_to_4.begin(), aligned_to_4.end());
+  // location as possible.  Using stable_sort ensures that the output is
+  // consistent across runs.
+  stable_sort(aligned_to_4.begin(), aligned_to_4.end());
 
   // Now group fields aligned to 4 bytes (or the 4-field groups created above)
   // into pairs, and treat those like a single field aligned to 8 bytes.
@@ -271,9 +265,8 @@ void OptimizePadding(vector<const FieldDescriptor*>* fields) {
     }
     aligned_to_8.push_back(field_group);
   }
-  // Sort by preferred location to keep fields as close to their original
-  // location as possible.
-  sort(aligned_to_8.begin(), aligned_to_8.end());
+  // Sort by preferred location.
+  stable_sort(aligned_to_8.begin(), aligned_to_8.end());
 
   // Now pull out all the FieldDescriptors in order.
   fields->clear();
@@ -284,22 +277,26 @@ void OptimizePadding(vector<const FieldDescriptor*>* fields) {
   }
 }
 
+string MessageTypeProtoName(const FieldDescriptor* field) {
+  return field->message_type()->full_name();
+}
+
 }
 
 // ===================================================================
 
 MessageGenerator::MessageGenerator(const Descriptor* descriptor,
                                    const Options& options)
-  : descriptor_(descriptor),
-    classname_(ClassName(descriptor, false)),
-    options_(options),
-    field_generators_(descriptor, options),
-    nested_generators_(new scoped_ptr<MessageGenerator>[
-      descriptor->nested_type_count()]),
-    enum_generators_(new scoped_ptr<EnumGenerator>[
-      descriptor->enum_type_count()]),
-    extension_generators_(new scoped_ptr<ExtensionGenerator>[
-      descriptor->extension_count()]) {
+    : descriptor_(descriptor),
+      classname_(ClassName(descriptor, false)),
+      options_(options),
+      field_generators_(descriptor, options),
+      nested_generators_(new scoped_ptr<
+          MessageGenerator>[descriptor->nested_type_count()]),
+      enum_generators_(
+          new scoped_ptr<EnumGenerator>[descriptor->enum_type_count()]),
+      extension_generators_(new scoped_ptr<
+          ExtensionGenerator>[descriptor->extension_count()]) {
 
   for (int i = 0; i < descriptor->nested_type_count(); i++) {
     nested_generators_[i].reset(
@@ -383,6 +380,14 @@ GenerateFieldAccessorDeclarations(io::Printer* printer) {
       "GOOGLE_PROTOBUF_EXTENSION_ACCESSORS($classname$)\n",
       "classname", classname_);
   }
+
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "inline $camel_oneof_name$Case $oneof_name$_case() const;\n",
+        "camel_oneof_name",
+        UnderscoresToCamelCase(descriptor_->oneof_decl(i)->name(), true),
+        "oneof_name", descriptor_->oneof_decl(i)->name());
+  }
 }
 
 void MessageGenerator::
@@ -403,6 +408,18 @@ GenerateFieldAccessorDefinitions(io::Printer* printer) {
         "inline int $classname$::$name$_size() const {\n"
         "  return $name$_.size();\n"
         "}\n");
+    } else if (field->containing_oneof()) {
+      // Singular field in a oneof
+      vars["field_name"] = UnderscoresToCamelCase(field->name(), true);
+      vars["oneof_name"] = field->containing_oneof()->name();
+      vars["oneof_index"] = SimpleItoa(field->containing_oneof()->index());
+      printer->Print(vars,
+        "inline bool $classname$::has_$name$() const {\n"
+        "  return $oneof_name$_case() == k$field_name$;\n"
+        "}\n"
+        "inline void $classname$::set_has_$name$() {\n"
+        "  _oneof_case_[$oneof_index$] = k$field_name$;\n"
+        "}\n");
     } else {
       // Singular field.
       char buffer[kFastToBufferSize];
@@ -426,14 +443,27 @@ GenerateFieldAccessorDefinitions(io::Printer* printer) {
       "inline void $classname$::clear_$name$() {\n");
 
     printer->Indent();
-    field_generators_.get(field).GenerateClearingCode(printer);
-    printer->Outdent();
 
-    if (!field->is_repeated()) {
+    if (field->containing_oneof()) {
+      // Clear this field only if it is the active field in this oneof,
+      // otherwise ignore
       printer->Print(vars,
-                     "  clear_has_$name$();\n");
+        "if (has_$name$()) {\n");
+      printer->Indent();
+      field_generators_.get(field).GenerateClearingCode(printer);
+      printer->Print(vars,
+        "clear_has_$oneof_name$();\n");
+      printer->Outdent();
+      printer->Print("}\n");
+    } else {
+      field_generators_.get(field).GenerateClearingCode(printer);
+      if (!field->is_repeated()) {
+        printer->Print(vars,
+                       "clear_has_$name$();\n");
+      }
     }
 
+    printer->Outdent();
     printer->Print("}\n");
 
     // Generate type-specific accessors.
@@ -441,6 +471,49 @@ GenerateFieldAccessorDefinitions(io::Printer* printer) {
 
     printer->Print("\n");
   }
+
+  // Generate has_$name$() and clear_has_$name$() functions for oneofs
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    map<string, string> vars;
+    vars["oneof_name"] = descriptor_->oneof_decl(i)->name();
+    vars["oneof_index"] = SimpleItoa(descriptor_->oneof_decl(i)->index());
+    vars["cap_oneof_name"] =
+        ToUpper(descriptor_->oneof_decl(i)->name());
+    vars["classname"] = classname_;
+    printer->Print(
+      vars,
+      "inline bool $classname$::has_$oneof_name$() {\n"
+      "  return $oneof_name$_case() != $cap_oneof_name$_NOT_SET;\n"
+      "}\n"
+      "inline void $classname$::clear_has_$oneof_name$() {\n"
+      "  _oneof_case_[$oneof_index$] = $cap_oneof_name$_NOT_SET;\n"
+      "}\n");
+  }
+}
+
+// Helper for the code that emits the Clear() method.
+static bool CanClearByZeroing(const FieldDescriptor* field) {
+  if (field->is_repeated() || field->is_extension()) return false;
+  switch (field->cpp_type()) {
+    case internal::WireFormatLite::CPPTYPE_ENUM:
+      return field->default_value_enum()->number() == 0;
+    case internal::WireFormatLite::CPPTYPE_INT32:
+      return field->default_value_int32() == 0;
+    case internal::WireFormatLite::CPPTYPE_INT64:
+      return field->default_value_int64() == 0;
+    case internal::WireFormatLite::CPPTYPE_UINT32:
+      return field->default_value_uint32() == 0;
+    case internal::WireFormatLite::CPPTYPE_UINT64:
+      return field->default_value_uint64() == 0;
+    case internal::WireFormatLite::CPPTYPE_FLOAT:
+      return field->default_value_float() == 0;
+    case internal::WireFormatLite::CPPTYPE_DOUBLE:
+      return field->default_value_double() == 0;
+    case internal::WireFormatLite::CPPTYPE_BOOL:
+      return field->default_value_bool() == false;
+    default:
+      return false;
+  }
 }
 
 void MessageGenerator::
@@ -455,6 +528,7 @@ GenerateClassDefinition(io::Printer* printer) {
   map<string, string> vars;
   vars["classname"] = classname_;
   vars["field_count"] = SimpleItoa(descriptor_->field_count());
+  vars["oneof_decl_count"] = SimpleItoa(descriptor_->oneof_decl_count());
   if (options_.dllexport_decl.empty()) {
     vars["dllexport"] = "";
   } else {
@@ -479,7 +553,7 @@ GenerateClassDefinition(io::Printer* printer) {
     "}\n"
     "\n");
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
       "inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {\n"
       "  return _unknown_fields_;\n"
@@ -489,6 +563,16 @@ GenerateClassDefinition(io::Printer* printer) {
       "  return &_unknown_fields_;\n"
       "}\n"
       "\n");
+  } else {
+    printer->Print(
+      "inline const ::std::string& unknown_fields() const {\n"
+      "  return _unknown_fields_;\n"
+      "}\n"
+      "\n"
+      "inline ::std::string* mutable_unknown_fields() {\n"
+      "  return &_unknown_fields_;\n"
+      "}\n"
+      "\n");
   }
 
   // Only generate this member if it's not disabled.
@@ -502,6 +586,33 @@ GenerateClassDefinition(io::Printer* printer) {
     "static const $classname$& default_instance();\n"
     "\n");
 
+  // Generate enum values for every field in oneofs. One list is generated for
+  // each oneof with an additional *_NOT_SET value.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "enum $camel_oneof_name$Case {\n",
+        "camel_oneof_name",
+        UnderscoresToCamelCase(descriptor_->oneof_decl(i)->name(), true));
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      printer->Print(
+          "k$field_name$ = $field_number$,\n",
+          "field_name",
+          UnderscoresToCamelCase(
+              descriptor_->oneof_decl(i)->field(j)->name(), true),
+          "field_number",
+          SimpleItoa(descriptor_->oneof_decl(i)->field(j)->number()));
+    }
+    printer->Print(
+        "$cap_oneof_name$_NOT_SET = 0,\n",
+        "cap_oneof_name",
+        ToUpper(descriptor_->oneof_decl(i)->name()));
+    printer->Outdent();
+    printer->Print(
+        "};\n"
+        "\n");
+  }
+
   if (!StaticInitializersForced(descriptor_->file())) {
     printer->Print(vars,
       "#ifdef GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER\n"
@@ -545,20 +656,50 @@ GenerateClassDefinition(io::Printer* printer) {
       "    ::google::protobuf::io::CodedInputStream* input);\n"
       "void SerializeWithCachedSizes(\n"
       "    ::google::protobuf::io::CodedOutputStream* output) const;\n");
+    // DiscardUnknownFields() is implemented in message.cc using reflections. We
+    // need to implement this function in generated code for messages.
+    if (!UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "void DiscardUnknownFields();\n");
+    }
     if (HasFastArraySerialization(descriptor_->file())) {
       printer->Print(
         "::google::protobuf::uint8* SerializeWithCachedSizesToArray(::google::protobuf::uint8* output) const;\n");
     }
   }
 
-  printer->Print(vars,
+  // Check all FieldDescriptors including those in oneofs to estimate
+  // whether ::std::string is likely to be used, and depending on that
+  // estimate, set uses_string_ to true or false.  That contols
+  // whether to force initialization of empty_string_ in SharedCtor().
+  // It's often advantageous to do so to keep "is empty_string_
+  // inited?" code from appearing all over the place.
+  vector<const FieldDescriptor*> descriptors;
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    descriptors.push_back(descriptor_->field(i));
+  }
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      descriptors.push_back(descriptor_->oneof_decl(i)->field(j));
+    }
+  }
+  uses_string_ = false;
+  for (int i = 0; i < descriptors.size(); i++) {
+    const FieldDescriptor* field = descriptors[i];
+    if (field->cpp_type() == FieldDescriptor::CPPTYPE_STRING) {
+      switch (field->options().ctype()) {
+        default: uses_string_ = true; break;
+      }
+    }
+  }
+
+  printer->Print(
     "int GetCachedSize() const { return _cached_size_; }\n"
     "private:\n"
     "void SharedCtor();\n"
     "void SharedDtor();\n"
     "void SetCachedSize(int size) const;\n"
-    "public:\n"
-    "\n");
+    "public:\n");
 
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(
@@ -621,13 +762,44 @@ GenerateClassDefinition(io::Printer* printer) {
       printer->Print(
         "inline void set_has_$name$();\n",
         "name", FieldName(descriptor_->field(i)));
-      printer->Print(
-        "inline void clear_has_$name$();\n",
-        "name", FieldName(descriptor_->field(i)));
+      if (!descriptor_->field(i)->containing_oneof()) {
+        printer->Print(
+          "inline void clear_has_$name$();\n",
+          "name", FieldName(descriptor_->field(i)));
+      }
     }
   }
   printer->Print("\n");
 
+  // Generate oneof function declarations
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "inline bool has_$oneof_name$();\n"
+        "void clear_$oneof_name$();\n"
+        "inline void clear_has_$oneof_name$();\n\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name());
+  }
+
+  // Prepare decls for _cached_size_ and _has_bits_.  Their position in the
+  // output will be determined later.
+
+  bool need_to_emit_cached_size = true;
+  // TODO(kenton):  Make _cached_size_ an atomic<int> when C++ supports it.
+  const string cached_size_decl = "mutable int _cached_size_;\n";
+
+  // TODO(jieluo) - Optimize _has_bits_ for repeated and oneof fields.
+  size_t sizeof_has_bits = (descriptor_->field_count() + 31) / 32 * 4;
+  if (descriptor_->field_count() == 0) {
+    // Zero-size arrays aren't technically allowed, and MSVC in particular
+    // doesn't like them.  We still need to declare these arrays to make
+    // other code compile.  Since this is an uncommon case, we'll just declare
+    // them with size 1 and waste some space.  Oh well.
+    sizeof_has_bits = 4;
+  }
+  const string has_bits_decl = sizeof_has_bits == 0 ? "" :
+      "::google::protobuf::uint32 _has_bits_[" + SimpleItoa(sizeof_has_bits / 4) + "];\n";
+
+
   // To minimize padding, data members are divided into three sections:
   // (1) members assumed to align to 8 bytes
   // (2) members corresponding to message fields, re-ordered to optimize
@@ -642,42 +814,92 @@ GenerateClassDefinition(io::Printer* printer) {
       "\n");
   }
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
       "::google::protobuf::UnknownFieldSet _unknown_fields_;\n"
       "\n");
+  } else {
+    printer->Print(
+      "::std::string _unknown_fields_;\n"
+      "\n");
+  }
+
+  // _has_bits_ is frequently accessed, so to reduce code size and improve
+  // speed, it should be close to the start of the object.  But, try not to
+  // waste space:_has_bits_ by itself always makes sense if its size is a
+  // multiple of 8, but, otherwise, maybe _has_bits_ and cached_size_ together
+  // will work well.
+  printer->Print(has_bits_decl.c_str());
+  if ((sizeof_has_bits % 8) != 0) {
+    printer->Print(cached_size_decl.c_str());
+    need_to_emit_cached_size = false;
   }
 
   // Field members:
 
+  // List fields which doesn't belong to any oneof
   vector<const FieldDescriptor*> fields;
+  hash_map<string, int> fieldname_to_chunk;
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    fields.push_back(descriptor_->field(i));
+    if (!descriptor_->field(i)->containing_oneof()) {
+      const FieldDescriptor* field = descriptor_->field(i);
+      fields.push_back(field);
+      fieldname_to_chunk[FieldName(field)] = i / 8;
+    }
   }
   OptimizePadding(&fields);
+  // Emit some private and static members
+  runs_of_fields_ = vector< vector<string> >(1);
   for (int i = 0; i < fields.size(); ++i) {
-    field_generators_.get(fields[i]).GeneratePrivateMembers(printer);
+    const FieldDescriptor* field = fields[i];
+    const FieldGenerator& generator = field_generators_.get(field);
+    generator.GenerateStaticMembers(printer);
+    generator.GeneratePrivateMembers(printer);
+    if (CanClearByZeroing(field)) {
+      const string& fieldname = FieldName(field);
+      if (!runs_of_fields_.back().empty() &&
+          (fieldname_to_chunk[runs_of_fields_.back().back()] !=
+           fieldname_to_chunk[fieldname])) {
+        runs_of_fields_.push_back(vector<string>());
+      }
+      runs_of_fields_.back().push_back(fieldname);
+    } else if (!runs_of_fields_.back().empty()) {
+      runs_of_fields_.push_back(vector<string>());
+    }
+  }
+
+  // For each oneof generate a union
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "union $camel_oneof_name$Union {\n",
+        "camel_oneof_name",
+        UnderscoresToCamelCase(descriptor_->oneof_decl(i)->name(), true));
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      field_generators_.get(descriptor_->oneof_decl(i)->
+                            field(j)).GeneratePrivateMembers(printer);
+    }
+    printer->Outdent();
+    printer->Print(
+        "} $oneof_name$_;\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name());
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      field_generators_.get(descriptor_->oneof_decl(i)->
+                            field(j)).GenerateStaticMembers(printer);
+    }
   }
 
   // Members assumed to align to 4 bytes:
 
-  // TODO(kenton):  Make _cached_size_ an atomic<int> when C++ supports it.
-  printer->Print(
-      "\n"
-      "mutable int _cached_size_;\n");
+  if (need_to_emit_cached_size) {
+    printer->Print(cached_size_decl.c_str());
+    need_to_emit_cached_size = false;
+  }
 
-  // Generate _has_bits_.
-  if (descriptor_->field_count() > 0) {
+  // Generate _oneof_case_.
+  if (descriptor_->oneof_decl_count() > 0) {
     printer->Print(vars,
-      "::google::protobuf::uint32 _has_bits_[($field_count$ + 31) / 32];\n"
-      "\n");
-  } else {
-    // Zero-size arrays aren't technically allowed, and MSVC in particular
-    // doesn't like them.  We still need to declare these arrays to make
-    // other code compile.  Since this is an uncommon case, we'll just declare
-    // them with size 1 and waste some space.  Oh well.
-    printer->Print(
-      "::google::protobuf::uint32 _has_bits_[1];\n"
+      "::google::protobuf::uint32 _oneof_case_[$oneof_decl_count$];\n"
       "\n");
   }
 
@@ -710,6 +932,7 @@ GenerateClassDefinition(io::Printer* printer) {
 
   printer->Outdent();
   printer->Print(vars, "};");
+  GOOGLE_DCHECK(!need_to_emit_cached_size);
 }
 
 void MessageGenerator::
@@ -721,6 +944,23 @@ GenerateInlineMethods(io::Printer* printer) {
   }
 
   GenerateFieldAccessorDefinitions(printer);
+
+  // Generate oneof_case() functions.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    map<string, string> vars;
+    vars["class_name"] = classname_;
+    vars["camel_oneof_name"] = UnderscoresToCamelCase(
+        descriptor_->oneof_decl(i)->name(), true);
+    vars["oneof_name"] = descriptor_->oneof_decl(i)->name();
+    vars["oneof_index"] = SimpleItoa(descriptor_->oneof_decl(i)->index());
+    printer->Print(
+        vars,
+        "inline $class_name$::$camel_oneof_name$Case $class_name$::"
+        "$oneof_name$_case() const {\n"
+        "  return $class_name$::$camel_oneof_name$Case("
+        "_oneof_case_[$oneof_index$]);\n"
+        "}\n");
+  }
 }
 
 void MessageGenerator::
@@ -731,6 +971,25 @@ GenerateDescriptorDeclarations(io::Printer* printer) {
     "  $name$_reflection_ = NULL;\n",
     "name", classname_);
 
+  // Generate oneof default instance for reflection usage.
+  if (descriptor_->oneof_decl_count() > 0) {
+    printer->Print("struct $name$OneofInstance {\n",
+                   "name", classname_);
+    for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+      for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+        const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+        printer->Print("  ");
+        if (IsStringOrMessage(field)) {
+          printer->Print("const ");
+        }
+        field_generators_.get(field).GeneratePrivateMembers(printer);
+      }
+    }
+
+    printer->Print("}* $name$_default_oneof_instance_ = NULL;\n",
+                   "name", classname_);
+  }
+
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     nested_generators_[i]->GenerateDescriptorDeclarations(printer);
   }
@@ -783,6 +1042,14 @@ GenerateDescriptorInitializer(io::Printer* printer, int index) {
     printer->Print(vars,
       "    -1,\n");
   }
+
+  if (descriptor_->oneof_decl_count() > 0) {
+    printer->Print(vars,
+    "    $classname$_default_oneof_instance_,\n"
+    "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET("
+      "$classname$, _oneof_case_[0]),\n");
+  }
+
   printer->Print(
     "    ::google::protobuf::DescriptorPool::generated_pool(),\n");
   printer->Print(vars,
@@ -830,6 +1097,13 @@ GenerateDefaultInstanceAllocator(io::Printer* printer) {
     "$classname$::default_instance_ = new $classname$();\n",
     "classname", classname_);
 
+  if ((descriptor_->oneof_decl_count() > 0) &&
+      HasDescriptorMethods(descriptor_->file())) {
+    printer->Print(
+    "$classname$_default_oneof_instance_ = new $classname$OneofInstance;\n",
+    "classname", classname_);
+  }
+
   // Handle nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     nested_generators_[i]->GenerateDefaultInstanceAllocator(printer);
@@ -861,6 +1135,11 @@ GenerateShutdownCode(io::Printer* printer) {
     "classname", classname_);
 
   if (HasDescriptorMethods(descriptor_->file())) {
+    if (descriptor_->oneof_decl_count() > 0) {
+      printer->Print(
+        "delete $classname$_default_oneof_instance_;\n",
+        "classname", classname_);
+    }
     printer->Print(
       "delete $classname$_reflection_;\n",
       "classname", classname_);
@@ -918,6 +1197,11 @@ GenerateClassMethods(io::Printer* printer) {
   GenerateStructors(printer);
   printer->Print("\n");
 
+  if (descriptor_->oneof_decl_count() > 0) {
+    GenerateOneofClear(printer);
+    printer->Print("\n");
+  }
+
   if (HasGeneratedMethods(descriptor_->file())) {
     GenerateClear(printer);
     printer->Print("\n");
@@ -977,15 +1261,33 @@ GenerateOffsets(io::Printer* printer) {
   printer->Print(
     "static const int $classname$_offsets_[$field_count$] = {\n",
     "classname", classname_,
-    "field_count", SimpleItoa(max(1, descriptor_->field_count())));
+    "field_count", SimpleItoa(max(
+        1, descriptor_->field_count() + descriptor_->oneof_decl_count())));
   printer->Indent();
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
+    if (field->containing_oneof()) {
+      printer->Print(
+          "PROTO2_GENERATED_DEFAULT_ONEOF_FIELD_OFFSET("
+          "$classname$_default_oneof_instance_, $name$_),\n",
+          "classname", classname_,
+          "name", FieldName(field));
+    } else {
+      printer->Print(
+          "GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET($classname$, "
+                                                 "$name$_),\n",
+          "classname", classname_,
+          "name", FieldName(field));
+    }
+  }
+
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    const OneofDescriptor* oneof = descriptor_->oneof_decl(i);
     printer->Print(
       "GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET($classname$, $name$_),\n",
       "classname", classname_,
-      "name", FieldName(field));
+      "name", oneof->name());
   }
 
   printer->Outdent();
@@ -999,17 +1301,26 @@ GenerateSharedConstructorCode(io::Printer* printer) {
     "classname", classname_);
   printer->Indent();
 
-  printer->Print(
-    "_cached_size_ = 0;\n");
+  printer->Print(StrCat(
+      uses_string_ ? "::google::protobuf::internal::GetEmptyString();\n" : "",
+      "_cached_size_ = 0;\n").c_str());
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    field_generators_.get(descriptor_->field(i))
-                     .GenerateConstructorCode(printer);
+    if (!descriptor_->field(i)->containing_oneof()) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateConstructorCode(printer);
+    }
   }
 
   printer->Print(
     "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
 
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "clear_has_$oneof_name$();\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name());
+  }
+
   printer->Outdent();
   printer->Print("}\n\n");
 }
@@ -1020,10 +1331,21 @@ GenerateSharedDestructorCode(io::Printer* printer) {
     "void $classname$::SharedDtor() {\n",
     "classname", classname_);
   printer->Indent();
-  // Write the destructors for each field.
+  // Write the destructors for each field except oneof members.
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    field_generators_.get(descriptor_->field(i))
-                     .GenerateDestructorCode(printer);
+    if (!descriptor_->field(i)->containing_oneof()) {
+      field_generators_.get(descriptor_->field(i))
+                       .GenerateDestructorCode(printer);
+    }
+  }
+
+  // Generate code to destruct oneofs. Clearing should do the work.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "if (has_$oneof_name$()) {\n"
+        "  clear_$oneof_name$();\n"
+        "}\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name());
   }
 
   PrintHandlingOptionalStaticInitializers(
@@ -1042,8 +1364,12 @@ GenerateSharedDestructorCode(io::Printer* printer) {
 
     if (!field->is_repeated() &&
         field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
-      printer->Print("  delete $name$_;\n",
-                     "name", FieldName(field));
+      // Skip oneof members
+      if (!field->containing_oneof()) {
+        printer->Print(
+            "  delete $name$_;\n",
+            "name", FieldName(field));
+      }
     }
   }
 
@@ -1063,9 +1389,11 @@ GenerateStructors(io::Printer* printer) {
     "$classname$::$classname$()\n"
     "  : $superclass$() {\n"
     "  SharedCtor();\n"
+    "  // @@protoc_insertion_point(constructor:$full_name$)\n"
     "}\n",
     "classname", classname_,
-    "superclass", superclass);
+    "superclass", superclass,
+    "full_name", descriptor_->full_name());
 
   printer->Print(
     "\n"
@@ -1082,7 +1410,14 @@ GenerateStructors(io::Printer* printer) {
     const FieldDescriptor* field = descriptor_->field(i);
 
     if (!field->is_repeated() &&
-        field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
+        field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE &&
+        (field->containing_oneof() == NULL ||
+         HasDescriptorMethods(descriptor_->file()))) {
+      string name;
+      if (field->containing_oneof()) {
+        name = classname_ + "_default_oneof_instance_->";
+      }
+      name += FieldName(field);
       PrintHandlingOptionalStaticInitializers(
         descriptor_->file(), printer,
         // With static initializers.
@@ -1091,8 +1426,12 @@ GenerateStructors(io::Printer* printer) {
         "  $name$_ = const_cast< $type$*>(\n"
         "      $type$::internal_default_instance());\n",
         // Vars.
-        "name", FieldName(field),
+        "name", name,
         "type", FieldMessageTypeName(field));
+    } else if (field->containing_oneof() &&
+               HasDescriptorMethods(descriptor_->file())) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateConstructorCode(printer);
     }
   }
   printer->Print(
@@ -1105,10 +1444,12 @@ GenerateStructors(io::Printer* printer) {
     "  : $superclass$() {\n"
     "  SharedCtor();\n"
     "  MergeFrom(from);\n"
+    "  // @@protoc_insertion_point(copy_constructor:$full_name$)\n"
     "}\n"
     "\n",
     "classname", classname_,
-    "superclass", superclass);
+    "superclass", superclass,
+    "full_name", descriptor_->full_name());
 
   // Generate the shared constructor code.
   GenerateSharedConstructorCode(printer);
@@ -1116,10 +1457,12 @@ GenerateStructors(io::Printer* printer) {
   // Generate the destructor.
   printer->Print(
     "$classname$::~$classname$() {\n"
+    "  // @@protoc_insertion_point(destructor:$full_name$)\n"
     "  SharedDtor();\n"
     "}\n"
     "\n",
-    "classname", classname_);
+    "classname", classname_,
+    "full_name", descriptor_->full_name());
 
   // Generate the shared destructor code.
   GenerateSharedDestructorCode(printer);
@@ -1166,13 +1509,25 @@ GenerateStructors(io::Printer* printer) {
     "}\n"
     "\n"
     "$classname$* $classname$::default_instance_ = NULL;\n"
-    "\n"
+    "\n",
+    "classname", classname_);
+
+  printer->Print(
     "$classname$* $classname$::New() const {\n"
     "  return new $classname$;\n"
     "}\n",
-    "classname", classname_,
-    "adddescriptorsname",
-    GlobalAddDescriptorsName(descriptor_->file()->name()));
+    "classname", classname_);
+
+}
+
+// Return the number of bits set in n, a non-negative integer.
+static int popcnt(uint32 n) {
+  int result = 0;
+  while (n != 0) {
+    result += (n & 1);
+    n = n / 2;
+  }
+  return result;
 }
 
 void MessageGenerator::
@@ -1181,64 +1536,133 @@ GenerateClear(io::Printer* printer) {
                  "classname", classname_);
   printer->Indent();
 
-  int last_index = -1;
-
+  // Step 1: Extensions
   if (descriptor_->extension_range_count() > 0) {
     printer->Print("_extensions_.Clear();\n");
   }
 
+  // Step 2: Everything but extensions, repeateds, unions.
+  // These are handled in chunks of 8.  The first chunk is
+  // the non-extensions-non-repeateds-non-unions in
+  //  descriptor_->field(0), descriptor_->field(1), ... descriptor_->field(7),
+  // and the second chunk is the same for
+  //  descriptor_->field(8), descriptor_->field(9), ... descriptor_->field(15),
+  // etc.
+  set<int> step2_indices;
+  hash_map<string, int> fieldname_to_chunk;
+  hash_map<int, string> memsets_for_chunk;
+  hash_map<int, int> memset_field_count_for_chunk;
+  hash_set<string> handled;  // fields that appear anywhere in memsets_for_chunk
+  hash_map<int, uint32> fields_mask_for_chunk;
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
+    if (!field->is_repeated() && !field->containing_oneof()) {
+      step2_indices.insert(i);
+      int chunk = i / 8;
+      fieldname_to_chunk[FieldName(field)] = chunk;
+      fields_mask_for_chunk[chunk] |= static_cast<uint32>(1) << (i % 32);
+    }
+  }
 
-    if (!field->is_repeated()) {
-      // We can use the fact that _has_bits_ is a giant bitfield to our
-      // advantage:  We can check up to 32 bits at a time for equality to
-      // zero, and skip the whole range if so.  This can improve the speed
-      // of Clear() for messages which contain a very large number of
-      // optional fields of which only a few are used at a time.  Here,
-      // we've chosen to check 8 bits at a time rather than 32.
-      if (i / 8 != last_index / 8 || last_index < 0) {
-        if (last_index >= 0) {
-          printer->Outdent();
-          printer->Print("}\n");
-        }
-        printer->Print(
-          "if (_has_bits_[$index$ / 32] & (0xffu << ($index$ % 32))) {\n",
-          "index", SimpleItoa(field->index()));
-        printer->Indent();
+  // Step 2a: Greedily seek runs of fields that can be cleared by memset-to-0.
+  // The generated code uses two macros to help it clear runs of fields:
+  // OFFSET_OF_FIELD_ computes the offset (in bytes) of a field in the Message.
+  // ZR_ zeroes a non-empty range of fields via memset.
+  const char* macros =
+      "#define OFFSET_OF_FIELD_(f) (reinterpret_cast<char*>(      \\\n"
+      "  &reinterpret_cast<$classname$*>(16)->f) - \\\n"
+      "   reinterpret_cast<char*>(16))\n\n"
+      "#define ZR_(first, last) do {                              \\\n"
+      "    size_t f = OFFSET_OF_FIELD_(first);                    \\\n"
+      "    size_t n = OFFSET_OF_FIELD_(last) - f + sizeof(last);  \\\n"
+      "    ::memset(&first, 0, n);                                \\\n"
+      "  } while (0)\n\n";
+  for (int i = 0; i < runs_of_fields_.size(); i++) {
+    const vector<string>& run = runs_of_fields_[i];
+    if (run.size() < 2) continue;
+    const string& first_field_name = run[0];
+    const string& last_field_name = run.back();
+    int chunk = fieldname_to_chunk[run[0]];
+    memsets_for_chunk[chunk].append(
+      "ZR_(" + first_field_name + "_, " + last_field_name + "_);\n");
+    for (int j = 0; j < run.size(); j++) {
+      GOOGLE_DCHECK_EQ(chunk, fieldname_to_chunk[run[j]]);
+      handled.insert(run[j]);
+    }
+    memset_field_count_for_chunk[chunk] += run.size();
+  }
+  const bool macros_are_needed = handled.size() > 0;
+  if (macros_are_needed) {
+    printer->Outdent();
+    printer->Print(macros,
+                   "classname", classname_);
+    printer->Indent();
+  }
+  // Step 2b: Finish step 2, ignoring fields handled in step 2a.
+  int last_index = -1;
+  bool chunk_block_in_progress = false;
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    if (step2_indices.count(i) == 0) continue;
+    const FieldDescriptor* field = descriptor_->field(i);
+    const string fieldname = FieldName(field);
+    if (i / 8 != last_index / 8 || last_index < 0) {
+      // End previous chunk, if there was one.
+      if (chunk_block_in_progress) {
+        printer->Outdent();
+        printer->Print("}\n");
+        chunk_block_in_progress = false;
       }
-      last_index = i;
-
-      // It's faster to just overwrite primitive types, but we should
-      // only clear strings and messages if they were set.
-      // TODO(kenton):  Let the CppFieldGenerator decide this somehow.
-      bool should_check_bit =
-        field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE ||
-        field->cpp_type() == FieldDescriptor::CPPTYPE_STRING;
-
-      if (should_check_bit) {
+      // Start chunk.
+      const string& memsets = memsets_for_chunk[i / 8];
+      uint32 mask = fields_mask_for_chunk[i / 8];
+      int count = popcnt(mask);
+      if (count == 1 ||
+          (count <= 4 && count == memset_field_count_for_chunk[i / 8])) {
+        // No "if" here because the chunk is trivial.
+      } else {
         printer->Print(
-          "if (has_$name$()) {\n",
-          "name", FieldName(field));
+          "if (_has_bits_[$index$ / 32] & $mask$) {\n",
+          "index", SimpleItoa(i / 8 * 8),
+          "mask", SimpleItoa(mask));
         printer->Indent();
+        chunk_block_in_progress = true;
       }
+      printer->Print(memsets.c_str());
+    }
+    last_index = i;
+    if (handled.count(fieldname) > 0) continue;
+
+    // It's faster to just overwrite primitive types, but we should
+    // only clear strings and messages if they were set.
+    // TODO(kenton):  Let the CppFieldGenerator decide this somehow.
+    bool should_check_bit =
+      field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE ||
+      field->cpp_type() == FieldDescriptor::CPPTYPE_STRING;
+
+    if (should_check_bit) {
+      printer->Print("if (has_$name$()) {\n", "name", fieldname);
+      printer->Indent();
+    }
 
-      field_generators_.get(field).GenerateClearingCode(printer);
+    field_generators_.get(field).GenerateClearingCode(printer);
 
-      if (should_check_bit) {
-        printer->Outdent();
-        printer->Print("}\n");
-      }
+    if (should_check_bit) {
+      printer->Outdent();
+      printer->Print("}\n");
     }
   }
 
-  if (last_index >= 0) {
+  if (chunk_block_in_progress) {
     printer->Outdent();
     printer->Print("}\n");
   }
+  if (macros_are_needed) {
+    printer->Outdent();
+    printer->Print("\n#undef OFFSET_OF_FIELD_\n#undef ZR_\n\n");
+    printer->Indent();
+  }
 
-  // Repeated fields don't use _has_bits_ so we clear them in a separate
-  // pass.
+  // Step 3: Repeated fields don't use _has_bits_; emit code to clear them here.
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
 
@@ -1247,12 +1671,23 @@ GenerateClear(io::Printer* printer) {
     }
   }
 
+  // Step 4: Unions.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "clear_$oneof_name$();\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name());
+  }
+
+  // Step 5: Everything else.
   printer->Print(
     "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
       "mutable_unknown_fields()->Clear();\n");
+  } else {
+    printer->Print(
+      "mutable_unknown_fields()->clear();\n");
   }
 
   printer->Outdent();
@@ -1260,6 +1695,58 @@ GenerateClear(io::Printer* printer) {
 }
 
 void MessageGenerator::
+GenerateOneofClear(io::Printer* printer) {
+  // Generated function clears the active field and union case (e.g. foo_case_).
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "void $classname$::clear_$oneofname$() {\n",
+        "classname", classname_,
+        "oneofname", descriptor_->oneof_decl(i)->name());
+    printer->Indent();
+    printer->Print(
+        "switch($oneofname$_case()) {\n",
+        "oneofname", descriptor_->oneof_decl(i)->name());
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+      printer->Print(
+          "case k$field_name$: {\n",
+          "field_name", UnderscoresToCamelCase(field->name(), true));
+      printer->Indent();
+      // We clear only allocated objects in oneofs
+      if (!IsStringOrMessage(field)) {
+        printer->Print(
+            "// No need to clear\n");
+      } else {
+        field_generators_.get(field).GenerateClearingCode(printer);
+      }
+      printer->Print(
+          "break;\n");
+      printer->Outdent();
+      printer->Print(
+          "}\n");
+    }
+    printer->Print(
+        "case $cap_oneof_name$_NOT_SET: {\n"
+        "  break;\n"
+        "}\n",
+        "cap_oneof_name",
+        ToUpper(descriptor_->oneof_decl(i)->name()));
+    printer->Outdent();
+    printer->Print(
+        "}\n"
+        "_oneof_case_[$oneof_index$] = $cap_oneof_name$_NOT_SET;\n",
+        "oneof_index", SimpleItoa(i),
+        "cap_oneof_name",
+        ToUpper(descriptor_->oneof_decl(i)->name()));
+    printer->Outdent();
+    printer->Print(
+        "}\n"
+        "\n");
+  }
+}
+
+void MessageGenerator::
 GenerateSwap(io::Printer* printer) {
   // Generate the Swap member function.
   printer->Print("void $classname$::Swap($classname$* other) {\n",
@@ -1274,13 +1761,23 @@ GenerateSwap(io::Printer* printer) {
       field_generators_.get(field).GenerateSwappingCode(printer);
     }
 
+    for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+      printer->Print(
+        "std::swap($oneof_name$_, other->$oneof_name$_);\n"
+        "std::swap(_oneof_case_[$i$], other->_oneof_case_[$i$]);\n",
+        "oneof_name", descriptor_->oneof_decl(i)->name(),
+        "i", SimpleItoa(i));
+    }
+
     for (int i = 0; i < (descriptor_->field_count() + 31) / 32; ++i) {
       printer->Print("std::swap(_has_bits_[$i$], other->_has_bits_[$i$]);\n",
                      "i", SimpleItoa(i));
     }
 
-    if (HasUnknownFields(descriptor_->file())) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
       printer->Print("_unknown_fields_.Swap(&other->_unknown_fields_);\n");
+    } else {
+      printer->Print("_unknown_fields_.swap(other->_unknown_fields_);\n");
     }
     printer->Print("std::swap(_cached_size_, other->_cached_size_);\n");
     if (descriptor_->extension_range_count() > 0) {
@@ -1352,13 +1849,43 @@ GenerateMergeFrom(io::Printer* printer) {
     }
   }
 
+  // Merge oneof fields. Oneof field requires oneof case check.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); ++i) {
+    printer->Print(
+        "switch (from.$oneofname$_case()) {\n",
+        "oneofname", descriptor_->oneof_decl(i)->name());
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+      printer->Print(
+          "case k$field_name$: {\n",
+          "field_name", UnderscoresToCamelCase(field->name(), true));
+      printer->Indent();
+      field_generators_.get(field).GenerateMergingCode(printer);
+      printer->Print(
+          "break;\n");
+      printer->Outdent();
+      printer->Print(
+          "}\n");
+    }
+    printer->Print(
+        "case $cap_oneof_name$_NOT_SET: {\n"
+        "  break;\n"
+        "}\n",
+        "cap_oneof_name",
+        ToUpper(descriptor_->oneof_decl(i)->name()));
+    printer->Outdent();
+    printer->Print(
+        "}\n");
+  }
+
   // Merge Optional and Required fields (after a _has_bit check).
   int last_index = -1;
 
   for (int i = 0; i < descriptor_->field_count(); ++i) {
     const FieldDescriptor* field = descriptor_->field(i);
 
-    if (!field->is_repeated()) {
+    if (!field->is_repeated() && !field->containing_oneof()) {
       // See above in GenerateClear for an explanation of this.
       if (i / 8 != last_index / 8 || last_index < 0) {
         if (last_index >= 0) {
@@ -1394,9 +1921,12 @@ GenerateMergeFrom(io::Printer* printer) {
     printer->Print("_extensions_.MergeFrom(from._extensions_);\n");
   }
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
       "mutable_unknown_fields()->MergeFrom(from.unknown_fields());\n");
+  } else {
+    printer->Print(
+      "mutable_unknown_fields()->append(from.unknown_fields());\n");
   }
 
   printer->Outdent();
@@ -1465,14 +1995,39 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
   printer->Print(
     "bool $classname$::MergePartialFromCodedStream(\n"
     "    ::google::protobuf::io::CodedInputStream* input) {\n"
-    "#define DO_(EXPRESSION) if (!(EXPRESSION)) return false\n"
-    "  ::google::protobuf::uint32 tag;\n"
-    "  while ((tag = input->ReadTag()) != 0) {\n",
+    "#define DO_(EXPRESSION) if (!(EXPRESSION)) goto failure\n"
+    "  ::google::protobuf::uint32 tag;\n",
     "classname", classname_);
 
+  if (!UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(
+      "  ::google::protobuf::io::StringOutputStream unknown_fields_string(\n"
+      "      mutable_unknown_fields());\n"
+      "  ::google::protobuf::io::CodedOutputStream unknown_fields_stream(\n"
+      "      &unknown_fields_string);\n");
+  }
+
+  printer->Print(
+    "  // @@protoc_insertion_point(parse_start:$full_name$)\n",
+    "full_name", descriptor_->full_name());
+
   printer->Indent();
+  printer->Print("for (;;) {\n");
   printer->Indent();
 
+  scoped_array<const FieldDescriptor*> ordered_fields(
+      SortFieldsByNumber(descriptor_));
+  uint32 maxtag = descriptor_->field_count() == 0 ? 0 :
+      WireFormat::MakeTag(ordered_fields[descriptor_->field_count() - 1]);
+  const int kCutoff0 = 127;               // fits in 1-byte varint
+  const int kCutoff1 = (127 << 7) + 127;  // fits in 2-byte varint
+  printer->Print("::std::pair< ::google::protobuf::uint32, bool> p = "
+                 "input->ReadTagWithCutoff($max$);\n"
+                 "tag = p.first;\n"
+                 "if (!p.second) goto handle_unusual;\n",
+                 "max", SimpleItoa(maxtag <= kCutoff0 ? kCutoff0 :
+                                   (maxtag <= kCutoff1 ? kCutoff1 :
+                                    maxtag)));
   if (descriptor_->field_count() > 0) {
     // We don't even want to print the switch() if we have no fields because
     // MSVC dislikes switch() statements that contain only a default value.
@@ -1482,14 +2037,11 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
     // of each case.  However, this is actually a bit slower in practice as it
     // creates a jump table that is 8x larger and sparser, and meanwhile the
     // if()s are highly predictable.
-    printer->Print(
-      "switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {\n");
+    printer->Print("switch (::google::protobuf::internal::WireFormatLite::"
+                   "GetTagFieldNumber(tag)) {\n");
 
     printer->Indent();
 
-    scoped_array<const FieldDescriptor*> ordered_fields(
-      SortFieldsByNumber(descriptor_));
-
     for (int i = 0; i < descriptor_->field_count(); i++) {
       const FieldDescriptor* field = ordered_fields[i];
 
@@ -1502,10 +2054,8 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
       const FieldGenerator& field_generator = field_generators_.get(field);
 
       // Emit code to parse the common, expected case.
-      printer->Print(
-        "if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==\n"
-        "    ::google::protobuf::internal::WireFormatLite::WIRETYPE_$wiretype$) {\n",
-        "wiretype", kWireTypeNames[WireFormat::WireTypeForField(field)]);
+      printer->Print("if (tag == $commontag$) {\n",
+                     "commontag", SimpleItoa(WireFormat::MakeTag(field)));
 
       if (i > 0 || (field->is_repeated() && !field->options().packed())) {
         printer->Print(
@@ -1523,20 +2073,22 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
 
       // Emit code to parse unexpectedly packed or unpacked values.
       if (field->is_packable() && field->options().packed()) {
-        printer->Print(
-          "} else if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag)\n"
-          "           == ::google::protobuf::internal::WireFormatLite::\n"
-          "              WIRETYPE_$wiretype$) {\n",
-          "wiretype",
-          kWireTypeNames[WireFormat::WireTypeForFieldType(field->type())]);
+        internal::WireFormatLite::WireType wiretype =
+            WireFormat::WireTypeForFieldType(field->type());
+        printer->Print("} else if (tag == $uncommontag$) {\n",
+                       "uncommontag", SimpleItoa(
+                           internal::WireFormatLite::MakeTag(
+                               field->number(), wiretype)));
         printer->Indent();
         field_generator.GenerateMergeFromCodedStream(printer);
         printer->Outdent();
       } else if (field->is_packable() && !field->options().packed()) {
-        printer->Print(
-          "} else if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag)\n"
-          "           == ::google::protobuf::internal::WireFormatLite::\n"
-          "              WIRETYPE_LENGTH_DELIMITED) {\n");
+        internal::WireFormatLite::WireType wiretype =
+            internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED;
+        printer->Print("} else if (tag == $uncommontag$) {\n",
+                       "uncommontag", SimpleItoa(
+                           internal::WireFormatLite::MakeTag(
+                               field->number(), wiretype)));
         printer->Indent();
         field_generator.GenerateMergeFromCodedStreamWithPacking(printer);
         printer->Outdent();
@@ -1544,7 +2096,7 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
 
       printer->Print(
         "} else {\n"
-        "  goto handle_uninterpreted;\n"
+        "  goto handle_unusual;\n"
         "}\n");
 
       // switch() is slow since it can't be predicted well.  Insert some if()s
@@ -1568,7 +2120,7 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
         // Expect EOF.
         // TODO(kenton):  Expect group end-tag?
         printer->Print(
-          "if (input->ExpectAtEnd()) return true;\n");
+          "if (input->ExpectAtEnd()) goto success;\n");
       }
 
       printer->Print(
@@ -1578,17 +2130,19 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
       printer->Print("}\n\n");
     }
 
-    printer->Print(
-      "default: {\n"
-      "handle_uninterpreted:\n");
+    printer->Print("default: {\n");
     printer->Indent();
   }
 
-  // Is this an end-group tag?  If so, this must be the end of the message.
+  printer->Outdent();
+  printer->Print("handle_unusual:\n");
+  printer->Indent();
+  // If tag is 0 or an end-group tag then this must be the end of the message.
   printer->Print(
-    "if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==\n"
+    "if (tag == 0 ||\n"
+    "    ::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==\n"
     "    ::google::protobuf::internal::WireFormatLite::WIRETYPE_END_GROUP) {\n"
-    "  return true;\n"
+    "  goto success;\n"
     "}\n");
 
   // Handle extension ranges.
@@ -1617,7 +2171,7 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
       }
     }
     printer->Print(") {\n");
-    if (HasUnknownFields(descriptor_->file())) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
       PrintHandlingOptionalStaticInitializers(
         descriptor_->file(), printer,
         // With static initializers.
@@ -1630,9 +2184,11 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
       PrintHandlingOptionalStaticInitializers(
         descriptor_->file(), printer,
         // With static initializers.
-        "  DO_(_extensions_.ParseField(tag, input, default_instance_));\n",
+        "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
+        "                              &unknown_fields_stream));\n",
         // Without.
-        "  DO_(_extensions_.ParseField(tag, input, &default_instance()));\n");
+        "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
+        "                              &unknown_fields_stream));\n");
     }
     printer->Print(
       "  continue;\n"
@@ -1640,13 +2196,14 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
   }
 
   // We really don't recognize this tag.  Skip it.
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
       "DO_(::google::protobuf::internal::WireFormat::SkipField(\n"
       "      input, tag, mutable_unknown_fields()));\n");
   } else {
     printer->Print(
-      "DO_(::google::protobuf::internal::WireFormatLite::SkipField(input, tag));\n");
+      "DO_(::google::protobuf::internal::WireFormatLite::SkipField(\n"
+      "    input, tag, &unknown_fields_stream));\n");
   }
 
   if (descriptor_->field_count() > 0) {
@@ -1660,10 +2217,15 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
   printer->Outdent();
   printer->Outdent();
   printer->Print(
-    "  }\n"                   // while
+    "  }\n"                   // for (;;)
+    "success:\n"
+    "  // @@protoc_insertion_point(parse_success:$full_name$)\n"
     "  return true;\n"
+    "failure:\n"
+    "  // @@protoc_insertion_point(parse_failure:$full_name$)\n"
+    "  return false;\n"
     "#undef DO_\n"
-    "}\n");
+    "}\n", "full_name", descriptor_->full_name());
 }
 
 void MessageGenerator::GenerateSerializeOneField(
@@ -1719,11 +2281,10 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) {
       "    ::google::protobuf::io::CodedOutputStream* output) const {\n"
       "  _extensions_.SerializeMessageSetWithCachedSizes(output);\n",
       "classname", classname_);
-    if (HasUnknownFields(descriptor_->file())) {
-      printer->Print(
-        "  ::google::protobuf::internal::WireFormat::SerializeUnknownMessageSetItems(\n"
-        "      unknown_fields(), output);\n");
-    }
+    GOOGLE_CHECK(UseUnknownFieldSet(descriptor_->file()));
+    printer->Print(
+      "  ::google::protobuf::internal::WireFormat::SerializeUnknownMessageSetItems(\n"
+      "      unknown_fields(), output);\n");
     printer->Print(
       "}\n");
     return;
@@ -1735,8 +2296,16 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) {
     "classname", classname_);
   printer->Indent();
 
+  printer->Print(
+    "// @@protoc_insertion_point(serialize_start:$full_name$)\n",
+    "full_name", descriptor_->full_name());
+
   GenerateSerializeWithCachedSizesBody(printer, false);
 
+  printer->Print(
+    "// @@protoc_insertion_point(serialize_end:$full_name$)\n",
+    "full_name", descriptor_->full_name());
+
   printer->Outdent();
   printer->Print(
     "}\n");
@@ -1752,12 +2321,11 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) {
       "  target =\n"
       "      _extensions_.SerializeMessageSetWithCachedSizesToArray(target);\n",
       "classname", classname_);
-    if (HasUnknownFields(descriptor_->file())) {
-      printer->Print(
-        "  target = ::google::protobuf::internal::WireFormat::\n"
-        "             SerializeUnknownMessageSetItemsToArray(\n"
-        "               unknown_fields(), target);\n");
-    }
+    GOOGLE_CHECK(UseUnknownFieldSet(descriptor_->file()));
+    printer->Print(
+      "  target = ::google::protobuf::internal::WireFormat::\n"
+      "             SerializeUnknownMessageSetItemsToArray(\n"
+      "               unknown_fields(), target);\n");
     printer->Print(
       "  return target;\n"
       "}\n");
@@ -1770,8 +2338,16 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) {
     "classname", classname_);
   printer->Indent();
 
+  printer->Print(
+    "// @@protoc_insertion_point(serialize_to_array_start:$full_name$)\n",
+    "full_name", descriptor_->full_name());
+
   GenerateSerializeWithCachedSizesBody(printer, true);
 
+  printer->Print(
+    "// @@protoc_insertion_point(serialize_to_array_end:$full_name$)\n",
+    "full_name", descriptor_->full_name());
+
   printer->Outdent();
   printer->Print(
     "  return target;\n"
@@ -1781,7 +2357,7 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) {
 void MessageGenerator::
 GenerateSerializeWithCachedSizesBody(io::Printer* printer, bool to_array) {
   scoped_array<const FieldDescriptor*> ordered_fields(
-    SortFieldsByNumber(descriptor_));
+      SortFieldsByNumber(descriptor_));
 
   vector<const Descriptor::ExtensionRange*> sorted_extensions;
   for (int i = 0; i < descriptor_->extension_range_count(); ++i) {
@@ -1810,7 +2386,7 @@ GenerateSerializeWithCachedSizesBody(io::Printer* printer, bool to_array) {
     }
   }
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print("if (!unknown_fields().empty()) {\n");
     printer->Indent();
     if (to_array) {
@@ -1827,6 +2403,10 @@ GenerateSerializeWithCachedSizesBody(io::Printer* printer, bool to_array) {
 
     printer->Print(
       "}\n");
+  } else {
+    printer->Print(
+      "output->WriteRaw(unknown_fields().data(),\n"
+      "                 unknown_fields().size());\n");
   }
 }
 
@@ -1838,11 +2418,10 @@ GenerateByteSize(io::Printer* printer) {
       "int $classname$::ByteSize() const {\n"
       "  int total_size = _extensions_.MessageSetByteSize();\n",
       "classname", classname_);
-    if (HasUnknownFields(descriptor_->file())) {
-      printer->Print(
-        "  total_size += ::google::protobuf::internal::WireFormat::\n"
-        "      ComputeUnknownMessageSetItemsSize(unknown_fields());\n");
-    }
+    GOOGLE_CHECK(UseUnknownFieldSet(descriptor_->file()));
+    printer->Print(
+      "  total_size += ::google::protobuf::internal::WireFormat::\n"
+      "      ComputeUnknownMessageSetItemsSize(unknown_fields());\n");
     printer->Print(
       "  GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();\n"
       "  _cached_size_ = total_size;\n"
@@ -1865,7 +2444,7 @@ GenerateByteSize(io::Printer* printer) {
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
 
-    if (!field->is_repeated()) {
+    if (!field->is_repeated() && !field->containing_oneof()) {
       // See above in GenerateClear for an explanation of this.
       // TODO(kenton):  Share code?  Unclear how to do so without
       //   over-engineering.
@@ -1915,13 +2494,45 @@ GenerateByteSize(io::Printer* printer) {
     }
   }
 
+  // Fields inside a oneof don't use _has_bits_ so we count them in a separate
+  // pass.
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+        "switch ($oneofname$_case()) {\n",
+        "oneofname", descriptor_->oneof_decl(i)->name());
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+      PrintFieldComment(printer, field);
+      printer->Print(
+          "case k$field_name$: {\n",
+          "field_name", UnderscoresToCamelCase(field->name(), true));
+      printer->Indent();
+      field_generators_.get(field).GenerateByteSize(printer);
+      printer->Print(
+          "break;\n");
+      printer->Outdent();
+      printer->Print(
+          "}\n");
+    }
+    printer->Print(
+        "case $cap_oneof_name$_NOT_SET: {\n"
+        "  break;\n"
+        "}\n",
+        "cap_oneof_name",
+        ToUpper(descriptor_->oneof_decl(i)->name()));
+    printer->Outdent();
+    printer->Print(
+        "}\n");
+  }
+
   if (descriptor_->extension_range_count() > 0) {
     printer->Print(
       "total_size += _extensions_.ByteSize();\n"
       "\n");
   }
 
-  if (HasUnknownFields(descriptor_->file())) {
+  if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print("if (!unknown_fields().empty()) {\n");
     printer->Indent();
     printer->Print(
@@ -1930,6 +2541,10 @@ GenerateByteSize(io::Printer* printer) {
       "    unknown_fields());\n");
     printer->Outdent();
     printer->Print("}\n");
+  } else {
+    printer->Print(
+      "total_size += unknown_fields().size();\n"
+      "\n");
   }
 
   // We update _cached_size_ even though this is a const method.  In theory,
@@ -1987,16 +2602,26 @@ GenerateIsInitialized(io::Printer* printer) {
         HasRequiredFields(field->message_type())) {
       if (field->is_repeated()) {
         printer->Print(
-          "for (int i = 0; i < $name$_size(); i++) {\n"
-          "  if (!this->$name$(i).IsInitialized()) return false;\n"
-          "}\n",
+          "if (!::google::protobuf::internal::AllAreInitialized(this->$name$()))"
+          " return false;\n",
           "name", FieldName(field));
       } else {
-        printer->Print(
-          "if (has_$name$()) {\n"
-          "  if (!this->$name$().IsInitialized()) return false;\n"
-          "}\n",
-          "name", FieldName(field));
+        if (field->options().weak()) {
+          // For weak fields, use the data member (google::protobuf::Message*) instead
+          // of the getter to avoid a link dependency on the weak message type
+          // which is only forward declared.
+          printer->Print(
+            "if (has_$name$()) {\n"
+            "  if (!this->$name$_->IsInitialized()) return false;\n"
+            "}\n",
+            "name", FieldName(field));
+        } else {
+          printer->Print(
+            "if (has_$name$()) {\n"
+            "  if (!this->$name$().IsInitialized()) return false;\n"
+            "}\n",
+            "name", FieldName(field));
+        }
       }
     }
   }
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.h b/src/google/protobuf/compiler/cpp/cpp_message.h
index a7e43d9c..3b4085dc 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.h
+++ b/src/google/protobuf/compiler/cpp/cpp_message.h
@@ -35,8 +35,9 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_CPP_MESSAGE_H__
 #define GOOGLE_PROTOBUF_COMPILER_CPP_MESSAGE_H__
 
+#include <memory>
 #include <string>
-#include <google/protobuf/stubs/common.h>
+#include <vector>
 #include <google/protobuf/compiler/cpp/cpp_field.h>
 #include <google/protobuf/compiler/cpp/cpp_options.h>
 
@@ -132,6 +133,7 @@ class MessageGenerator {
 
   // Generate standard Message methods.
   void GenerateClear(io::Printer* printer);
+  void GenerateOneofClear(io::Printer* printer);
   void GenerateMergeFromCodedStream(io::Printer* printer);
   void GenerateSerializeWithCachedSizes(io::Printer* printer);
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer);
@@ -156,9 +158,11 @@ class MessageGenerator {
   string classname_;
   Options options_;
   FieldGeneratorMap field_generators_;
+  vector< vector<string> > runs_of_fields_;  // that might be trivially cleared
   scoped_array<scoped_ptr<MessageGenerator> > nested_generators_;
   scoped_array<scoped_ptr<EnumGenerator> > enum_generators_;
   scoped_array<scoped_ptr<ExtensionGenerator> > extension_generators_;
+  bool uses_string_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageGenerator);
 };
diff --git a/src/google/protobuf/compiler/cpp/cpp_message_field.cc b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
index 447f975f..08a4f257 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
@@ -53,6 +53,12 @@ void SetMessageVariables(const FieldDescriptor* descriptor,
       (HasFastArraySerialization(descriptor->message_type()->file()) ?
        "MaybeToArray" :
        "");
+  // NOTE: Escaped here to unblock proto1->proto2 migration.
+  // TODO(liujisi): Extend this to apply for other conflicting methods.
+  (*variables)["release_name"] =
+      SafeFunctionName(descriptor->containing_type(),
+                       descriptor, "release_");
+  (*variables)["full_name"] = descriptor->full_name();
 }
 
 }  // namespace
@@ -78,14 +84,15 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
   printer->Print(variables_,
     "inline const $type$& $name$() const$deprecation$;\n"
     "inline $type$* mutable_$name$()$deprecation$;\n"
-    "inline $type$* release_$name$()$deprecation$;\n"
+    "inline $type$* $release_name$()$deprecation$;\n"
     "inline void set_allocated_$name$($type$* $name$)$deprecation$;\n");
 }
 
 void MessageFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
-    "inline const $type$& $classname$::$name$() const {\n");
+    "inline const $type$& $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n");
 
   PrintHandlingOptionalStaticInitializers(
     variables_, descriptor_->file(), printer,
@@ -99,9 +106,10 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "inline $type$* $classname$::mutable_$name$() {\n"
     "  set_has_$name$();\n"
     "  if ($name$_ == NULL) $name$_ = new $type$;\n"
+    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
-    "inline $type$* $classname$::release_$name$() {\n"
+    "inline $type$* $classname$::$release_name$() {\n"
     "  clear_has_$name$();\n"
     "  $type$* temp = $name$_;\n"
     "  $name$_ = NULL;\n"
@@ -115,6 +123,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "  } else {\n"
     "    clear_has_$name$();\n"
     "  }\n"
+    "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
     "}\n");
 }
 
@@ -178,6 +187,69 @@ GenerateByteSize(io::Printer* printer) const {
 
 // ===================================================================
 
+MessageOneofFieldGenerator::
+MessageOneofFieldGenerator(const FieldDescriptor* descriptor,
+                           const Options& options)
+  : MessageFieldGenerator(descriptor, options) {
+  SetCommonOneofFieldVariables(descriptor, &variables_);
+}
+
+MessageOneofFieldGenerator::~MessageOneofFieldGenerator() {}
+
+void MessageOneofFieldGenerator::
+GenerateInlineAccessorDefinitions(io::Printer* printer) const {
+  printer->Print(variables_,
+    "inline const $type$& $classname$::$name$() const {\n"
+    "  return has_$name$() ? *$oneof_prefix$$name$_\n"
+    "                      : $type$::default_instance();\n"
+    "}\n"
+    "inline $type$* $classname$::mutable_$name$() {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = new $type$;\n"
+    "  }\n"
+    "  return $oneof_prefix$$name$_;\n"
+    "}\n"
+    "inline $type$* $classname$::$release_name$() {\n"
+    "  if (has_$name$()) {\n"
+    "    clear_has_$oneof_name$();\n"
+    "    $type$* temp = $oneof_prefix$$name$_;\n"
+    "    $oneof_prefix$$name$_ = NULL;\n"
+    "    return temp;\n"
+    "  } else {\n"
+    "    return NULL;\n"
+    "  }\n"
+    "}\n"
+    "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
+    "  clear_$oneof_name$();\n"
+    "  if ($name$) {\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = $name$;\n"
+    "  }\n"
+    "}\n");
+}
+
+void MessageOneofFieldGenerator::
+GenerateClearingCode(io::Printer* printer) const {
+  // if it is the active field, it cannot be NULL.
+  printer->Print(variables_,
+    "delete $oneof_prefix$$name$_;\n");
+}
+
+void MessageOneofFieldGenerator::
+GenerateSwappingCode(io::Printer* printer) const {
+  // Don't print any swapping code. Swapping the union will swap this field.
+}
+
+void MessageOneofFieldGenerator::
+GenerateConstructorCode(io::Printer* printer) const {
+  // Don't print any constructor code. The field is in a union. We allocate
+  // space only when this field is used.
+}
+
+// ===================================================================
+
 RepeatedMessageFieldGenerator::
 RepeatedMessageFieldGenerator(const FieldDescriptor* descriptor,
                               const Options& options)
@@ -210,21 +282,26 @@ void RepeatedMessageFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline const $type$& $classname$::$name$(int index) const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return $name$_.$cppget$(index);\n"
     "}\n"
     "inline $type$* $classname$::mutable_$name$(int index) {\n"
+    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
     "  return $name$_.Mutable(index);\n"
     "}\n"
     "inline $type$* $classname$::add_$name$() {\n"
+    "  // @@protoc_insertion_point(field_add:$full_name$)\n"
     "  return $name$_.Add();\n"
     "}\n");
   printer->Print(variables_,
     "inline const ::google::protobuf::RepeatedPtrField< $type$ >&\n"
     "$classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_list:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
     "inline ::google::protobuf::RepeatedPtrField< $type$ >*\n"
     "$classname$::mutable_$name$() {\n"
+    "  // @@protoc_insertion_point(field_mutable_list:$full_name$)\n"
     "  return &$name$_;\n"
     "}\n");
 }
diff --git a/src/google/protobuf/compiler/cpp/cpp_message_field.h b/src/google/protobuf/compiler/cpp/cpp_message_field.h
index a5ed68a5..4c01795c 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_message_field.h
@@ -63,13 +63,30 @@ class MessageFieldGenerator : public FieldGenerator {
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const;
   void GenerateByteSize(io::Printer* printer) const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
 
+ private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageFieldGenerator);
 };
 
+class MessageOneofFieldGenerator : public MessageFieldGenerator {
+ public:
+  explicit MessageOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                      const Options& options);
+  ~MessageOneofFieldGenerator();
+
+  // implements FieldGenerator ---------------------------------------
+  void GenerateInlineAccessorDefinitions(io::Printer* printer) const;
+  void GenerateClearingCode(io::Printer* printer) const;
+  void GenerateSwappingCode(io::Printer* printer) const;
+  void GenerateConstructorCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageOneofFieldGenerator);
+};
+
 class RepeatedMessageFieldGenerator : public FieldGenerator {
  public:
   explicit RepeatedMessageFieldGenerator(const FieldDescriptor* descriptor,
diff --git a/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc b/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
index 5c4aa4fb..697b95f0 100644
--- a/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
@@ -34,6 +34,8 @@
 //   It seemed like parameterizing it would add more complexity than it is
 //   worth.
 
+#include <memory>
+
 #include <google/protobuf/compiler/cpp/cpp_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
 #include <google/protobuf/io/zero_copy_stream.h>
@@ -73,7 +75,7 @@ class TestGenerator : public CodeGenerator {
   void TryInsert(const string& filename, const string& insertion_point,
                  GeneratorContext* context) const {
     scoped_ptr<io::ZeroCopyOutputStream> output(
-      context->OpenForInsert(filename, insertion_point));
+        context->OpenForInsert(filename, insertion_point));
     io::Printer printer(output.get(), '$');
     printer.Print("// inserted $name$\n", "name", insertion_point);
   }
@@ -83,13 +85,13 @@ class TestGenerator : public CodeGenerator {
 // not verify that they are correctly-placed; that would require actually
 // compiling the output which is a bit more than I care to do for this test.
 TEST(CppPluginTest, PluginTest) {
-  File::WriteStringToFileOrDie(
-      "syntax = \"proto2\";\n"
-      "package foo;\n"
-      "message Bar {\n"
-      "  message Baz {}\n"
-      "}\n",
-      TestTempDir() + "/test.proto");
+  GOOGLE_CHECK_OK(File::SetContents(TestTempDir() + "/test.proto",
+                             "syntax = \"proto2\";\n"
+                             "package foo;\n"
+                             "message Bar {\n"
+                             "  message Baz {}\n"
+                             "}\n",
+                             true));
 
   google::protobuf::compiler::CommandLineInterface cli;
   cli.SetInputsAreProtoPathRelative(true);
diff --git a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
index 1c35fefa..cb72fb1d 100644
--- a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
@@ -93,6 +93,7 @@ void SetPrimitiveVariables(const FieldDescriptor* descriptor,
   (*variables)["wire_format_field_type"] =
       "::google::protobuf::internal::WireFormatLite::" + FieldDescriptorProto_Type_Name(
           static_cast<FieldDescriptorProto_Type>(descriptor->type()));
+  (*variables)["full_name"] = descriptor->full_name();
 }
 
 }  // namespace
@@ -124,11 +125,13 @@ void PrimitiveFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
     "inline void $classname$::set_$name$($type$ value) {\n"
     "  set_has_$name$();\n"
     "  $name$_ = value;\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
 }
 
@@ -191,6 +194,62 @@ GenerateByteSize(io::Printer* printer) const {
 
 // ===================================================================
 
+PrimitiveOneofFieldGenerator::
+PrimitiveOneofFieldGenerator(const FieldDescriptor* descriptor,
+                             const Options& options)
+  : PrimitiveFieldGenerator(descriptor, options) {
+  SetCommonOneofFieldVariables(descriptor, &variables_);
+}
+
+PrimitiveOneofFieldGenerator::~PrimitiveOneofFieldGenerator() {}
+
+void PrimitiveOneofFieldGenerator::
+GenerateInlineAccessorDefinitions(io::Printer* printer) const {
+  printer->Print(variables_,
+    "inline $type$ $classname$::$name$() const {\n"
+    "  if (has_$name$()) {\n"
+    "    return $oneof_prefix$$name$_;\n"
+    "  }\n"
+    "  return $default$;\n"
+    "}\n"
+    "inline void $classname$::set_$name$($type$ value) {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "  }\n"
+    "  $oneof_prefix$$name$_ = value;\n"
+    "}\n");
+}
+
+void PrimitiveOneofFieldGenerator::
+GenerateClearingCode(io::Printer* printer) const {
+  printer->Print(variables_, "$oneof_prefix$$name$_ = $default$;\n");
+}
+
+void PrimitiveOneofFieldGenerator::
+GenerateSwappingCode(io::Printer* printer) const {
+  // Don't print any swapping code. Swapping the union will swap this field.
+}
+
+void PrimitiveOneofFieldGenerator::
+GenerateConstructorCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "  $classname$_default_oneof_instance_->$name$_ = $default$;\n");
+}
+
+void PrimitiveOneofFieldGenerator::
+GenerateMergeFromCodedStream(io::Printer* printer) const {
+  printer->Print(variables_,
+    "clear_$oneof_name$();\n"
+    "DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<\n"
+    "         $type$, $wire_format_field_type$>(\n"
+    "       input, &$oneof_prefix$$name$_)));\n"
+    "set_has_$name$();\n");
+}
+
+// ===================================================================
+
 RepeatedPrimitiveFieldGenerator::
 RepeatedPrimitiveFieldGenerator(const FieldDescriptor* descriptor,
                                 const Options& options)
@@ -235,21 +294,26 @@ void RepeatedPrimitiveFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$(int index) const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return $name$_.Get(index);\n"
     "}\n"
     "inline void $classname$::set_$name$(int index, $type$ value) {\n"
     "  $name$_.Set(index, value);\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n"
     "inline void $classname$::add_$name$($type$ value) {\n"
     "  $name$_.Add(value);\n"
+    "  // @@protoc_insertion_point(field_add:$full_name$)\n"
     "}\n");
   printer->Print(variables_,
     "inline const ::google::protobuf::RepeatedField< $type$ >&\n"
     "$classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_list:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
     "inline ::google::protobuf::RepeatedField< $type$ >*\n"
     "$classname$::mutable_$name$() {\n"
+    "  // @@protoc_insertion_point(field_mutable_list:$full_name$)\n"
     "  return &$name$_;\n"
     "}\n");
 }
diff --git a/src/google/protobuf/compiler/cpp/cpp_primitive_field.h b/src/google/protobuf/compiler/cpp/cpp_primitive_field.h
index 48249c40..1f66c9df 100644
--- a/src/google/protobuf/compiler/cpp/cpp_primitive_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_primitive_field.h
@@ -63,13 +63,31 @@ class PrimitiveFieldGenerator : public FieldGenerator {
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const;
   void GenerateByteSize(io::Printer* printer) const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
 
+ private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(PrimitiveFieldGenerator);
 };
 
+class PrimitiveOneofFieldGenerator : public PrimitiveFieldGenerator {
+ public:
+  explicit PrimitiveOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                        const Options& options);
+  ~PrimitiveOneofFieldGenerator();
+
+  // implements FieldGenerator ---------------------------------------
+  void GenerateInlineAccessorDefinitions(io::Printer* printer) const;
+  void GenerateClearingCode(io::Printer* printer) const;
+  void GenerateSwappingCode(io::Printer* printer) const;
+  void GenerateConstructorCode(io::Printer* printer) const;
+  void GenerateMergeFromCodedStream(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(PrimitiveOneofFieldGenerator);
+};
+
 class RepeatedPrimitiveFieldGenerator : public FieldGenerator {
  public:
   explicit RepeatedPrimitiveFieldGenerator(const FieldDescriptor* descriptor,
diff --git a/src/google/protobuf/compiler/cpp/cpp_service.h b/src/google/protobuf/compiler/cpp/cpp_service.h
index 820f9f5f..493f314a 100644
--- a/src/google/protobuf/compiler/cpp/cpp_service.h
+++ b/src/google/protobuf/compiler/cpp/cpp_service.h
@@ -37,7 +37,6 @@
 
 #include <map>
 #include <string>
-#include <google/protobuf/stubs/common.h>
 #include <google/protobuf/compiler/cpp/cpp_options.h>
 #include <google/protobuf/descriptor.h>
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_string_field.cc b/src/google/protobuf/compiler/cpp/cpp_string_field.cc
index 0b58b981..d41b5bcd 100644
--- a/src/google/protobuf/compiler/cpp/cpp_string_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_string_field.cc
@@ -53,10 +53,16 @@ void SetStringVariables(const FieldDescriptor* descriptor,
   (*variables)["default_length"] =
       SimpleItoa(descriptor->default_value_string().length());
   (*variables)["default_variable"] = descriptor->default_value_string().empty()
-      ? "&::google::protobuf::internal::GetEmptyString()"
+      ? "&::google::protobuf::internal::GetEmptyStringAlreadyInited()"
       : "_default_" + FieldName(descriptor) + "_";
   (*variables)["pointer_type"] =
       descriptor->type() == FieldDescriptor::TYPE_BYTES ? "void" : "char";
+  // NOTE: Escaped here to unblock proto1->proto2 migration.
+  // TODO(liujisi): Extend this to apply for other conflicting methods.
+  (*variables)["release_name"] =
+      SafeFunctionName(descriptor->containing_type(),
+                       descriptor, "release_");
+  (*variables)["full_name"] = descriptor->full_name();
 }
 
 }  // namespace
@@ -75,6 +81,10 @@ StringFieldGenerator::~StringFieldGenerator() {}
 void StringFieldGenerator::
 GeneratePrivateMembers(io::Printer* printer) const {
   printer->Print(variables_, "::std::string* $name$_;\n");
+}
+
+void StringFieldGenerator::
+GenerateStaticMembers(io::Printer* printer) const {
   if (!descriptor_->default_value_string().empty()) {
     printer->Print(variables_, "static ::std::string* $default_variable$;\n");
   }
@@ -113,7 +123,7 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
     "inline void set_$name$(const $pointer_type$* value, size_t size)"
                  "$deprecation$;\n"
     "inline ::std::string* mutable_$name$()$deprecation$;\n"
-    "inline ::std::string* release_$name$()$deprecation$;\n"
+    "inline ::std::string* $release_name$()$deprecation$;\n"
     "inline void set_allocated_$name$(::std::string* $name$)$deprecation$;\n");
 
 
@@ -128,6 +138,7 @@ void StringFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline const ::std::string& $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return *$name$_;\n"
     "}\n"
     "inline void $classname$::set_$name$(const ::std::string& value) {\n"
@@ -136,6 +147,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "    $name$_ = new ::std::string;\n"
     "  }\n"
     "  $name$_->assign(value);\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n"
     "inline void $classname$::set_$name$(const char* value) {\n"
     "  set_has_$name$();\n"
@@ -143,6 +155,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "    $name$_ = new ::std::string;\n"
     "  }\n"
     "  $name$_->assign(value);\n"
+    "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
     "}\n"
     "inline "
     "void $classname$::set_$name$(const $pointer_type$* value, size_t size) {\n"
@@ -151,6 +164,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "    $name$_ = new ::std::string;\n"
     "  }\n"
     "  $name$_->assign(reinterpret_cast<const char*>(value), size);\n"
+    "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
     "}\n"
     "inline ::std::string* $classname$::mutable_$name$() {\n"
     "  set_has_$name$();\n"
@@ -164,9 +178,10 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   }
   printer->Print(variables_,
     "  }\n"
+    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
-    "inline ::std::string* $classname$::release_$name$() {\n"
+    "inline ::std::string* $classname$::$release_name$() {\n"
     "  clear_has_$name$();\n"
     "  if ($name$_ == $default_variable$) {\n"
     "    return NULL;\n"
@@ -187,6 +202,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "    clear_has_$name$();\n"
     "    $name$_ = const_cast< ::std::string*>($default_variable$);\n"
     "  }\n"
+    "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
     "}\n");
 }
 
@@ -263,9 +279,10 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
-      "  ::google::protobuf::internal::WireFormat::PARSE);\n");
+      "  ::google::protobuf::internal::WireFormat::PARSE,\n"
+      "  \"$name$\");\n");
   }
 }
 
@@ -274,12 +291,13 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
-      "  ::google::protobuf::internal::WireFormat::SERIALIZE);\n");
+      "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
+      "  \"$name$\");\n");
   }
   printer->Print(variables_,
-    "::google::protobuf::internal::WireFormatLite::Write$declared_type$(\n"
+    "::google::protobuf::internal::WireFormatLite::Write$declared_type$MaybeAliased(\n"
     "  $number$, this->$name$(), output);\n");
 }
 
@@ -288,9 +306,10 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
-      "  ::google::protobuf::internal::WireFormat::SERIALIZE);\n");
+      "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
+      "  \"$name$\");\n");
   }
   printer->Print(variables_,
     "target =\n"
@@ -308,6 +327,125 @@ GenerateByteSize(io::Printer* printer) const {
 
 // ===================================================================
 
+StringOneofFieldGenerator::
+StringOneofFieldGenerator(const FieldDescriptor* descriptor,
+                          const Options& options)
+  : StringFieldGenerator(descriptor, options) {
+  SetCommonOneofFieldVariables(descriptor, &variables_);
+}
+
+StringOneofFieldGenerator::~StringOneofFieldGenerator() {}
+
+void StringOneofFieldGenerator::
+GenerateInlineAccessorDefinitions(io::Printer* printer) const {
+  printer->Print(variables_,
+    "inline const ::std::string& $classname$::$name$() const {\n"
+    "  if (has_$name$()) {\n"
+    "    return *$oneof_prefix$$name$_;\n"
+    "  }\n");
+  if (descriptor_->default_value_string().empty()) {
+    printer->Print(variables_,
+      "  return ::google::protobuf::internal::GetEmptyStringAlreadyInited();\n");
+  } else {
+    printer->Print(variables_,
+      "  return *$default_variable$;\n");
+  }
+  printer->Print(variables_,
+    "}\n"
+    "inline void $classname$::set_$name$(const ::std::string& value) {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = new ::std::string;\n"
+    "  }\n"
+    "  $oneof_prefix$$name$_->assign(value);\n"
+    "}\n"
+    "inline void $classname$::set_$name$(const char* value) {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = new ::std::string;\n"
+    "  }\n"
+    "  $oneof_prefix$$name$_->assign(value);\n"
+    "}\n"
+    "inline "
+    "void $classname$::set_$name$(const $pointer_type$* value, size_t size) {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = new ::std::string;\n"
+    "  }\n"
+    "  $oneof_prefix$$name$_->assign(\n"
+    "      reinterpret_cast<const char*>(value), size);\n"
+    "}\n"
+    "inline ::std::string* $classname$::mutable_$name$() {\n"
+    "  if (!has_$name$()) {\n"
+    "    clear_$oneof_name$();\n"
+    "    set_has_$name$();\n");
+  if (descriptor_->default_value_string().empty()) {
+    printer->Print(variables_,
+      "    $oneof_prefix$$name$_ = new ::std::string;\n");
+  } else {
+    printer->Print(variables_,
+      "    $oneof_prefix$$name$_ = new ::std::string(*$default_variable$);\n");
+  }
+  printer->Print(variables_,
+    "  }\n"
+    "  return $oneof_prefix$$name$_;\n"
+    "}\n"
+    "inline ::std::string* $classname$::$release_name$() {\n"
+    "  if (has_$name$()) {\n"
+    "    clear_has_$oneof_name$();\n"
+    "    ::std::string* temp = $oneof_prefix$$name$_;\n"
+    "    $oneof_prefix$$name$_ = NULL;\n"
+    "    return temp;\n"
+    "  } else {\n"
+    "    return NULL;\n"
+    "  }\n"
+    "}\n"
+    "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
+    "  clear_$oneof_name$();\n"
+    "  if ($name$) {\n"
+    "    set_has_$name$();\n"
+    "    $oneof_prefix$$name$_ = $name$;\n"
+    "  }\n"
+    "}\n");
+}
+
+void StringOneofFieldGenerator::
+GenerateClearingCode(io::Printer* printer) const {
+    printer->Print(variables_,
+      "delete $oneof_prefix$$name$_;\n");
+}
+
+void StringOneofFieldGenerator::
+GenerateSwappingCode(io::Printer* printer) const {
+  // Don't print any swapping code. Swapping the union will swap this field.
+}
+
+void StringOneofFieldGenerator::
+GenerateConstructorCode(io::Printer* printer) const {
+  if (!descriptor_->default_value_string().empty()) {
+    printer->Print(variables_,
+      "  $classname$_default_oneof_instance_->$name$_ = "
+      "$classname$::$default_variable$;\n");
+  } else {
+    printer->Print(variables_,
+      "  $classname$_default_oneof_instance_->$name$_ = "
+      "$default_variable$;\n");
+  }
+}
+
+void StringOneofFieldGenerator::
+GenerateDestructorCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (has_$name$()) {\n"
+    "  delete $oneof_prefix$$name$_;\n"
+    "}\n");
+}
+
+// ===================================================================
+
 RepeatedStringFieldGenerator::
 RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
                              const Options& options)
@@ -365,43 +503,53 @@ void RepeatedStringFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline const ::std::string& $classname$::$name$(int index) const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return $name$_.$cppget$(index);\n"
     "}\n"
     "inline ::std::string* $classname$::mutable_$name$(int index) {\n"
+    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
     "  return $name$_.Mutable(index);\n"
     "}\n"
     "inline void $classname$::set_$name$(int index, const ::std::string& value) {\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "  $name$_.Mutable(index)->assign(value);\n"
     "}\n"
     "inline void $classname$::set_$name$(int index, const char* value) {\n"
     "  $name$_.Mutable(index)->assign(value);\n"
+    "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
     "}\n"
     "inline void "
     "$classname$::set_$name$"
     "(int index, const $pointer_type$* value, size_t size) {\n"
     "  $name$_.Mutable(index)->assign(\n"
     "    reinterpret_cast<const char*>(value), size);\n"
+    "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
     "}\n"
     "inline ::std::string* $classname$::add_$name$() {\n"
     "  return $name$_.Add();\n"
     "}\n"
     "inline void $classname$::add_$name$(const ::std::string& value) {\n"
     "  $name$_.Add()->assign(value);\n"
+    "  // @@protoc_insertion_point(field_add:$full_name$)\n"
     "}\n"
     "inline void $classname$::add_$name$(const char* value) {\n"
     "  $name$_.Add()->assign(value);\n"
+    "  // @@protoc_insertion_point(field_add_char:$full_name$)\n"
     "}\n"
     "inline void "
     "$classname$::add_$name$(const $pointer_type$* value, size_t size) {\n"
     "  $name$_.Add()->assign(reinterpret_cast<const char*>(value), size);\n"
+    "  // @@protoc_insertion_point(field_add_pointer:$full_name$)\n"
     "}\n");
   printer->Print(variables_,
     "inline const ::google::protobuf::RepeatedPtrField< ::std::string>&\n"
     "$classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_list:$full_name$)\n"
     "  return $name$_;\n"
     "}\n"
     "inline ::google::protobuf::RepeatedPtrField< ::std::string>*\n"
     "$classname$::mutable_$name$() {\n"
+    "  // @@protoc_insertion_point(field_mutable_list:$full_name$)\n"
     "  return &$name$_;\n"
     "}\n");
 }
@@ -434,10 +582,11 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$(this->$name$_size() - 1).data(),\n"
       "  this->$name$(this->$name$_size() - 1).length(),\n"
-      "  ::google::protobuf::internal::WireFormat::PARSE);\n");
+      "  ::google::protobuf::internal::WireFormat::PARSE,\n"
+      "  \"$name$\");\n");
   }
 }
 
@@ -448,9 +597,10 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$(i).data(), this->$name$(i).length(),\n"
-      "  ::google::protobuf::internal::WireFormat::SERIALIZE);\n");
+      "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
+      "  \"$name$\");\n");
   }
   printer->Print(variables_,
     "  ::google::protobuf::internal::WireFormatLite::Write$declared_type$(\n"
@@ -465,9 +615,10 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const {
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
-      "  ::google::protobuf::internal::WireFormat::VerifyUTF8String(\n"
+      "  ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "    this->$name$(i).data(), this->$name$(i).length(),\n"
-      "    ::google::protobuf::internal::WireFormat::SERIALIZE);\n");
+      "    ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
+      "    \"$name$\");\n");
   }
   printer->Print(variables_,
     "  target = ::google::protobuf::internal::WireFormatLite::\n"
diff --git a/src/google/protobuf/compiler/cpp/cpp_string_field.h b/src/google/protobuf/compiler/cpp/cpp_string_field.h
index 3264134a..65f605c0 100644
--- a/src/google/protobuf/compiler/cpp/cpp_string_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_string_field.h
@@ -52,6 +52,7 @@ class StringFieldGenerator : public FieldGenerator {
 
   // implements FieldGenerator ---------------------------------------
   void GeneratePrivateMembers(io::Printer* printer) const;
+  void GenerateStaticMembers(io::Printer* printer) const;
   void GenerateAccessorDeclarations(io::Printer* printer) const;
   void GenerateInlineAccessorDefinitions(io::Printer* printer) const;
   void GenerateNonInlineAccessorDefinitions(io::Printer* printer) const;
@@ -67,13 +68,31 @@ class StringFieldGenerator : public FieldGenerator {
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const;
   void GenerateByteSize(io::Printer* printer) const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
 
+ private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringFieldGenerator);
 };
 
+class StringOneofFieldGenerator : public StringFieldGenerator {
+ public:
+  explicit StringOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                     const Options& options);
+  ~StringOneofFieldGenerator();
+
+  // implements FieldGenerator ---------------------------------------
+  void GenerateInlineAccessorDefinitions(io::Printer* printer) const;
+  void GenerateClearingCode(io::Printer* printer) const;
+  void GenerateSwappingCode(io::Printer* printer) const;
+  void GenerateConstructorCode(io::Printer* printer) const;
+  void GenerateDestructorCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringOneofFieldGenerator);
+};
+
 class RepeatedStringFieldGenerator : public FieldGenerator {
  public:
   explicit RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
diff --git a/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto b/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
index e14a818c..8b9ff5ae 100644
--- a/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
+++ b/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
@@ -98,6 +98,7 @@ message TestConflictingSymbolNames {
   // Some keywords.
   optional uint32 int = 30;
   optional uint32 friend = 31;
+  optional uint32 class = 37;
 
   // The generator used to #define a macro called "DO" inside the .cc file.
   message DO {}
@@ -107,6 +108,14 @@ message TestConflictingSymbolNames {
   optional int32 field_type = 33;
   optional bool is_packed = 34;
 
+  // test conflicting release_$name$. "length" and "do" field in this message
+  // must remain string or message fields to make the test valid.
+  optional string release_length = 35;
+  // A more extreme case, the field name "do" here is a keyword, which will be
+  // escaped to "do_" already. Test there is no conflict even with escaped field
+  // names.
+  optional DO release_do = 36;
+
   extensions 1000 to max;
 }
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_unittest.cc b/src/google/protobuf/compiler/cpp/cpp_unittest.cc
index 1eae29b5..4ef1da1e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_unittest.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_unittest.cc
@@ -46,6 +46,7 @@
 
 #include <google/protobuf/compiler/cpp/cpp_unittest.h>
 
+#include <memory>
 #include <vector>
 
 #include <google/protobuf/unittest.pb.h>
@@ -53,6 +54,7 @@
 #include <google/protobuf/unittest_embed_optimize_for.pb.h>
 #include <google/protobuf/unittest_no_generic_services.pb.h>
 #include <google/protobuf/test_util.h>
+#include <google/protobuf/compiler/cpp/cpp_helpers.h>
 #include <google/protobuf/compiler/cpp/cpp_test_bad_identifiers.pb.h>
 #include <google/protobuf/compiler/importer.h>
 #include <google/protobuf/io/coded_stream.h>
@@ -148,6 +150,19 @@ TEST(GeneratedMessageTest, Defaults) {
             &message.optional_import_message());
 }
 
+TEST(GeneratedMessageTest, Int32StringConversion) {
+  EXPECT_EQ("971", Int32ToString(971));
+  EXPECT_EQ("(~0x7fffffff)", Int32ToString(kint32min));
+  EXPECT_EQ("2147483647", Int32ToString(kint32max));
+}
+
+TEST(GeneratedMessageTest, Int64StringConversion) {
+  EXPECT_EQ("GOOGLE_LONGLONG(971)", Int64ToString(971));
+  EXPECT_EQ("GOOGLE_LONGLONG(-2147483648)", Int64ToString(kint32min));
+  EXPECT_EQ("GOOGLE_LONGLONG(-0x8000000000000000)", Int64ToString(kint64min));
+  EXPECT_EQ("GOOGLE_LONGLONG(9223372036854775807)", Int64ToString(kint64max));
+}
+
 TEST(GeneratedMessageTest, FloatingPointDefaults) {
   const unittest::TestExtremeDefaultValues& extreme_default =
       unittest::TestExtremeDefaultValues::default_instance();
@@ -233,11 +248,10 @@ TEST(GeneratedMessageTest, ReleaseString) {
 
   message.set_default_string("blah");
   EXPECT_TRUE(message.has_default_string());
-  string* str = message.release_default_string();
+  scoped_ptr<string> str(message.release_default_string());
   EXPECT_FALSE(message.has_default_string());
   ASSERT_TRUE(str != NULL);
   EXPECT_EQ("blah", *str);
-  delete str;
 
   EXPECT_EQ(NULL, message.release_default_string());
   EXPECT_FALSE(message.has_default_string());
@@ -253,12 +267,11 @@ TEST(GeneratedMessageTest, ReleaseMessage) {
   EXPECT_FALSE(message.has_optional_nested_message());
 
   message.mutable_optional_nested_message()->set_bb(1);
-  unittest::TestAllTypes::NestedMessage* nest =
-      message.release_optional_nested_message();
+  scoped_ptr<unittest::TestAllTypes::NestedMessage> nest(
+      message.release_optional_nested_message());
   EXPECT_FALSE(message.has_optional_nested_message());
   ASSERT_TRUE(nest != NULL);
   EXPECT_EQ(1, nest->bb());
-  delete nest;
 
   EXPECT_EQ(NULL, message.release_optional_nested_message());
   EXPECT_FALSE(message.has_optional_nested_message());
@@ -381,6 +394,7 @@ TEST(GeneratedMessageTest, StringCharStarLength) {
   EXPECT_EQ("wx", message.repeated_string(0));
 }
 
+
 TEST(GeneratedMessageTest, CopyFrom) {
   unittest::TestAllTypes message1, message2;
 
@@ -393,6 +407,7 @@ TEST(GeneratedMessageTest, CopyFrom) {
   TestUtil::ExpectAllFieldsSet(message2);
 }
 
+
 TEST(GeneratedMessageTest, SwapWithEmpty) {
   unittest::TestAllTypes message1, message2;
   TestUtil::SetAllFields(&message1);
@@ -763,6 +778,9 @@ TEST(GeneratedMessageTest, TestConflictingSymbolNames) {
   message.set_friend_(5);
   EXPECT_EQ(5, message.friend_());
 
+  message.set_class_(6);
+  EXPECT_EQ(6, message.class_());
+
   // Instantiate extension template functions to test conflicting template
   // parameter names.
   typedef protobuf_unittest::TestConflictingSymbolNamesExtension ExtensionMessage;
@@ -840,6 +858,40 @@ TEST(GeneratedMessageTest, TestSpaceUsed) {
             message1.SpaceUsed());
 }
 
+TEST(GeneratedMessageTest, TestOneofSpaceUsed) {
+  unittest::TestOneof2 message1;
+  EXPECT_LE(sizeof(unittest::TestOneof2), message1.SpaceUsed());
+
+  const int empty_message_size = message1.SpaceUsed();
+  // Setting primitive types shouldn't affect the space used.
+  message1.set_foo_int(123);
+  message1.set_bar_int(12345);
+  EXPECT_EQ(empty_message_size, message1.SpaceUsed());
+
+  // Setting a string in oneof to a small value should only increase SpaceUsed()
+  // by the size of a string object.
+  message1.set_foo_string("abc");
+  EXPECT_LE(empty_message_size + sizeof(string), message1.SpaceUsed());
+
+  // Setting a string in oneof to a value larger than the string object itself
+  // should increase SpaceUsed(), because it cannot store the value internally.
+  message1.set_foo_string(string(sizeof(string) + 1, 'x'));
+  int min_expected_increase = message1.foo_string().capacity() +
+      sizeof(string);
+  EXPECT_LE(empty_message_size + min_expected_increase,
+            message1.SpaceUsed());
+
+  // Setting a message in oneof should delete the other fields and increase the
+  // size by the size of the nested message type. NestedMessage is simple enough
+  // that it is equal to sizeof(NestedMessage)
+  message1.mutable_foo_message();
+  ASSERT_EQ(sizeof(unittest::TestOneof2::NestedMessage),
+            message1.foo_message().SpaceUsed());
+  EXPECT_EQ(empty_message_size +
+            sizeof(unittest::TestOneof2::NestedMessage),
+            message1.SpaceUsed());
+}
+
 #endif  // !PROTOBUF_TEST_NO_DESCRIPTORS
 
 
@@ -887,6 +939,9 @@ TEST(GeneratedEnumTest, EnumValuesAsSwitchCases) {
     case unittest::TestAllTypes::BAZ:
       i = 3;
       break;
+    case unittest::TestAllTypes::NEG:
+      i = -1;
+      break;
     // no default case:  We want to make sure the compiler recognizes that
     //   all cases are covered.  (GCC warns if you do not cover all cases of
     //   an enum in a switch.)
@@ -915,7 +970,7 @@ TEST(GeneratedEnumTest, IsValidValue) {
 }
 
 TEST(GeneratedEnumTest, MinAndMax) {
-  EXPECT_EQ(unittest::TestAllTypes::FOO,
+  EXPECT_EQ(unittest::TestAllTypes::NEG,
             unittest::TestAllTypes::NestedEnum_MIN);
   EXPECT_EQ(unittest::TestAllTypes::BAZ,
             unittest::TestAllTypes::NestedEnum_MAX);
@@ -989,6 +1044,20 @@ TEST(GeneratedEnumTest, GetEnumDescriptor) {
             GetEnumDescriptor<unittest::TestSparseEnum>());
 }
 
+enum NonProtoEnum {
+  kFoo = 1,
+};
+
+TEST(GeneratedEnumTest, IsProtoEnumTypeTrait) {
+  EXPECT_TRUE(is_proto_enum<unittest::TestAllTypes::NestedEnum>::value);
+  EXPECT_TRUE(is_proto_enum<unittest::ForeignEnum>::value);
+  EXPECT_TRUE(is_proto_enum<unittest::TestEnumWithDupValue>::value);
+  EXPECT_TRUE(is_proto_enum<unittest::TestSparseEnum>::value);
+
+  EXPECT_FALSE(is_proto_enum<int>::value);
+  EXPECT_FALSE(is_proto_enum<NonProtoEnum>::value);
+}
+
 #endif  // PROTOBUF_TEST_NO_DESCRIPTORS
 
 // ===================================================================
@@ -1288,6 +1357,657 @@ TEST_F(GeneratedServiceTest, NotImplemented) {
   EXPECT_TRUE(controller.called_);
 }
 
+// ===================================================================
+
+class OneofTest : public testing::Test {
+ protected:
+  virtual void SetUp() {
+  }
+
+  void ExpectEnumCasesWork(const unittest::TestOneof2 &message) {
+    switch (message.foo_case()) {
+      case unittest::TestOneof2::kFooInt:
+        EXPECT_TRUE(message.has_foo_int());
+        break;
+      case unittest::TestOneof2::kFooString:
+        EXPECT_TRUE(message.has_foo_string());
+        break;
+      case unittest::TestOneof2::kFooBytes:
+        EXPECT_TRUE(message.has_foo_bytes());
+        break;
+      case unittest::TestOneof2::kFooEnum:
+        EXPECT_TRUE(message.has_foo_enum());
+        break;
+      case unittest::TestOneof2::kFooMessage:
+        EXPECT_TRUE(message.has_foo_message());
+        break;
+      case unittest::TestOneof2::kFoogroup:
+        EXPECT_TRUE(message.has_foogroup());
+        break;
+      case unittest::TestOneof2::FOO_NOT_SET:
+        break;
+    }
+  }
+};
+
+TEST_F(OneofTest, SettingOneFieldClearsOthers) {
+  unittest::TestOneof2 message;
+
+  message.set_foo_int(123);
+  EXPECT_TRUE(message.has_foo_int());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+  message.set_foo_string("foo");
+  EXPECT_TRUE(message.has_foo_string());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+
+  message.set_foo_bytes("qux");
+  EXPECT_TRUE(message.has_foo_bytes());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+  message.set_foo_enum(unittest::TestOneof2::FOO);
+  EXPECT_TRUE(message.has_foo_enum());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+  message.mutable_foo_message()->set_qux_int(234);
+  EXPECT_TRUE(message.has_foo_message());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+  message.mutable_foogroup()->set_a(345);
+  EXPECT_TRUE(message.has_foogroup());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+
+
+  // we repeat this because we didn't test if this properly clears other fields
+  // at the beginning.
+  message.set_foo_int(123);
+  EXPECT_TRUE(message.has_foo_int());
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message);
+}
+
+TEST_F(OneofTest, EnumCases) {
+  unittest::TestOneof2 message;
+
+  message.set_foo_int(123);
+  ExpectEnumCasesWork(message);
+  message.set_foo_string("foo");
+  ExpectEnumCasesWork(message);
+  message.set_foo_bytes("qux");
+  ExpectEnumCasesWork(message);
+  message.set_foo_enum(unittest::TestOneof2::FOO);
+  ExpectEnumCasesWork(message);
+  message.mutable_foo_message()->set_qux_int(234);
+  ExpectEnumCasesWork(message);
+  message.mutable_foogroup()->set_a(345);
+  ExpectEnumCasesWork(message);
+}
+
+TEST_F(OneofTest, PrimitiveType) {
+  unittest::TestOneof2 message;
+  // Unset field returns default value
+  EXPECT_EQ(message.foo_int(), 0);
+
+  message.set_foo_int(123);
+  EXPECT_TRUE(message.has_foo_int());
+  EXPECT_EQ(message.foo_int(), 123);
+  message.clear_foo_int();
+  EXPECT_FALSE(message.has_foo_int());
+}
+
+TEST_F(OneofTest, EnumType) {
+  unittest::TestOneof2 message;
+  // Unset field returns default value
+  EXPECT_EQ(message.foo_enum(), 1);
+
+  message.set_foo_enum(unittest::TestOneof2::FOO);
+  EXPECT_TRUE(message.has_foo_enum());
+  EXPECT_EQ(message.foo_enum(), unittest::TestOneof2::FOO);
+  message.clear_foo_enum();
+  EXPECT_FALSE(message.has_foo_enum());
+}
+
+TEST_F(OneofTest, SetString) {
+  // Check that setting a string field in various ways works
+  unittest::TestOneof2 message;
+
+  // Unset field returns default value
+  EXPECT_EQ(message.foo_string(), "");
+
+  message.set_foo_string("foo");
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "foo");
+  message.clear_foo_string();
+  EXPECT_FALSE(message.has_foo_string());
+
+  message.set_foo_string(string("bar"));
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "bar");
+  message.clear_foo_string();
+  EXPECT_FALSE(message.has_foo_string());
+
+
+  message.set_foo_string("qux", 3);
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "qux");
+  message.clear_foo_string();
+  EXPECT_FALSE(message.has_foo_string());
+
+  message.mutable_foo_string()->assign("quux");
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "quux");
+  message.clear_foo_string();
+  EXPECT_FALSE(message.has_foo_string());
+
+  message.set_foo_string("corge");
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "corge");
+  message.clear_foo_string();
+  EXPECT_FALSE(message.has_foo_string());
+}
+
+TEST_F(OneofTest, ReleaseString) {
+  // Check that release_foo() starts out NULL, and gives us a value
+  // that we can delete after it's been set.
+  unittest::TestOneof2 message;
+
+  EXPECT_EQ(NULL, message.release_foo_string());
+  EXPECT_FALSE(message.has_foo_string());
+
+  message.set_foo_string("blah");
+  EXPECT_TRUE(message.has_foo_string());
+  scoped_ptr<string> str(message.release_foo_string());
+  EXPECT_FALSE(message.has_foo_string());
+  ASSERT_TRUE(str != NULL);
+  EXPECT_EQ("blah", *str);
+
+  EXPECT_EQ(NULL, message.release_foo_string());
+  EXPECT_FALSE(message.has_foo_string());
+}
+
+TEST_F(OneofTest, SetAllocatedString) {
+  // Check that set_allocated_foo() works for strings.
+  unittest::TestOneof2 message;
+
+  EXPECT_FALSE(message.has_foo_string());
+  const string kHello("hello");
+  message.set_foo_string(kHello);
+  EXPECT_TRUE(message.has_foo_string());
+
+  message.set_allocated_foo_string(NULL);
+  EXPECT_FALSE(message.has_foo_string());
+  EXPECT_EQ("", message.foo_string());
+
+  message.set_allocated_foo_string(new string(kHello));
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(kHello, message.foo_string());
+}
+
+
+TEST_F(OneofTest, SetMessage) {
+  // Check that setting a message field works
+  unittest::TestOneof2 message;
+
+  // Unset field returns default instance
+  EXPECT_EQ(&message.foo_message(),
+            &unittest::TestOneof2_NestedMessage::default_instance());
+  EXPECT_EQ(message.foo_message().qux_int(), 0);
+
+  message.mutable_foo_message()->set_qux_int(234);
+  EXPECT_TRUE(message.has_foo_message());
+  EXPECT_EQ(message.foo_message().qux_int(), 234);
+  message.clear_foo_message();
+  EXPECT_FALSE(message.has_foo_message());
+}
+
+TEST_F(OneofTest, ReleaseMessage) {
+  // Check that release_foo() starts out NULL, and gives us a value
+  // that we can delete after it's been set.
+  unittest::TestOneof2 message;
+
+  EXPECT_EQ(NULL, message.release_foo_message());
+  EXPECT_FALSE(message.has_foo_message());
+
+  message.mutable_foo_message()->set_qux_int(1);
+  EXPECT_TRUE(message.has_foo_message());
+  scoped_ptr<unittest::TestOneof2_NestedMessage> mes(
+      message.release_foo_message());
+  EXPECT_FALSE(message.has_foo_message());
+  ASSERT_TRUE(mes != NULL);
+  EXPECT_EQ(1, mes->qux_int());
+
+  EXPECT_EQ(NULL, message.release_foo_message());
+  EXPECT_FALSE(message.has_foo_message());
+}
+
+TEST_F(OneofTest, SetAllocatedMessage) {
+  // Check that set_allocated_foo() works for messages.
+  unittest::TestOneof2 message;
+
+  EXPECT_FALSE(message.has_foo_message());
+
+  message.mutable_foo_message()->set_qux_int(1);
+  EXPECT_TRUE(message.has_foo_message());
+
+  message.set_allocated_foo_message(NULL);
+  EXPECT_FALSE(message.has_foo_message());
+  EXPECT_EQ(&message.foo_message(),
+            &unittest::TestOneof2_NestedMessage::default_instance());
+
+  message.mutable_foo_message()->set_qux_int(1);
+  unittest::TestOneof2_NestedMessage* mes = message.release_foo_message();
+  ASSERT_TRUE(mes != NULL);
+  EXPECT_FALSE(message.has_foo_message());
+
+  message.set_allocated_foo_message(mes);
+  EXPECT_TRUE(message.has_foo_message());
+  EXPECT_EQ(1, message.foo_message().qux_int());
+}
+
+
+TEST_F(OneofTest, Clear) {
+  unittest::TestOneof2 message;
+
+  message.set_foo_int(1);
+  EXPECT_TRUE(message.has_foo_int());
+  message.clear_foo_int();
+  EXPECT_FALSE(message.has_foo_int());
+}
+
+TEST_F(OneofTest, Defaults) {
+  unittest::TestOneof2 message;
+
+  EXPECT_FALSE(message.has_foo_int());
+  EXPECT_EQ(message.foo_int(), 0);
+
+  EXPECT_FALSE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "");
+
+
+  EXPECT_FALSE(message.has_foo_bytes());
+  EXPECT_EQ(message.foo_bytes(), "");
+
+  EXPECT_FALSE(message.has_foo_enum());
+  EXPECT_EQ(message.foo_enum(), 1);
+
+  EXPECT_FALSE(message.has_foo_message());
+  EXPECT_EQ(message.foo_message().qux_int(), 0);
+
+  EXPECT_FALSE(message.has_foogroup());
+  EXPECT_EQ(message.foogroup().a(), 0);
+
+
+  EXPECT_FALSE(message.has_bar_int());
+  EXPECT_EQ(message.bar_int(), 5);
+
+  EXPECT_FALSE(message.has_bar_string());
+  EXPECT_EQ(message.bar_string(), "STRING");
+
+
+  EXPECT_FALSE(message.has_bar_bytes());
+  EXPECT_EQ(message.bar_bytes(), "BYTES");
+
+  EXPECT_FALSE(message.has_bar_enum());
+  EXPECT_EQ(message.bar_enum(), 2);
+}
+
+TEST_F(OneofTest, SwapWithEmpty) {
+  unittest::TestOneof2 message1, message2;
+  message1.set_foo_string("FOO");
+  EXPECT_TRUE(message1.has_foo_string());
+  message1.Swap(&message2);
+  EXPECT_FALSE(message1.has_foo_string());
+  EXPECT_TRUE(message2.has_foo_string());
+  EXPECT_EQ(message2.foo_string(), "FOO");
+}
+
+TEST_F(OneofTest, SwapWithSelf) {
+  unittest::TestOneof2 message;
+  message.set_foo_string("FOO");
+  EXPECT_TRUE(message.has_foo_string());
+  message.Swap(&message);
+  EXPECT_TRUE(message.has_foo_string());
+  EXPECT_EQ(message.foo_string(), "FOO");
+}
+
+TEST_F(OneofTest, SwapBothHasFields) {
+  unittest::TestOneof2 message1, message2;
+
+  message1.set_foo_string("FOO");
+  EXPECT_TRUE(message1.has_foo_string());
+  message2.mutable_foo_message()->set_qux_int(1);
+  EXPECT_TRUE(message2.has_foo_message());
+
+  message1.Swap(&message2);
+  EXPECT_FALSE(message1.has_foo_string());
+  EXPECT_FALSE(message2.has_foo_message());
+  EXPECT_TRUE(message1.has_foo_message());
+  EXPECT_EQ(message1.foo_message().qux_int(), 1);
+  EXPECT_TRUE(message2.has_foo_string());
+  EXPECT_EQ(message2.foo_string(), "FOO");
+}
+
+TEST_F(OneofTest, CopyContructor) {
+  unittest::TestOneof2 message1;
+  message1.set_foo_bytes("FOO");
+
+  unittest::TestOneof2 message2(message1);
+  EXPECT_TRUE(message2.has_foo_bytes());
+  EXPECT_EQ(message2.foo_bytes(), "FOO");
+}
+
+TEST_F(OneofTest, CopyFrom) {
+  unittest::TestOneof2 message1, message2;
+  message1.set_foo_enum(unittest::TestOneof2::BAR);
+  EXPECT_TRUE(message1.has_foo_enum());
+
+  message2.CopyFrom(message1);
+  EXPECT_TRUE(message2.has_foo_enum());
+  EXPECT_EQ(message2.foo_enum(), unittest::TestOneof2::BAR);
+
+  // Copying from self should be a no-op.
+  message2.CopyFrom(message2);
+  EXPECT_TRUE(message2.has_foo_enum());
+  EXPECT_EQ(message2.foo_enum(), unittest::TestOneof2::BAR);
+}
+
+TEST_F(OneofTest, CopyAssignmentOperator) {
+  unittest::TestOneof2 message1;
+  message1.mutable_foo_message()->set_qux_int(123);
+  EXPECT_TRUE(message1.has_foo_message());
+
+  unittest::TestOneof2 message2;
+  message2 = message1;
+  EXPECT_EQ(message2.foo_message().qux_int(), 123);
+
+  // Make sure that self-assignment does something sane.
+  message2 = message2;
+  EXPECT_EQ(message2.foo_message().qux_int(), 123);
+}
+
+TEST_F(OneofTest, UpcastCopyFrom) {
+  // Test the CopyFrom method that takes in the generic const Message&
+  // parameter.
+  unittest::TestOneof2 message1, message2;
+  message1.mutable_foogroup()->set_a(123);
+  EXPECT_TRUE(message1.has_foogroup());
+
+  const Message* source = implicit_cast<const Message*>(&message1);
+  message2.CopyFrom(*source);
+
+  EXPECT_TRUE(message2.has_foogroup());
+  EXPECT_EQ(message2.foogroup().a(), 123);
+}
+
+// Test the generated SerializeWithCachedSizesToArray(),
+// This indirectly tests MergePartialFromCodedStream()
+// We have to test each field type separately because we cannot set them at the
+// same time
+TEST_F(OneofTest, SerializationToArray) {
+  // Primitive type
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_int(123);
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_int(), 123);
+  }
+
+  // String
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_string("foo");
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_string(), "foo");
+  }
+
+
+  // Bytes
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_bytes("qux");
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_bytes(), "qux");
+  }
+
+  // Enum
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_enum(unittest::TestOneof2::FOO);
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_enum(), unittest::TestOneof2::FOO);
+  }
+
+  // Message
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.mutable_foo_message()->set_qux_int(234);
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_message().qux_int(), 234);
+  }
+
+  // Group
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.mutable_foogroup()->set_a(345);
+    int size = message1.ByteSize();
+    data.resize(size);
+    uint8* start = reinterpret_cast<uint8*>(string_as_array(&data));
+    uint8* end = message1.SerializeWithCachedSizesToArray(start);
+    EXPECT_EQ(size, end - start);
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foogroup().a(), 345);
+  }
+
+}
+
+// Test the generated SerializeWithCachedSizes() by forcing the buffer to write
+// one byte at a time.
+// This indirectly tests MergePartialFromCodedStream()
+// We have to test each field type separately because we cannot set them at the
+// same time
+TEST_F(OneofTest, SerializationToStream) {
+  // Primitive type
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_int(123);
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_int(), 123);
+  }
+
+  // String
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_string("foo");
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_string(), "foo");
+  }
+
+
+  // Bytes
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_bytes("qux");
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_bytes(), "qux");
+  }
+
+  // Enum
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.set_foo_enum(unittest::TestOneof2::FOO);
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_enum(), unittest::TestOneof2::FOO);
+  }
+
+  // Message
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.mutable_foo_message()->set_qux_int(234);
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foo_message().qux_int(), 234);
+  }
+
+  // Group
+  {
+    unittest::TestOneof2 message1, message2;
+    string data;
+    message1.mutable_foogroup()->set_a(345);
+    int size = message1.ByteSize();
+    data.resize(size);
+
+    {
+      // Allow the output stream to buffer only one byte at a time.
+      io::ArrayOutputStream array_stream(string_as_array(&data), size, 1);
+      io::CodedOutputStream output_stream(&array_stream);
+      message1.SerializeWithCachedSizes(&output_stream);
+      EXPECT_FALSE(output_stream.HadError());
+      EXPECT_EQ(size, output_stream.ByteCount());
+    }
+
+    EXPECT_TRUE(message2.ParseFromString(data));
+    EXPECT_EQ(message2.foogroup().a(), 345);
+  }
+
+}
+
+TEST_F(OneofTest, MergeFrom) {
+  unittest::TestOneof2 message1, message2;
+
+  message1.set_foo_int(123);
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foo_int());
+  EXPECT_EQ(message2.foo_int(), 123);
+
+  message1.set_foo_string("foo");
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foo_string());
+  EXPECT_EQ(message2.foo_string(), "foo");
+
+
+  message1.set_foo_bytes("qux");
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foo_bytes());
+  EXPECT_EQ(message2.foo_bytes(), "qux");
+
+  message1.set_foo_enum(unittest::TestOneof2::FOO);
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foo_enum());
+  EXPECT_EQ(message2.foo_enum(), unittest::TestOneof2::FOO);
+
+  message1.mutable_foo_message()->set_qux_int(234);
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foo_message());
+  EXPECT_EQ(message2.foo_message().qux_int(), 234);
+
+  message1.mutable_foogroup()->set_a(345);
+  message2.MergeFrom(message1);
+  TestUtil::ExpectAtMostOneFieldSetInOneof(message2);
+  EXPECT_TRUE(message2.has_foogroup());
+  EXPECT_EQ(message2.foogroup().a(), 345);
+
+}
+
 }  // namespace cpp_unittest
 }  // namespace cpp
 }  // namespace compiler
diff --git a/src/google/protobuf/compiler/importer.cc b/src/google/protobuf/compiler/importer.cc
index 422f759f..701ac483 100644
--- a/src/google/protobuf/compiler/importer.cc
+++ b/src/google/protobuf/compiler/importer.cc
@@ -43,6 +43,7 @@
 #include <errno.h>
 
 #include <algorithm>
+#include <memory>
 
 #include <google/protobuf/compiler/importer.h>
 
@@ -124,7 +125,8 @@ bool SourceTreeDescriptorDatabase::FindFileByName(
   scoped_ptr<io::ZeroCopyInputStream> input(source_tree_->Open(filename));
   if (input == NULL) {
     if (error_collector_ != NULL) {
-      error_collector_->AddError(filename, -1, 0, "File not found.");
+      error_collector_->AddError(filename, -1, 0,
+                                 source_tree_->GetLastErrorMessage());
     }
     return false;
   }
@@ -186,6 +188,7 @@ Importer::Importer(SourceTree* source_tree,
                    MultiFileErrorCollector* error_collector)
   : database_(source_tree),
     pool_(&database_, database_.GetValidationErrorCollector()) {
+  pool_.EnforceWeakDependencies(true);
   database_.RecordErrorsTo(error_collector);
 }
 
@@ -195,10 +198,22 @@ const FileDescriptor* Importer::Import(const string& filename) {
   return pool_.FindFileByName(filename);
 }
 
+void Importer::AddUnusedImportTrackFile(const string& file_name) {
+  pool_.AddUnusedImportTrackFile(file_name);
+}
+
+void Importer::ClearUnusedImportTrackFiles() {
+  pool_.ClearUnusedImportTrackFiles();
+}
+
 // ===================================================================
 
 SourceTree::~SourceTree() {}
 
+string SourceTree::GetLastErrorMessage() {
+  return "File not found.";
+}
+
 DiskSourceTree::DiskSourceTree() {}
 
 DiskSourceTree::~DiskSourceTree() {}
@@ -239,9 +254,9 @@ static string CanonicalizePath(string path) {
   }
 #endif
 
-  vector<string> parts;
   vector<string> canonical_parts;
-  SplitStringUsing(path, "/", &parts);  // Note:  Removes empty parts.
+  vector<string> parts = Split(
+      path, "/", true);  // Note:  Removes empty parts.
   for (int i = 0; i < parts.size(); i++) {
     if (parts[i] == ".") {
       // Ignore.
@@ -249,7 +264,7 @@ static string CanonicalizePath(string path) {
       canonical_parts.push_back(parts[i]);
     }
   }
-  string result = JoinStrings(canonical_parts, "/");
+  string result = Join(canonical_parts, "/");
   if (!path.empty() && path[0] == '/') {
     // Restore leading slash.
     result = '/' + result;
@@ -395,8 +410,8 @@ DiskSourceTree::DiskFileToVirtualFile(
 
 bool DiskSourceTree::VirtualFileToDiskFile(const string& virtual_file,
                                            string* disk_file) {
-  scoped_ptr<io::ZeroCopyInputStream> stream(OpenVirtualFile(virtual_file,
-                                                             disk_file));
+  scoped_ptr<io::ZeroCopyInputStream> stream(
+      OpenVirtualFile(virtual_file, disk_file));
   return stream != NULL;
 }
 
@@ -404,6 +419,10 @@ io::ZeroCopyInputStream* DiskSourceTree::Open(const string& filename) {
   return OpenVirtualFile(filename, NULL);
 }
 
+string DiskSourceTree::GetLastErrorMessage() {
+  return last_error_message_;
+}
+
 io::ZeroCopyInputStream* DiskSourceTree::OpenVirtualFile(
     const string& virtual_file,
     string* disk_file) {
@@ -412,6 +431,8 @@ io::ZeroCopyInputStream* DiskSourceTree::OpenVirtualFile(
     // We do not allow importing of paths containing things like ".." or
     // consecutive slashes since the compiler expects files to be uniquely
     // identified by file name.
+    last_error_message_ = "Backslashes, consecutive slashes, \".\", or \"..\" "
+                          "are not allowed in the virtual path";
     return NULL;
   }
 
@@ -429,13 +450,13 @@ io::ZeroCopyInputStream* DiskSourceTree::OpenVirtualFile(
 
       if (errno == EACCES) {
         // The file exists but is not readable.
-        // TODO(kenton):  Find a way to report this more nicely.
-        GOOGLE_LOG(WARNING) << "Read access is denied for file: " << temp_disk_file;
+        last_error_message_ = "Read access is denied for file: " +
+                              temp_disk_file;
         return NULL;
       }
     }
   }
-
+  last_error_message_ = "File not found.";
   return NULL;
 }
 
diff --git a/src/google/protobuf/compiler/importer.h b/src/google/protobuf/compiler/importer.h
index 7a62fa0e..0171d2fa 100644
--- a/src/google/protobuf/compiler/importer.h
+++ b/src/google/protobuf/compiler/importer.h
@@ -166,6 +166,9 @@ class LIBPROTOBUF_EXPORT Importer {
     return &pool_;
   }
 
+  void AddUnusedImportTrackFile(const string& file_name);
+  void ClearUnusedImportTrackFiles();
+
  private:
   SourceTreeDescriptorDatabase database_;
   DescriptorPool pool_;
@@ -204,6 +207,13 @@ class LIBPROTOBUF_EXPORT SourceTree {
   // contain "." or ".." components.
   virtual io::ZeroCopyInputStream* Open(const string& filename) = 0;
 
+  // If Open() returns NULL, calling this method immediately will return an
+  // description of the error.
+  // Subclasses should implement this method and return a meaningful value for
+  // better error reporting.
+  // TODO(xiaofeng): change this to a pure virtual function.
+  virtual string GetLastErrorMessage();
+
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(SourceTree);
 };
@@ -273,7 +283,9 @@ class LIBPROTOBUF_EXPORT DiskSourceTree : public SourceTree {
   bool VirtualFileToDiskFile(const string& virtual_file, string* disk_file);
 
   // implements SourceTree -------------------------------------------
-  io::ZeroCopyInputStream* Open(const string& filename);
+  virtual io::ZeroCopyInputStream* Open(const string& filename);
+
+  virtual string GetLastErrorMessage();
 
  private:
   struct Mapping {
@@ -285,6 +297,7 @@ class LIBPROTOBUF_EXPORT DiskSourceTree : public SourceTree {
       : virtual_path(virtual_path_param), disk_path(disk_path_param) {}
   };
   vector<Mapping> mappings_;
+  string last_error_message_;
 
   // Like Open(), but returns the on-disk path in disk_file if disk_file is
   // non-NULL and the file could be successfully opened.
diff --git a/src/google/protobuf/compiler/importer_unittest.cc b/src/google/protobuf/compiler/importer_unittest.cc
index 56fad56e..b54d9b73 100644
--- a/src/google/protobuf/compiler/importer_unittest.cc
+++ b/src/google/protobuf/compiler/importer_unittest.cc
@@ -33,12 +33,13 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/stubs/hash.h>
+#include <memory>
 
 #include <google/protobuf/compiler/importer.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
 
-#include <google/protobuf/stubs/map-util.h>
+#include <google/protobuf/stubs/map_util.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/testing/file.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -92,6 +93,10 @@ class MockSourceTree : public SourceTree {
     }
   }
 
+  string GetLastErrorMessage() {
+    return "File not found.";
+  }
+
  private:
   hash_map<string, const char*> files_;
 };
@@ -324,6 +329,7 @@ TEST_F(ImporterTest, MapFieldKeyNotScalar) {
   EXPECT_SUBSTRING("must name a scalar or string", error());
 }
 
+
 // ===================================================================
 
 class DiskSourceTreeTest : public testing::Test {
@@ -336,7 +342,7 @@ class DiskSourceTreeTest : public testing::Test {
       if (File::Exists(dirnames_[i])) {
         File::DeleteRecursively(dirnames_[i], NULL, NULL);
       }
-      GOOGLE_CHECK(File::CreateDir(dirnames_[i].c_str(), DEFAULT_FILE_MODE));
+      GOOGLE_CHECK_OK(File::CreateDir(dirnames_[i], 0777));
     }
   }
 
@@ -347,11 +353,11 @@ class DiskSourceTreeTest : public testing::Test {
   }
 
   void AddFile(const string& filename, const char* contents) {
-    File::WriteStringToFileOrDie(contents, filename);
+    GOOGLE_CHECK_OK(File::SetContents(filename, contents, true));
   }
 
   void AddSubdir(const string& dirname) {
-    GOOGLE_CHECK(File::CreateDir(dirname.c_str(), DEFAULT_FILE_MODE));
+    GOOGLE_CHECK_OK(File::CreateDir(dirname, 0777));
   }
 
   void ExpectFileContents(const string& filename,
@@ -371,9 +377,11 @@ class DiskSourceTreeTest : public testing::Test {
     EXPECT_EQ(expected_contents, file_contents);
   }
 
-  void ExpectFileNotFound(const string& filename) {
+  void ExpectCannotOpenFile(const string& filename,
+                            const string& error_message) {
     scoped_ptr<io::ZeroCopyInputStream> input(source_tree_.Open(filename));
     EXPECT_TRUE(input == NULL);
+    EXPECT_EQ(error_message, source_tree_.GetLastErrorMessage());
   }
 
   DiskSourceTree source_tree_;
@@ -389,7 +397,7 @@ TEST_F(DiskSourceTreeTest, MapRoot) {
   source_tree_.MapPath("", dirnames_[0]);
 
   ExpectFileContents("foo", "Hello World!");
-  ExpectFileNotFound("bar");
+  ExpectCannotOpenFile("bar", "File not found.");
 }
 
 TEST_F(DiskSourceTreeTest, MapDirectory) {
@@ -400,15 +408,21 @@ TEST_F(DiskSourceTreeTest, MapDirectory) {
   source_tree_.MapPath("baz", dirnames_[0]);
 
   ExpectFileContents("baz/foo", "Hello World!");
-  ExpectFileNotFound("baz/bar");
-  ExpectFileNotFound("foo");
-  ExpectFileNotFound("bar");
+  ExpectCannotOpenFile("baz/bar", "File not found.");
+  ExpectCannotOpenFile("foo", "File not found.");
+  ExpectCannotOpenFile("bar", "File not found.");
 
   // Non-canonical file names should not work.
-  ExpectFileNotFound("baz//foo");
-  ExpectFileNotFound("baz/../baz/foo");
-  ExpectFileNotFound("baz/./foo");
-  ExpectFileNotFound("baz/foo/");
+  ExpectCannotOpenFile("baz//foo",
+                       "Backslashes, consecutive slashes, \".\", or \"..\" are "
+                       "not allowed in the virtual path");
+  ExpectCannotOpenFile("baz/../baz/foo",
+                       "Backslashes, consecutive slashes, \".\", or \"..\" are "
+                       "not allowed in the virtual path");
+  ExpectCannotOpenFile("baz/./foo",
+                       "Backslashes, consecutive slashes, \".\", or \"..\" are "
+                       "not allowed in the virtual path");
+  ExpectCannotOpenFile("baz/foo/", "File not found.");
 }
 
 TEST_F(DiskSourceTreeTest, NoParent) {
@@ -420,8 +434,12 @@ TEST_F(DiskSourceTreeTest, NoParent) {
   source_tree_.MapPath("", dirnames_[0] + "/bar");
 
   ExpectFileContents("baz", "Blah.");
-  ExpectFileNotFound("../foo");
-  ExpectFileNotFound("../bar/baz");
+  ExpectCannotOpenFile("../foo",
+                       "Backslashes, consecutive slashes, \".\", or \"..\" are "
+                       "not allowed in the virtual path");
+  ExpectCannotOpenFile("../bar/baz",
+                       "Backslashes, consecutive slashes, \".\", or \"..\" are "
+                       "not allowed in the virtual path");
 }
 
 TEST_F(DiskSourceTreeTest, MapFile) {
@@ -431,7 +449,7 @@ TEST_F(DiskSourceTreeTest, MapFile) {
   source_tree_.MapPath("foo", dirnames_[0] + "/foo");
 
   ExpectFileContents("foo", "Hello World!");
-  ExpectFileNotFound("bar");
+  ExpectCannotOpenFile("bar", "File not found.");
 }
 
 TEST_F(DiskSourceTreeTest, SearchMultipleDirectories) {
@@ -445,7 +463,7 @@ TEST_F(DiskSourceTreeTest, SearchMultipleDirectories) {
 
   ExpectFileContents("foo", "Hello World!");
   ExpectFileContents("bar", "Goodbye World!");
-  ExpectFileNotFound("baz");
+  ExpectCannotOpenFile("baz", "File not found.");
 }
 
 TEST_F(DiskSourceTreeTest, OrderingTrumpsSpecificity) {
@@ -453,8 +471,7 @@ TEST_F(DiskSourceTreeTest, OrderingTrumpsSpecificity) {
   // directory is more-specific than a former one.
 
   // Create the "bar" directory so we can put a file in it.
-  ASSERT_TRUE(File::CreateDir((dirnames_[0] + "/bar").c_str(),
-                              DEFAULT_FILE_MODE));
+  GOOGLE_CHECK_OK(File::CreateDir(dirnames_[0] + "/bar", 0777));
 
   // Add files and map paths.
   AddFile(dirnames_[0] + "/bar/foo", "Hello World!");
diff --git a/src/google/protobuf/compiler/java/java_context.cc b/src/google/protobuf/compiler/java/java_context.cc
new file mode 100644
index 00000000..67ac0ef3
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_context.cc
@@ -0,0 +1,195 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/compiler/java/java_context.h>
+
+#include <google/protobuf/compiler/java/java_field.h>
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/descriptor.h>
+#include <google/protobuf/stubs/strutil.h>
+#include <google/protobuf/stubs/map_util.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+Context::Context(const FileDescriptor* file)
+    : name_resolver_(new ClassNameResolver) {
+  InitializeFieldGeneratorInfo(file);
+}
+
+Context::~Context() {
+}
+
+ClassNameResolver* Context::GetNameResolver() {
+  return name_resolver_.get();
+}
+
+namespace {
+// Whether two fields have conflicting accessors (assuming name1 and name2
+// are different). name1 and name2 are field1 and field2's camel-case name
+// respectively.
+bool IsConflicting(const FieldDescriptor* field1, const string& name1,
+                   const FieldDescriptor* field2, const string& name2,
+                   string* info) {
+  if (field1->is_repeated()) {
+    if (field2->is_repeated()) {
+      // Both fields are repeated.
+      return false;
+    } else {
+      // field1 is repeated, and field2 is not.
+      if (name1 + "Count" == name2) {
+        *info = "both repeated field \"" + field1->name() + "\" and singular " +
+            "field \"" + field2->name() + "\" generates the method \"" +
+            "get" + name1 + "Count()\"";
+        return true;
+      }
+      if (name1 + "List" == name2) {
+        *info = "both repeated field \"" + field1->name() + "\" and singular " +
+            "field \"" + field2->name() + "\" generates the method \"" +
+            "get" + name1 + "List()\"";
+        return true;
+      }
+      // Well, there are obviously many more conflicting cases, but it probably
+      // doesn't worth the effort to exhaust all of them because they rarely
+      // happen and as we are continuing adding new methods/changing existing
+      // methods the number of different conflicting cases will keep growing.
+      // We can just add more cases here when they are found in the real world.
+      return false;
+    }
+  } else {
+    if (field2->is_repeated()) {
+      return IsConflicting(field2, name2, field1, name1, info);
+    } else {
+      // None of the two fields are repeated.
+      return false;
+    }
+  }
+}
+}  // namespace
+
+void Context::InitializeFieldGeneratorInfo(const FileDescriptor* file) {
+  for (int i = 0; i < file->message_type_count(); ++i) {
+    InitializeFieldGeneratorInfoForMessage(file->message_type(i));
+  }
+}
+
+void Context::InitializeFieldGeneratorInfoForMessage(
+    const Descriptor* message) {
+  for (int i = 0; i < message->nested_type_count(); ++i) {
+    InitializeFieldGeneratorInfoForMessage(message->nested_type(i));
+  }
+  vector<const FieldDescriptor*> fields;
+  for (int i = 0; i < message->field_count(); ++i) {
+    fields.push_back(message->field(i));
+  }
+  InitializeFieldGeneratorInfoForFields(fields);
+
+  for (int i = 0; i < message->oneof_decl_count(); ++i) {
+    const OneofDescriptor* oneof = message->oneof_decl(i);
+    OneofGeneratorInfo info;
+    info.name = UnderscoresToCamelCase(oneof->name(), false);
+    info.capitalized_name = UnderscoresToCamelCase(oneof->name(), true);
+    oneof_generator_info_map_[oneof] = info;
+  }
+}
+
+void Context::InitializeFieldGeneratorInfoForFields(
+    const vector<const FieldDescriptor*>& fields) {
+  // Find out all fields that conflict with some other field in the same
+  // message.
+  vector<bool> is_conflict(fields.size());
+  vector<string> conflict_reason(fields.size());
+  for (int i = 0; i < fields.size(); ++i) {
+    const FieldDescriptor* field = fields[i];
+    const string& name = UnderscoresToCapitalizedCamelCase(field);
+    for (int j = i + 1; j < fields.size(); ++j) {
+      const FieldDescriptor* other = fields[j];
+      const string& other_name = UnderscoresToCapitalizedCamelCase(other);
+      if (name == other_name) {
+        is_conflict[i] = is_conflict[j] = true;
+        conflict_reason[i] = conflict_reason[j] =
+            "capitalized name of field \"" + field->name() +
+            "\" conflicts with field \"" + other->name() + "\"";
+      } else if (IsConflicting(field, name, other, other_name,
+                               &conflict_reason[j])) {
+        is_conflict[i] = is_conflict[j] = true;
+        conflict_reason[i] = conflict_reason[j];
+      }
+    }
+    if (is_conflict[i]) {
+      GOOGLE_LOG(WARNING) << "field \"" << field->full_name() << "\" is conflicting "
+                   << "with another field: " << conflict_reason[i];
+    }
+  }
+  for (int i = 0; i < fields.size(); ++i) {
+    const FieldDescriptor* field = fields[i];
+    FieldGeneratorInfo info;
+    info.name = UnderscoresToCamelCase(field);
+    info.capitalized_name = UnderscoresToCapitalizedCamelCase(field);
+    // For fields conflicting with some other fields, we append the field
+    // number to their field names in generated code to avoid conflicts.
+    if (is_conflict[i]) {
+      info.name += SimpleItoa(field->number());
+      info.capitalized_name += SimpleItoa(field->number());
+      info.disambiguated_reason = conflict_reason[i];
+    }
+    field_generator_info_map_[field] = info;
+  }
+}
+
+const FieldGeneratorInfo* Context::GetFieldGeneratorInfo(
+    const FieldDescriptor* field) const {
+  const FieldGeneratorInfo* result =
+      FindOrNull(field_generator_info_map_, field);
+  if (result == NULL) {
+    GOOGLE_LOG(FATAL) << "Can not find FieldGeneratorInfo for field: "
+               << field->full_name();
+  }
+  return result;
+}
+
+const OneofGeneratorInfo* Context::GetOneofGeneratorInfo(
+    const OneofDescriptor* oneof) const {
+  const OneofGeneratorInfo* result =
+      FindOrNull(oneof_generator_info_map_, oneof);
+  if (result == NULL) {
+    GOOGLE_LOG(FATAL) << "Can not find OneofGeneratorInfo for oneof: "
+               << oneof->name();
+  }
+  return result;
+}
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_context.h b/src/google/protobuf/compiler/java/java_context.h
new file mode 100644
index 00000000..c622b319
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_context.h
@@ -0,0 +1,95 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_CONTEXT_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_CONTEXT_H__
+
+#include <map>
+#include <memory>
+#include <vector>
+
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+  class FileDescriptor;
+  class FieldDescriptor;
+  class OneofDescriptor;
+  class Descriptor;
+  namespace compiler {
+    namespace java {
+      class ClassNameResolver;  // name_resolver.h
+    }
+  }
+}  // namespace protobuf
+
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+struct FieldGeneratorInfo;
+struct OneofGeneratorInfo;
+// A context object holds the information that is shared among all code
+// generators.
+class Context {
+ public:
+  explicit Context(const FileDescriptor* file);
+  ~Context();
+
+  // Get the name resolver associated with this context. The resolver
+  // can be used to map descriptors to Java class names.
+  ClassNameResolver* GetNameResolver();
+
+  // Get the FieldGeneratorInfo for a given field.
+  const FieldGeneratorInfo* GetFieldGeneratorInfo(
+      const FieldDescriptor* field) const;
+
+  // Get the OneofGeneratorInfo for a given oneof.
+  const OneofGeneratorInfo* GetOneofGeneratorInfo(
+      const OneofDescriptor* oneof) const;
+
+ private:
+  void InitializeFieldGeneratorInfo(const FileDescriptor* file);
+  void InitializeFieldGeneratorInfoForMessage(const Descriptor* message);
+  void InitializeFieldGeneratorInfoForFields(
+      const vector<const FieldDescriptor*>& fields);
+
+  scoped_ptr<ClassNameResolver> name_resolver_;
+  map<const FieldDescriptor*, FieldGeneratorInfo> field_generator_info_map_;
+  map<const OneofDescriptor*, OneofGeneratorInfo> oneof_generator_info_map_;
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(Context);
+};
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_CONTEXT_H__
diff --git a/src/google/protobuf/compiler/java/java_doc_comment.cc b/src/google/protobuf/compiler/java/java_doc_comment.cc
index 60b4f2ac..23127b7f 100644
--- a/src/google/protobuf/compiler/java/java_doc_comment.cc
+++ b/src/google/protobuf/compiler/java/java_doc_comment.cc
@@ -70,12 +70,10 @@ string EscapeJavadoc(const string& input) {
         }
         break;
       case '@':
-        // "{@" starts Javadoc markup.
-        if (prev == '{') {
-          result.append("&#64;");
-        } else {
-          result.push_back(c);
-        }
+        // '@' starts javadoc tags including the @deprecated tag, which will
+        // cause a compile-time error if inserted before a declaration that
+        // does not have a corresponding @Deprecated annotation.
+        result.append("&#64;");
         break;
       case '<':
         // Avoid interpretation as HTML.
@@ -117,8 +115,7 @@ static void WriteDocCommentBodyForLocation(
     // HTML-escape them so that they don't accidentally close the doc comment.
     comments = EscapeJavadoc(comments);
 
-    vector<string> lines;
-    SplitStringAllowEmpty(comments, "\n", &lines);
+    vector<string> lines = Split(comments, "\n");
     while (!lines.empty() && lines.back().empty()) {
       lines.pop_back();
     }
diff --git a/src/google/protobuf/compiler/java/java_doc_comment_unittest.cc b/src/google/protobuf/compiler/java/java_doc_comment_unittest.cc
index 28b6d8b4..41ea9f42 100644
--- a/src/google/protobuf/compiler/java/java_doc_comment_unittest.cc
+++ b/src/google/protobuf/compiler/java/java_doc_comment_unittest.cc
@@ -46,6 +46,7 @@ TEST(JavaDocCommentTest, Escaping) {
   EXPECT_EQ("{&#64;foo}", EscapeJavadoc("{@foo}"));
   EXPECT_EQ("&lt;i&gt;&amp;&lt;/i&gt;", EscapeJavadoc("<i>&</i>"));
   EXPECT_EQ("foo&#92;u1234bar", EscapeJavadoc("foo\\u1234bar"));
+  EXPECT_EQ("&#64;deprecated", EscapeJavadoc("@deprecated"));
 }
 
 // TODO(kenton):  It's hard to write a robust test of the doc comments -- we
diff --git a/src/google/protobuf/compiler/java/java_enum.cc b/src/google/protobuf/compiler/java/java_enum.cc
index cfed815f..6bebe213 100644
--- a/src/google/protobuf/compiler/java/java_enum.cc
+++ b/src/google/protobuf/compiler/java/java_enum.cc
@@ -35,9 +35,11 @@
 #include <map>
 #include <string>
 
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_enum.h>
 #include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -47,8 +49,22 @@ namespace protobuf {
 namespace compiler {
 namespace java {
 
-EnumGenerator::EnumGenerator(const EnumDescriptor* descriptor)
-  : descriptor_(descriptor) {
+namespace {
+bool EnumHasCustomOptions(const EnumDescriptor* descriptor) {
+  if (descriptor->options().unknown_fields().field_count() > 0) return true;
+  for (int i = 0; i < descriptor->value_count(); ++i) {
+    const EnumValueDescriptor* value = descriptor->value(i);
+    if (value->options().unknown_fields().field_count() > 0) return true;
+  }
+  return false;
+}
+}  // namespace
+
+EnumGenerator::EnumGenerator(const EnumDescriptor* descriptor,
+                             bool immutable_api,
+                             Context* context)
+  : descriptor_(descriptor), immutable_api_(immutable_api),
+    name_resolver_(context->GetNameResolver())  {
   for (int i = 0; i < descriptor_->value_count(); i++) {
     const EnumValueDescriptor* value = descriptor_->value(i);
     const EnumValueDescriptor* canonical_value =
@@ -88,6 +104,9 @@ void EnumGenerator::Generate(io::Printer* printer) {
     vars["index"] = SimpleItoa(canonical_values_[i]->index());
     vars["number"] = SimpleItoa(canonical_values_[i]->number());
     WriteEnumValueDocComment(printer, canonical_values_[i]);
+    if (canonical_values_[i]->options().deprecated()) {
+      printer->Print("@java.lang.Deprecated\n");
+    }
     printer->Print(vars,
       "$name$($index$, $number$),\n");
   }
@@ -178,15 +197,58 @@ void EnumGenerator::Generate(io::Printer* printer) {
     //   at module init time because it wouldn't work with descriptor.proto, but
     //   we can cache the value the first time getDescriptor() is called.
     if (descriptor_->containing_type() == NULL) {
-      printer->Print(
-        "  return $file$.getDescriptor().getEnumTypes().get($index$);\n",
-        "file", ClassName(descriptor_->file()),
-        "index", SimpleItoa(descriptor_->index()));
+      if (!MultipleJavaFiles(descriptor_->file(), immutable_api_)) {
+        printer->Print(
+          "  return $file$.getDescriptor().getEnumTypes().get($index$);\n",
+          "file", name_resolver_->GetClassName(descriptor_->file(),
+                                               immutable_api_),
+          "index", SimpleItoa(descriptor_->index()));
+      } else {
+        printer->Indent();
+        if (EnumHasCustomOptions(descriptor_)) {
+          // We need to load the immutable classes in order to parse custom
+          // options. However, since file level enums (no outer class) are
+          // shared by immutable code and mutable code, the immutable classes
+          // may not exist. So we try to use Java reflection to retrieve the
+          // descriptor from immutable classes.
+          printer->Print(
+            "try {\n"
+            "  java.lang.Class immutableFileClass =\n"
+            "      java.lang.Class.forName(\"$immutable_file_class_name$\");\n"
+            "  @java.lang.SuppressWarnings(\"unchecked\")\n"
+            "  java.lang.reflect.Method m =\n"
+            "      immutableFileClass.getMethod(\"getDescriptor\");\n"
+            "  com.google.protobuf.Descriptors.FileDescriptor file =\n"
+            "      (com.google.protobuf.Descriptors.FileDescriptor)\n"
+            "          m.invoke(immutableFileClass);\n"
+            "  return file.getEnumTypes().get($index$);\n"
+            "} catch (Exception e) {\n"
+            // Immutable classes cannot be found. Proceed as if custom options
+            // don't exist.
+            "}\n",
+            "immutable_file_class_name",
+            name_resolver_->GetImmutableClassName(descriptor_->file()),
+            "index", SimpleItoa(descriptor_->index()));
+        }
+        printer->Print(
+          "return $immutable_package$.$descriptor_class$.descriptor\n"
+          "    .getEnumTypes().get($index$);\n",
+          "immutable_package", FileJavaPackage(descriptor_->file(), true),
+          "descriptor_class",
+          name_resolver_->GetDescriptorClassName(descriptor_->file()),
+          "index", SimpleItoa(descriptor_->index()));
+        printer->Outdent();
+      }
     } else {
       printer->Print(
-        "  return $parent$.getDescriptor().getEnumTypes().get($index$);\n",
-        "parent", ClassName(descriptor_->containing_type()),
-        "index", SimpleItoa(descriptor_->index()));
+          "  return $parent$.$descriptor$.getEnumTypes().get($index$);\n",
+          "parent", name_resolver_->GetClassName(descriptor_->containing_type(),
+                                                 immutable_api_),
+          "descriptor", descriptor_->containing_type()->options()
+                        .no_standard_descriptor_accessor()
+                        ? "getDefaultInstance().getDescriptorForType()"
+                        : "getDescriptor()",
+          "index", SimpleItoa(descriptor_->index()));
     }
 
     printer->Print(
diff --git a/src/google/protobuf/compiler/java/java_enum.h b/src/google/protobuf/compiler/java/java_enum.h
index 9a9e5742..af0cd15d 100644
--- a/src/google/protobuf/compiler/java/java_enum.h
+++ b/src/google/protobuf/compiler/java/java_enum.h
@@ -41,6 +41,12 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
   namespace io {
     class Printer;             // printer.h
   }
@@ -52,7 +58,9 @@ namespace java {
 
 class EnumGenerator {
  public:
-  explicit EnumGenerator(const EnumDescriptor* descriptor);
+  explicit EnumGenerator(const EnumDescriptor* descriptor,
+                         bool immutable_api,
+                         Context* context);
   ~EnumGenerator();
 
   void Generate(io::Printer* printer);
@@ -73,6 +81,11 @@ class EnumGenerator {
   };
   vector<Alias> aliases_;
 
+  bool immutable_api_;
+
+  Context* context_;
+  ClassNameResolver* name_resolver_;
+
   bool CanUseEnumValues();
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(EnumGenerator);
diff --git a/src/google/protobuf/compiler/java/java_enum_field.cc b/src/google/protobuf/compiler/java/java_enum_field.cc
index ec0b067e..cab9bd0e 100644
--- a/src/google/protobuf/compiler/java/java_enum_field.cc
+++ b/src/google/protobuf/compiler/java/java_enum_field.cc
@@ -35,10 +35,12 @@
 #include <map>
 #include <string>
 
-#include <google/protobuf/compiler/java/java_enum_field.h>
-#include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_doc_comment.h>
+#include <google/protobuf/compiler/java/java_enum_field.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -50,20 +52,19 @@ namespace java {
 
 namespace {
 
-// TODO(kenton):  Factor out a "SetCommonFieldVariables()" to get rid of
-//   repeat code between this and the other field types.
 void SetEnumVariables(const FieldDescriptor* descriptor,
                       int messageBitIndex,
                       int builderBitIndex,
+                      const FieldGeneratorInfo* info,
+                      ClassNameResolver* name_resolver,
                       map<string, string>* variables) {
-  (*variables)["name"] =
-    UnderscoresToCamelCase(descriptor);
-  (*variables)["capitalized_name"] =
-    UnderscoresToCapitalizedCamelCase(descriptor);
-  (*variables)["constant_name"] = FieldConstantName(descriptor);
-  (*variables)["number"] = SimpleItoa(descriptor->number());
-  (*variables)["type"] = ClassName(descriptor->enum_type());
-  (*variables)["default"] = DefaultValue(descriptor);
+  SetCommonFieldVariables(descriptor, info, variables);
+
+  (*variables)["type"] =
+      name_resolver->GetImmutableClassName(descriptor->enum_type());
+  (*variables)["mutable_type"] =
+      name_resolver->GetMutableClassName(descriptor->enum_type());
+  (*variables)["default"] = ImmutableDefaultValue(descriptor, name_resolver);
   (*variables)["tag"] = SimpleItoa(internal::WireFormat::MakeTag(descriptor));
   (*variables)["tag_size"] = SimpleItoa(
       internal::WireFormat::TagSize(descriptor->number(), GetType(descriptor)));
@@ -74,14 +75,28 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
   (*variables)["on_changed"] =
       HasDescriptorMethods(descriptor->containing_type()) ? "onChanged();" : "";
 
-  // For singular messages and builders, one bit is used for the hasField bit.
-  (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
-  (*variables)["set_has_field_bit_message"] = GenerateSetBit(messageBitIndex);
+  if (SupportFieldPresence(descriptor->file())) {
+    // For singular messages and builders, one bit is used for the hasField bit.
+    (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
+    (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
+
+    // Note that these have a trailing ";".
+    (*variables)["set_has_field_bit_message"] =
+        GenerateSetBit(messageBitIndex) + ";";
+    (*variables)["set_has_field_bit_builder"] =
+        GenerateSetBit(builderBitIndex) + ";";
+    (*variables)["clear_has_field_bit_builder"] =
+        GenerateClearBit(builderBitIndex) + ";";
+
+    (*variables)["is_field_present_message"] = GenerateGetBit(messageBitIndex);
+  } else {
+    (*variables)["set_has_field_bit_message"] = "";
+    (*variables)["set_has_field_bit_builder"] = "";
+    (*variables)["clear_has_field_bit_builder"] = "";
 
-  (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
-  (*variables)["set_has_field_bit_builder"] = GenerateSetBit(builderBitIndex);
-  (*variables)["clear_has_field_bit_builder"] =
-      GenerateClearBit(builderBitIndex);
+    (*variables)["is_field_present_message"] =
+          (*variables)["name"] + "_ != " + (*variables)["default"];
+  }
 
   // For repated builders, one bit is used for whether the array is immutable.
   (*variables)["get_mutable_bit_builder"] = GenerateGetBit(builderBitIndex);
@@ -105,44 +120,53 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
 
 // ===================================================================
 
-EnumFieldGenerator::
-EnumFieldGenerator(const FieldDescriptor* descriptor,
-                      int messageBitIndex,
-                      int builderBitIndex)
+ImmutableEnumFieldGenerator::
+ImmutableEnumFieldGenerator(const FieldDescriptor* descriptor,
+                            int messageBitIndex,
+                            int builderBitIndex,
+                            Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
-  SetEnumVariables(descriptor, messageBitIndex, builderBitIndex, &variables_);
+    builderBitIndex_(builderBitIndex),
+    name_resolver_(context->GetNameResolver()) {
+  SetEnumVariables(descriptor, messageBitIndex, builderBitIndex,
+                   context->GetFieldGeneratorInfo(descriptor),
+                   name_resolver_, &variables_);
 }
 
-EnumFieldGenerator::~EnumFieldGenerator() {}
+ImmutableEnumFieldGenerator::~ImmutableEnumFieldGenerator() {}
 
-int EnumFieldGenerator::GetNumBitsForMessage() const {
+int ImmutableEnumFieldGenerator::GetNumBitsForMessage() const {
   return 1;
 }
 
-int EnumFieldGenerator::GetNumBitsForBuilder() const {
+int ImmutableEnumFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$boolean has$capitalized_name$();\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$boolean has$capitalized_name$();\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$$type$ get$capitalized_name$();\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $type$ $name$_;\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_message$;\n"
-    "}\n");
+  PrintExtraFieldInfo(variables_, printer);
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_message$;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
@@ -150,15 +174,17 @@ GenerateMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $type$ $name$_ = $default$;\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_builder$;\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_builder$;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
@@ -170,7 +196,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "  if (value == null) {\n"
     "    throw new NullPointerException();\n"
     "  }\n"
-    "  $set_has_field_bit_builder$;\n"
+    "  $set_has_field_bit_builder$\n"
     "  $name$_ = value;\n"
     "  $on_changed$\n"
     "  return this;\n"
@@ -178,129 +204,274 @@ GenerateBuilderMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public Builder clear$capitalized_name$() {\n"
-    "  $clear_has_field_bit_builder$;\n"
+    "  $clear_has_field_bit_builder$\n"
     "  $name$_ = $default$;\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for enums
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = $default$;\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
-      "$name$_ = $default$;\n"
-      "$clear_has_field_bit_builder$;\n");
+    "$name$_ = $default$;\n"
+    "$clear_has_field_bit_builder$\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "if (other.has$capitalized_name$()) {\n"
-    "  set$capitalized_name$(other.get$capitalized_name$());\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "if (other.has$capitalized_name$()) {\n"
+      "  set$capitalized_name$(other.get$capitalized_name$());\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "if (other.get$capitalized_name$() != $default$) {\n"
+      "  set$capitalized_name$(other.get$capitalized_name$());\n"
+      "}\n");
+  }
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "if ($get_has_field_bit_from_local$) {\n"
+      "  $set_has_field_bit_to_local$;\n"
+      "}\n");
+  }
   printer->Print(variables_,
-    "if ($get_has_field_bit_from_local$) {\n"
-    "  $set_has_field_bit_to_local$;\n"
-    "}\n"
     "result.$name$_ = $name$_;\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "int rawValue = input.readEnum();\n"
-    "$type$ value = $type$.valueOf(rawValue);\n");
-  if (HasUnknownFields(descriptor_->containing_type())) {
+    "$type$ value = $type$.valueOf(rawValue);\n"
+    "if (value == null) {\n");
+  if (UseUnknownFieldSet(descriptor_->containing_type())) {
     printer->Print(variables_,
-      "if (value == null) {\n"
-      "  unknownFields.mergeVarintField($number$, rawValue);\n"
-      "} else {\n");
+      "  unknownFields.mergeVarintField($number$, rawValue);\n");
   } else {
     printer->Print(variables_,
-      "if (value != null) {\n");
+      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
+      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
   }
   printer->Print(variables_,
-    "  $set_has_field_bit_message$;\n"
+    "} else {\n"
+    "  $set_has_field_bit_message$\n"
     "  $name$_ = value;\n"
     "}\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   // noop for enums
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  output.writeEnum($number$, $name$_.getNumber());\n"
     "}\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
     "    .computeEnumSize($number$, $name$_.getNumber());\n"
     "}\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result &&\n"
     "    (get$capitalized_name$() == other.get$capitalized_name$());\n");
 }
 
-void EnumFieldGenerator::
+void ImmutableEnumFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "hash = (37 * hash) + $constant_name$;\n"
-    "hash = (53 * hash) + hashEnum(get$capitalized_name$());\n");
+    "hash = (53 * hash) + com.google.protobuf.Internal.hashEnum(\n"
+    "    get$capitalized_name$());\n");
+}
+
+string ImmutableEnumFieldGenerator::GetBoxedType() const {
+  return name_resolver_->GetImmutableClassName(descriptor_->enum_type());
+}
+
+// ===================================================================
+
+ImmutableEnumOneofFieldGenerator::
+ImmutableEnumOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                 int messageBitIndex,
+                                 int builderBitIndex,
+                                 Context* context)
+    : ImmutableEnumFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+  const OneofGeneratorInfo* info =
+      context->GetOneofGeneratorInfo(descriptor->containing_oneof());
+  SetCommonOneofVariables(descriptor, info, &variables_);
+}
+
+ImmutableEnumOneofFieldGenerator::
+~ImmutableEnumOneofFieldGenerator() {}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  PrintExtraFieldInfo(variables_, printer);
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($type$) $oneof_name$_;\n"
+    "  }\n"
+    "  return $default$;\n"
+    "}\n");
 }
 
-string EnumFieldGenerator::GetBoxedType() const {
-  return ClassName(descriptor_->enum_type());
+void ImmutableEnumOneofFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($type$) $oneof_name$_;\n"
+    "  }\n"
+    "  return $default$;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder set$capitalized_name$($type$ value) {\n"
+    "  if (value == null) {\n"
+    "    throw new NullPointerException();\n"
+    "  }\n"
+    "  $set_oneof_case_message$;\n"
+    "  $oneof_name$_ = value;\n"
+    "  $on_changed$\n"
+    "  return this;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder clear$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    $clear_oneof_case_message$;\n"
+    "    $oneof_name$_ = null;\n"
+    "    $on_changed$\n"
+    "  }\n"
+    "  return this;\n"
+    "}\n");
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  result.$oneof_name$_ = $oneof_name$_;\n"
+    "}\n");
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "set$capitalized_name$(other.get$capitalized_name$());\n");
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "int rawValue = input.readEnum();\n"
+    "$type$ value = $type$.valueOf(rawValue);\n"
+    "if (value == null) {\n");
+  if (UseUnknownFieldSet(descriptor_->containing_type())) {
+    printer->Print(variables_,
+      "  unknownFields.mergeVarintField($number$, rawValue);\n");
+  } else {
+    printer->Print(variables_,
+      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
+      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
+  }
+  printer->Print(variables_,
+    "} else {\n"
+    "  $set_oneof_case_message$;\n"
+    "  $oneof_name$_ = value;\n"
+    "}\n");
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  output.writeEnum($number$, (($type$) $oneof_name$_).getNumber());\n"
+    "}\n");
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .computeEnumSize($number$, (($type$) $oneof_name$_).getNumber());\n"
+    "}\n");
 }
 
 // ===================================================================
 
-RepeatedEnumFieldGenerator::
-RepeatedEnumFieldGenerator(const FieldDescriptor* descriptor,
-                           int messageBitIndex,
-                           int builderBitIndex)
+RepeatedImmutableEnumFieldGenerator::
+RepeatedImmutableEnumFieldGenerator(const FieldDescriptor* descriptor,
+                                    int messageBitIndex,
+                                    int builderBitIndex,
+                                    Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
-  SetEnumVariables(descriptor, messageBitIndex, builderBitIndex, &variables_);
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
+  SetEnumVariables(descriptor, messageBitIndex, builderBitIndex,
+                   context->GetFieldGeneratorInfo(descriptor),
+                   name_resolver_, &variables_);
 }
 
-RepeatedEnumFieldGenerator::~RepeatedEnumFieldGenerator() {}
+RepeatedImmutableEnumFieldGenerator::~RepeatedImmutableEnumFieldGenerator() {}
 
-int RepeatedEnumFieldGenerator::GetNumBitsForMessage() const {
+int RepeatedImmutableEnumFieldGenerator::GetNumBitsForMessage() const {
   return 0;
 }
 
-int RepeatedEnumFieldGenerator::GetNumBitsForBuilder() const {
+int RepeatedImmutableEnumFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -313,10 +484,11 @@ GenerateInterfaceMembers(io::Printer* printer) const {
     "$deprecation$$type$ get$capitalized_name$(int index);\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private java.util.List<$type$> $name$_;\n");
+  PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public java.util.List<$type$> get$capitalized_name$List() {\n"
@@ -340,7 +512,7 @@ GenerateMembers(io::Printer* printer) const {
   }
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     // One field is the list and the other field keeps track of whether the
@@ -409,7 +581,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "$deprecation$public Builder addAll$capitalized_name$(\n"
     "    java.lang.Iterable<? extends $type$> values) {\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  super.addAll(values, $name$_);\n"
+    "  com.google.protobuf.AbstractMessageLite.Builder.addAll(\n"
+    "      values, $name$_);\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -423,24 +596,24 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for enums
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = java.util.Collections.emptyList();\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$name$_ = java.util.Collections.emptyList();\n"
     "$clear_mutable_bit_builder$;\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   // The code below does two optimizations:
   //   1. If the other list is empty, there's nothing to do. This ensures we
@@ -460,7 +633,7 @@ GenerateMergingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   // The code below ensures that the result has an immutable list. If our
   // list is immutable, we can just reuse it. If not, we make it immutable.
@@ -472,22 +645,23 @@ GenerateBuildingCode(io::Printer* printer) const {
     "result.$name$_ = $name$_;\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   // Read and store the enum
   printer->Print(variables_,
     "int rawValue = input.readEnum();\n"
-    "$type$ value = $type$.valueOf(rawValue);\n");
-  if (HasUnknownFields(descriptor_->containing_type())) {
+    "$type$ value = $type$.valueOf(rawValue);\n"
+    "if (value == null) {\n");
+  if (UseUnknownFieldSet(descriptor_->containing_type())) {
     printer->Print(variables_,
-      "if (value == null) {\n"
-      "  unknownFields.mergeVarintField($number$, rawValue);\n"
-      "} else {\n");
+      "  unknownFields.mergeVarintField($number$, rawValue);\n");
   } else {
     printer->Print(variables_,
-      "if (value != null) {\n");
+      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
+      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
   }
   printer->Print(variables_,
+    "  } else {\n"
     "  if (!$get_mutable_bit_parser$) {\n"
     "    $name$_ = new java.util.ArrayList<$type$>();\n"
     "    $set_mutable_bit_parser$;\n"
@@ -496,7 +670,7 @@ GenerateParsingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateParsingCodeFromPacked(io::Printer* printer) const {
   // Wrap GenerateParsingCode's contents with a while loop.
 
@@ -514,7 +688,7 @@ GenerateParsingCodeFromPacked(io::Printer* printer) const {
     "input.popLimit(oldLimit);\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($get_mutable_bit_parser$) {\n"
@@ -522,7 +696,7 @@ GenerateParsingDoneCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   if (descriptor_->options().packed()) {
     printer->Print(variables_,
@@ -541,7 +715,7 @@ GenerateSerializationCode(io::Printer* printer) const {
   }
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "{\n"
@@ -577,24 +751,25 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print("}\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$List()\n"
     "    .equals(other.get$capitalized_name$List());\n");
 }
 
-void RepeatedEnumFieldGenerator::
+void RepeatedImmutableEnumFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (get$capitalized_name$Count() > 0) {\n"
     "  hash = (37 * hash) + $constant_name$;\n"
-    "  hash = (53 * hash) + hashEnumList(get$capitalized_name$List());\n"
+    "  hash = (53 * hash) + com.google.protobuf.Internal.hashEnumList(\n"
+    "      get$capitalized_name$List());\n"
     "}\n");
 }
 
-string RepeatedEnumFieldGenerator::GetBoxedType() const {
-  return ClassName(descriptor_->enum_type());
+string RepeatedImmutableEnumFieldGenerator::GetBoxedType() const {
+  return name_resolver_->GetImmutableClassName(descriptor_->enum_type());
 }
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_enum_field.h b/src/google/protobuf/compiler/java/java_enum_field.h
index 90fae639..a3afb160 100644
--- a/src/google/protobuf/compiler/java/java_enum_field.h
+++ b/src/google/protobuf/compiler/java/java_enum_field.h
@@ -41,16 +41,26 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;            // context.h
+      class ClassNameResolver;  // name_resolver.h
+    }
+  }
+}
+
+namespace protobuf {
 namespace compiler {
 namespace java {
 
-class EnumFieldGenerator : public FieldGenerator {
+class ImmutableEnumFieldGenerator : public ImmutableFieldGenerator {
  public:
-  explicit EnumFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~EnumFieldGenerator();
+  explicit ImmutableEnumFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableEnumFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -70,22 +80,45 @@ class EnumFieldGenerator : public FieldGenerator {
 
   string GetBoxedType() const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(EnumFieldGenerator);
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableEnumFieldGenerator);
+};
+
+class ImmutableEnumOneofFieldGenerator : public ImmutableEnumFieldGenerator {
+ public:
+  ImmutableEnumOneofFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableEnumOneofFieldGenerator();
+
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableEnumOneofFieldGenerator);
 };
 
-class RepeatedEnumFieldGenerator : public FieldGenerator {
+class RepeatedImmutableEnumFieldGenerator : public ImmutableFieldGenerator {
  public:
-  explicit RepeatedEnumFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~RepeatedEnumFieldGenerator();
+  explicit RepeatedImmutableEnumFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~RepeatedImmutableEnumFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -111,8 +144,10 @@ class RepeatedEnumFieldGenerator : public FieldGenerator {
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedEnumFieldGenerator);
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedImmutableEnumFieldGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_extension.cc b/src/google/protobuf/compiler/java/java_extension.cc
index 921fe658..c62dbfaf 100644
--- a/src/google/protobuf/compiler/java/java_extension.cc
+++ b/src/google/protobuf/compiler/java/java_extension.cc
@@ -33,74 +33,50 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/java/java_extension.h>
+
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
-#include <google/protobuf/stubs/strutil.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/printer.h>
+#include <google/protobuf/stubs/strutil.h>
 
 namespace google {
 namespace protobuf {
 namespace compiler {
 namespace java {
 
-namespace {
-
-const char* TypeName(FieldDescriptor::Type field_type) {
-  switch (field_type) {
-    case FieldDescriptor::TYPE_INT32   : return "INT32";
-    case FieldDescriptor::TYPE_UINT32  : return "UINT32";
-    case FieldDescriptor::TYPE_SINT32  : return "SINT32";
-    case FieldDescriptor::TYPE_FIXED32 : return "FIXED32";
-    case FieldDescriptor::TYPE_SFIXED32: return "SFIXED32";
-    case FieldDescriptor::TYPE_INT64   : return "INT64";
-    case FieldDescriptor::TYPE_UINT64  : return "UINT64";
-    case FieldDescriptor::TYPE_SINT64  : return "SINT64";
-    case FieldDescriptor::TYPE_FIXED64 : return "FIXED64";
-    case FieldDescriptor::TYPE_SFIXED64: return "SFIXED64";
-    case FieldDescriptor::TYPE_FLOAT   : return "FLOAT";
-    case FieldDescriptor::TYPE_DOUBLE  : return "DOUBLE";
-    case FieldDescriptor::TYPE_BOOL    : return "BOOL";
-    case FieldDescriptor::TYPE_STRING  : return "STRING";
-    case FieldDescriptor::TYPE_BYTES   : return "BYTES";
-    case FieldDescriptor::TYPE_ENUM    : return "ENUM";
-    case FieldDescriptor::TYPE_GROUP   : return "GROUP";
-    case FieldDescriptor::TYPE_MESSAGE : return "MESSAGE";
-
-    // No default because we want the compiler to complain if any new
-    // types are added.
-  }
-
-  GOOGLE_LOG(FATAL) << "Can't get here.";
-  return NULL;
-}
-
-}
-
-ExtensionGenerator::ExtensionGenerator(const FieldDescriptor* descriptor)
-  : descriptor_(descriptor) {
+ImmutableExtensionGenerator::ImmutableExtensionGenerator(
+    const FieldDescriptor* descriptor, Context* context)
+  : descriptor_(descriptor), context_(context),
+    name_resolver_(context->GetNameResolver()) {
   if (descriptor_->extension_scope() != NULL) {
-    scope_ = ClassName(descriptor_->extension_scope());
+    scope_ = name_resolver_->GetImmutableClassName(
+        descriptor_->extension_scope());
   } else {
-    scope_ = ClassName(descriptor_->file());
+    scope_ = name_resolver_->GetImmutableClassName(descriptor_->file());
   }
 }
 
-ExtensionGenerator::~ExtensionGenerator() {}
+ImmutableExtensionGenerator::~ImmutableExtensionGenerator() {}
 
 // Initializes the vars referenced in the generated code templates.
-void InitTemplateVars(const FieldDescriptor* descriptor,
-                      const string& scope,
-                      map<string, string>* vars_pointer) {
+void ExtensionGenerator::InitTemplateVars(const FieldDescriptor* descriptor,
+                                          const string& scope,
+                                          bool immutable,
+                                          ClassNameResolver* name_resolver,
+                                          map<string, string>* vars_pointer) {
   map<string, string> &vars = *vars_pointer;
   vars["scope"] = scope;
   vars["name"] = UnderscoresToCamelCase(descriptor);
-  vars["containing_type"] = ClassName(descriptor->containing_type());
+  vars["containing_type"] =
+      name_resolver->GetClassName(descriptor->containing_type(), immutable);
   vars["number"] = SimpleItoa(descriptor->number());
   vars["constant_name"] = FieldConstantName(descriptor);
   vars["index"] = SimpleItoa(descriptor->index());
-  vars["default"] =
-      descriptor->is_repeated() ? "" : DefaultValue(descriptor);
-  vars["type_constant"] = TypeName(GetType(descriptor));
+  vars["default"] = descriptor->is_repeated() ?
+      "" : DefaultValue(descriptor, immutable, name_resolver);
+  vars["type_constant"] = FieldTypeName(GetType(descriptor));
   vars["packed"] = descriptor->options().packed() ? "true" : "false";
   vars["enum_map"] = "null";
   vars["prototype"] = "null";
@@ -109,13 +85,21 @@ void InitTemplateVars(const FieldDescriptor* descriptor,
   string singular_type;
   switch (java_type) {
     case JAVATYPE_MESSAGE:
-      singular_type = ClassName(descriptor->message_type());
+      singular_type = name_resolver->GetClassName(descriptor->message_type(),
+                                                   immutable);
       vars["prototype"] = singular_type + ".getDefaultInstance()";
       break;
     case JAVATYPE_ENUM:
-      singular_type = ClassName(descriptor->enum_type());
+      singular_type = name_resolver->GetClassName(descriptor->enum_type(),
+                                                   immutable);
       vars["enum_map"] = singular_type + ".internalGetValueMap()";
       break;
+    case JAVATYPE_STRING:
+      singular_type = "java.lang.String";
+      break;
+    case JAVATYPE_BYTES:
+      singular_type = immutable ? "com.google.protobuf.ByteString" : "byte[]";
+      break;
     default:
       singular_type = BoxedPrimitiveTypeName(java_type);
       break;
@@ -125,9 +109,11 @@ void InitTemplateVars(const FieldDescriptor* descriptor,
   vars["singular_type"] = singular_type;
 }
 
-void ExtensionGenerator::Generate(io::Printer* printer) {
+void ImmutableExtensionGenerator::Generate(io::Printer* printer) {
   map<string, string> vars;
-  InitTemplateVars(descriptor_, scope_, &vars);
+  const bool kUseImmutableNames = true;
+  InitTemplateVars(descriptor_, scope_, kUseImmutableNames, name_resolver_,
+                   &vars);
   printer->Print(vars,
       "public static final int $constant_name$ = $number$;\n");
 
@@ -174,7 +160,8 @@ void ExtensionGenerator::Generate(io::Printer* printer) {
           "      $enum_map$,\n"
           "      $number$,\n"
           "      com.google.protobuf.WireFormat.FieldType.$type_constant$,\n"
-          "      $packed$);\n");
+          "      $packed$,\n"
+          "      $singular_type$.class);\n");
     } else {
       printer->Print(
           vars,
@@ -188,12 +175,13 @@ void ExtensionGenerator::Generate(io::Printer* printer) {
           "      $prototype$,\n"
           "      $enum_map$,\n"
           "      $number$,\n"
-          "      com.google.protobuf.WireFormat.FieldType.$type_constant$);\n");
+          "      com.google.protobuf.WireFormat.FieldType.$type_constant$,\n"
+          "      $singular_type$.class);\n");
     }
   }
 }
 
-void ExtensionGenerator::GenerateNonNestedInitializationCode(
+void ImmutableExtensionGenerator::GenerateNonNestedInitializationCode(
     io::Printer* printer) {
   if (descriptor_->extension_scope() == NULL &&
       HasDescriptorMethods(descriptor_->file())) {
@@ -205,7 +193,8 @@ void ExtensionGenerator::GenerateNonNestedInitializationCode(
   }
 }
 
-void ExtensionGenerator::GenerateRegistrationCode(io::Printer* printer) {
+void ImmutableExtensionGenerator::GenerateRegistrationCode(
+    io::Printer* printer) {
   printer->Print(
     "registry.add($scope$.$name$);\n",
     "scope", scope_,
diff --git a/src/google/protobuf/compiler/java/java_extension.h b/src/google/protobuf/compiler/java/java_extension.h
index 009ed9ff..69686ef2 100644
--- a/src/google/protobuf/compiler/java/java_extension.h
+++ b/src/google/protobuf/compiler/java/java_extension.h
@@ -35,6 +35,7 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_EXTENSION_H__
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_EXTENSION_H__
 
+#include <map>
 #include <string>
 
 #include <google/protobuf/stubs/common.h>
@@ -42,6 +43,12 @@
 namespace google {
 namespace protobuf {
   class FieldDescriptor;       // descriptor.h
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
   namespace io {
     class Printer;             // printer.h
   }
@@ -56,17 +63,42 @@ namespace java {
 // since extensions are just simple identifiers with interesting types.
 class ExtensionGenerator {
  public:
-  explicit ExtensionGenerator(const FieldDescriptor* descriptor);
-  ~ExtensionGenerator();
+  explicit ExtensionGenerator() {}
+  virtual ~ExtensionGenerator() {}
+
+  virtual void Generate(io::Printer* printer) = 0;
+  virtual void GenerateNonNestedInitializationCode(io::Printer* printer) = 0;
+  virtual void GenerateRegistrationCode(io::Printer* printer) = 0;
 
-  void Generate(io::Printer* printer);
-  void GenerateNonNestedInitializationCode(io::Printer* printer);
-  void GenerateRegistrationCode(io::Printer* printer);
+ protected:
+  static void InitTemplateVars(const FieldDescriptor* descriptor,
+                               const string& scope,
+                               bool immutable,
+                               ClassNameResolver* name_resolver,
+                               map<string, string>* vars_pointer);
 
  private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ExtensionGenerator);
+};
+
+class ImmutableExtensionGenerator : public ExtensionGenerator {
+ public:
+  explicit ImmutableExtensionGenerator(const FieldDescriptor* descriptor,
+                                       Context* context);
+  virtual ~ImmutableExtensionGenerator();
+
+  virtual void Generate(io::Printer* printer);
+  virtual void GenerateNonNestedInitializationCode(io::Printer* printer);
+  virtual void GenerateRegistrationCode(io::Printer* printer);
+
+ protected:
   const FieldDescriptor* descriptor_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
   string scope_;
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ExtensionGenerator);
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableExtensionGenerator);
 };
 
 }  // namespace java
@@ -74,4 +106,4 @@ class ExtensionGenerator {
 }  // namespace protobuf
 
 }  // namespace google
-#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_MESSAGE_H__
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_EXTENSION_H__
diff --git a/src/google/protobuf/compiler/java/java_field.cc b/src/google/protobuf/compiler/java/java_field.cc
index c7d433c8..f670477c 100644
--- a/src/google/protobuf/compiler/java/java_field.cc
+++ b/src/google/protobuf/compiler/java/java_field.cc
@@ -33,102 +33,178 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/java/java_field.h>
-#include <google/protobuf/compiler/java/java_helpers.h>
-#include <google/protobuf/compiler/java/java_primitive_field.h>
+
+#include <memory>
+
+#include <google/protobuf/stubs/common.h>
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_enum_field.h>
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_lazy_message_field.h>
 #include <google/protobuf/compiler/java/java_message_field.h>
+#include <google/protobuf/compiler/java/java_primitive_field.h>
 #include <google/protobuf/compiler/java/java_string_field.h>
-#include <google/protobuf/stubs/common.h>
+#include <google/protobuf/io/printer.h>
+#include <google/protobuf/stubs/strutil.h>
+#include <google/protobuf/stubs/substitute.h>
 
 namespace google {
 namespace protobuf {
 namespace compiler {
 namespace java {
 
-FieldGenerator::~FieldGenerator() {}
+namespace {
+
+ImmutableFieldGenerator* MakeImmutableGenerator(
+    const FieldDescriptor* field, int messageBitIndex, int builderBitIndex,
+    Context* context) {
+  if (field->is_repeated()) {
+    switch (GetJavaType(field)) {
+      case JAVATYPE_MESSAGE:
+        if (IsLazy(field)) {
+          return new RepeatedImmutableLazyMessageFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        } else {
+          return new RepeatedImmutableMessageFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        }
+      case JAVATYPE_ENUM:
+        return new RepeatedImmutableEnumFieldGenerator(
+            field, messageBitIndex, builderBitIndex, context);
+      case JAVATYPE_STRING:
+        return new RepeatedImmutableStringFieldGenerator(
+            field, messageBitIndex, builderBitIndex, context);
+      default:
+        return new RepeatedImmutablePrimitiveFieldGenerator(
+            field, messageBitIndex, builderBitIndex, context);
+    }
+  } else {
+    if (field->containing_oneof()) {
+      switch (GetJavaType(field)) {
+        case JAVATYPE_MESSAGE:
+          if (IsLazy(field)) {
+            return new ImmutableLazyMessageOneofFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          } else {
+            return new ImmutableMessageOneofFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          }
+        case JAVATYPE_ENUM:
+          return new ImmutableEnumOneofFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        case JAVATYPE_STRING:
+          return new ImmutableStringOneofFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        default:
+          return new ImmutablePrimitiveOneofFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+      }
+    } else {
+      switch (GetJavaType(field)) {
+        case JAVATYPE_MESSAGE:
+          if (IsLazy(field)) {
+            return new ImmutableLazyMessageFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          } else {
+            return new ImmutableMessageFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          }
+        case JAVATYPE_ENUM:
+          return new ImmutableEnumFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        case JAVATYPE_STRING:
+          return new ImmutableStringFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+        default:
+          return new ImmutablePrimitiveFieldGenerator(
+              field, messageBitIndex, builderBitIndex, context);
+      }
+    }
+  }
+}
+
 
-void FieldGenerator::GenerateParsingCodeFromPacked(io::Printer* printer) const {
+static inline void ReportUnexpectedPackedFieldsCall(io::Printer* printer) {
   // Reaching here indicates a bug. Cases are:
-  //   - This FieldGenerator should support packing, but this method should be
-  //     overridden.
-  //   - This FieldGenerator doesn't support packing, and this method should
-  //     never have been called.
+  //   - This FieldGenerator should support packing,
+  //     but this method should be overridden.
+  //   - This FieldGenerator doesn't support packing, and this method
+  //     should never have been called.
   GOOGLE_LOG(FATAL) << "GenerateParsingCodeFromPacked() "
              << "called on field generator that does not support packing.";
 }
 
-FieldGeneratorMap::FieldGeneratorMap(const Descriptor* descriptor)
-  : descriptor_(descriptor),
-    field_generators_(
-      new scoped_ptr<FieldGenerator>[descriptor->field_count()]),
-    extension_generators_(
-      new scoped_ptr<FieldGenerator>[descriptor->extension_count()]) {
+}  // namespace
+
+ImmutableFieldGenerator::~ImmutableFieldGenerator() {}
+
+void ImmutableFieldGenerator::
+GenerateParsingCodeFromPacked(io::Printer* printer) const {
+  ReportUnexpectedPackedFieldsCall(printer);
+}
+
+// ===================================================================
+
+template <>
+FieldGeneratorMap<ImmutableFieldGenerator>::FieldGeneratorMap(
+    const Descriptor* descriptor, Context* context)
+    : descriptor_(descriptor),
+      field_generators_(new scoped_ptr<
+          ImmutableFieldGenerator>[descriptor->field_count()]) {
 
   // Construct all the FieldGenerators and assign them bit indices for their
   // bit fields.
   int messageBitIndex = 0;
   int builderBitIndex = 0;
   for (int i = 0; i < descriptor->field_count(); i++) {
-    FieldGenerator* generator = MakeGenerator(descriptor->field(i),
-        messageBitIndex, builderBitIndex);
+    ImmutableFieldGenerator* generator = MakeImmutableGenerator(
+        descriptor->field(i), messageBitIndex, builderBitIndex, context);
     field_generators_[i].reset(generator);
     messageBitIndex += generator->GetNumBitsForMessage();
     builderBitIndex += generator->GetNumBitsForBuilder();
   }
-  for (int i = 0; i < descriptor->extension_count(); i++) {
-    FieldGenerator* generator = MakeGenerator(descriptor->extension(i),
-        messageBitIndex, builderBitIndex);
-    extension_generators_[i].reset(generator);
-    messageBitIndex += generator->GetNumBitsForMessage();
-    builderBitIndex += generator->GetNumBitsForBuilder();
-  }
 }
 
-FieldGenerator* FieldGeneratorMap::MakeGenerator(
-    const FieldDescriptor* field, int messageBitIndex, int builderBitIndex) {
-  if (field->is_repeated()) {
-    switch (GetJavaType(field)) {
-      case JAVATYPE_MESSAGE:
-        return new RepeatedMessageFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      case JAVATYPE_ENUM:
-        return new RepeatedEnumFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      case JAVATYPE_STRING:
-        return new RepeatedStringFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      default:
-        return new RepeatedPrimitiveFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-    }
-  } else {
-    switch (GetJavaType(field)) {
-      case JAVATYPE_MESSAGE:
-        return new MessageFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      case JAVATYPE_ENUM:
-        return new EnumFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      case JAVATYPE_STRING:
-        return new StringFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-      default:
-        return new PrimitiveFieldGenerator(
-            field, messageBitIndex, builderBitIndex);
-    }
-  }
-}
+template<>
+FieldGeneratorMap<ImmutableFieldGenerator>::~FieldGeneratorMap() {}
 
-FieldGeneratorMap::~FieldGeneratorMap() {}
 
-const FieldGenerator& FieldGeneratorMap::get(
-    const FieldDescriptor* field) const {
-  GOOGLE_CHECK_EQ(field->containing_type(), descriptor_);
-  return *field_generators_[field->index()];
+void SetCommonFieldVariables(const FieldDescriptor* descriptor,
+                             const FieldGeneratorInfo* info,
+                             map<string, string>* variables) {
+  (*variables)["field_name"] = descriptor->name();
+  (*variables)["name"] = info->name;
+  (*variables)["capitalized_name"] = info->capitalized_name;
+  (*variables)["disambiguated_reason"] = info->disambiguated_reason;
+  (*variables)["constant_name"] = FieldConstantName(descriptor);
+  (*variables)["number"] = SimpleItoa(descriptor->number());
 }
 
-const FieldGenerator& FieldGeneratorMap::get_extension(int index) const {
-  return *extension_generators_[index];
+void SetCommonOneofVariables(const FieldDescriptor* descriptor,
+                             const OneofGeneratorInfo* info,
+                             map<string, string>* variables) {
+  (*variables)["oneof_name"] = info->name;
+  (*variables)["oneof_capitalized_name"] = info->capitalized_name;
+  (*variables)["oneof_index"] =
+      SimpleItoa(descriptor->containing_oneof()->index());
+  (*variables)["set_oneof_case_message"] = info->name +
+      "Case_ = " + SimpleItoa(descriptor->number());
+  (*variables)["clear_oneof_case_message"] = info->name +
+      "Case_ = 0";
+  (*variables)["has_oneof_case_message"] = info->name +
+      "Case_ == " + SimpleItoa(descriptor->number());
+}
+
+void PrintExtraFieldInfo(const map<string, string>& variables,
+                         io::Printer* printer) {
+  const map<string, string>::const_iterator it =
+      variables.find("disambiguated_reason");
+  if (it != variables.end() && !it->second.empty()) {
+    printer->Print(
+        variables,
+        "// An alternative name is used for field \"$field_name$\" because:\n"
+        "//     $disambiguated_reason$\n");
+  }
 }
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_field.h b/src/google/protobuf/compiler/java/java_field.h
index 4dd0efd6..a4aa3bce 100644
--- a/src/google/protobuf/compiler/java/java_field.h
+++ b/src/google/protobuf/compiler/java/java_field.h
@@ -35,14 +35,23 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_FIELD_H__
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_FIELD_H__
 
+#include <map>
+#include <memory>
 #include <string>
+
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/descriptor.h>
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;                // context.h
+      class ClassNameResolver;      // name_resolver.h
+    }
+  }
   namespace io {
-    class Printer;             // printer.h
+    class Printer;                  // printer.h
   }
 }
 
@@ -50,10 +59,10 @@ namespace protobuf {
 namespace compiler {
 namespace java {
 
-class FieldGenerator {
+class ImmutableFieldGenerator {
  public:
-  FieldGenerator() {}
-  virtual ~FieldGenerator();
+  ImmutableFieldGenerator() {}
+  virtual ~ImmutableFieldGenerator();
 
   virtual int GetNumBitsForMessage() const = 0;
   virtual int GetNumBitsForBuilder() const = 0;
@@ -78,29 +87,73 @@ class FieldGenerator {
   virtual string GetBoxedType() const = 0;
 
  private:
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FieldGenerator);
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableFieldGenerator);
 };
 
+
 // Convenience class which constructs FieldGenerators for a Descriptor.
+template<typename FieldGeneratorType>
 class FieldGeneratorMap {
  public:
-  explicit FieldGeneratorMap(const Descriptor* descriptor);
+  explicit FieldGeneratorMap(const Descriptor* descriptor,
+                             Context* context);
   ~FieldGeneratorMap();
 
-  const FieldGenerator& get(const FieldDescriptor* field) const;
-  const FieldGenerator& get_extension(int index) const;
+  const FieldGeneratorType& get(const FieldDescriptor* field) const;
 
  private:
   const Descriptor* descriptor_;
-  scoped_array<scoped_ptr<FieldGenerator> > field_generators_;
-  scoped_array<scoped_ptr<FieldGenerator> > extension_generators_;
-
-  static FieldGenerator* MakeGenerator(const FieldDescriptor* field,
-      int messageBitIndex, int builderBitIndex);
+  Context* context_;
+  ClassNameResolver* name_resolver_;
+  scoped_array<scoped_ptr<FieldGeneratorType> > field_generators_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FieldGeneratorMap);
 };
 
+template<typename FieldGeneratorType>
+inline const FieldGeneratorType&
+FieldGeneratorMap<FieldGeneratorType>::get(const FieldDescriptor* field) const {
+  GOOGLE_CHECK_EQ(field->containing_type(), descriptor_);
+  return *field_generators_[field->index()];
+}
+
+// Instantiate template for mutable and immutable maps.
+template<>
+FieldGeneratorMap<ImmutableFieldGenerator>::
+FieldGeneratorMap(const Descriptor* descriptor,
+                  Context* context);
+
+template<>
+FieldGeneratorMap<ImmutableFieldGenerator>::~FieldGeneratorMap();
+
+
+// Field information used in FieldGeneartors.
+struct FieldGeneratorInfo {
+  string name;
+  string capitalized_name;
+  string disambiguated_reason;
+};
+
+// Oneof information used in OneofFieldGeneartors.
+struct OneofGeneratorInfo {
+  string name;
+  string capitalized_name;
+};
+
+// Set some common variables used in variable FieldGenerators.
+void SetCommonFieldVariables(const FieldDescriptor* descriptor,
+                             const FieldGeneratorInfo* info,
+                             map<string, string>* variables);
+
+// Set some common oneof variables used in OneofFieldGenerators.
+void SetCommonOneofVariables(const FieldDescriptor* descriptor,
+                             const OneofGeneratorInfo* info,
+                             map<string, string>* variables);
+
+// Print useful comments before a field's accessors.
+void PrintExtraFieldInfo(const map<string, string>& variables,
+                         io::Printer* printer);
+
 }  // namespace java
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/java/java_file.cc b/src/google/protobuf/compiler/java/java_file.cc
index f43e5500..deec0e71 100644
--- a/src/google/protobuf/compiler/java/java_file.cc
+++ b/src/google/protobuf/compiler/java/java_file.cc
@@ -33,11 +33,17 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/java/java_file.h>
+
+#include <memory>
+
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_enum.h>
-#include <google/protobuf/compiler/java/java_service.h>
 #include <google/protobuf/compiler/java/java_extension.h>
+#include <google/protobuf/compiler/java/java_generator_factory.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
 #include <google/protobuf/compiler/java/java_message.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/compiler/java/java_service.h>
 #include <google/protobuf/compiler/code_generator.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/io/zero_copy_stream.h>
@@ -132,10 +138,27 @@ void CollectExtensions(const FileDescriptorProto& file_proto,
 
 }  // namespace
 
-FileGenerator::FileGenerator(const FileDescriptor* file)
-  : file_(file),
-    java_package_(FileJavaPackage(file)),
-    classname_(FileClassName(file)) {
+FileGenerator::FileGenerator(const FileDescriptor* file, bool immutable_api)
+    : file_(file),
+      java_package_(FileJavaPackage(file, immutable_api)),
+      message_generators_(
+          new scoped_ptr<MessageGenerator>[file->message_type_count()]),
+      extension_generators_(
+          new scoped_ptr<ExtensionGenerator>[file->extension_count()]),
+      context_(new Context(file)),
+      name_resolver_(context_->GetNameResolver()),
+      immutable_api_(immutable_api) {
+  classname_ = name_resolver_->GetFileClassName(file, immutable_api);
+  generator_factory_.reset(
+      new ImmutableGeneratorFactory(context_.get()));
+  for (int i = 0; i < file_->message_type_count(); ++i) {
+    message_generators_[i].reset(
+        generator_factory_->NewMessageGenerator(file_->message_type(i)));
+  }
+  for (int i = 0; i < file_->extension_count(); ++i) {
+    extension_generators_[i].reset(
+        generator_factory_->NewExtensionGenerator(file_->extension(i)));
+  }
 }
 
 FileGenerator::~FileGenerator() {}
@@ -145,25 +168,7 @@ bool FileGenerator::Validate(string* error) {
   // problem that leads to Java compile errors that can be hard to understand.
   // It's especially bad when using the java_multiple_files, since we would
   // end up overwriting the outer class with one of the inner ones.
-
-  bool found_conflict = false;
-  for (int i = 0; i < file_->enum_type_count() && !found_conflict; i++) {
-    if (file_->enum_type(i)->name() == classname_) {
-      found_conflict = true;
-    }
-  }
-  for (int i = 0; i < file_->message_type_count() && !found_conflict; i++) {
-    if (file_->message_type(i)->name() == classname_) {
-      found_conflict = true;
-    }
-  }
-  for (int i = 0; i < file_->service_count() && !found_conflict; i++) {
-    if (file_->service(i)->name() == classname_) {
-      found_conflict = true;
-    }
-  }
-
-  if (found_conflict) {
+  if (name_resolver_->HasConflictingClassName(file_, classname_)) {
     error->assign(file_->name());
     error->append(
       ": Cannot generate Java output because the file's outer class name, \"");
@@ -174,7 +179,29 @@ bool FileGenerator::Validate(string* error) {
       "option to specify a different outer class name for the .proto file.");
     return false;
   }
-
+  // If java_outer_classname option is not set and the default outer class name
+  // conflicts with a type defined in the message, we will append a suffix to
+  // avoid the conflict. This allows proto1 API protos to be dual-compiled into
+  // proto2 API without code change. When this happens we'd like to issue an
+  // warning to let the user know that the outer class name has been changed.
+  // Although we only do this automatic naming fix for immutable API, mutable
+  // outer class name will also be affected as it's contructed from immutable
+  // outer class name with an additional "Mutable" prefix. Since the naming
+  // change in mutable API is not caused by a naming conflict, we generate the
+  // warning for immutable API only.
+  if (immutable_api_ && !file_->options().has_java_outer_classname()) {
+    string default_classname =
+        name_resolver_->GetFileDefaultImmutableClassName(file_);
+    if (default_classname != classname_) {
+      GOOGLE_LOG(WARNING) << file_->name() << ": The default outer class name, \""
+                   << default_classname << "\", conflicts with a type "
+                   << "declared in the proto file and an alternative outer "
+                   << "class name is used: \"" << classname_ << "\". To avoid "
+                   << "this warning, please use the java_outer_classname "
+                   << "option to specify a different outer class name for "
+                   << "the .proto file.";
+    }
+  }
   return true;
 }
 
@@ -208,12 +235,11 @@ void FileGenerator::Generate(io::Printer* printer) {
   printer->Indent();
 
   for (int i = 0; i < file_->extension_count(); i++) {
-    ExtensionGenerator(file_->extension(i)).GenerateRegistrationCode(printer);
+    extension_generators_[i]->GenerateRegistrationCode(printer);
   }
 
   for (int i = 0; i < file_->message_type_count(); i++) {
-    MessageGenerator(file_->message_type(i))
-      .GenerateExtensionRegistrationCode(printer);
+    message_generators_[i]->GenerateExtensionRegistrationCode(printer);
   }
 
   printer->Outdent();
@@ -222,18 +248,20 @@ void FileGenerator::Generate(io::Printer* printer) {
 
   // -----------------------------------------------------------------
 
-  if (!file_->options().java_multiple_files()) {
+  if (!MultipleJavaFiles(file_, immutable_api_)) {
     for (int i = 0; i < file_->enum_type_count(); i++) {
-      EnumGenerator(file_->enum_type(i)).Generate(printer);
+      EnumGenerator(file_->enum_type(i), immutable_api_, context_.get())
+          .Generate(printer);
     }
     for (int i = 0; i < file_->message_type_count(); i++) {
-      MessageGenerator messageGenerator(file_->message_type(i));
-      messageGenerator.GenerateInterface(printer);
-      messageGenerator.Generate(printer);
+      message_generators_[i]->GenerateInterface(printer);
+      message_generators_[i]->Generate(printer);
     }
     if (HasGenericServices(file_)) {
       for (int i = 0; i < file_->service_count(); i++) {
-        ServiceGenerator(file_->service(i)).Generate(printer);
+        scoped_ptr<ServiceGenerator> generator(
+            generator_factory_->NewServiceGenerator(file_->service(i)));
+        generator->Generate(printer);
       }
     }
   }
@@ -241,28 +269,29 @@ void FileGenerator::Generate(io::Printer* printer) {
   // Extensions must be generated in the outer class since they are values,
   // not classes.
   for (int i = 0; i < file_->extension_count(); i++) {
-    ExtensionGenerator(file_->extension(i)).Generate(printer);
+    extension_generators_[i]->Generate(printer);
   }
 
   // Static variables.
   for (int i = 0; i < file_->message_type_count(); i++) {
-    // TODO(kenton):  Reuse MessageGenerator objects?
-    MessageGenerator(file_->message_type(i)).GenerateStaticVariables(printer);
+    message_generators_[i]->GenerateStaticVariables(printer);
   }
 
   printer->Print("\n");
 
   if (HasDescriptorMethods(file_)) {
-    GenerateEmbeddedDescriptor(printer);
+    if (immutable_api_) {
+      GenerateDescriptorInitializationCodeForImmutable(printer);
+    } else {
+      GenerateDescriptorInitializationCodeForMutable(printer);
+    }
   } else {
     printer->Print(
       "static {\n");
     printer->Indent();
 
     for (int i = 0; i < file_->message_type_count(); i++) {
-      // TODO(kenton):  Reuse MessageGenerator objects?
-      MessageGenerator(file_->message_type(i))
-        .GenerateStaticVariableInitializers(printer);
+      message_generators_[i]->GenerateStaticVariableInitializers(printer);
     }
 
     printer->Outdent();
@@ -278,23 +307,8 @@ void FileGenerator::Generate(io::Printer* printer) {
   printer->Print("}\n");
 }
 
-void FileGenerator::GenerateEmbeddedDescriptor(io::Printer* printer) {
-  // Embed the descriptor.  We simply serialize the entire FileDescriptorProto
-  // and embed it as a string literal, which is parsed and built into real
-  // descriptors at initialization time.  We unfortunately have to put it in
-  // a string literal, not a byte array, because apparently using a literal
-  // byte array causes the Java compiler to generate *instructions* to
-  // initialize each and every byte of the array, e.g. as if you typed:
-  //   b[0] = 123; b[1] = 456; b[2] = 789;
-  // This makes huge bytecode files and can easily hit the compiler's internal
-  // code size limits (error "code to large").  String literals are apparently
-  // embedded raw, which is what we want.
-  FileDescriptorProto file_proto;
-  file_->CopyTo(&file_proto);
-
-  string file_data;
-  file_proto.SerializeToString(&file_data);
-
+void FileGenerator::GenerateDescriptorInitializationCodeForImmutable(
+    io::Printer* printer) {
   printer->Print(
     "public static com.google.protobuf.Descriptors.FileDescriptor\n"
     "    getDescriptor() {\n"
@@ -302,55 +316,18 @@ void FileGenerator::GenerateEmbeddedDescriptor(io::Printer* printer) {
     "}\n"
     "private static com.google.protobuf.Descriptors.FileDescriptor\n"
     "    descriptor;\n"
-    "static {\n"
-    "  java.lang.String[] descriptorData = {\n");
+    "static {\n");
   printer->Indent();
-  printer->Indent();
-
-  // Only write 40 bytes per line.
-  static const int kBytesPerLine = 40;
-  for (int i = 0; i < file_data.size(); i += kBytesPerLine) {
-    if (i > 0) {
-      // Every 400 lines, start a new string literal, in order to avoid the
-      // 64k length limit.
-      if (i % 400 == 0) {
-        printer->Print(",\n");
-      } else {
-        printer->Print(" +\n");
-      }
-    }
-    printer->Print("\"$data$\"",
-      "data", CEscape(file_data.substr(i, kBytesPerLine)));
-  }
-
-  printer->Outdent();
-  printer->Print("\n};\n");
-
-  // -----------------------------------------------------------------
-  // Create the InternalDescriptorAssigner.
 
   printer->Print(
-    "com.google.protobuf.Descriptors.FileDescriptor."
-      "InternalDescriptorAssigner assigner =\n"
-    "  new com.google.protobuf.Descriptors.FileDescriptor."
-      "InternalDescriptorAssigner() {\n"
-    "    public com.google.protobuf.ExtensionRegistry assignDescriptors(\n"
-    "        com.google.protobuf.Descriptors.FileDescriptor root) {\n"
-    "      descriptor = root;\n");
-
-  printer->Indent();
-  printer->Indent();
-  printer->Indent();
+    "descriptor = $descriptor_classname$.descriptor;\n",
+    "descriptor_classname", name_resolver_->GetDescriptorClassName(file_));
 
   for (int i = 0; i < file_->message_type_count(); i++) {
-    // TODO(kenton):  Reuse MessageGenerator objects?
-    MessageGenerator(file_->message_type(i))
-      .GenerateStaticVariableInitializers(printer);
+    message_generators_[i]->GenerateStaticVariableInitializers(printer);
   }
   for (int i = 0; i < file_->extension_count(); i++) {
-    // TODO(kenton):  Reuse ExtensionGenerator objects?
-    ExtensionGenerator(file_->extension(i))
-        .GenerateNonNestedInitializationCode(printer);
+    extension_generators_[i]->GenerateNonNestedInitializationCode(printer);
   }
 
   // Proto compiler builds a DescriptorPool, which holds all the descriptors to
@@ -368,52 +345,107 @@ void FileGenerator::GenerateEmbeddedDescriptor(io::Printer* printer) {
   // To find those extensions, we need to parse the data into a dynamic message
   // of the FileDescriptor based on the builder-pool, then we can use
   // reflections to find all extension fields
+  FileDescriptorProto file_proto;
+  file_->CopyTo(&file_proto);
+  string file_data;
+  file_proto.SerializeToString(&file_data);
   vector<const FieldDescriptor*> extensions;
   CollectExtensions(file_proto, *file_->pool(), &extensions, file_data);
 
   if (extensions.size() > 0) {
     // Must construct an ExtensionRegistry containing all existing extensions
-    // and return it.
+    // and use it to parse the descriptor data again to recognize extensions.
     printer->Print(
       "com.google.protobuf.ExtensionRegistry registry =\n"
-      "  com.google.protobuf.ExtensionRegistry.newInstance();\n");
+      "    com.google.protobuf.ExtensionRegistry.newInstance();\n");
     for (int i = 0; i < extensions.size(); i++) {
-      ExtensionGenerator(extensions[i]).GenerateRegistrationCode(printer);
+      scoped_ptr<ExtensionGenerator> generator(
+          generator_factory_->NewExtensionGenerator(extensions[i]));
+      generator->GenerateRegistrationCode(printer);
     }
     printer->Print(
-      "return registry;\n");
-  } else {
-    printer->Print(
-      "return null;\n");
+      "com.google.protobuf.Descriptors.FileDescriptor\n"
+      "    .internalUpdateFileDescriptor(descriptor, registry);\n");
   }
 
-  printer->Outdent();
-  printer->Outdent();
-  printer->Outdent();
+  // Force descriptor initialization of all dependencies.
+  for (int i = 0; i < file_->dependency_count(); i++) {
+    if (ShouldIncludeDependency(file_->dependency(i), true)) {
+      string dependency =
+          name_resolver_->GetImmutableClassName(file_->dependency(i));
+      printer->Print(
+        "$dependency$.getDescriptor();\n",
+        "dependency", dependency);
+    }
+  }
 
+  printer->Outdent();
   printer->Print(
-    "    }\n"
-    "  };\n");
+    "}\n");
+}
 
-  // -----------------------------------------------------------------
-  // Invoke internalBuildGeneratedFileFrom() to build the file.
+void FileGenerator::GenerateDescriptorInitializationCodeForMutable(io::Printer* printer) {
+  printer->Print(
+    "public static com.google.protobuf.Descriptors.FileDescriptor\n"
+    "    getDescriptor() {\n"
+    "  return descriptor;\n"
+    "}\n"
+    "private static com.google.protobuf.Descriptors.FileDescriptor\n"
+    "    descriptor;\n"
+    "static {\n");
+  printer->Indent();
 
   printer->Print(
-    "com.google.protobuf.Descriptors.FileDescriptor\n"
-    "  .internalBuildGeneratedFileFrom(descriptorData,\n"
-    "    new com.google.protobuf.Descriptors.FileDescriptor[] {\n");
+    "descriptor = $immutable_package$.$descriptor_classname$.descriptor;\n",
+    "immutable_package", FileJavaPackage(file_, true),
+    "descriptor_classname", name_resolver_->GetDescriptorClassName(file_));
 
+  for (int i = 0; i < file_->message_type_count(); i++) {
+    message_generators_[i]->GenerateStaticVariableInitializers(printer);
+  }
+  for (int i = 0; i < file_->extension_count(); i++) {
+    extension_generators_[i]->GenerateNonNestedInitializationCode(printer);
+  }
+
+  // Check if custom options exist. If any, try to load immutable classes since
+  // custom options are only represented with immutable messages.
+  FileDescriptorProto file_proto;
+  file_->CopyTo(&file_proto);
+  string file_data;
+  file_proto.SerializeToString(&file_data);
+  vector<const FieldDescriptor*> extensions;
+  CollectExtensions(file_proto, *file_->pool(), &extensions, file_data);
+
+  if (extensions.size() > 0) {
+    // Try to load immutable messages' outer class. Its initialization code
+    // will take care of interpreting custom options.
+    printer->Print(
+      "try {\n"
+      // Note that we have to load the immutable class dynamically here as
+      // we want the mutable code to be independent from the immutable code
+      // at compile time. It is required to implement dual-compile for
+      // mutable and immutable API in blaze.
+      "  java.lang.Class immutableClass = java.lang.Class.forName(\n"
+      "      \"$immutable_classname$\");\n"
+      "} catch (java.lang.ClassNotFoundException e) {\n"
+      // The immutable class can not be found. Custom options are left
+      // as unknown fields.
+      // TODO(xiaofeng): inform the user with a warning?
+      "}\n",
+      "immutable_classname", name_resolver_->GetImmutableClassName(file_));
+  }
+
+  // Force descriptor initialization of all dependencies.
   for (int i = 0; i < file_->dependency_count(); i++) {
-    if (ShouldIncludeDependency(file_->dependency(i))) {
+    if (ShouldIncludeDependency(file_->dependency(i), false)) {
+      string dependency = name_resolver_->GetMutableClassName(
+          file_->dependency(i));
       printer->Print(
-        "      $dependency$.getDescriptor(),\n",
-        "dependency", ClassName(file_->dependency(i)));
+        "$dependency$.getDescriptor();\n",
+        "dependency", dependency);
     }
   }
 
-  printer->Print(
-    "    }, assigner);\n");
-
   printer->Outdent();
   printer->Print(
     "}\n");
@@ -426,6 +458,7 @@ static void GenerateSibling(const string& package_dir,
                             GeneratorContext* context,
                             vector<string>* file_list,
                             const string& name_suffix,
+                            GeneratorClass* generator,
                             void (GeneratorClass::*pfn)(io::Printer* printer)) {
   string filename = package_dir + descriptor->name() + name_suffix + ".java";
   file_list->push_back(filename);
@@ -445,42 +478,53 @@ static void GenerateSibling(const string& package_dir,
       "package", java_package);
   }
 
-  GeneratorClass generator(descriptor);
-  (generator.*pfn)(&printer);
+  (generator->*pfn)(&printer);
 }
 
 void FileGenerator::GenerateSiblings(const string& package_dir,
                                      GeneratorContext* context,
                                      vector<string>* file_list) {
-  if (file_->options().java_multiple_files()) {
+  if (MultipleJavaFiles(file_, immutable_api_)) {
     for (int i = 0; i < file_->enum_type_count(); i++) {
+      EnumGenerator generator(file_->enum_type(i), immutable_api_,
+                              context_.get());
       GenerateSibling<EnumGenerator>(package_dir, java_package_,
                                      file_->enum_type(i),
                                      context, file_list, "",
+                                     &generator,
                                      &EnumGenerator::Generate);
     }
     for (int i = 0; i < file_->message_type_count(); i++) {
-      GenerateSibling<MessageGenerator>(package_dir, java_package_,
-                                        file_->message_type(i),
-                                        context, file_list, "OrBuilder",
-                                        &MessageGenerator::GenerateInterface);
+      if (immutable_api_) {
+        GenerateSibling<MessageGenerator>(package_dir, java_package_,
+                                          file_->message_type(i),
+                                          context, file_list,
+                                          "OrBuilder",
+                                          message_generators_[i].get(),
+                                          &MessageGenerator::GenerateInterface);
+      }
       GenerateSibling<MessageGenerator>(package_dir, java_package_,
                                         file_->message_type(i),
                                         context, file_list, "",
+                                        message_generators_[i].get(),
                                         &MessageGenerator::Generate);
     }
     if (HasGenericServices(file_)) {
       for (int i = 0; i < file_->service_count(); i++) {
+        scoped_ptr<ServiceGenerator> generator(
+            generator_factory_->NewServiceGenerator(file_->service(i)));
         GenerateSibling<ServiceGenerator>(package_dir, java_package_,
                                           file_->service(i),
                                           context, file_list, "",
+                                          generator.get(),
                                           &ServiceGenerator::Generate);
       }
     }
   }
 }
 
-bool FileGenerator::ShouldIncludeDependency(const FileDescriptor* descriptor) {
+bool FileGenerator::ShouldIncludeDependency(
+    const FileDescriptor* descriptor, bool immutable_api) {
   return true;
 }
 
diff --git a/src/google/protobuf/compiler/java/java_file.h b/src/google/protobuf/compiler/java/java_file.h
index 59911462..7f289491 100644
--- a/src/google/protobuf/compiler/java/java_file.h
+++ b/src/google/protobuf/compiler/java/java_file.h
@@ -35,18 +35,26 @@
 #ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_FILE_H__
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_FILE_H__
 
+#include <memory>
 #include <string>
 #include <vector>
 #include <google/protobuf/stubs/common.h>
 
 namespace google {
 namespace protobuf {
-  class FileDescriptor;        // descriptor.h
+  class FileDescriptor;          // descriptor.h
   namespace io {
-    class Printer;             // printer.h
+    class Printer;               // printer.h
   }
   namespace compiler {
-    class GeneratorContext;     // code_generator.h
+    class GeneratorContext;      // code_generator.h
+    namespace java {
+      class Context;             // context.h
+      class MessageGenerator;    // message.h
+      class GeneratorFactory;    // generator_factory.h
+      class ExtensionGenerator;  // extension.h
+      class ClassNameResolver;   // name_resolver.h
+    }
   }
 }
 
@@ -56,7 +64,7 @@ namespace java {
 
 class FileGenerator {
  public:
-  explicit FileGenerator(const FileDescriptor* file);
+  FileGenerator(const FileDescriptor* file, bool immutable_api = true);
   ~FileGenerator();
 
   // Checks for problems that would otherwise lead to cryptic compile errors.
@@ -78,17 +86,23 @@ class FileGenerator {
 
 
  private:
-  // Returns whether the dependency should be included in the output file.
-  // Always returns true for opensource, but used internally at Google to help
-  // improve compatibility with version 1 of protocol buffers.
-  bool ShouldIncludeDependency(const FileDescriptor* descriptor);
+  void GenerateDescriptorInitializationCodeForImmutable(io::Printer* printer);
+  void GenerateDescriptorInitializationCodeForMutable(io::Printer* printer);
+
+  bool ShouldIncludeDependency(const FileDescriptor* descriptor,
+                               bool immutable_api_);
 
   const FileDescriptor* file_;
   string java_package_;
   string classname_;
 
+  scoped_array<scoped_ptr<MessageGenerator> > message_generators_;
+  scoped_array<scoped_ptr<ExtensionGenerator> > extension_generators_;
+  scoped_ptr<GeneratorFactory> generator_factory_;
+  scoped_ptr<Context> context_;
+  ClassNameResolver* name_resolver_;
+  bool immutable_api_;
 
-  void GenerateEmbeddedDescriptor(io::Printer* printer);
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(FileGenerator);
 };
diff --git a/src/google/protobuf/compiler/java/java_generator.cc b/src/google/protobuf/compiler/java/java_generator.cc
index e6c79abc..b713797b 100644
--- a/src/google/protobuf/compiler/java/java_generator.cc
+++ b/src/google/protobuf/compiler/java/java_generator.cc
@@ -33,8 +33,13 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/java/java_generator.h>
+
+#include <memory>
+
 #include <google/protobuf/compiler/java/java_file.h>
+#include <google/protobuf/compiler/java/java_generator_factory.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_shared_code_generator.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/io/zero_copy_stream.h>
 #include <google/protobuf/descriptor.pb.h>
@@ -64,55 +69,89 @@ bool JavaGenerator::Generate(const FileDescriptor* file,
   vector<pair<string, string> > options;
   ParseGeneratorParameter(parameter, &options);
 
+  bool generate_immutable_code = false;
+  bool generate_mutable_code = false;
+  bool generate_shared_code = false;
   for (int i = 0; i < options.size(); i++) {
     if (options[i].first == "output_list_file") {
       output_list_file = options[i].second;
+    } else if (options[i].first == "immutable") {
+      generate_immutable_code = true;
+    } else if (options[i].first == "mutable") {
+      generate_mutable_code = true;
+    } else if (options[i].first == "shared") {
+      generate_shared_code = true;
     } else {
       *error = "Unknown generator option: " + options[i].first;
       return false;
     }
   }
 
+  // By default we generate immutable code and shared code for immutable API.
+  if (!generate_immutable_code && !generate_mutable_code &&
+      !generate_shared_code) {
+    generate_immutable_code = true;
+    generate_shared_code = true;
+  }
+
   // -----------------------------------------------------------------
 
 
-  if (file->options().optimize_for() == FileOptions::LITE_RUNTIME &&
-      file->options().java_generate_equals_and_hash()) {
-    *error = "The \"java_generate_equals_and_hash\" option is incompatible "
-             "with \"optimize_for = LITE_RUNTIME\".  You must optimize for "
-             "SPEED or CODE_SIZE if you want to use this option.";
-    return false;
+  vector<string> all_files;
+
+  if (generate_shared_code) {
+    // Generate code shared between immutable and mutable API.
+    SharedCodeGenerator shared_code_generator(file);
+    shared_code_generator.Generate(context, &all_files);
   }
 
-  FileGenerator file_generator(file);
-  if (!file_generator.Validate(error)) {
-    return false;
+  vector<FileGenerator*> file_generators;
+  if (generate_immutable_code) {
+    file_generators.push_back(new FileGenerator(file, /* immutable = */ true));
+  }
+  if (generate_mutable_code) {
+    file_generators.push_back(new FileGenerator(file, /* mutable = */ false));
+  }
+  for (int i = 0; i < file_generators.size(); ++i) {
+    if (!file_generators[i]->Validate(error)) {
+      for (int j = 0; j < file_generators.size(); ++j) {
+        delete file_generators[j];
+      }
+      return false;
+    }
   }
 
-  string package_dir = JavaPackageToDir(file_generator.java_package());
+  for (int i = 0; i < file_generators.size(); ++i) {
+    FileGenerator* file_generator = file_generators[i];
 
-  vector<string> all_files;
+    string package_dir = JavaPackageToDir(file_generator->java_package());
 
-  string java_filename = package_dir;
-  java_filename += file_generator.classname();
-  java_filename += ".java";
-  all_files.push_back(java_filename);
+    string java_filename = package_dir;
+    java_filename += file_generator->classname();
+    java_filename += ".java";
+    all_files.push_back(java_filename);
 
-  // Generate main java file.
-  scoped_ptr<io::ZeroCopyOutputStream> output(
-    context->Open(java_filename));
-  io::Printer printer(output.get(), '$');
-  file_generator.Generate(&printer);
+    // Generate main java file.
+    scoped_ptr<io::ZeroCopyOutputStream> output(
+        context->Open(java_filename));
+    io::Printer printer(output.get(), '$');
+    file_generator->Generate(&printer);
 
-  // Generate sibling files.
-  file_generator.GenerateSiblings(package_dir, context, &all_files);
+    // Generate sibling files.
+    file_generator->GenerateSiblings(package_dir, context, &all_files);
+  }
+
+  for (int i = 0; i < file_generators.size(); ++i) {
+    delete file_generators[i];
+  }
+  file_generators.clear();
 
   // Generate output list if requested.
   if (!output_list_file.empty()) {
     // Generate output list.  This is just a simple text file placed in a
     // deterministic location which lists the .java files being generated.
     scoped_ptr<io::ZeroCopyOutputStream> srclist_raw_output(
-      context->Open(output_list_file));
+        context->Open(output_list_file));
     io::Printer srclist_printer(srclist_raw_output.get(), '$');
     for (int i = 0; i < all_files.size(); i++) {
       srclist_printer.Print("$filename$\n", "filename", all_files[i]);
diff --git a/src/google/protobuf/compiler/java/java_generator_factory.cc b/src/google/protobuf/compiler/java/java_generator_factory.cc
new file mode 100644
index 00000000..ce71d436
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_generator_factory.cc
@@ -0,0 +1,77 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: liujisi@google.com (Pherl Liu)
+
+#include <google/protobuf/compiler/java/java_generator_factory.h>
+
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_enum_field.h>
+#include <google/protobuf/compiler/java/java_extension.h>
+#include <google/protobuf/compiler/java/java_field.h>
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_message.h>
+#include <google/protobuf/compiler/java/java_service.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+GeneratorFactory::GeneratorFactory() {}
+GeneratorFactory::~GeneratorFactory() {}
+
+// ===================================================================
+
+ImmutableGeneratorFactory::ImmutableGeneratorFactory(
+    Context* context) : context_(context) {
+}
+ImmutableGeneratorFactory::~ImmutableGeneratorFactory() {}
+
+MessageGenerator* ImmutableGeneratorFactory::NewMessageGenerator(
+    const Descriptor* descriptor) const {
+  return new ImmutableMessageGenerator(descriptor, context_);
+}
+
+ExtensionGenerator* ImmutableGeneratorFactory::NewExtensionGenerator(
+    const FieldDescriptor* descriptor) const {
+  return new ImmutableExtensionGenerator(descriptor, context_);
+}
+
+ServiceGenerator* ImmutableGeneratorFactory::NewServiceGenerator(
+    const ServiceDescriptor* descriptor) const {
+  return new ImmutableServiceGenerator(descriptor, context_);
+}
+
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_generator_factory.h b/src/google/protobuf/compiler/java/java_generator_factory.h
new file mode 100644
index 00000000..abf894f6
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_generator_factory.h
@@ -0,0 +1,101 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: liujisi@google.com (Pherl Liu)
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_FACTORY_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_FACTORY_H__
+
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+  class FieldDescriptor;         // descriptor.h
+  class Descriptor;              // descriptor.h
+  class ServiceDescriptor;       // descriptor.h
+  namespace compiler {
+    namespace java {
+      class MessageGenerator;    // message.h
+      class ExtensionGenerator;  // extension.h
+      class ServiceGenerator;    // service.h
+      class Context;             // context.h
+    }
+  }
+}
+
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+class GeneratorFactory {
+ public:
+  GeneratorFactory();
+  virtual ~GeneratorFactory();
+
+  virtual MessageGenerator* NewMessageGenerator(
+      const Descriptor* descriptor) const = 0;
+
+  virtual ExtensionGenerator* NewExtensionGenerator(
+      const FieldDescriptor* descriptor) const = 0;
+
+  virtual ServiceGenerator* NewServiceGenerator(
+      const ServiceDescriptor* descriptor) const = 0;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(GeneratorFactory);
+};
+
+// Factory that creates generators for immutable-default messages.
+class ImmutableGeneratorFactory : public GeneratorFactory {
+ public:
+  ImmutableGeneratorFactory(Context* context);
+  virtual ~ImmutableGeneratorFactory();
+
+  virtual MessageGenerator* NewMessageGenerator(
+      const Descriptor* descriptor) const;
+
+  virtual ExtensionGenerator* NewExtensionGenerator(
+      const FieldDescriptor* descriptor) const;
+
+  virtual ServiceGenerator* NewServiceGenerator(
+      const ServiceDescriptor* descriptor) const;
+
+ private:
+  Context* context_;
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableGeneratorFactory);
+};
+
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_GENERATOR_FACTORY_H__
diff --git a/src/google/protobuf/compiler/java/java_helpers.cc b/src/google/protobuf/compiler/java/java_helpers.cc
index cf241b8a..fdd4e5e5 100644
--- a/src/google/protobuf/compiler/java/java_helpers.cc
+++ b/src/google/protobuf/compiler/java/java_helpers.cc
@@ -32,11 +32,15 @@
 //  Based on original Protocol Buffers design by
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
+#include <algorithm>
+#include <google/protobuf/stubs/hash.h>
 #include <limits>
 #include <vector>
 
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/descriptor.pb.h>
+#include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
 
@@ -45,6 +49,9 @@ namespace protobuf {
 namespace compiler {
 namespace java {
 
+using internal::WireFormat;
+using internal::WireFormatLite;
+
 const char kThickSeparator[] =
   "// ===================================================================\n";
 const char kThinSeparator[] =
@@ -54,18 +61,47 @@ namespace {
 
 const char* kDefaultPackage = "";
 
-const string& FieldName(const FieldDescriptor* field) {
+// Names that should be avoided as field names.
+// Using them will cause the compiler to generate accessors whose names are
+// colliding with methods defined in base classes.
+const char* kForbiddenWordList[] = {
+  // message base class:
+  "cached_size", "serialized_size",
+  // java.lang.Object:
+  "class",
+};
+
+bool IsForbidden(const string& field_name) {
+  for (int i = 0; i < GOOGLE_ARRAYSIZE(kForbiddenWordList); ++i) {
+    if (field_name == kForbiddenWordList[i]) {
+      return true;
+    }
+  }
+  return false;
+}
+
+string FieldName(const FieldDescriptor* field) {
+  string field_name;
   // Groups are hacky:  The name of the field is just the lower-cased name
   // of the group type.  In Java, though, we would like to retain the original
   // capitalization of the type name.
   if (GetType(field) == FieldDescriptor::TYPE_GROUP) {
-    return field->message_type()->name();
+    field_name = field->message_type()->name();
   } else {
-    return field->name();
+    field_name = field->name();
+  }
+  if (IsForbidden(field_name)) {
+    // Append a trailing "#" to indicate that the name should be decorated to
+    // avoid collision with other names.
+    field_name += "#";
   }
+  return field_name;
 }
 
-string UnderscoresToCamelCaseImpl(const string& input, bool cap_next_letter) {
+
+}  // namespace
+
+string UnderscoresToCamelCase(const string& input, bool cap_next_letter) {
   string result;
   // Note:  I distrust ctype.h due to locales.
   for (int i = 0; i < input.size(); i++) {
@@ -93,21 +129,27 @@ string UnderscoresToCamelCaseImpl(const string& input, bool cap_next_letter) {
       cap_next_letter = true;
     }
   }
+  // Add a trailing "_" if the name should be altered.
+  if (input[input.size() - 1] == '#') {
+    result += '_';
+  }
   return result;
 }
 
-}  // namespace
-
 string UnderscoresToCamelCase(const FieldDescriptor* field) {
-  return UnderscoresToCamelCaseImpl(FieldName(field), false);
+  return UnderscoresToCamelCase(FieldName(field), false);
 }
 
 string UnderscoresToCapitalizedCamelCase(const FieldDescriptor* field) {
-  return UnderscoresToCamelCaseImpl(FieldName(field), true);
+  return UnderscoresToCamelCase(FieldName(field), true);
 }
 
 string UnderscoresToCamelCase(const MethodDescriptor* method) {
-  return UnderscoresToCamelCaseImpl(method->name(), false);
+  return UnderscoresToCamelCase(method->name(), false);
+}
+
+string UniqueFileScopeIdentifier(const Descriptor* descriptor) {
+  return "static_" + StringReplace(descriptor->full_name(), ".", "_", true);
 }
 
 string StripProto(const string& filename) {
@@ -118,22 +160,12 @@ string StripProto(const string& filename) {
   }
 }
 
-string FileClassName(const FileDescriptor* file) {
-  if (file->options().has_java_outer_classname()) {
-    return file->options().java_outer_classname();
-  } else {
-    string basename;
-    string::size_type last_slash = file->name().find_last_of('/');
-    if (last_slash == string::npos) {
-      basename = file->name();
-    } else {
-      basename = file->name().substr(last_slash + 1);
-    }
-    return UnderscoresToCamelCaseImpl(StripProto(basename), true);
-  }
+string FileClassName(const FileDescriptor* file, bool immutable) {
+  ClassNameResolver name_resolver;
+  return name_resolver.GetFileClassName(file, immutable);
 }
 
-string FileJavaPackage(const FileDescriptor* file) {
+string FileJavaPackage(const FileDescriptor* file, bool immutable) {
   string result;
 
   if (file->options().has_java_package()) {
@@ -146,7 +178,6 @@ string FileJavaPackage(const FileDescriptor* file) {
     }
   }
 
-
   return result;
 }
 
@@ -157,7 +188,10 @@ string JavaPackageToDir(string package_name) {
   return package_dir;
 }
 
-string ToJavaName(const string& full_name, const FileDescriptor* file) {
+// TODO(xiaofeng): This function is only kept for it's publicly referenced.
+// It should be removed after mutable API up-integration.
+string ToJavaName(const string& full_name,
+                  const FileDescriptor* file) {
   string result;
   if (file->options().java_multiple_files()) {
     result = FileJavaPackage(file);
@@ -178,22 +212,42 @@ string ToJavaName(const string& full_name, const FileDescriptor* file) {
 }
 
 string ClassName(const Descriptor* descriptor) {
-  return ToJavaName(descriptor->full_name(), descriptor->file());
+  ClassNameResolver name_resolver;
+  return name_resolver.GetClassName(descriptor, true);
 }
 
 string ClassName(const EnumDescriptor* descriptor) {
-  return ToJavaName(descriptor->full_name(), descriptor->file());
+  ClassNameResolver name_resolver;
+  return name_resolver.GetClassName(descriptor, true);
 }
 
 string ClassName(const ServiceDescriptor* descriptor) {
-  return ToJavaName(descriptor->full_name(), descriptor->file());
+  ClassNameResolver name_resolver;
+  return name_resolver.GetClassName(descriptor, true);
 }
 
 string ClassName(const FileDescriptor* descriptor) {
-  string result = FileJavaPackage(descriptor);
-  if (!result.empty()) result += '.';
-  result += FileClassName(descriptor);
-  return result;
+  ClassNameResolver name_resolver;
+  return name_resolver.GetClassName(descriptor, true);
+}
+
+string ExtraMessageInterfaces(const Descriptor* descriptor) {
+  string interfaces = "// @@protoc_insertion_point(message_implements:"
+      + descriptor->full_name() + ")";
+  return interfaces;
+}
+
+
+string ExtraBuilderInterfaces(const Descriptor* descriptor) {
+  string interfaces = "// @@protoc_insertion_point(builder_implements:"
+      + descriptor->full_name() + ")";
+  return interfaces;
+}
+
+string ExtraMessageOrBuilderInterfaces(const Descriptor* descriptor) {
+  string interfaces = "// @@protoc_insertion_point(interface_extends:"
+      + descriptor->full_name() + ")";
+  return interfaces;
 }
 
 string FieldConstantName(const FieldDescriptor *field) {
@@ -272,6 +326,35 @@ const char* BoxedPrimitiveTypeName(JavaType type) {
   return NULL;
 }
 
+const char* FieldTypeName(FieldDescriptor::Type field_type) {
+  switch (field_type) {
+    case FieldDescriptor::TYPE_INT32   : return "INT32";
+    case FieldDescriptor::TYPE_UINT32  : return "UINT32";
+    case FieldDescriptor::TYPE_SINT32  : return "SINT32";
+    case FieldDescriptor::TYPE_FIXED32 : return "FIXED32";
+    case FieldDescriptor::TYPE_SFIXED32: return "SFIXED32";
+    case FieldDescriptor::TYPE_INT64   : return "INT64";
+    case FieldDescriptor::TYPE_UINT64  : return "UINT64";
+    case FieldDescriptor::TYPE_SINT64  : return "SINT64";
+    case FieldDescriptor::TYPE_FIXED64 : return "FIXED64";
+    case FieldDescriptor::TYPE_SFIXED64: return "SFIXED64";
+    case FieldDescriptor::TYPE_FLOAT   : return "FLOAT";
+    case FieldDescriptor::TYPE_DOUBLE  : return "DOUBLE";
+    case FieldDescriptor::TYPE_BOOL    : return "BOOL";
+    case FieldDescriptor::TYPE_STRING  : return "STRING";
+    case FieldDescriptor::TYPE_BYTES   : return "BYTES";
+    case FieldDescriptor::TYPE_ENUM    : return "ENUM";
+    case FieldDescriptor::TYPE_GROUP   : return "GROUP";
+    case FieldDescriptor::TYPE_MESSAGE : return "MESSAGE";
+
+    // No default because we want the compiler to complain if any new
+    // types are added.
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return NULL;
+}
+
 bool AllAscii(const string& text) {
   for (int i = 0; i < text.size(); i++) {
     if ((text[i] & 0x80) != 0) {
@@ -281,7 +364,8 @@ bool AllAscii(const string& text) {
   return true;
 }
 
-string DefaultValue(const FieldDescriptor* field) {
+string DefaultValue(const FieldDescriptor* field, bool immutable,
+                    ClassNameResolver* name_resolver) {
   // Switch on CppType since we need to know which default_value_* method
   // of FieldDescriptor to call.
   switch (field->cpp_type()) {
@@ -344,11 +428,12 @@ string DefaultValue(const FieldDescriptor* field) {
       }
 
     case FieldDescriptor::CPPTYPE_ENUM:
-      return ClassName(field->enum_type()) + "." +
+      return name_resolver->GetClassName(field->enum_type(), immutable) + "." +
           field->default_value_enum()->name();
 
     case FieldDescriptor::CPPTYPE_MESSAGE:
-      return ClassName(field->message_type()) + ".getDefaultInstance()";
+      return name_resolver->GetClassName(field->message_type(), immutable) +
+          ".getDefaultInstance()";
 
     // No default because we want the compiler to complain if any new
     // types are added.
@@ -494,6 +579,158 @@ string GenerateSetBitMutableLocal(int bitIndex) {
   return GenerateSetBitInternal("mutable_", bitIndex);
 }
 
+bool IsReferenceType(JavaType type) {
+  switch (type) {
+    case JAVATYPE_INT    : return false;
+    case JAVATYPE_LONG   : return false;
+    case JAVATYPE_FLOAT  : return false;
+    case JAVATYPE_DOUBLE : return false;
+    case JAVATYPE_BOOLEAN: return false;
+    case JAVATYPE_STRING : return true;
+    case JAVATYPE_BYTES  : return true;
+    case JAVATYPE_ENUM   : return true;
+    case JAVATYPE_MESSAGE: return true;
+
+    // No default because we want the compiler to complain if any new
+    // JavaTypes are added.
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return false;
+}
+
+const char* GetCapitalizedType(const FieldDescriptor* field, bool immutable) {
+  switch (GetType(field)) {
+    case FieldDescriptor::TYPE_INT32   : return "Int32";
+    case FieldDescriptor::TYPE_UINT32  : return "UInt32";
+    case FieldDescriptor::TYPE_SINT32  : return "SInt32";
+    case FieldDescriptor::TYPE_FIXED32 : return "Fixed32";
+    case FieldDescriptor::TYPE_SFIXED32: return "SFixed32";
+    case FieldDescriptor::TYPE_INT64   : return "Int64";
+    case FieldDescriptor::TYPE_UINT64  : return "UInt64";
+    case FieldDescriptor::TYPE_SINT64  : return "SInt64";
+    case FieldDescriptor::TYPE_FIXED64 : return "Fixed64";
+    case FieldDescriptor::TYPE_SFIXED64: return "SFixed64";
+    case FieldDescriptor::TYPE_FLOAT   : return "Float";
+    case FieldDescriptor::TYPE_DOUBLE  : return "Double";
+    case FieldDescriptor::TYPE_BOOL    : return "Bool";
+    case FieldDescriptor::TYPE_STRING  : return "String";
+    case FieldDescriptor::TYPE_BYTES   : {
+      return "Bytes";
+    }
+    case FieldDescriptor::TYPE_ENUM    : return "Enum";
+    case FieldDescriptor::TYPE_GROUP   : return "Group";
+    case FieldDescriptor::TYPE_MESSAGE : return "Message";
+
+    // No default because we want the compiler to complain if any new
+    // types are added.
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return NULL;
+}
+
+// For encodings with fixed sizes, returns that size in bytes.  Otherwise
+// returns -1.
+int FixedSize(FieldDescriptor::Type type) {
+  switch (type) {
+    case FieldDescriptor::TYPE_INT32   : return -1;
+    case FieldDescriptor::TYPE_INT64   : return -1;
+    case FieldDescriptor::TYPE_UINT32  : return -1;
+    case FieldDescriptor::TYPE_UINT64  : return -1;
+    case FieldDescriptor::TYPE_SINT32  : return -1;
+    case FieldDescriptor::TYPE_SINT64  : return -1;
+    case FieldDescriptor::TYPE_FIXED32 : return WireFormatLite::kFixed32Size;
+    case FieldDescriptor::TYPE_FIXED64 : return WireFormatLite::kFixed64Size;
+    case FieldDescriptor::TYPE_SFIXED32: return WireFormatLite::kSFixed32Size;
+    case FieldDescriptor::TYPE_SFIXED64: return WireFormatLite::kSFixed64Size;
+    case FieldDescriptor::TYPE_FLOAT   : return WireFormatLite::kFloatSize;
+    case FieldDescriptor::TYPE_DOUBLE  : return WireFormatLite::kDoubleSize;
+
+    case FieldDescriptor::TYPE_BOOL    : return WireFormatLite::kBoolSize;
+    case FieldDescriptor::TYPE_ENUM    : return -1;
+
+    case FieldDescriptor::TYPE_STRING  : return -1;
+    case FieldDescriptor::TYPE_BYTES   : return -1;
+    case FieldDescriptor::TYPE_GROUP   : return -1;
+    case FieldDescriptor::TYPE_MESSAGE : return -1;
+
+    // No default because we want the compiler to complain if any new
+    // types are added.
+  }
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return -1;
+}
+
+// Sort the fields of the given Descriptor by number into a new[]'d array
+// and return it. The caller should delete the returned array.
+const FieldDescriptor** SortFieldsByNumber(const Descriptor* descriptor) {
+  const FieldDescriptor** fields =
+    new const FieldDescriptor*[descriptor->field_count()];
+  for (int i = 0; i < descriptor->field_count(); i++) {
+    fields[i] = descriptor->field(i);
+  }
+  sort(fields, fields + descriptor->field_count(),
+       FieldOrderingByNumber());
+  return fields;
+}
+
+// Returns true if the message type has any required fields.  If it doesn't,
+// we can optimize out calls to its isInitialized() method.
+//
+// already_seen is used to avoid checking the same type multiple times
+// (and also to protect against recursion).
+bool HasRequiredFields(
+    const Descriptor* type,
+    hash_set<const Descriptor*>* already_seen) {
+  if (already_seen->count(type) > 0) {
+    // The type is already in cache.  This means that either:
+    // a. The type has no required fields.
+    // b. We are in the midst of checking if the type has required fields,
+    //    somewhere up the stack.  In this case, we know that if the type
+    //    has any required fields, they'll be found when we return to it,
+    //    and the whole call to HasRequiredFields() will return true.
+    //    Therefore, we don't have to check if this type has required fields
+    //    here.
+    return false;
+  }
+  already_seen->insert(type);
+
+  // If the type has extensions, an extension with message type could contain
+  // required fields, so we have to be conservative and assume such an
+  // extension exists.
+  if (type->extension_range_count() > 0) return true;
+
+  for (int i = 0; i < type->field_count(); i++) {
+    const FieldDescriptor* field = type->field(i);
+    if (field->is_required()) {
+      return true;
+    }
+    if (GetJavaType(field) == JAVATYPE_MESSAGE) {
+      if (HasRequiredFields(field->message_type(), already_seen)) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+bool HasRequiredFields(const Descriptor* type) {
+  hash_set<const Descriptor*> already_seen;
+  return HasRequiredFields(type, &already_seen);
+}
+
+bool HasRepeatedFields(const Descriptor* descriptor) {
+  for (int i = 0; i < descriptor->field_count(); ++i) {
+    const FieldDescriptor* field = descriptor->field(i);
+    if (field->is_repeated()) {
+      return true;
+    }
+  }
+  return false;
+}
+
 }  // namespace java
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/java/java_helpers.h b/src/google/protobuf/compiler/java/java_helpers.h
index 3937f069..6d1eae0a 100644
--- a/src/google/protobuf/compiler/java/java_helpers.h
+++ b/src/google/protobuf/compiler/java/java_helpers.h
@@ -49,6 +49,9 @@ namespace java {
 extern const char kThickSeparator[];
 extern const char kThinSeparator[];
 
+// Converts a name to camel-case. If cap_first_letter is true, capitalize the
+// first letter.
+string UnderscoresToCamelCase(const string& name, bool cap_first_letter);
 // Converts the field's name to camel-case, e.g. "foo_bar_baz" becomes
 // "fooBarBaz" or "FooBarBaz", respectively.
 string UnderscoresToCamelCase(const FieldDescriptor* field);
@@ -58,15 +61,22 @@ string UnderscoresToCapitalizedCamelCase(const FieldDescriptor* field);
 // of lower-casing the first letter of the name.)
 string UnderscoresToCamelCase(const MethodDescriptor* method);
 
+// Get an identifier that uniquely identifies this type within the file.
+// This is used to declare static variables related to this type at the
+// outermost file scope.
+string UniqueFileScopeIdentifier(const Descriptor* descriptor);
+
 // Strips ".proto" or ".protodevel" from the end of a filename.
 string StripProto(const string& filename);
 
-// Gets the unqualified class name for the file.  Each .proto file becomes a
-// single Java class, with all its contents nested in that class.
-string FileClassName(const FileDescriptor* file);
+// Gets the unqualified class name for the file.  For each .proto file, there
+// will be one Java class containing all the immutable messages and another
+// Java class containing all the mutable messages.
+// TODO(xiaofeng): remove the default value after updating client code.
+string FileClassName(const FileDescriptor* file, bool immutable = true);
 
 // Returns the file's Java package name.
-string FileJavaPackage(const FileDescriptor* file);
+string FileJavaPackage(const FileDescriptor* file, bool immutable = true);
 
 // Returns output directory for the given package name.
 string JavaPackageToDir(string package_name);
@@ -74,17 +84,46 @@ string JavaPackageToDir(string package_name);
 // Converts the given fully-qualified name in the proto namespace to its
 // fully-qualified name in the Java namespace, given that it is in the given
 // file.
-string ToJavaName(const string& full_name, const FileDescriptor* file);
-
-// These return the fully-qualified class name corresponding to the given
-// descriptor.
+// TODO(xiaofeng): this method is deprecated and should be removed in the
+// future.
+string ToJavaName(const string& full_name,
+                  const FileDescriptor* file);
+
+// TODO(xiaofeng): the following methods are kept for they are exposed
+// publicly in //google/protobuf/compiler/java/names.h. They return
+// immutable names only and should be removed after mutable API is
+// integrated into google3.
 string ClassName(const Descriptor* descriptor);
 string ClassName(const EnumDescriptor* descriptor);
 string ClassName(const ServiceDescriptor* descriptor);
 string ClassName(const FileDescriptor* descriptor);
 
-inline string ExtensionIdentifierName(const FieldDescriptor* descriptor) {
-  return ToJavaName(descriptor->full_name(), descriptor->file());
+// Comma-separate list of option-specified interfaces implemented by the
+// Message, to follow the "implements" declaration of the Message definition.
+string ExtraMessageInterfaces(const Descriptor* descriptor);
+// Comma-separate list of option-specified interfaces implemented by the
+// MutableMessage, to follow the "implements" declaration of the MutableMessage
+// definition.
+string ExtraMutableMessageInterfaces(const Descriptor* descriptor);
+// Comma-separate list of option-specified interfaces implemented by the
+// Builder, to follow the "implements" declaration of the Builder definition.
+string ExtraBuilderInterfaces(const Descriptor* descriptor);
+// Comma-separate list of option-specified interfaces extended by the
+// MessageOrBuilder, to follow the "extends" declaration of the
+// MessageOrBuilder definition.
+string ExtraMessageOrBuilderInterfaces(const Descriptor* descriptor);
+
+// Get the unqualified Java class name for mutable messages. i.e. without
+// package or outer classnames.
+inline string ShortMutableJavaClassName(const Descriptor* descriptor) {
+  return descriptor->name();
+}
+
+
+// Whether we should generate multiple java files for messages.
+inline bool MultipleJavaFiles(
+    const FileDescriptor* descriptor, bool immutable) {
+  return descriptor->options().java_multiple_files();
 }
 
 // Get the unqualified name that should be used for a field's field
@@ -115,11 +154,23 @@ JavaType GetJavaType(const FieldDescriptor* field);
 // types.
 const char* BoxedPrimitiveTypeName(JavaType type);
 
-string DefaultValue(const FieldDescriptor* field);
+// Get the name of the java enum constant representing this type. E.g.,
+// "INT32" for FieldDescriptor::TYPE_INT32. The enum constant's full
+// name is "com.google.protobuf.WireFormat.FieldType.INT32".
+const char* FieldTypeName(const FieldDescriptor::Type field_type);
+
+class ClassNameResolver;
+string DefaultValue(const FieldDescriptor* field, bool immutable,
+                    ClassNameResolver* name_resolver);
+inline string ImmutableDefaultValue(const FieldDescriptor* field,
+                                    ClassNameResolver* name_resolver) {
+  return DefaultValue(field, true, name_resolver);
+}
 bool IsDefaultValueJavaDefault(const FieldDescriptor* field);
 
-// Does this message class keep track of unknown fields?
-inline bool HasUnknownFields(const Descriptor* descriptor) {
+// Does this message class use UnknownFieldSet?
+// Otherwise, unknown fields will be stored in a ByteString object
+inline bool UseUnknownFieldSet(const Descriptor* descriptor) {
   return descriptor->file()->options().optimize_for() !=
            FileOptions::LITE_RUNTIME;
 }
@@ -163,6 +214,15 @@ inline bool HasGenericServices(const FileDescriptor *file) {
          file->options().java_generic_services();
 }
 
+inline bool IsLazy(const FieldDescriptor* descriptor) {
+  // Currently, the proto-lite version suports lazy field.
+  // TODO(niwasaki): Support lazy fields also for other proto runtimes.
+  if (descriptor->file()->options().optimize_for() !=
+      FileOptions::LITE_RUNTIME) {
+    return false;
+  }
+  return descriptor->options().lazy();
+}
 
 // Methods for shared bitfields.
 
@@ -212,6 +272,48 @@ string GenerateGetBitMutableLocal(int bitIndex);
 // Example: "mutable_bitField1_ = (mutable_bitField1_ | 0x04)"
 string GenerateSetBitMutableLocal(int bitIndex);
 
+// Returns whether the JavaType is a reference type.
+bool IsReferenceType(JavaType type);
+
+// Returns the capitalized name for calling relative functions in
+// CodedInputStream
+const char* GetCapitalizedType(const FieldDescriptor* field, bool immutable);
+
+// For encodings with fixed sizes, returns that size in bytes.  Otherwise
+// returns -1.
+int FixedSize(FieldDescriptor::Type type);
+
+// Comparators used to sort fields in MessageGenerator
+struct FieldOrderingByNumber {
+  inline bool operator()(const FieldDescriptor* a,
+                         const FieldDescriptor* b) const {
+    return a->number() < b->number();
+  }
+};
+
+struct ExtensionRangeOrdering {
+  bool operator()(const Descriptor::ExtensionRange* a,
+                  const Descriptor::ExtensionRange* b) const {
+    return a->start < b->start;
+  }
+};
+
+// Sort the fields of the given Descriptor by number into a new[]'d array
+// and return it. The caller should delete the returned array.
+const FieldDescriptor** SortFieldsByNumber(const Descriptor* descriptor);
+
+// Check a message type and its sub-message types recursively to see if any of
+// them has a required field. Return true if a required field is found.
+bool HasRequiredFields(const Descriptor* descriptor);
+
+// Whether a .proto file supports field presence test for non-message types.
+inline bool SupportFieldPresence(const FileDescriptor* descriptor) {
+  return true;
+}
+
+// Check whether a mesasge has repeated fields.
+bool HasRepeatedFields(const Descriptor* descriptor);
+
 }  // namespace java
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/java/java_lazy_message_field.cc b/src/google/protobuf/compiler/java/java_lazy_message_field.cc
new file mode 100644
index 00000000..32d97b6f
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_lazy_message_field.cc
@@ -0,0 +1,826 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: niwasaki@google.com (Naoki Iwasaki)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_lazy_message_field.h>
+#include <google/protobuf/compiler/java/java_doc_comment.h>
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/io/printer.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+ImmutableLazyMessageFieldGenerator::
+ImmutableLazyMessageFieldGenerator(
+    const FieldDescriptor* descriptor,
+    int messageBitIndex,
+    int builderBitIndex,
+    Context* context)
+    : ImmutableMessageFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+}
+
+ImmutableLazyMessageFieldGenerator::~ImmutableLazyMessageFieldGenerator() {}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  printer->Print(variables_,
+    "private com.google.protobuf.LazyFieldLite $name$_ =\n"
+    "    new com.google.protobuf.LazyFieldLite();\n");
+
+  PrintExtraFieldInfo(variables_, printer);
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public boolean has$capitalized_name$() {\n"
+    "  return $get_has_field_bit_message$;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  return ($type$) $name$_.getValue($type$.getDefaultInstance());\n"
+   "}\n");
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
+      "  return $name$_;\n"
+      "}\n");
+  }
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  // When using nested-builders, the code initially works just like the
+  // non-nested builder case. It only creates a nested builder lazily on
+  // demand and then forever delegates to it after creation.
+
+  printer->Print(variables_,
+    "private com.google.protobuf.LazyFieldLite $name$_ =\n"
+    "    new com.google.protobuf.LazyFieldLite();\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    printer->Print(variables_,
+      // If this builder is non-null, it is used and the other fields are
+      // ignored.
+      "private com.google.protobuf.SingleFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> $name$Builder_;"
+      "\n");
+  }
+
+  // The comments above the methods below are based on a hypothetical
+  // field of type "Field" called "Field".
+
+  // boolean hasField()
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public boolean has$capitalized_name$() {\n"
+    "  return $get_has_field_bit_builder$;\n"
+    "}\n");
+
+    printer->Print(variables_,
+      "$deprecation$public $type$ get$capitalized_name$() {\n"
+      "  return ($type$) $name$_.getValue($type$.getDefaultInstance());\n"
+      "}\n");
+
+  // Field.Builder setField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$($type$ value)",
+
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "$name$_.setValue(value);\n"
+    "$on_changed$\n",
+
+     NULL,  // Lazy fields are supported only for lite-runtime.
+
+    "$set_has_field_bit_builder$;\n"
+    "return this;\n");
+
+  // Field.Builder setField(Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    $type$.Builder builderForValue)",
+
+    "$name$_.setValue(builderForValue.build());\n"
+    "$on_changed$\n",
+
+    NULL,
+
+    "$set_has_field_bit_builder$;\n"
+    "return this;\n");
+
+  // Field.Builder mergeField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder merge$capitalized_name$($type$ value)",
+
+    "if ($get_has_field_bit_builder$ &&\n"
+    "    !$name$_.containsDefaultInstance()) {\n"
+    "  $name$_.setValue(\n"
+    "    $type$.newBuilder(\n"
+    "        get$capitalized_name$()).mergeFrom(value).buildPartial());\n"
+    "} else {\n"
+    "  $name$_.setValue(value);\n"
+    "}\n"
+    "$on_changed$\n",
+
+    NULL,
+
+    "$set_has_field_bit_builder$;\n"
+    "return this;\n");
+
+  // Field.Builder clearField()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder clear$capitalized_name$()",
+
+    "$name$_.clear();\n"
+    "$on_changed$\n",
+
+    NULL,
+
+    "$clear_has_field_bit_builder$;\n"
+    "return this;\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$.Builder get$capitalized_name$Builder() {\n"
+      "  $set_has_field_bit_builder$;\n"
+      "  $on_changed$\n"
+      "  return get$capitalized_name$FieldBuilder().getBuilder();\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
+      "  if ($name$Builder_ != null) {\n"
+      "    return $name$Builder_.getMessageOrBuilder();\n"
+      "  } else {\n"
+      "    return $name$_;\n"
+      "  }\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "private com.google.protobuf.SingleFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> \n"
+      "    get$capitalized_name$FieldBuilder() {\n"
+      "  if ($name$Builder_ == null) {\n"
+      "    $name$Builder_ = new com.google.protobuf.SingleFieldBuilder<\n"
+      "        $type$, $type$.Builder, $type$OrBuilder>(\n"
+      "            $name$_,\n"
+      "            getParentForChildren(),\n"
+      "            isClean());\n"
+      "    $name$_ = null;\n"
+      "  }\n"
+      "  return $name$Builder_;\n"
+      "}\n");
+  }
+}
+
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateInitializationCode(io::Printer* printer) const {
+  printer->Print(variables_, "$name$_.clear();\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateBuilderClearCode(io::Printer* printer) const {
+  printer->Print(variables_, "$name$_.clear();\n");
+  printer->Print(variables_, "$clear_has_field_bit_builder$;\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (other.has$capitalized_name$()) {\n"
+    "  $name$_.merge(other.$name$_);\n"
+    "  $set_has_field_bit_builder$;\n"
+    "}\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+      "if ($get_has_field_bit_from_local$) {\n"
+      "  $set_has_field_bit_to_local$;\n"
+      "}\n");
+
+  printer->Print(variables_,
+      "result.$name$_.setByteString(\n"
+      "    $name$_.toByteString(),\n"
+      "    $name$_.getExtensionRegistry());\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "$name$_.setByteString(input.readBytes(), extensionRegistry);\n");
+  printer->Print(variables_,
+    "$set_has_field_bit_message$;\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  // Do not de-serialize lazy fields.
+  printer->Print(variables_,
+    "if ($get_has_field_bit_message$) {\n"
+    "  output.writeBytes($number$, $name$_.toByteString());\n"
+    "}\n");
+}
+
+void ImmutableLazyMessageFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($get_has_field_bit_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .computeLazyFieldSize($number$, $name$_);\n"
+    "}\n");
+}
+
+// ===================================================================
+
+ImmutableLazyMessageOneofFieldGenerator::
+ImmutableLazyMessageOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                        int messageBitIndex,
+                                        int builderBitIndex,
+                                        Context* context)
+    : ImmutableLazyMessageFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+  const OneofGeneratorInfo* info =
+      context->GetOneofGeneratorInfo(descriptor->containing_oneof());
+  SetCommonOneofVariables(descriptor, info, &variables_);
+  variables_["lazy_type"] = "com.google.protobuf.LazyFieldLite";
+}
+
+ImmutableLazyMessageOneofFieldGenerator::
+~ImmutableLazyMessageOneofFieldGenerator() {}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  PrintExtraFieldInfo(variables_, printer);
+  WriteFieldDocComment(printer, descriptor_);
+
+  printer->Print(variables_,
+    "$deprecation$public boolean has$capitalized_name$() {\n"
+    "  return $has_oneof_case_message$;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($type$) (($lazy_type$) $oneof_name$_).getValue(\n"
+    "        $type$.getDefaultInstance());\n"
+    "  }\n"
+    "  return $type$.getDefaultInstance();\n"
+    "}\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  // boolean hasField()
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public boolean has$capitalized_name$() {\n"
+    "  return $has_oneof_case_message$;\n"
+    "}\n");
+
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($type$) (($lazy_type$) $oneof_name$_).getValue(\n"
+    "        $type$.getDefaultInstance());\n"
+    "  }\n"
+    "  return $type$.getDefaultInstance();\n"
+    "}\n");
+
+  // Field.Builder setField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$($type$ value)",
+
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "if (!($has_oneof_case_message$)) {\n"
+    "  $oneof_name$_ = new $lazy_type$();\n"
+    "  $set_oneof_case_message$;\n"
+    "}\n"
+    "(($lazy_type$) $oneof_name$_).setValue(value);\n"
+    "$on_changed$\n",
+
+     NULL,  // Lazy fields are supported only for lite-runtime.
+
+    "return this;\n");
+
+  // Field.Builder setField(Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    $type$.Builder builderForValue)",
+
+    "if (!($has_oneof_case_message$)) {\n"
+    "  $oneof_name$_ = new $lazy_type$();\n"
+    "  $set_oneof_case_message$;\n"
+    "}\n"
+    "(($lazy_type$) $oneof_name$_).setValue(builderForValue.build());\n"
+    "$on_changed$\n",
+
+    NULL,
+
+    "return this;\n");
+
+  // Field.Builder mergeField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder merge$capitalized_name$($type$ value)",
+
+    "if ($has_oneof_case_message$ &&\n"
+    "    !(($lazy_type$) $oneof_name$_).containsDefaultInstance()) {\n"
+    "  (($lazy_type$) $oneof_name$_).setValue(\n"
+    "    $type$.newBuilder(\n"
+    "        get$capitalized_name$()).mergeFrom(value).buildPartial());\n"
+    "} else {\n"
+    "  if (!($has_oneof_case_message$)) {\n"
+    "    $oneof_name$_ = new $lazy_type$();\n"
+    "    $set_oneof_case_message$;\n"
+    "  }\n"
+    "  (($lazy_type$) $oneof_name$_).setValue(value);\n"
+    "}\n"
+    "$on_changed$\n",
+
+    NULL,
+
+    "return this;\n");
+
+  // Field.Builder clearField()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder clear$capitalized_name$()",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  $clear_oneof_case_message$;\n"
+    "  $oneof_name$_ = null;\n"
+    "  $on_changed$\n"
+    "}\n",
+
+    NULL,
+
+    "return this;\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (!($has_oneof_case_message$)) {\n"
+    "  $oneof_name$_ = new $lazy_type$();\n"
+    "}\n"
+    "(($lazy_type$) $oneof_name$_).merge(\n"
+    "    ($lazy_type$) other.$oneof_name$_);\n"
+    "$set_oneof_case_message$;\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+                 "if ($has_oneof_case_message$) {\n");
+  printer->Indent();
+
+  printer->Print(variables_,
+      "result.$oneof_name$_ = new $lazy_type$();\n"
+      "(($lazy_type$) result.$oneof_name$_).setByteString(\n"
+      "    (($lazy_type$) $oneof_name$_).toByteString(),\n"
+      "    (($lazy_type$) $oneof_name$_).getExtensionRegistry());\n");
+  printer->Outdent();
+  printer->Print("}\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (!($has_oneof_case_message$)) {\n"
+    "  $oneof_name$_ = new $lazy_type$();\n"
+    "}\n"
+    "(($lazy_type$) $oneof_name$_).setByteString(\n"
+    "    input.readBytes(), extensionRegistry);\n"
+    "$set_oneof_case_message$;\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  // Do not de-serialize lazy fields.
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  output.writeBytes(\n"
+    "      $number$, (($lazy_type$) $oneof_name$_).toByteString());\n"
+    "}\n");
+}
+
+void ImmutableLazyMessageOneofFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .computeLazyFieldSize($number$, ($lazy_type$) $oneof_name$_);\n"
+    "}\n");
+}
+
+// ===================================================================
+
+RepeatedImmutableLazyMessageFieldGenerator::
+RepeatedImmutableLazyMessageFieldGenerator(
+    const FieldDescriptor* descriptor,
+    int messageBitIndex,
+    int builderBitIndex,
+    Context* context)
+    : RepeatedImmutableMessageFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+}
+
+
+RepeatedImmutableLazyMessageFieldGenerator::
+~RepeatedImmutableLazyMessageFieldGenerator() {}
+
+void RepeatedImmutableLazyMessageFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  printer->Print(variables_,
+    "private java.util.List<com.google.protobuf.LazyFieldLite> $name$_;\n");
+  PrintExtraFieldInfo(variables_, printer);
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public java.util.List<$type$>\n"
+    "    get$capitalized_name$List() {\n"
+    "  java.util.List<$type$> list =\n"
+    "      new java.util.ArrayList<$type$>($name$_.size());\n"
+    "  for (com.google.protobuf.LazyFieldLite lf : $name$_) {\n"
+    "    list.add(($type$) lf.getValue($type$.getDefaultInstance()));\n"
+    "  }\n"
+    "  return list;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public java.util.List<? extends $type$OrBuilder>\n"
+    "    get$capitalized_name$OrBuilderList() {\n"
+    "  return get$capitalized_name$List();\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public int get$capitalized_name$Count() {\n"
+    "  return $name$_.size();\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$(int index) {\n"
+    "  return ($type$)\n"
+    "      $name$_.get(index).getValue($type$.getDefaultInstance());\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder(\n"
+    "    int index) {\n"
+    "  return ($type$OrBuilder)\n"
+    "      $name$_.get(index).getValue($type$.getDefaultInstance());\n"
+    "}\n");
+}
+
+void RepeatedImmutableLazyMessageFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  // When using nested-builders, the code initially works just like the
+  // non-nested builder case. It only creates a nested builder lazily on
+  // demand and then forever delegates to it after creation.
+
+  printer->Print(variables_,
+    "private java.util.List<com.google.protobuf.LazyFieldLite> $name$_ =\n"
+    "  java.util.Collections.emptyList();\n"
+
+    "private void ensure$capitalized_name$IsMutable() {\n"
+    "  if (!$get_mutable_bit_builder$) {\n"
+    "    $name$_ =\n"
+    "        new java.util.ArrayList<com.google.protobuf.LazyFieldLite>(\n"
+    "            $name$_);\n"
+    "    $set_mutable_bit_builder$;\n"
+    "   }\n"
+    "}\n"
+    "\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    printer->Print(variables_,
+      // If this builder is non-null, it is used and the other fields are
+      // ignored.
+      "private com.google.protobuf.RepeatedFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> $name$Builder_;\n"
+      "\n");
+  }
+
+  // The comments above the methods below are based on a hypothetical
+  // repeated field of type "Field" called "RepeatedField".
+
+  // List<Field> getRepeatedFieldList()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public java.util.List<$type$> get$capitalized_name$List()",
+
+    "java.util.List<$type$> list =\n"
+    "    new java.util.ArrayList<$type$>($name$_.size());\n"
+    "for (com.google.protobuf.LazyFieldLite lf : $name$_) {\n"
+    "  list.add(($type$) lf.getValue($type$.getDefaultInstance()));\n"
+    "}\n"
+    "return java.util.Collections.unmodifiableList(list);\n",
+
+    "return $name$Builder_.getMessageList();\n",
+
+    NULL);
+
+  // int getRepeatedFieldCount()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public int get$capitalized_name$Count()",
+
+    "return $name$_.size();\n",
+    "return $name$Builder_.getCount();\n",
+
+    NULL);
+
+  // Field getRepeatedField(int index)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public $type$ get$capitalized_name$(int index)",
+
+    "return ($type$) $name$_.get(index).getValue(\n"
+    "    $type$.getDefaultInstance());\n",
+
+    "return $name$Builder_.getMessage(index);\n",
+
+    NULL);
+
+  // Builder setRepeatedField(int index, Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    int index, $type$ value)",
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.set(index, com.google.protobuf.LazyFieldLite.fromValue(value));\n"
+    "$on_changed$\n",
+    "$name$Builder_.setMessage(index, value);\n",
+    "return this;\n");
+
+  // Builder setRepeatedField(int index, Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    int index, $type$.Builder builderForValue)",
+
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.set(index, com.google.protobuf.LazyFieldLite.fromValue(\n"
+    "    builderForValue.build()));\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.setMessage(index, builderForValue.build());\n",
+
+    "return this;\n");
+
+  // Builder addRepeatedField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder add$capitalized_name$($type$ value)",
+
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.add(com.google.protobuf.LazyFieldLite.fromValue(value));\n"
+
+    "$on_changed$\n",
+
+    "$name$Builder_.addMessage(value);\n",
+
+    "return this;\n");
+
+  // Builder addRepeatedField(int index, Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder add$capitalized_name$(\n"
+    "    int index, $type$ value)",
+
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.add(index, com.google.protobuf.LazyFieldLite.fromValue(value));\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.addMessage(index, value);\n",
+
+    "return this;\n");
+
+  // Builder addRepeatedField(Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder add$capitalized_name$(\n"
+    "    $type$.Builder builderForValue)",
+
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.add(com.google.protobuf.LazyFieldLite.fromValue(\n"
+    "    builderForValue.build()));\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.addMessage(builderForValue.build());\n",
+
+    "return this;\n");
+
+  // Builder addRepeatedField(int index, Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder add$capitalized_name$(\n"
+    "    int index, $type$.Builder builderForValue)",
+
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.add(index, com.google.protobuf.LazyFieldLite.fromValue(\n"
+    "    builderForValue.build()));\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.addMessage(index, builderForValue.build());\n",
+
+    "return this;\n");
+
+  // Builder addAllRepeatedField(Iterable<Field> values)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder addAll$capitalized_name$(\n"
+    "    java.lang.Iterable<? extends $type$> values)",
+
+    "ensure$capitalized_name$IsMutable();\n"
+    "for (com.google.protobuf.MessageLite v : values) {\n"
+    "  $name$_.add(com.google.protobuf.LazyFieldLite.fromValue(v));\n"
+    "}\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.addAllMessages(values);\n",
+
+    "return this;\n");
+
+  // Builder clearAllRepeatedField()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder clear$capitalized_name$()",
+
+    "$name$_ = java.util.Collections.emptyList();\n"
+    "$clear_mutable_bit_builder$;\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.clear();\n",
+
+    "return this;\n");
+
+  // Builder removeRepeatedField(int index)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder remove$capitalized_name$(int index)",
+
+    "ensure$capitalized_name$IsMutable();\n"
+    "$name$_.remove(index);\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.remove(index);\n",
+
+    "return this;\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$.Builder get$capitalized_name$Builder(\n"
+      "    int index) {\n"
+      "  return get$capitalized_name$FieldBuilder().getBuilder(index);\n"
+      "}\n");
+
+    WriteFieldDocComment(printer, descriptor_);
+        printer->Print(variables_,
+      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder(\n"
+      "    int index) {\n"
+      "  if ($name$Builder_ == null) {\n"
+      "    return $name$_.get(index);"
+      "  } else {\n"
+      "    return $name$Builder_.getMessageOrBuilder(index);\n"
+      "  }\n"
+      "}\n");
+
+    WriteFieldDocComment(printer, descriptor_);
+        printer->Print(variables_,
+      "$deprecation$public java.util.List<? extends $type$OrBuilder> \n"
+      "     get$capitalized_name$OrBuilderList() {\n"
+      "  if ($name$Builder_ != null) {\n"
+      "    return $name$Builder_.getMessageOrBuilderList();\n"
+      "  } else {\n"
+      "    return java.util.Collections.unmodifiableList($name$_);\n"
+      "  }\n"
+      "}\n");
+
+    WriteFieldDocComment(printer, descriptor_);
+        printer->Print(variables_,
+      "$deprecation$public $type$.Builder add$capitalized_name$Builder() {\n"
+      "  return get$capitalized_name$FieldBuilder().addBuilder(\n"
+      "      $type$.getDefaultInstance());\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+        printer->Print(variables_,
+      "$deprecation$public $type$.Builder add$capitalized_name$Builder(\n"
+      "    int index) {\n"
+      "  return get$capitalized_name$FieldBuilder().addBuilder(\n"
+      "      index, $type$.getDefaultInstance());\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+        printer->Print(variables_,
+      "$deprecation$public java.util.List<$type$.Builder> \n"
+      "     get$capitalized_name$BuilderList() {\n"
+      "  return get$capitalized_name$FieldBuilder().getBuilderList();\n"
+      "}\n"
+      "private com.google.protobuf.RepeatedFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> \n"
+      "    get$capitalized_name$FieldBuilder() {\n"
+      "  if ($name$Builder_ == null) {\n"
+      "    $name$Builder_ = new com.google.protobuf.RepeatedFieldBuilder<\n"
+      "        $type$, $type$.Builder, $type$OrBuilder>(\n"
+      "            $name$_,\n"
+      "            $get_mutable_bit_builder$,\n"
+      "            getParentForChildren(),\n"
+      "            isClean());\n"
+      "    $name$_ = null;\n"
+      "  }\n"
+      "  return $name$Builder_;\n"
+      "}\n");
+  }
+}
+
+void RepeatedImmutableLazyMessageFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if (!$get_mutable_bit_parser$) {\n"
+    "  $name$_ =\n"
+    "      new java.util.ArrayList<com.google.protobuf.LazyFieldLite>();\n"
+    "  $set_mutable_bit_parser$;\n"
+    "}\n"
+    "$name$_.add(new com.google.protobuf.LazyFieldLite(\n"
+    "    extensionRegistry, input.readBytes()));\n");
+}
+
+void RepeatedImmutableLazyMessageFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "for (int i = 0; i < $name$_.size(); i++) {\n"
+    "  output.writeBytes($number$, $name$_.get(i).toByteString());\n"
+    "}\n");
+}
+
+void RepeatedImmutableLazyMessageFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "for (int i = 0; i < $name$_.size(); i++) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .computeLazyFieldSize($number$, $name$_.get(i));\n"
+    "}\n");
+}
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_lazy_message_field.h b/src/google/protobuf/compiler/java/java_lazy_message_field.h
new file mode 100644
index 00000000..2a1f8574
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_lazy_message_field.h
@@ -0,0 +1,121 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: niwasaki@google.com (Naoki Iwasaki)
+//  Based on original Protocol Buffers design by
+//  Sanjay Ghemawat, Jeff Dean, and others.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_LAZY_MESSAGE_FIELD_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_LAZY_MESSAGE_FIELD_H__
+
+#include <google/protobuf/compiler/java/java_field.h>
+#include <google/protobuf/compiler/java/java_message_field.h>
+
+namespace google {
+namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;  // context.h
+    }
+  }
+}
+
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+class ImmutableLazyMessageFieldGenerator
+    : public ImmutableMessageFieldGenerator {
+ public:
+  explicit ImmutableLazyMessageFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableLazyMessageFieldGenerator();
+
+  // overroads ImmutableMessageFieldGenerator ---------------------------------
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateInitializationCode(io::Printer* printer) const;
+  void GenerateBuilderClearCode(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableLazyMessageFieldGenerator);
+};
+
+class ImmutableLazyMessageOneofFieldGenerator
+    : public ImmutableLazyMessageFieldGenerator {
+ public:
+  ImmutableLazyMessageOneofFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableLazyMessageOneofFieldGenerator();
+
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableLazyMessageOneofFieldGenerator);
+};
+
+class RepeatedImmutableLazyMessageFieldGenerator
+    : public RepeatedImmutableMessageFieldGenerator {
+ public:
+  explicit RepeatedImmutableLazyMessageFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~RepeatedImmutableLazyMessageFieldGenerator();
+
+  // overroads RepeatedImmutableMessageFieldGenerator -------------------------
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedImmutableLazyMessageFieldGenerator);
+};
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_LAZY_MESSAGE_FIELD_H__
diff --git a/src/google/protobuf/compiler/java/java_message.cc b/src/google/protobuf/compiler/java/java_message.cc
index 9322e242..1cd08f7d 100644
--- a/src/google/protobuf/compiler/java/java_message.cc
+++ b/src/google/protobuf/compiler/java/java_message.cc
@@ -37,12 +37,16 @@
 #include <algorithm>
 #include <google/protobuf/stubs/hash.h>
 #include <map>
+#include <memory>
 #include <vector>
 
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_enum.h>
 #include <google/protobuf/compiler/java/java_extension.h>
+#include <google/protobuf/compiler/java/java_generator_factory.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/coded_stream.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/descriptor.pb.h>
@@ -59,107 +63,31 @@ using internal::WireFormat;
 using internal::WireFormatLite;
 
 namespace {
-
-void PrintFieldComment(io::Printer* printer, const FieldDescriptor* field) {
-  // Print the field's proto-syntax definition as a comment.  We don't want to
-  // print group bodies so we cut off after the first line.
-  string def = field->DebugString();
-  printer->Print("// $def$\n",
-    "def", def.substr(0, def.find_first_of('\n')));
+bool GenerateHasBits(const Descriptor* descriptor) {
+  return SupportFieldPresence(descriptor->file()) ||
+      HasRepeatedFields(descriptor);
 }
-
-struct FieldOrderingByNumber {
-  inline bool operator()(const FieldDescriptor* a,
-                         const FieldDescriptor* b) const {
-    return a->number() < b->number();
-  }
-};
-
-struct ExtensionRangeOrdering {
-  bool operator()(const Descriptor::ExtensionRange* a,
-                  const Descriptor::ExtensionRange* b) const {
-    return a->start < b->start;
-  }
-};
-
-// Sort the fields of the given Descriptor by number into a new[]'d array
-// and return it.
-const FieldDescriptor** SortFieldsByNumber(const Descriptor* descriptor) {
-  const FieldDescriptor** fields =
-    new const FieldDescriptor*[descriptor->field_count()];
-  for (int i = 0; i < descriptor->field_count(); i++) {
-    fields[i] = descriptor->field(i);
-  }
-  sort(fields, fields + descriptor->field_count(),
-       FieldOrderingByNumber());
-  return fields;
-}
-
-// Get an identifier that uniquely identifies this type within the file.
-// This is used to declare static variables related to this type at the
-// outermost file scope.
-string UniqueFileScopeIdentifier(const Descriptor* descriptor) {
-  return "static_" + StringReplace(descriptor->full_name(), ".", "_", true);
-}
-
-// Returns true if the message type has any required fields.  If it doesn't,
-// we can optimize out calls to its isInitialized() method.
-//
-// already_seen is used to avoid checking the same type multiple times
-// (and also to protect against recursion).
-static bool HasRequiredFields(
-    const Descriptor* type,
-    hash_set<const Descriptor*>* already_seen) {
-  if (already_seen->count(type) > 0) {
-    // The type is already in cache.  This means that either:
-    // a. The type has no required fields.
-    // b. We are in the midst of checking if the type has required fields,
-    //    somewhere up the stack.  In this case, we know that if the type
-    //    has any required fields, they'll be found when we return to it,
-    //    and the whole call to HasRequiredFields() will return true.
-    //    Therefore, we don't have to check if this type has required fields
-    //    here.
-    return false;
-  }
-  already_seen->insert(type);
-
-  // If the type has extensions, an extension with message type could contain
-  // required fields, so we have to be conservative and assume such an
-  // extension exists.
-  if (type->extension_range_count() > 0) return true;
-
-  for (int i = 0; i < type->field_count(); i++) {
-    const FieldDescriptor* field = type->field(i);
-    if (field->is_required()) {
-      return true;
-    }
-    if (GetJavaType(field) == JAVATYPE_MESSAGE) {
-      if (HasRequiredFields(field->message_type(), already_seen)) {
-        return true;
-      }
-    }
-  }
-
-  return false;
-}
-
-static bool HasRequiredFields(const Descriptor* type) {
-  hash_set<const Descriptor*> already_seen;
-  return HasRequiredFields(type, &already_seen);
-}
-
 }  // namespace
 
 // ===================================================================
 
 MessageGenerator::MessageGenerator(const Descriptor* descriptor)
-  : descriptor_(descriptor),
-    field_generators_(descriptor) {
-}
+  : descriptor_(descriptor) {}
 
 MessageGenerator::~MessageGenerator() {}
 
-void MessageGenerator::GenerateStaticVariables(io::Printer* printer) {
+// ===================================================================
+// TODO(api): Move this class to a separate immutable_message.cc file.
+ImmutableMessageGenerator::ImmutableMessageGenerator(
+    const Descriptor* descriptor, Context* context)
+  : MessageGenerator(descriptor), context_(context),
+    name_resolver_(context->GetNameResolver()),
+    field_generators_(descriptor, context_) {
+}
+
+ImmutableMessageGenerator::~ImmutableMessageGenerator() {}
+
+void ImmutableMessageGenerator::GenerateStaticVariables(io::Printer* printer) {
   if (HasDescriptorMethods(descriptor_)) {
     // Because descriptor.proto (com.google.protobuf.DescriptorProtos) is
     // used in the construction of descriptors, we have a tricky bootstrapping
@@ -171,12 +99,12 @@ void MessageGenerator::GenerateStaticVariables(io::Printer* printer) {
     map<string, string> vars;
     vars["identifier"] = UniqueFileScopeIdentifier(descriptor_);
     vars["index"] = SimpleItoa(descriptor_->index());
-    vars["classname"] = ClassName(descriptor_);
+    vars["classname"] = name_resolver_->GetImmutableClassName(descriptor_);
     if (descriptor_->containing_type() != NULL) {
       vars["parent"] = UniqueFileScopeIdentifier(
           descriptor_->containing_type());
     }
-    if (descriptor_->file()->options().java_multiple_files()) {
+    if (MultipleJavaFiles(descriptor_->file(), /* immutable = */ true)) {
       // We can only make these package-private since the classes that use them
       // are in separate files.
       vars["private"] = "";
@@ -186,31 +114,28 @@ void MessageGenerator::GenerateStaticVariables(io::Printer* printer) {
 
     // The descriptor for this type.
     printer->Print(vars,
-      "$private$static com.google.protobuf.Descriptors.Descriptor\n"
+      "$private$static final com.google.protobuf.Descriptors.Descriptor\n"
       "  internal_$identifier$_descriptor;\n");
 
     // And the FieldAccessorTable.
-    printer->Print(vars,
-      "$private$static\n"
-      "  com.google.protobuf.GeneratedMessage.FieldAccessorTable\n"
-      "    internal_$identifier$_fieldAccessorTable;\n");
+    GenerateFieldAccessorTable(printer);
   }
 
   // Generate static members for all nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     // TODO(kenton):  Reuse MessageGenerator objects?
-    MessageGenerator(descriptor_->nested_type(i))
+    ImmutableMessageGenerator(descriptor_->nested_type(i), context_)
       .GenerateStaticVariables(printer);
   }
 }
 
-void MessageGenerator::GenerateStaticVariableInitializers(
+void ImmutableMessageGenerator::GenerateStaticVariableInitializers(
     io::Printer* printer) {
   if (HasDescriptorMethods(descriptor_)) {
     map<string, string> vars;
     vars["identifier"] = UniqueFileScopeIdentifier(descriptor_);
     vars["index"] = SimpleItoa(descriptor_->index());
-    vars["classname"] = ClassName(descriptor_);
+    vars["classname"] = name_resolver_->GetImmutableClassName(descriptor_);
     if (descriptor_->containing_type() != NULL) {
       vars["parent"] = UniqueFileScopeIdentifier(
           descriptor_->containing_type());
@@ -228,56 +153,95 @@ void MessageGenerator::GenerateStaticVariableInitializers(
     }
 
     // And the FieldAccessorTable.
-    printer->Print(vars,
-      "internal_$identifier$_fieldAccessorTable = new\n"
-      "  com.google.protobuf.GeneratedMessage.FieldAccessorTable(\n"
-      "    internal_$identifier$_descriptor,\n"
-      "    new java.lang.String[] { ");
-    for (int i = 0; i < descriptor_->field_count(); i++) {
-      printer->Print(
-        "\"$field_name$\", ",
-        "field_name",
-          UnderscoresToCapitalizedCamelCase(descriptor_->field(i)));
-    }
-    printer->Print(
-        "});\n");
+    GenerateFieldAccessorTableInitializer(printer);
   }
 
   // Generate static member initializers for all nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
     // TODO(kenton):  Reuse MessageGenerator objects?
-    MessageGenerator(descriptor_->nested_type(i))
+    ImmutableMessageGenerator(descriptor_->nested_type(i), context_)
       .GenerateStaticVariableInitializers(printer);
   }
 }
 
+void ImmutableMessageGenerator::
+GenerateFieldAccessorTable(io::Printer* printer) {
+  map<string, string> vars;
+  vars["identifier"] = UniqueFileScopeIdentifier(descriptor_);
+  if (MultipleJavaFiles(descriptor_->file(), /* immutable = */ true)) {
+    // We can only make these package-private since the classes that use them
+    // are in separate files.
+    vars["private"] = "";
+  } else {
+    vars["private"] = "private ";
+  }
+  printer->Print(vars,
+    "$private$static\n"
+    "  com.google.protobuf.GeneratedMessage.FieldAccessorTable\n"
+    "    internal_$identifier$_fieldAccessorTable;\n");
+}
+
+void ImmutableMessageGenerator::
+GenerateFieldAccessorTableInitializer(io::Printer* printer) {
+  printer->Print(
+    "internal_$identifier$_fieldAccessorTable = new\n"
+    "  com.google.protobuf.GeneratedMessage.FieldAccessorTable(\n"
+    "    internal_$identifier$_descriptor,\n"
+    "    new java.lang.String[] { ",
+    "identifier",
+    UniqueFileScopeIdentifier(descriptor_));
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    const FieldDescriptor* field = descriptor_->field(i);
+    const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
+    printer->Print(
+      "\"$field_name$\", ",
+      "field_name", info->capitalized_name);
+  }
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    const OneofDescriptor* oneof = descriptor_->oneof_decl(i);
+    const OneofGeneratorInfo* info = context_->GetOneofGeneratorInfo(oneof);
+    printer->Print(
+      "\"$oneof_name$\", ",
+      "oneof_name", info->capitalized_name);
+  }
+  printer->Print("});\n");
+}
+
 // ===================================================================
 
-void MessageGenerator::GenerateInterface(io::Printer* printer) {
+void ImmutableMessageGenerator::GenerateInterface(io::Printer* printer) {
   if (descriptor_->extension_range_count() > 0) {
     if (HasDescriptorMethods(descriptor_)) {
       printer->Print(
         "public interface $classname$OrBuilder extends\n"
+        "    $extra_interfaces$\n"
         "    com.google.protobuf.GeneratedMessage.\n"
         "        ExtendableMessageOrBuilder<$classname$> {\n",
+        "extra_interfaces", ExtraMessageOrBuilderInterfaces(descriptor_),
         "classname", descriptor_->name());
     } else {
       printer->Print(
         "public interface $classname$OrBuilder extends \n"
+        "    $extra_interfaces$\n"
         "     com.google.protobuf.GeneratedMessageLite.\n"
         "          ExtendableMessageOrBuilder<$classname$> {\n",
+        "extra_interfaces", ExtraMessageOrBuilderInterfaces(descriptor_),
         "classname", descriptor_->name());
     }
   } else {
     if (HasDescriptorMethods(descriptor_)) {
       printer->Print(
-        "public interface $classname$OrBuilder\n"
-        "    extends com.google.protobuf.MessageOrBuilder {\n",
+        "public interface $classname$OrBuilder extends\n"
+        "    $extra_interfaces$\n"
+        "    com.google.protobuf.MessageOrBuilder {\n",
+        "extra_interfaces", ExtraMessageOrBuilderInterfaces(descriptor_),
         "classname", descriptor_->name());
     } else {
       printer->Print(
-        "public interface $classname$OrBuilder\n"
-        "    extends com.google.protobuf.MessageLiteOrBuilder {\n",
+        "public interface $classname$OrBuilder extends\n"
+        "    $extra_interfaces$\n"
+        "    com.google.protobuf.MessageLiteOrBuilder {\n",
+        "extra_interfaces", ExtraMessageOrBuilderInterfaces(descriptor_),
         "classname", descriptor_->name());
     }
   }
@@ -285,7 +249,6 @@ void MessageGenerator::GenerateInterface(io::Printer* printer) {
   printer->Indent();
     for (int i = 0; i < descriptor_->field_count(); i++) {
       printer->Print("\n");
-      PrintFieldComment(printer, descriptor_->field(i));
       field_generators_.get(descriptor_->field(i))
                        .GenerateInterfaceMembers(printer);
     }
@@ -296,10 +259,10 @@ void MessageGenerator::GenerateInterface(io::Printer* printer) {
 
 // ===================================================================
 
-void MessageGenerator::Generate(io::Printer* printer) {
+void ImmutableMessageGenerator::Generate(io::Printer* printer) {
   bool is_own_file =
     descriptor_->containing_type() == NULL &&
-    descriptor_->file()->options().java_multiple_files();
+    MultipleJavaFiles(descriptor_->file(), /* immutable = */ true);
 
   WriteMessageDocComment(printer, descriptor_);
 
@@ -308,41 +271,51 @@ void MessageGenerator::Generate(io::Printer* printer) {
   if (descriptor_->extension_range_count() > 0) {
     if (HasDescriptorMethods(descriptor_)) {
       printer->Print(
-        "public $static$ final class $classname$ extends\n"
+        "public$static$final class $classname$ extends\n"
         "    com.google.protobuf.GeneratedMessage.ExtendableMessage<\n"
-        "      $classname$> implements $classname$OrBuilder {\n",
-        "static", is_own_file ? "" : "static",
-        "classname", descriptor_->name());
+        "      $classname$> implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "static", is_own_file ? " " : " static ",
+        "classname", descriptor_->name(),
+        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
       builder_type = strings::Substitute(
           "com.google.protobuf.GeneratedMessage.ExtendableBuilder<$0, ?>",
-          ClassName(descriptor_));
+          name_resolver_->GetImmutableClassName(descriptor_));
     } else {
       printer->Print(
-        "public $static$ final class $classname$ extends\n"
+        "public$static$final class $classname$ extends\n"
         "    com.google.protobuf.GeneratedMessageLite.ExtendableMessage<\n"
-        "      $classname$> implements $classname$OrBuilder {\n",
-        "static", is_own_file ? "" : "static",
-        "classname", descriptor_->name());
+        "      $classname$> implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "static", is_own_file ? " " : " static ",
+        "classname", descriptor_->name(),
+        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
       builder_type = strings::Substitute(
           "com.google.protobuf.GeneratedMessageLite.ExtendableBuilder<$0, ?>",
-          ClassName(descriptor_));
+          name_resolver_->GetImmutableClassName(descriptor_));
     }
   } else {
     if (HasDescriptorMethods(descriptor_)) {
       printer->Print(
-        "public $static$ final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessage\n"
-        "    implements $classname$OrBuilder {\n",
-        "static", is_own_file ? "" : "static",
-        "classname", descriptor_->name());
+        "public$static$final class $classname$ extends\n"
+        "    com.google.protobuf.GeneratedMessage implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "static", is_own_file ? " " : " static ",
+        "classname", descriptor_->name(),
+        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
       builder_type = "com.google.protobuf.GeneratedMessage.Builder<?>";
     } else {
       printer->Print(
-        "public $static$ final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessageLite\n"
-        "    implements $classname$OrBuilder {\n",
-        "static", is_own_file ? "" : "static",
-        "classname", descriptor_->name());
+        "public$static$final class $classname$ extends\n"
+        "    com.google.protobuf.GeneratedMessageLite implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "static", is_own_file ? " " : " static ",
+        "classname", descriptor_->name(),
+        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
       builder_type = "com.google.protobuf.GeneratedMessageLite.Builder";
     }
   }
@@ -359,8 +332,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "}\n",
     "classname", descriptor_->name(),
     "buildertype", builder_type,
-    "set_unknown_fields", HasUnknownFields(descriptor_)
-        ? "  this.unknownFields = builder.getUnknownFields();" : "");
+    "set_unknown_fields",
+    "  this.unknownFields = builder.getUnknownFields();");
   printer->Print(
     // Used when constructing the default instance, which cannot be initialized
     // immediately because it may cyclically refer to other default instances.
@@ -376,11 +349,12 @@ void MessageGenerator::Generate(io::Printer* printer) {
     "}\n"
     "\n",
     "classname", descriptor_->name(),
-    "set_default_unknown_fields", HasUnknownFields(descriptor_)
+    "set_default_unknown_fields", UseUnknownFieldSet(descriptor_)
         ? " this.unknownFields ="
-          " com.google.protobuf.UnknownFieldSet.getDefaultInstance(); " : "");
+          " com.google.protobuf.UnknownFieldSet.getDefaultInstance(); "
+        : " this.unknownFields = com.google.protobuf.ByteString.EMPTY;");
 
-  if (HasUnknownFields(descriptor_)) {
+  if (UseUnknownFieldSet(descriptor_)) {
     printer->Print(
         "private final com.google.protobuf.UnknownFieldSet unknownFields;\n"
         ""
@@ -389,6 +363,9 @@ void MessageGenerator::Generate(io::Printer* printer) {
         "    getUnknownFields() {\n"
         "  return this.unknownFields;\n"
         "}\n");
+  } else {
+    printer->Print(
+        "private final com.google.protobuf.ByteString unknownFields;\n");
   }
 
   if (HasGeneratedMethods(descriptor_)) {
@@ -400,30 +377,102 @@ void MessageGenerator::Generate(io::Printer* printer) {
 
   // Nested types
   for (int i = 0; i < descriptor_->enum_type_count(); i++) {
-    EnumGenerator(descriptor_->enum_type(i)).Generate(printer);
+    EnumGenerator(descriptor_->enum_type(i), true, context_)
+        .Generate(printer);
   }
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
-    MessageGenerator messageGenerator(descriptor_->nested_type(i));
+    ImmutableMessageGenerator messageGenerator(
+        descriptor_->nested_type(i), context_);
     messageGenerator.GenerateInterface(printer);
     messageGenerator.Generate(printer);
   }
 
-  // Integers for bit fields.
-  int totalBits = 0;
-  for (int i = 0; i < descriptor_->field_count(); i++) {
-    totalBits += field_generators_.get(descriptor_->field(i))
-        .GetNumBitsForMessage();
+  if (GenerateHasBits(descriptor_)) {
+    // Integers for bit fields.
+    int totalBits = 0;
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      totalBits += field_generators_.get(descriptor_->field(i))
+          .GetNumBitsForMessage();
+    }
+    int totalInts = (totalBits + 31) / 32;
+    for (int i = 0; i < totalInts; i++) {
+      printer->Print("private int $bit_field_name$;\n",
+        "bit_field_name", GetBitFieldName(i));
+    }
   }
-  int totalInts = (totalBits + 31) / 32;
-  for (int i = 0; i < totalInts; i++) {
-    printer->Print("private int $bit_field_name$;\n",
-      "bit_field_name", GetBitFieldName(i));
+
+  // oneof
+  map<string, string> vars;
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    vars["oneof_name"] = context_->GetOneofGeneratorInfo(
+        descriptor_->oneof_decl(i))->name;
+    vars["oneof_capitalized_name"] = context_->GetOneofGeneratorInfo(
+        descriptor_->oneof_decl(i))->capitalized_name;
+    vars["oneof_index"] = SimpleItoa(descriptor_->oneof_decl(i)->index());
+    // oneofCase_ and oneof_
+    printer->Print(vars,
+      "private int $oneof_name$Case_ = 0;\n"
+      "private java.lang.Object $oneof_name$_;\n");
+    // OneofCase enum
+    printer->Print(vars,
+      "public enum $oneof_capitalized_name$Case\n"
+      "    implements com.google.protobuf.Internal.EnumLite {\n");
+    printer->Indent();
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+      printer->Print(
+        "$field_name$($field_number$),\n",
+        "field_name",
+        ToUpper(field->name()),
+        "field_number",
+        SimpleItoa(field->number()));
+    }
+    printer->Print(
+      "$cap_oneof_name$_NOT_SET(0);\n",
+      "cap_oneof_name",
+      ToUpper(vars["oneof_name"]));
+    printer->Print(vars,
+      "private int value = 0;\n"
+      "private $oneof_capitalized_name$Case(int value) {\n"
+      "  this.value = value;\n"
+      "}\n");
+    printer->Print(vars,
+      "public static $oneof_capitalized_name$Case valueOf(int value) {\n"
+      "  switch (value) {\n");
+    for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+      const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+      printer->Print(
+        "    case $field_number$: return $field_name$;\n",
+        "field_number",
+        SimpleItoa(field->number()),
+        "field_name",
+        ToUpper(field->name()));
+    }
+    printer->Print(
+      "    case 0: return $cap_oneof_name$_NOT_SET;\n"
+      "    default: throw new java.lang.IllegalArgumentException(\n"
+      "      \"Value is undefined for this oneof enum.\");\n"
+      "  }\n"
+      "}\n"
+      "public int getNumber() {\n"
+      "  return this.value;\n"
+      "}\n",
+      "cap_oneof_name", ToUpper(vars["oneof_name"]));
+    printer->Outdent();
+    printer->Print("};\n\n");
+    // oneofCase()
+    printer->Print(vars,
+      "public $oneof_capitalized_name$Case\n"
+      "get$oneof_capitalized_name$Case() {\n"
+      "  return $oneof_capitalized_name$Case.valueOf(\n"
+      "      $oneof_name$Case_);\n"
+      "}\n"
+      "\n");
   }
 
   // Fields
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    PrintFieldComment(printer, descriptor_->field(i));
     printer->Print("public static final int $constant_name$ = $number$;\n",
       "constant_name", FieldConstantName(descriptor_->field(i)),
       "number", SimpleItoa(descriptor_->field(i)->number()));
@@ -436,9 +485,12 @@ void MessageGenerator::Generate(io::Printer* printer) {
   printer->Print("private void initFields() {\n");
   printer->Indent();
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    field_generators_.get(descriptor_->field(i))
-                     .GenerateInitializationCode(printer);
+    if (!descriptor_->field(i)->containing_oneof()) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateInitializationCode(printer);
+    }
   }
+
   printer->Outdent();
   printer->Print("}\n");
 
@@ -451,6 +503,7 @@ void MessageGenerator::Generate(io::Printer* printer) {
     GenerateEqualsAndHashCode(printer);
   }
 
+
   GenerateParseFromMethods(printer);
   GenerateBuilder(printer);
 
@@ -471,7 +524,8 @@ void MessageGenerator::Generate(io::Printer* printer) {
   // because the defaultInstance is used by the extension to lazily retrieve
   // the outer class's FileDescriptor.
   for (int i = 0; i < descriptor_->extension_count(); i++) {
-    ExtensionGenerator(descriptor_->extension(i)).Generate(printer);
+    ImmutableExtensionGenerator(descriptor_->extension(i), context_)
+        .Generate(printer);
   }
 
   printer->Outdent();
@@ -481,10 +535,10 @@ void MessageGenerator::Generate(io::Printer* printer) {
 
 // ===================================================================
 
-void MessageGenerator::
+void ImmutableMessageGenerator::
 GenerateMessageSerializationMethods(io::Printer* printer) {
   scoped_array<const FieldDescriptor*> sorted_fields(
-    SortFieldsByNumber(descriptor_));
+      SortFieldsByNumber(descriptor_));
 
   vector<const Descriptor::ExtensionRange*> sorted_extensions;
   for (int i = 0; i < descriptor_->extension_range_count(); ++i) {
@@ -513,14 +567,14 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
         "  .ExtendableMessage<$classname$>.ExtensionWriter extensionWriter =\n"
         "    newMessageSetExtensionWriter();\n",
         "lite", HasDescriptorMethods(descriptor_) ? "" : "Lite",
-        "classname", ClassName(descriptor_));
+        "classname", name_resolver_->GetImmutableClassName(descriptor_));
     } else {
       printer->Print(
         "com.google.protobuf.GeneratedMessage$lite$\n"
         "  .ExtendableMessage<$classname$>.ExtensionWriter extensionWriter =\n"
         "    newExtensionWriter();\n",
         "lite", HasDescriptorMethods(descriptor_) ? "" : "Lite",
-        "classname", ClassName(descriptor_));
+        "classname", name_resolver_->GetImmutableClassName(descriptor_));
     }
   }
 
@@ -539,7 +593,7 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     }
   }
 
-  if (HasUnknownFields(descriptor_)) {
+  if (UseUnknownFieldSet(descriptor_)) {
     if (descriptor_->options().message_set_wire_format()) {
       printer->Print(
         "getUnknownFields().writeAsMessageSetTo(output);\n");
@@ -547,6 +601,9 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
       printer->Print(
         "getUnknownFields().writeTo(output);\n");
     }
+  } else {
+    printer->Print(
+      "output.writeRawBytes(unknownFields);\n");
   }
 
   printer->Outdent();
@@ -575,7 +632,7 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     }
   }
 
-  if (HasUnknownFields(descriptor_)) {
+  if (UseUnknownFieldSet(descriptor_)) {
     if (descriptor_->options().message_set_wire_format()) {
       printer->Print(
         "size += getUnknownFields().getSerializedSizeAsMessageSet();\n");
@@ -583,6 +640,9 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
       printer->Print(
         "size += getUnknownFields().getSerializedSize();\n");
     }
+  } else {
+    printer->Print(
+      "size += unknownFields.size();\n");
   }
 
   printer->Outdent();
@@ -602,7 +662,7 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     "\n");
 }
 
-void MessageGenerator::
+void ImmutableMessageGenerator::
 GenerateParseFromMethods(io::Printer* printer) {
   // Note:  These are separate from GenerateMessageSerializationMethods()
   //   because they need to be generated even for messages that are optimized
@@ -661,15 +721,15 @@ GenerateParseFromMethods(io::Printer* printer) {
     "  return PARSER.parseFrom(input, extensionRegistry);\n"
     "}\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 }
 
-void MessageGenerator::GenerateSerializeOneField(
+void ImmutableMessageGenerator::GenerateSerializeOneField(
     io::Printer* printer, const FieldDescriptor* field) {
   field_generators_.get(field).GenerateSerializationCode(printer);
 }
 
-void MessageGenerator::GenerateSerializeOneExtensionRange(
+void ImmutableMessageGenerator::GenerateSerializeOneExtensionRange(
     io::Printer* printer, const Descriptor::ExtensionRange* range) {
   printer->Print(
     "extensionWriter.writeUntil($end$, output);\n",
@@ -678,7 +738,7 @@ void MessageGenerator::GenerateSerializeOneExtensionRange(
 
 // ===================================================================
 
-void MessageGenerator::GenerateBuilder(io::Printer* printer) {
+void ImmutableMessageGenerator::GenerateBuilder(io::Printer* printer) {
   printer->Print(
     "public static Builder newBuilder() { return Builder.create(); }\n"
     "public Builder newBuilderForType() { return newBuilder(); }\n"
@@ -687,7 +747,7 @@ void MessageGenerator::GenerateBuilder(io::Printer* printer) {
     "}\n"
     "public Builder toBuilder() { return newBuilder(this); }\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   if (HasNestedBuilders(descriptor_)) {
      printer->Print(
@@ -706,29 +766,40 @@ void MessageGenerator::GenerateBuilder(io::Printer* printer) {
       printer->Print(
         "public static final class Builder extends\n"
         "    com.google.protobuf.GeneratedMessage.ExtendableBuilder<\n"
-        "      $classname$, Builder> implements $classname$OrBuilder {\n",
-        "classname", ClassName(descriptor_));
+        "      $classname$, Builder> implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "classname", name_resolver_->GetImmutableClassName(descriptor_),
+        "extra_interfaces", ExtraBuilderInterfaces(descriptor_));
     } else {
       printer->Print(
         "public static final class Builder extends\n"
         "    com.google.protobuf.GeneratedMessageLite.ExtendableBuilder<\n"
-        "      $classname$, Builder> implements $classname$OrBuilder {\n",
-        "classname", ClassName(descriptor_));
+        "      $classname$, Builder> implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "classname", name_resolver_->GetImmutableClassName(descriptor_),
+        "extra_interfaces", ExtraBuilderInterfaces(descriptor_));
     }
   } else {
     if (HasDescriptorMethods(descriptor_)) {
       printer->Print(
         "public static final class Builder extends\n"
-        "    com.google.protobuf.GeneratedMessage.Builder<Builder>\n"
-         "   implements $classname$OrBuilder {\n",
-        "classname", ClassName(descriptor_));
+        "    com.google.protobuf.GeneratedMessage.Builder<Builder> implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "classname", name_resolver_->GetImmutableClassName(descriptor_),
+        "extra_interfaces", ExtraBuilderInterfaces(descriptor_));
     } else {
       printer->Print(
         "public static final class Builder extends\n"
         "    com.google.protobuf.GeneratedMessageLite.Builder<\n"
         "      $classname$, Builder>\n"
-        "    implements $classname$OrBuilder {\n",
-        "classname", ClassName(descriptor_));
+        "    implements\n"
+        "    $extra_interfaces$\n"
+        "    $classname$OrBuilder {\n",
+        "classname", name_resolver_->GetImmutableClassName(descriptor_),
+        "extra_interfaces", ExtraBuilderInterfaces(descriptor_));
     }
   }
   printer->Indent();
@@ -741,21 +812,54 @@ void MessageGenerator::GenerateBuilder(io::Printer* printer) {
     GenerateBuilderParsingMethods(printer);
   }
 
-  // Integers for bit fields.
-  int totalBits = 0;
-  for (int i = 0; i < descriptor_->field_count(); i++) {
-    totalBits += field_generators_.get(descriptor_->field(i))
-        .GetNumBitsForBuilder();
+  // oneof
+  map<string, string> vars;
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    vars["oneof_name"] = context_->GetOneofGeneratorInfo(
+        descriptor_->oneof_decl(i))->name;
+    vars["oneof_capitalized_name"] = context_->GetOneofGeneratorInfo(
+        descriptor_->oneof_decl(i))->capitalized_name;
+    vars["oneof_index"] = SimpleItoa(descriptor_->oneof_decl(i)->index());
+    // oneofCase_ and oneof_
+    printer->Print(vars,
+      "private int $oneof_name$Case_ = 0;\n"
+      "private java.lang.Object $oneof_name$_;\n");
+    // oneofCase() and clearOneof()
+    printer->Print(vars,
+      "public $oneof_capitalized_name$Case\n"
+      "    get$oneof_capitalized_name$Case() {\n"
+      "  return $oneof_capitalized_name$Case.valueOf(\n"
+      "      $oneof_name$Case_);\n"
+      "}\n"
+      "\n"
+      "public Builder clear$oneof_capitalized_name$() {\n"
+      "  $oneof_name$Case_ = 0;\n"
+      "  $oneof_name$_ = null;\n");
+    if (HasDescriptorMethods(descriptor_)) {
+      printer->Print("  onChanged();\n");
+    }
+    printer->Print(
+      "  return this;\n"
+      "}\n"
+      "\n");
   }
-  int totalInts = (totalBits + 31) / 32;
-  for (int i = 0; i < totalInts; i++) {
-    printer->Print("private int $bit_field_name$;\n",
-      "bit_field_name", GetBitFieldName(i));
+
+  if (GenerateHasBits(descriptor_)) {
+    // Integers for bit fields.
+    int totalBits = 0;
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      totalBits += field_generators_.get(descriptor_->field(i))
+          .GetNumBitsForBuilder();
+    }
+    int totalInts = (totalBits + 31) / 32;
+    for (int i = 0; i < totalInts; i++) {
+      printer->Print("private int $bit_field_name$;\n",
+        "bit_field_name", GetBitFieldName(i));
+    }
   }
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
     printer->Print("\n");
-    PrintFieldComment(printer, descriptor_->field(i));
     field_generators_.get(descriptor_->field(i))
                      .GenerateBuilderMembers(printer);
   }
@@ -769,7 +873,8 @@ void MessageGenerator::GenerateBuilder(io::Printer* printer) {
   printer->Print("}\n");
 }
 
-void MessageGenerator::GenerateDescriptorMethods(io::Printer* printer) {
+void ImmutableMessageGenerator::
+GenerateDescriptorMethods(io::Printer* printer) {
   if (HasDescriptorMethods(descriptor_)) {
     if (!descriptor_->options().no_standard_descriptor_accessor()) {
       printer->Print(
@@ -778,7 +883,7 @@ void MessageGenerator::GenerateDescriptorMethods(io::Printer* printer) {
         "  return $fileclass$.internal_$identifier$_descriptor;\n"
         "}\n"
         "\n",
-        "fileclass", ClassName(descriptor_->file()),
+        "fileclass", name_resolver_->GetImmutableClassName(descriptor_->file()),
         "identifier", UniqueFileScopeIdentifier(descriptor_));
     }
     printer->Print(
@@ -789,22 +894,23 @@ void MessageGenerator::GenerateDescriptorMethods(io::Printer* printer) {
       "          $classname$.class, $classname$.Builder.class);\n"
       "}\n"
       "\n",
-      "classname", ClassName(descriptor_),
-      "fileclass", ClassName(descriptor_->file()),
+      "classname", name_resolver_->GetImmutableClassName(descriptor_),
+      "fileclass", name_resolver_->GetImmutableClassName(descriptor_->file()),
       "identifier", UniqueFileScopeIdentifier(descriptor_));
   }
 }
 
 // ===================================================================
 
-void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
+void ImmutableMessageGenerator::
+GenerateCommonBuilderMethods(io::Printer* printer) {
   printer->Print(
     "// Construct using $classname$.newBuilder()\n"
     "private Builder() {\n"
     "  maybeForceBuilderInitialization();\n"
     "}\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   if (HasDescriptorMethods(descriptor_)) {
     printer->Print(
@@ -813,7 +919,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
       "  super(parent);\n"
       "  maybeForceBuilderInitialization();\n"
       "}\n",
-      "classname", ClassName(descriptor_));
+      "classname", name_resolver_->GetImmutableClassName(descriptor_));
   }
 
 
@@ -825,8 +931,10 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     printer->Indent();
     printer->Indent();
     for (int i = 0; i < descriptor_->field_count(); i++) {
-      field_generators_.get(descriptor_->field(i))
-          .GenerateFieldBuilderInitializationCode(printer);
+      if (!descriptor_->field(i)->containing_oneof()) {
+        field_generators_.get(descriptor_->field(i))
+            .GenerateFieldBuilderInitializationCode(printer);
+      }
     }
     printer->Outdent();
     printer->Outdent();
@@ -847,13 +955,23 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "\n"
     "public Builder clear() {\n"
     "  super.clear();\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   printer->Indent();
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    field_generators_.get(descriptor_->field(i))
-        .GenerateBuilderClearCode(printer);
+    if (!descriptor_->field(i)->containing_oneof()) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateBuilderClearCode(printer);
+    }
+  }
+
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print(
+      "$oneof_name$Case_ = 0;\n"
+      "$oneof_name$_ = null;\n",
+      "oneof_name", context_->GetOneofGeneratorInfo(
+          descriptor_->oneof_decl(i))->name);
   }
 
   printer->Outdent();
@@ -866,7 +984,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "  return create().mergeFrom(buildPartial());\n"
     "}\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
   if (HasDescriptorMethods(descriptor_)) {
     printer->Print(
       "public com.google.protobuf.Descriptors.Descriptor\n"
@@ -874,7 +992,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
       "  return $fileclass$.internal_$identifier$_descriptor;\n"
       "}\n"
       "\n",
-      "fileclass", ClassName(descriptor_->file()),
+      "fileclass", name_resolver_->GetImmutableClassName(descriptor_->file()),
       "identifier", UniqueFileScopeIdentifier(descriptor_));
   }
   printer->Print(
@@ -882,7 +1000,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "  return $classname$.getDefaultInstance();\n"
     "}\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   // -----------------------------------------------------------------
 
@@ -897,30 +1015,34 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "\n"
     "public $classname$ buildPartial() {\n"
     "  $classname$ result = new $classname$(this);\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   printer->Indent();
 
-  // Local vars for from and to bit fields to avoid accessing the builder and
-  // message over and over for these fields. Seems to provide a slight
-  // perforamance improvement in micro benchmark and this is also what proto1
-  // code does.
   int totalBuilderBits = 0;
   int totalMessageBits = 0;
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    const FieldGenerator& field = field_generators_.get(descriptor_->field(i));
+    const ImmutableFieldGenerator& field =
+        field_generators_.get(descriptor_->field(i));
     totalBuilderBits += field.GetNumBitsForBuilder();
     totalMessageBits += field.GetNumBitsForMessage();
   }
   int totalBuilderInts = (totalBuilderBits + 31) / 32;
   int totalMessageInts = (totalMessageBits + 31) / 32;
-  for (int i = 0; i < totalBuilderInts; i++) {
-    printer->Print("int from_$bit_field_name$ = $bit_field_name$;\n",
-      "bit_field_name", GetBitFieldName(i));
-  }
-  for (int i = 0; i < totalMessageInts; i++) {
-    printer->Print("int to_$bit_field_name$ = 0;\n",
-      "bit_field_name", GetBitFieldName(i));
+
+  if (GenerateHasBits(descriptor_)) {
+    // Local vars for from and to bit fields to avoid accessing the builder and
+    // message over and over for these fields. Seems to provide a slight
+    // perforamance improvement in micro benchmark and this is also what proto1
+    // code does.
+    for (int i = 0; i < totalBuilderInts; i++) {
+      printer->Print("int from_$bit_field_name$ = $bit_field_name$;\n",
+        "bit_field_name", GetBitFieldName(i));
+    }
+    for (int i = 0; i < totalMessageInts; i++) {
+      printer->Print("int to_$bit_field_name$ = 0;\n",
+        "bit_field_name", GetBitFieldName(i));
+    }
   }
 
   // Output generation code for each field.
@@ -928,10 +1050,18 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     field_generators_.get(descriptor_->field(i)).GenerateBuildingCode(printer);
   }
 
-  // Copy the bit field results to the generated message
-  for (int i = 0; i < totalMessageInts; i++) {
-    printer->Print("result.$bit_field_name$ = to_$bit_field_name$;\n",
-      "bit_field_name", GetBitFieldName(i));
+  if (GenerateHasBits(descriptor_)) {
+    // Copy the bit field results to the generated message
+    for (int i = 0; i < totalMessageInts; i++) {
+      printer->Print("result.$bit_field_name$ = to_$bit_field_name$;\n",
+        "bit_field_name", GetBitFieldName(i));
+    }
+  }
+
+  for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
+    printer->Print("result.$oneof_name$Case_ = $oneof_name$Case_;\n",
+                   "oneof_name", context_->GetOneofGeneratorInfo(
+                       descriptor_->oneof_decl(i))->name);
   }
 
   printer->Outdent();
@@ -945,7 +1075,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
     "  return result;\n"
     "}\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   // -----------------------------------------------------------------
 
@@ -963,7 +1093,7 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
         "  }\n"
         "}\n"
         "\n",
-        "classname", ClassName(descriptor_));
+        "classname", name_resolver_->GetImmutableClassName(descriptor_));
     }
 
     printer->Print(
@@ -971,11 +1101,48 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
       // Optimization:  If other is the default instance, we know none of its
       //   fields are set so we can skip the merge.
       "  if (other == $classname$.getDefaultInstance()) return this;\n",
-      "classname", ClassName(descriptor_));
+      "classname", name_resolver_->GetImmutableClassName(descriptor_));
     printer->Indent();
 
     for (int i = 0; i < descriptor_->field_count(); i++) {
-      field_generators_.get(descriptor_->field(i)).GenerateMergingCode(printer);
+      if (!descriptor_->field(i)->containing_oneof()) {
+        field_generators_.get(
+            descriptor_->field(i)).GenerateMergingCode(printer);
+      }
+    }
+
+    // Merge oneof fields.
+    for (int i = 0; i < descriptor_->oneof_decl_count(); ++i) {
+      printer->Print(
+        "switch (other.get$oneof_capitalized_name$Case()) {\n",
+        "oneof_capitalized_name",
+        context_->GetOneofGeneratorInfo(
+            descriptor_->oneof_decl(i))->capitalized_name);
+      printer->Indent();
+      for (int j = 0; j < descriptor_->oneof_decl(i)->field_count(); j++) {
+        const FieldDescriptor* field = descriptor_->oneof_decl(i)->field(j);
+        printer->Print(
+          "case $field_name$: {\n",
+          "field_name",
+          ToUpper(field->name()));
+        printer->Indent();
+        field_generators_.get(field).GenerateMergingCode(printer);
+        printer->Print(
+            "break;\n");
+        printer->Outdent();
+        printer->Print(
+            "}\n");
+      }
+      printer->Print(
+        "case $cap_oneof_name$_NOT_SET: {\n"
+        "  break;\n"
+        "}\n",
+        "cap_oneof_name",
+        ToUpper(context_->GetOneofGeneratorInfo(
+            descriptor_->oneof_decl(i))->name));
+      printer->Outdent();
+      printer->Print(
+          "}\n");
     }
 
     printer->Outdent();
@@ -986,9 +1153,13 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
         "  this.mergeExtensionFields(other);\n");
     }
 
-    if (HasUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_)) {
       printer->Print(
         "  this.mergeUnknownFields(other.getUnknownFields());\n");
+    } else {
+      printer->Print(
+        "  setUnknownFields(\n"
+        "      getUnknownFields().concat(other.unknownFields));\n");
     }
 
     printer->Print(
@@ -1000,7 +1171,8 @@ void MessageGenerator::GenerateCommonBuilderMethods(io::Printer* printer) {
 
 // ===================================================================
 
-void MessageGenerator::GenerateBuilderParsingMethods(io::Printer* printer) {
+void ImmutableMessageGenerator::
+GenerateBuilderParsingMethods(io::Printer* printer) {
   printer->Print(
     "public Builder mergeFrom(\n"
     "    com.google.protobuf.CodedInputStream input,\n"
@@ -1019,12 +1191,12 @@ void MessageGenerator::GenerateBuilderParsingMethods(io::Printer* printer) {
     "  }\n"
     "  return this;\n"
     "}\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 }
 
 // ===================================================================
 
-void MessageGenerator::GenerateIsInitialized(
+void ImmutableMessageGenerator::GenerateIsInitialized(
     io::Printer* printer, UseMemoization useMemoization) {
   bool memoization = useMemoization == MEMOIZE;
   if (memoization) {
@@ -1039,9 +1211,11 @@ void MessageGenerator::GenerateIsInitialized(
   printer->Indent();
 
   if (memoization) {
+    // Don't directly compare to -1 to avoid an Android x86 JIT bug.
     printer->Print(
       "byte isInitialized = memoizedIsInitialized;\n"
-      "if (isInitialized != -1) return isInitialized == 1;\n"
+      "if (isInitialized == 1) return true;\n"
+      "if (isInitialized == 0) return false;\n"
       "\n");
   }
 
@@ -1050,6 +1224,7 @@ void MessageGenerator::GenerateIsInitialized(
   //   "has" fields into a single bitfield.
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
+    const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
 
     if (field->is_required()) {
       printer->Print(
@@ -1057,7 +1232,7 @@ void MessageGenerator::GenerateIsInitialized(
         "  $memoize$\n"
         "  return false;\n"
         "}\n",
-        "name", UnderscoresToCapitalizedCamelCase(field),
+        "name", info->capitalized_name,
         "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
     }
   }
@@ -1065,6 +1240,7 @@ void MessageGenerator::GenerateIsInitialized(
   // Now check that all embedded messages are initialized.
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
+    const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
     if (GetJavaType(field) == JAVATYPE_MESSAGE &&
         HasRequiredFields(field->message_type())) {
       switch (field->label()) {
@@ -1074,8 +1250,9 @@ void MessageGenerator::GenerateIsInitialized(
              "  $memoize$\n"
              "  return false;\n"
              "}\n",
-            "type", ClassName(field->message_type()),
-            "name", UnderscoresToCapitalizedCamelCase(field),
+            "type", name_resolver_->GetImmutableClassName(
+                field->message_type()),
+            "name", info->capitalized_name,
             "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
           break;
         case FieldDescriptor::LABEL_OPTIONAL:
@@ -1086,8 +1263,9 @@ void MessageGenerator::GenerateIsInitialized(
             "    return false;\n"
             "  }\n"
             "}\n",
-            "type", ClassName(field->message_type()),
-            "name", UnderscoresToCapitalizedCamelCase(field),
+            "type", name_resolver_->GetImmutableClassName(
+                field->message_type()),
+            "name", info->capitalized_name,
             "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
           break;
         case FieldDescriptor::LABEL_REPEATED:
@@ -1098,8 +1276,9 @@ void MessageGenerator::GenerateIsInitialized(
             "    return false;\n"
             "  }\n"
             "}\n",
-            "type", ClassName(field->message_type()),
-            "name", UnderscoresToCapitalizedCamelCase(field),
+            "type", name_resolver_->GetImmutableClassName(
+                field->message_type()),
+            "name", info->capitalized_name,
             "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
           break;
       }
@@ -1130,7 +1309,21 @@ void MessageGenerator::GenerateIsInitialized(
 
 // ===================================================================
 
-void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
+namespace {
+bool CheckHasBitsForEqualsAndHashCode(const FieldDescriptor* field) {
+  if (field->is_repeated()) {
+    return false;
+  }
+  if (SupportFieldPresence(field->file())) {
+    return true;
+  }
+  return GetJavaType(field) == JAVATYPE_MESSAGE &&
+      field->containing_oneof() == NULL;
+}
+}  // namespace
+
+void ImmutableMessageGenerator::
+GenerateEqualsAndHashCode(io::Printer* printer) {
   printer->Print(
     "@java.lang.Override\n"
     "public boolean equals(final java.lang.Object obj) {\n");
@@ -1144,20 +1337,22 @@ void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
     "}\n"
     "$classname$ other = ($classname$) obj;\n"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
 
   printer->Print("boolean result = true;\n");
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
-    if (!field->is_repeated()) {
+    const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
+    bool check_has_bits = CheckHasBitsForEqualsAndHashCode(field);
+    if (check_has_bits) {
       printer->Print(
         "result = result && (has$name$() == other.has$name$());\n"
         "if (has$name$()) {\n",
-        "name", UnderscoresToCapitalizedCamelCase(field));
+        "name", info->capitalized_name);
       printer->Indent();
     }
     field_generators_.get(field).GenerateEqualsCode(printer);
-    if (!field->is_repeated()) {
+    if (check_has_bits) {
       printer->Outdent();
       printer->Print(
         "}\n");
@@ -1181,8 +1376,6 @@ void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
     "\n");
 
   printer->Print(
-    "private int memoizedHashCode = 0;\n");
-  printer->Print(
     "@java.lang.Override\n"
     "public int hashCode() {\n");
   printer->Indent();
@@ -1194,18 +1387,29 @@ void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
   printer->Outdent();
   printer->Print(
     "}\n"
-    "int hash = 41;\n"
-    "hash = (19 * hash) + getDescriptorForType().hashCode();\n");
+    "int hash = 41;\n");
+
+  if (HasDescriptorMethods(descriptor_)) {
+    printer->Print("hash = (19 * hash) + getDescriptorForType().hashCode();\n");
+  } else {
+    // Include the hash of the class so that two objects with different types
+    // but the same field values will probably have different hashes.
+    printer->Print("hash = (19 * hash) + $classname$.class.hashCode();\n",
+      "classname", name_resolver_->GetImmutableClassName(descriptor_));
+  }
+
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
-    if (!field->is_repeated()) {
+    const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
+    bool check_has_bits = CheckHasBitsForEqualsAndHashCode(field);
+    if (check_has_bits) {
       printer->Print(
         "if (has$name$()) {\n",
-        "name", UnderscoresToCapitalizedCamelCase(field));
+        "name", info->capitalized_name);
       printer->Indent();
     }
     field_generators_.get(field).GenerateHashCode(printer);
-    if (!field->is_repeated()) {
+    if (check_has_bits) {
       printer->Outdent();
       printer->Print("}\n");
     }
@@ -1216,8 +1420,15 @@ void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
         "hash = hashFields(hash, getExtensionFields());\n");
     }
   }
+
+  if (UseUnknownFieldSet(descriptor_)) {
+    printer->Print(
+      "hash = (29 * hash) + getUnknownFields().hashCode();\n");
+  } else {
+    printer->Print(
+      "hash = (29 * hash) + unknownFields.hashCode();\n");
+  }
   printer->Print(
-    "hash = (29 * hash) + getUnknownFields().hashCode();\n"
     "memoizedHashCode = hash;\n"
     "return hash;\n");
   printer->Outdent();
@@ -1228,20 +1439,22 @@ void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
 
 // ===================================================================
 
-void MessageGenerator::GenerateExtensionRegistrationCode(io::Printer* printer) {
+void ImmutableMessageGenerator::
+GenerateExtensionRegistrationCode(io::Printer* printer) {
   for (int i = 0; i < descriptor_->extension_count(); i++) {
-    ExtensionGenerator(descriptor_->extension(i))
+    ImmutableExtensionGenerator(descriptor_->extension(i), context_)
       .GenerateRegistrationCode(printer);
   }
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
-    MessageGenerator(descriptor_->nested_type(i))
+    ImmutableMessageGenerator(descriptor_->nested_type(i), context_)
       .GenerateExtensionRegistrationCode(printer);
   }
 }
 
 // ===================================================================
-void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
+void ImmutableMessageGenerator::
+GenerateParsingConstructor(io::Printer* printer) {
   scoped_array<const FieldDescriptor*> sorted_fields(
       SortFieldsByNumber(descriptor_));
 
@@ -1260,7 +1473,8 @@ void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
   // Use builder bits to track mutable repeated fields.
   int totalBuilderBits = 0;
   for (int i = 0; i < descriptor_->field_count(); i++) {
-    const FieldGenerator& field = field_generators_.get(descriptor_->field(i));
+    const ImmutableFieldGenerator& field =
+        field_generators_.get(descriptor_->field(i));
     totalBuilderBits += field.GetNumBitsForBuilder();
   }
   int totalBuilderInts = (totalBuilderBits + 31) / 32;
@@ -1269,10 +1483,17 @@ void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
       "bit_field_name", GetBitFieldName(i));
   }
 
-  if (HasUnknownFields(descriptor_)) {
+  if (UseUnknownFieldSet(descriptor_)) {
     printer->Print(
       "com.google.protobuf.UnknownFieldSet.Builder unknownFields =\n"
       "    com.google.protobuf.UnknownFieldSet.newBuilder();\n");
+  } else {
+    printer->Print(
+      "com.google.protobuf.ByteString.Output unknownFieldsOutput =\n"
+      "    com.google.protobuf.ByteString.newOutput();\n"
+      "com.google.protobuf.CodedOutputStream unknownFieldsCodedOutput =\n"
+      "    com.google.protobuf.CodedOutputStream.newInstance(\n"
+      "        unknownFieldsOutput);\n");
   }
 
   printer->Print(
@@ -1300,8 +1521,8 @@ void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
     "  }\n"
     "  break;\n"
     "}\n",
-    "unknown_fields", HasUnknownFields(descriptor_)
-        ? " unknownFields," : "");
+    "unknown_fields", UseUnknownFieldSet(descriptor_)
+        ? " unknownFields," : " unknownFieldsCodedOutput,");
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = sorted_fields[i];
@@ -1362,9 +1583,18 @@ void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
   }
 
   // Make unknown fields immutable.
-  if (HasUnknownFields(descriptor_)) {
+  if (UseUnknownFieldSet(descriptor_)) {
     printer->Print(
         "this.unknownFields = unknownFields.build();\n");
+  } else {
+    printer->Print(
+        "try {\n"
+        "  unknownFieldsCodedOutput.flush();\n"
+        "} catch (java.io.IOException e) {\n"
+        "// Should not happen\n"
+        "} finally {\n"
+        "  unknownFields = unknownFieldsOutput.toByteString();\n"
+        "}\n");
   }
 
   // Make extensions immutable.
@@ -1379,7 +1609,7 @@ void MessageGenerator::GenerateParsingConstructor(io::Printer* printer) {
 }
 
 // ===================================================================
-void MessageGenerator::GenerateParser(io::Printer* printer) {
+void ImmutableMessageGenerator::GenerateParser(io::Printer* printer) {
   printer->Print(
       "public static com.google.protobuf.Parser<$classname$> PARSER =\n"
       "    new com.google.protobuf.AbstractParser<$classname$>() {\n",
@@ -1429,6 +1659,7 @@ void MessageGenerator::GenerateParser(io::Printer* printer) {
       "classname", descriptor_->name());
 }
 
+
 }  // namespace java
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/java/java_message.h b/src/google/protobuf/compiler/java/java_message.h
index a30f0202..406910dc 100644
--- a/src/google/protobuf/compiler/java/java_message.h
+++ b/src/google/protobuf/compiler/java/java_message.h
@@ -36,11 +36,17 @@
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_MESSAGE_H__
 
 #include <string>
-#include <google/protobuf/stubs/common.h>
+#include <map>
 #include <google/protobuf/compiler/java/java_field.h>
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
   namespace io {
     class Printer;             // printer.h
   }
@@ -53,26 +59,45 @@ namespace java {
 class MessageGenerator {
  public:
   explicit MessageGenerator(const Descriptor* descriptor);
-  ~MessageGenerator();
+  virtual ~MessageGenerator();
 
   // All static variables have to be declared at the top-level of the file
   // so that we can control initialization order, which is important for
   // DescriptorProto bootstrapping to work.
-  void GenerateStaticVariables(io::Printer* printer);
+  virtual void GenerateStaticVariables(io::Printer* printer) = 0;
 
   // Output code which initializes the static variables generated by
   // GenerateStaticVariables().
-  void GenerateStaticVariableInitializers(io::Printer* printer);
+  virtual void GenerateStaticVariableInitializers(io::Printer* printer) = 0;
 
   // Generate the class itself.
-  void Generate(io::Printer* printer);
+  virtual void Generate(io::Printer* printer) = 0;
 
   // Generates the base interface that both the class and its builder implement
-  void GenerateInterface(io::Printer* printer);
+  virtual void GenerateInterface(io::Printer* printer) = 0;
 
   // Generate code to register all contained extensions with an
   // ExtensionRegistry.
-  void GenerateExtensionRegistrationCode(io::Printer* printer);
+  virtual void GenerateExtensionRegistrationCode(io::Printer* printer) = 0;
+
+ protected:
+  const Descriptor* descriptor_;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageGenerator);
+};
+
+class ImmutableMessageGenerator : public MessageGenerator {
+ public:
+  explicit ImmutableMessageGenerator(const Descriptor* descriptor,
+                                     Context* context);
+  virtual ~ImmutableMessageGenerator();
+
+  virtual void Generate(io::Printer* printer);
+  virtual void GenerateInterface(io::Printer* printer);
+  virtual void GenerateExtensionRegistrationCode(io::Printer* printer);
+  virtual void GenerateStaticVariables(io::Printer* printer);
+  virtual void GenerateStaticVariableInitializers(io::Printer* printer);
 
  private:
   enum UseMemoization {
@@ -80,6 +105,9 @@ class MessageGenerator {
     DONT_MEMOIZE
   };
 
+  void GenerateFieldAccessorTable(io::Printer* printer);
+  void GenerateFieldAccessorTableInitializer(io::Printer* printer);
+
   void GenerateMessageSerializationMethods(io::Printer* printer);
   void GenerateParseFromMethods(io::Printer* printer);
   void GenerateSerializeOneField(io::Printer* printer,
@@ -94,14 +122,14 @@ class MessageGenerator {
   void GenerateIsInitialized(io::Printer* printer,
       UseMemoization useMemoization);
   void GenerateEqualsAndHashCode(io::Printer* printer);
-
   void GenerateParser(io::Printer* printer);
   void GenerateParsingConstructor(io::Printer* printer);
 
-  const Descriptor* descriptor_;
-  FieldGeneratorMap field_generators_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
+  FieldGeneratorMap<ImmutableFieldGenerator> field_generators_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageGenerator);
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableMessageGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_message_field.cc b/src/google/protobuf/compiler/java/java_message_field.cc
index b0b284f7..80b9a382 100644
--- a/src/google/protobuf/compiler/java/java_message_field.cc
+++ b/src/google/protobuf/compiler/java/java_message_field.cc
@@ -35,9 +35,11 @@
 #include <map>
 #include <string>
 
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_message_field.h>
 #include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -49,19 +51,18 @@ namespace java {
 
 namespace {
 
-// TODO(kenton):  Factor out a "SetCommonFieldVariables()" to get rid of
-//   repeat code between this and the other field types.
 void SetMessageVariables(const FieldDescriptor* descriptor,
                          int messageBitIndex,
                          int builderBitIndex,
+                         const FieldGeneratorInfo* info,
+                         ClassNameResolver* name_resolver,
                          map<string, string>* variables) {
-  (*variables)["name"] =
-    UnderscoresToCamelCase(descriptor);
-  (*variables)["capitalized_name"] =
-    UnderscoresToCapitalizedCamelCase(descriptor);
-  (*variables)["constant_name"] = FieldConstantName(descriptor);
-  (*variables)["number"] = SimpleItoa(descriptor->number());
-  (*variables)["type"] = ClassName(descriptor->message_type());
+  SetCommonFieldVariables(descriptor, info, variables);
+
+  (*variables)["type"] =
+      name_resolver->GetImmutableClassName(descriptor->message_type());
+  (*variables)["mutable_type"] =
+      name_resolver->GetMutableClassName(descriptor->message_type());
   (*variables)["group_or_message"] =
     (GetType(descriptor) == FieldDescriptor::TYPE_GROUP) ?
     "Group" : "Message";
@@ -72,14 +73,28 @@ void SetMessageVariables(const FieldDescriptor* descriptor,
   (*variables)["on_changed"] =
       HasDescriptorMethods(descriptor->containing_type()) ? "onChanged();" : "";
 
-  // For singular messages and builders, one bit is used for the hasField bit.
-  (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
-  (*variables)["set_has_field_bit_message"] = GenerateSetBit(messageBitIndex);
+  if (SupportFieldPresence(descriptor->file())) {
+    // For singular messages and builders, one bit is used for the hasField bit.
+    (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
+    (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
+
+    // Note that these have a trailing ";".
+    (*variables)["set_has_field_bit_message"] =
+        GenerateSetBit(messageBitIndex) + ";";
+    (*variables)["set_has_field_bit_builder"] =
+        GenerateSetBit(builderBitIndex) + ";";
+    (*variables)["clear_has_field_bit_builder"] =
+        GenerateClearBit(builderBitIndex) + ";";
 
-  (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
-  (*variables)["set_has_field_bit_builder"] = GenerateSetBit(builderBitIndex);
-  (*variables)["clear_has_field_bit_builder"] =
-      GenerateClearBit(builderBitIndex);
+    (*variables)["is_field_present_message"] = GenerateGetBit(messageBitIndex);
+  } else {
+    (*variables)["set_has_field_bit_message"] = "";
+    (*variables)["set_has_field_bit_builder"] = "";
+    (*variables)["clear_has_field_bit_builder"] = "";
+
+    (*variables)["is_field_present_message"] =
+        (*variables)["name"] + "_ != null";
+  }
 
   // For repated builders, one bit is used for whether the array is immutable.
   (*variables)["get_mutable_bit_builder"] = GenerateGetBit(builderBitIndex);
@@ -103,35 +118,41 @@ void SetMessageVariables(const FieldDescriptor* descriptor,
 
 // ===================================================================
 
-MessageFieldGenerator::
-MessageFieldGenerator(const FieldDescriptor* descriptor,
+ImmutableMessageFieldGenerator::
+ImmutableMessageFieldGenerator(const FieldDescriptor* descriptor,
                       int messageBitIndex,
-                      int builderBitIndex)
+                      int builderBitIndex,
+                      Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
-  SetMessageVariables(descriptor, messageBitIndex, builderBitIndex,
-                      &variables_);
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
+    SetMessageVariables(descriptor, messageBitIndex, builderBitIndex,
+                        context->GetFieldGeneratorInfo(descriptor),
+                        name_resolver_, &variables_);
 }
 
-MessageFieldGenerator::~MessageFieldGenerator() {}
+ImmutableMessageFieldGenerator::~ImmutableMessageFieldGenerator() {}
 
-int MessageFieldGenerator::GetNumBitsForMessage() const {
+int ImmutableMessageFieldGenerator::GetNumBitsForMessage() const {
   return 1;
 }
 
-int MessageFieldGenerator::GetNumBitsForBuilder() const {
+int ImmutableMessageFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
   // TODO(jonp): In the future, consider having a method specific to the
   // interface so that builders can choose dynamically to either return a
   // message or a nested builder, so that asking for the interface doesn't
   // cause a message to ever be built.
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$boolean has$capitalized_name$();\n");
+  if (SupportFieldPresence(descriptor_->file()) ||
+      descriptor_->containing_oneof() == NULL) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$boolean has$capitalized_name$();\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$$type$ get$capitalized_name$();\n");
@@ -143,31 +164,56 @@ GenerateInterfaceMembers(io::Printer* printer) const {
   }
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $type$ $name$_;\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_message$;\n"
-    "}\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public $type$ get$capitalized_name$() {\n"
-    "  return $name$_;\n"
-    "}\n");
+  PrintExtraFieldInfo(variables_, printer);
 
-  if (HasNestedBuilders(descriptor_->containing_type())) {
+  if (SupportFieldPresence(descriptor_->file())) {
     WriteFieldDocComment(printer, descriptor_);
     printer->Print(variables_,
-      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_message$;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$ get$capitalized_name$() {\n"
       "  return $name$_;\n"
       "}\n");
+
+    if (HasNestedBuilders(descriptor_->containing_type())) {
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(variables_,
+        "$deprecation$public $type$OrBuilder "
+        "get$capitalized_name$OrBuilder() {\n"
+        "  return $name$_;\n"
+        "}\n");
+    }
+  } else {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $name$_ != null;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$ get$capitalized_name$() {\n"
+      "  return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n"
+      "}\n");
+
+    if (HasNestedBuilders(descriptor_->containing_type())) {
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(variables_,
+        "$deprecation$public $type$OrBuilder "
+        "get$capitalized_name$OrBuilder() {\n"
+        "  return get$capitalized_name$();\n"
+        "}\n");
+    }
   }
 }
 
-void MessageFieldGenerator::PrintNestedBuilderCondition(
+void ImmutableMessageFieldGenerator::PrintNestedBuilderCondition(
     io::Printer* printer,
     const char* regular_case,
     const char* nested_builder_case) const {
@@ -186,7 +232,7 @@ void MessageFieldGenerator::PrintNestedBuilderCondition(
    }
 }
 
-void MessageFieldGenerator::PrintNestedBuilderFunction(
+void ImmutableMessageFieldGenerator::PrintNestedBuilderFunction(
     io::Printer* printer,
     const char* method_prototype,
     const char* regular_case,
@@ -203,15 +249,22 @@ void MessageFieldGenerator::PrintNestedBuilderFunction(
   printer->Print("}\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   // When using nested-builders, the code initially works just like the
   // non-nested builder case. It only creates a nested builder lazily on
   // demand and then forever delegates to it after creation.
 
-  printer->Print(variables_,
-    // Used when the builder is null.
-    "private $type$ $name$_ = $type$.getDefaultInstance();\n");
+  bool support_field_presence = SupportFieldPresence(descriptor_->file());
+
+  if (support_field_presence) {
+    printer->Print(variables_,
+      // Used when the builder is null.
+      "private $type$ $name$_ = $type$.getDefaultInstance();\n");
+  } else {
+    printer->Print(variables_,
+      "private $type$ $name$_ = null;\n");
+  }
 
   if (HasNestedBuilders(descriptor_->containing_type())) {
     printer->Print(variables_,
@@ -227,17 +280,26 @@ GenerateBuilderMembers(io::Printer* printer) const {
 
   // boolean hasField()
   WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_builder$;\n"
-    "}\n");
+  if (support_field_presence) {
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_builder$;\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $name$Builder_ != null || $name$_ != null;\n"
+      "}\n");
+  }
 
   // Field getField()
   WriteFieldDocComment(printer, descriptor_);
   PrintNestedBuilderFunction(printer,
     "$deprecation$public $type$ get$capitalized_name$()",
 
-    "return $name$_;\n",
+    support_field_presence
+        ?  "return $name$_;\n"
+        : "return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n",
 
     "return $name$Builder_.getMessage();\n",
 
@@ -256,7 +318,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
 
     "$name$Builder_.setMessage(value);\n",
 
-    "$set_has_field_bit_builder$;\n"
+    "$set_has_field_bit_builder$\n"
     "return this;\n");
 
   // Field.Builder setField(Field.Builder builderForValue)
@@ -270,7 +332,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
 
     "$name$Builder_.setMessage(builderForValue.build());\n",
 
-    "$set_has_field_bit_builder$;\n"
+    "$set_has_field_bit_builder$\n"
     "return this;\n");
 
   // Field.Builder mergeField(Field value)
@@ -278,18 +340,26 @@ GenerateBuilderMembers(io::Printer* printer) const {
   PrintNestedBuilderFunction(printer,
     "$deprecation$public Builder merge$capitalized_name$($type$ value)",
 
-    "if ($get_has_field_bit_builder$ &&\n"
-    "    $name$_ != $type$.getDefaultInstance()) {\n"
-    "  $name$_ =\n"
-    "    $type$.newBuilder($name$_).mergeFrom(value).buildPartial();\n"
-    "} else {\n"
-    "  $name$_ = value;\n"
-    "}\n"
-    "$on_changed$\n",
+    support_field_presence
+        ? "if ($get_has_field_bit_builder$ &&\n"
+          "    $name$_ != $type$.getDefaultInstance()) {\n"
+          "  $name$_ =\n"
+          "    $type$.newBuilder($name$_).mergeFrom(value).buildPartial();\n"
+          "} else {\n"
+          "  $name$_ = value;\n"
+          "}\n"
+          "$on_changed$\n"
+        : "if ($name$_ != null) {\n"
+          "  $name$_ =\n"
+          "    $type$.newBuilder($name$_).mergeFrom(value).buildPartial();\n"
+          "} else {\n"
+          "  $name$_ = value;\n"
+          "}\n"
+          "$on_changed$\n",
 
     "$name$Builder_.mergeFrom(value);\n",
 
-    "$set_has_field_bit_builder$;\n"
+    "$set_has_field_bit_builder$\n"
     "return this;\n");
 
   // Field.Builder clearField()
@@ -297,19 +367,25 @@ GenerateBuilderMembers(io::Printer* printer) const {
   PrintNestedBuilderFunction(printer,
     "$deprecation$public Builder clear$capitalized_name$()",
 
-    "$name$_ = $type$.getDefaultInstance();\n"
-    "$on_changed$\n",
+    support_field_presence
+        ? "$name$_ = $type$.getDefaultInstance();\n"
+          "$on_changed$\n"
+        : "$name$_ = null;\n"
+          "$on_changed$\n",
 
-    "$name$Builder_.clear();\n",
+    support_field_presence
+        ? "$name$Builder_.clear();\n"
+        : "$name$_ = null;\n"
+          "$name$Builder_ = null;\n",
 
-    "$clear_has_field_bit_builder$;\n"
+    "$clear_has_field_bit_builder$\n"
     "return this;\n");
 
   if (HasNestedBuilders(descriptor_->containing_type())) {
     WriteFieldDocComment(printer, descriptor_);
     printer->Print(variables_,
       "$deprecation$public $type$.Builder get$capitalized_name$Builder() {\n"
-      "  $set_has_field_bit_builder$;\n"
+      "  $set_has_field_bit_builder$\n"
       "  $on_changed$\n"
       "  return get$capitalized_name$FieldBuilder().getBuilder();\n"
       "}\n");
@@ -318,8 +394,16 @@ GenerateBuilderMembers(io::Printer* printer) const {
       "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
       "  if ($name$Builder_ != null) {\n"
       "    return $name$Builder_.getMessageOrBuilder();\n"
-      "  } else {\n"
-      "    return $name$_;\n"
+      "  } else {\n");
+    if (support_field_presence) {
+      printer->Print(variables_,
+        "    return $name$_;\n");
+    } else {
+      printer->Print(variables_,
+        "    return $name$_ == null ?\n"
+        "        $type$.getDefaultInstance() : $name$_;\n");
+    }
+    printer->Print(variables_,
       "  }\n"
       "}\n");
     WriteFieldDocComment(printer, descriptor_);
@@ -330,7 +414,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
       "  if ($name$Builder_ == null) {\n"
       "    $name$Builder_ = new com.google.protobuf.SingleFieldBuilder<\n"
       "        $type$, $type$.Builder, $type$OrBuilder>(\n"
-      "            $name$_,\n"
+      "            get$capitalized_name$(),\n"
       "            getParentForChildren(),\n"
       "            isClean());\n"
       "    $name$_ = null;\n"
@@ -340,28 +424,40 @@ GenerateBuilderMembers(io::Printer* printer) const {
   }
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
-  printer->Print(variables_,
-    "get$capitalized_name$FieldBuilder();\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "get$capitalized_name$FieldBuilder();\n");
+  }
 }
 
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_ = $type$.getDefaultInstance();\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_, "$name$_ = $type$.getDefaultInstance();\n");
+  }
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
-  PrintNestedBuilderCondition(printer,
-    "$name$_ = $type$.getDefaultInstance();\n",
+  if (SupportFieldPresence(descriptor_->file())) {
+    PrintNestedBuilderCondition(printer,
+      "$name$_ = $type$.getDefaultInstance();\n",
 
-    "$name$Builder_.clear();\n");
-  printer->Print(variables_, "$clear_has_field_bit_builder$;\n");
+      "$name$Builder_.clear();\n");
+    printer->Print(variables_, "$clear_has_field_bit_builder$\n");
+  } else {
+    PrintNestedBuilderCondition(printer,
+      "$name$_ = null;\n",
+
+      "$name$_ = null;\n"
+      "$name$Builder_ = null;\n");
+  }
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (other.has$capitalized_name$()) {\n"
@@ -369,13 +465,14 @@ GenerateMergingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
-
-  printer->Print(variables_,
-      "if ($get_has_field_bit_from_local$) {\n"
-      "  $set_has_field_bit_to_local$;\n"
-      "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+        "if ($get_has_field_bit_from_local$) {\n"
+        "  $set_has_field_bit_to_local$;\n"
+        "}\n");
+  }
 
   PrintNestedBuilderCondition(printer,
     "result.$name$_ = $name$_;\n",
@@ -383,11 +480,11 @@ GenerateBuildingCode(io::Printer* printer) const {
     "result.$name$_ = $name$Builder_.build();\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$type$.Builder subBuilder = null;\n"
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  subBuilder = $name$_.toBuilder();\n"
     "}\n");
 
@@ -404,74 +501,344 @@ GenerateParsingCode(io::Printer* printer) const {
     "if (subBuilder != null) {\n"
     "  subBuilder.mergeFrom($name$_);\n"
     "  $name$_ = subBuilder.buildPartial();\n"
-    "}\n");
-  printer->Print(variables_,
-    "$set_has_field_bit_message$;\n");
+    "}\n"
+    "$set_has_field_bit_message$\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   // noop for messages.
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  output.write$group_or_message$($number$, $name$_);\n"
     "}\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
     "    .compute$group_or_message$Size($number$, $name$_);\n"
     "}\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$()\n"
     "    .equals(other.get$capitalized_name$());\n");
 }
 
-void MessageFieldGenerator::
+void ImmutableMessageFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "hash = (37 * hash) + $constant_name$;\n"
     "hash = (53 * hash) + get$capitalized_name$().hashCode();\n");
 }
 
-string MessageFieldGenerator::GetBoxedType() const {
-  return ClassName(descriptor_->message_type());
+string ImmutableMessageFieldGenerator::GetBoxedType() const {
+  return name_resolver_->GetImmutableClassName(descriptor_->message_type());
+}
+
+// ===================================================================
+
+ImmutableMessageOneofFieldGenerator::
+ImmutableMessageOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                 int messageBitIndex,
+                                 int builderBitIndex,
+                                 Context* context)
+    : ImmutableMessageFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+  const OneofGeneratorInfo* info =
+      context->GetOneofGeneratorInfo(descriptor->containing_oneof());
+  SetCommonOneofVariables(descriptor, info, &variables_);
+}
+
+ImmutableMessageOneofFieldGenerator::
+~ImmutableMessageOneofFieldGenerator() {}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  PrintExtraFieldInfo(variables_, printer);
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "     return ($type$) $oneof_name$_;\n"
+    "  }\n"
+    "  return $type$.getDefaultInstance();\n"
+    "}\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
+      "  if ($has_oneof_case_message$) {\n"
+      "     return ($type$) $oneof_name$_;\n"
+      "  }\n"
+      "  return $type$.getDefaultInstance();\n"
+      "}\n");
+  }
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  // When using nested-builders, the code initially works just like the
+  // non-nested builder case. It only creates a nested builder lazily on
+  // demand and then forever delegates to it after creation.
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    printer->Print(variables_,
+      // If this builder is non-null, it is used and the other fields are
+      // ignored.
+      "private com.google.protobuf.SingleFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> $name$Builder_;"
+      "\n");
+  }
+
+  // The comments above the methods below are based on a hypothetical
+  // field of type "Field" called "Field".
+
+  if (SupportFieldPresence(descriptor_->file())) {
+    // boolean hasField()
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+
+  // Field getField()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public $type$ get$capitalized_name$()",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  return ($type$) $oneof_name$_;\n"
+    "}\n"
+    "return $type$.getDefaultInstance();\n",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  return $name$Builder_.getMessage();\n"
+    "}\n"
+    "return $type$.getDefaultInstance();\n",
+
+    NULL);
+
+  // Field.Builder setField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$($type$ value)",
+
+    "if (value == null) {\n"
+    "  throw new NullPointerException();\n"
+    "}\n"
+    "$oneof_name$_ = value;\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.setMessage(value);\n",
+
+    "$set_oneof_case_message$;\n"
+    "return this;\n");
+
+  // Field.Builder setField(Field.Builder builderForValue)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    $type$.Builder builderForValue)",
+
+    "$oneof_name$_ = builderForValue.build();\n"
+    "$on_changed$\n",
+
+    "$name$Builder_.setMessage(builderForValue.build());\n",
+
+    "$set_oneof_case_message$;\n"
+    "return this;\n");
+
+  // Field.Builder mergeField(Field value)
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder merge$capitalized_name$($type$ value)",
+
+    "if ($has_oneof_case_message$ &&\n"
+    "    $oneof_name$_ != $type$.getDefaultInstance()) {\n"
+    "  $oneof_name$_ = $type$.newBuilder(($type$) $oneof_name$_)\n"
+    "      .mergeFrom(value).buildPartial();\n"
+    "} else {\n"
+    "  $oneof_name$_ = value;\n"
+    "}\n"
+    "$on_changed$\n",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  $name$Builder_.mergeFrom(value);\n"
+    "}\n"
+    "$name$Builder_.setMessage(value);\n",
+
+    "$set_oneof_case_message$;\n"
+    "return this;\n");
+
+  // Field.Builder clearField()
+  WriteFieldDocComment(printer, descriptor_);
+  PrintNestedBuilderFunction(printer,
+    "$deprecation$public Builder clear$capitalized_name$()",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  $clear_oneof_case_message$;\n"
+    "  $oneof_name$_ = null;\n"
+    "  $on_changed$\n"
+    "}\n",
+
+    "if ($has_oneof_case_message$) {\n"
+    "  $clear_oneof_case_message$;\n"
+    "  $oneof_name$_ = null;\n"
+    "}\n"
+    "$name$Builder_.clear();\n",
+
+    "return this;\n");
+
+  if (HasNestedBuilders(descriptor_->containing_type())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$.Builder get$capitalized_name$Builder() {\n"
+      "  return get$capitalized_name$FieldBuilder().getBuilder();\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
+      "  if (($has_oneof_case_message$) && ($name$Builder_ != null)) {\n"
+      "    return $name$Builder_.getMessageOrBuilder();\n"
+      "  } else {\n"
+      "    if ($has_oneof_case_message$) {\n"
+      "      return ($type$) $oneof_name$_;\n"
+      "    }\n"
+      "    return $type$.getDefaultInstance();\n"
+      "  }\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "private com.google.protobuf.SingleFieldBuilder<\n"
+      "    $type$, $type$.Builder, $type$OrBuilder> \n"
+      "    get$capitalized_name$FieldBuilder() {\n"
+      "  if ($name$Builder_ == null) {\n"
+      "    if (!($has_oneof_case_message$)) {\n"
+      "      $oneof_name$_ = $type$.getDefaultInstance();\n"
+      "    }\n"
+      "    $name$Builder_ = new com.google.protobuf.SingleFieldBuilder<\n"
+      "        $type$, $type$.Builder, $type$OrBuilder>(\n"
+      "            ($type$) $oneof_name$_,\n"
+      "            getParentForChildren(),\n"
+      "            isClean());\n"
+      "    $oneof_name$_ = null;\n"
+      "  }\n"
+      "  $set_oneof_case_message$;\n"
+      "  return $name$Builder_;\n"
+      "}\n");
+  }
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+
+  printer->Print(variables_,
+                 "if ($has_oneof_case_message$) {\n");
+  printer->Indent();
+
+  PrintNestedBuilderCondition(printer,
+    "result.$oneof_name$_ = $oneof_name$_;\n",
+
+    "result.$oneof_name$_ = $name$Builder_.build();\n");
+
+  printer->Outdent();
+  printer->Print("}\n");
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "merge$capitalized_name$(other.get$capitalized_name$());\n");
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "$type$.Builder subBuilder = null;\n"
+    "if ($has_oneof_case_message$) {\n"
+    "  subBuilder = (($type$) $oneof_name$_).toBuilder();\n"
+    "}\n");
+
+  if (GetType(descriptor_) == FieldDescriptor::TYPE_GROUP) {
+    printer->Print(variables_,
+      "$oneof_name$_ = input.readGroup($number$, $type$.PARSER,\n"
+      "    extensionRegistry);\n");
+  } else {
+    printer->Print(variables_,
+      "$oneof_name$_ = input.readMessage($type$.PARSER, extensionRegistry);\n");
+  }
+
+  printer->Print(variables_,
+    "if (subBuilder != null) {\n"
+    "  subBuilder.mergeFrom(($type$) $oneof_name$_);\n"
+    "  $oneof_name$_ = subBuilder.buildPartial();\n"
+    "}\n");
+  printer->Print(variables_,
+    "$set_oneof_case_message$;\n");
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  output.write$group_or_message$($number$, ($type$) $oneof_name$_);\n"
+    "}\n");
+}
+
+void ImmutableMessageOneofFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .compute$group_or_message$Size($number$, ($type$) $oneof_name$_);\n"
+    "}\n");
 }
 
 // ===================================================================
 
-RepeatedMessageFieldGenerator::
-RepeatedMessageFieldGenerator(const FieldDescriptor* descriptor,
-                              int messageBitIndex,
-                              int builderBitIndex)
+RepeatedImmutableMessageFieldGenerator::
+RepeatedImmutableMessageFieldGenerator(const FieldDescriptor* descriptor,
+                                       int messageBitIndex,
+                                       int builderBitIndex,
+                                       Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver())  {
   SetMessageVariables(descriptor, messageBitIndex, builderBitIndex,
-                      &variables_);
+                      context->GetFieldGeneratorInfo(descriptor),
+                      name_resolver_, &variables_);
 }
 
-RepeatedMessageFieldGenerator::~RepeatedMessageFieldGenerator() {}
+RepeatedImmutableMessageFieldGenerator::
+~RepeatedImmutableMessageFieldGenerator() {}
 
-int RepeatedMessageFieldGenerator::GetNumBitsForMessage() const {
+int RepeatedImmutableMessageFieldGenerator::GetNumBitsForMessage() const {
   return 0;
 }
 
-int RepeatedMessageFieldGenerator::GetNumBitsForBuilder() const {
+int RepeatedImmutableMessageFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
   // TODO(jonp): In the future, consider having methods specific to the
   // interface so that builders can choose dynamically to either return a
@@ -499,10 +866,11 @@ GenerateInterfaceMembers(io::Printer* printer) const {
   }
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private java.util.List<$type$> $name$_;\n");
+  PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public java.util.List<$type$> get$capitalized_name$List() {\n"
@@ -533,7 +901,7 @@ GenerateMembers(io::Printer* printer) const {
 
 }
 
-void RepeatedMessageFieldGenerator::PrintNestedBuilderCondition(
+void RepeatedImmutableMessageFieldGenerator::PrintNestedBuilderCondition(
     io::Printer* printer,
     const char* regular_case,
     const char* nested_builder_case) const {
@@ -552,7 +920,7 @@ void RepeatedMessageFieldGenerator::PrintNestedBuilderCondition(
    }
 }
 
-void RepeatedMessageFieldGenerator::PrintNestedBuilderFunction(
+void RepeatedImmutableMessageFieldGenerator::PrintNestedBuilderFunction(
     io::Printer* printer,
     const char* method_prototype,
     const char* regular_case,
@@ -569,7 +937,7 @@ void RepeatedMessageFieldGenerator::PrintNestedBuilderFunction(
   printer->Print("}\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   // When using nested-builders, the code initially works just like the
   // non-nested builder case. It only creates a nested builder lazily on
@@ -737,7 +1105,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "    java.lang.Iterable<? extends $type$> values)",
 
     "ensure$capitalized_name$IsMutable();\n"
-    "super.addAll(values, $name$_);\n"
+    "com.google.protobuf.AbstractMessageLite.Builder.addAll(\n"
+    "    values, $name$_);\n"
     "$on_changed$\n",
 
     "$name$Builder_.addAllMessages(values);\n",
@@ -836,18 +1205,18 @@ GenerateBuilderMembers(io::Printer* printer) const {
   }
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   printer->Print(variables_,
     "get$capitalized_name$FieldBuilder();\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = java.util.Collections.emptyList();\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   PrintNestedBuilderCondition(printer,
     "$name$_ = java.util.Collections.emptyList();\n"
@@ -856,7 +1225,7 @@ GenerateBuilderClearCode(io::Printer* printer) const {
     "$name$Builder_.clear();\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   // The code below does two optimizations (non-nested builder case):
   //   1. If the other list is empty, there's nothing to do. This ensures we
@@ -890,7 +1259,7 @@ GenerateMergingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   // The code below (non-nested builder case) ensures that the result has an
   // immutable list. If our list is immutable, we can just reuse it. If not,
@@ -905,7 +1274,7 @@ GenerateBuildingCode(io::Printer* printer) const {
     "result.$name$_ = $name$Builder_.build();\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (!$get_mutable_bit_parser$) {\n"
@@ -923,7 +1292,7 @@ GenerateParsingCode(io::Printer* printer) const {
   }
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($get_mutable_bit_parser$) {\n"
@@ -931,7 +1300,7 @@ GenerateParsingDoneCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
     "for (int i = 0; i < $name$_.size(); i++) {\n"
@@ -939,7 +1308,7 @@ GenerateSerializationCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "for (int i = 0; i < $name$_.size(); i++) {\n"
@@ -948,14 +1317,14 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$List()\n"
     "    .equals(other.get$capitalized_name$List());\n");
 }
 
-void RepeatedMessageFieldGenerator::
+void RepeatedImmutableMessageFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (get$capitalized_name$Count() > 0) {\n"
@@ -964,8 +1333,8 @@ GenerateHashCode(io::Printer* printer) const {
     "}\n");
 }
 
-string RepeatedMessageFieldGenerator::GetBoxedType() const {
-  return ClassName(descriptor_->message_type());
+string RepeatedImmutableMessageFieldGenerator::GetBoxedType() const {
+  return name_resolver_->GetImmutableClassName(descriptor_->message_type());
 }
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_message_field.h b/src/google/protobuf/compiler/java/java_message_field.h
index 5c8078a1..f7b491e5 100644
--- a/src/google/protobuf/compiler/java/java_message_field.h
+++ b/src/google/protobuf/compiler/java/java_message_field.h
@@ -41,16 +41,26 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
+}
+
+namespace protobuf {
 namespace compiler {
 namespace java {
 
-class MessageFieldGenerator : public FieldGenerator {
+class ImmutableMessageFieldGenerator : public ImmutableFieldGenerator {
  public:
-  explicit MessageFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~MessageFieldGenerator();
+  explicit ImmutableMessageFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableMessageFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -70,13 +80,13 @@ class MessageFieldGenerator : public FieldGenerator {
 
   string GetBoxedType() const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
-
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageFieldGenerator);
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
   void PrintNestedBuilderCondition(io::Printer* printer,
       const char* regular_case, const char* nested_builder_case) const;
@@ -84,15 +94,39 @@ class MessageFieldGenerator : public FieldGenerator {
       const char* method_prototype, const char* regular_case,
       const char* nested_builder_case,
       const char* trailing_code) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableMessageFieldGenerator);
 };
 
-class RepeatedMessageFieldGenerator : public FieldGenerator {
+class ImmutableMessageOneofFieldGenerator
+    : public ImmutableMessageFieldGenerator {
  public:
-  explicit RepeatedMessageFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~RepeatedMessageFieldGenerator();
+  ImmutableMessageOneofFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableMessageOneofFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableMessageOneofFieldGenerator);
+};
+
+class RepeatedImmutableMessageFieldGenerator : public ImmutableFieldGenerator {
+ public:
+  explicit RepeatedImmutableMessageFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~RepeatedImmutableMessageFieldGenerator();
+
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -112,13 +146,13 @@ class RepeatedMessageFieldGenerator : public FieldGenerator {
 
   string GetBoxedType() const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
-
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedMessageFieldGenerator);
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
   void PrintNestedBuilderCondition(io::Printer* printer,
       const char* regular_case, const char* nested_builder_case) const;
@@ -126,6 +160,9 @@ class RepeatedMessageFieldGenerator : public FieldGenerator {
       const char* method_prototype, const char* regular_case,
       const char* nested_builder_case,
       const char* trailing_code) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedImmutableMessageFieldGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_name_resolver.cc b/src/google/protobuf/compiler/java/java_name_resolver.cc
new file mode 100644
index 00000000..7f52d234
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_name_resolver.cc
@@ -0,0 +1,266 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+
+#include <map>
+#include <string>
+
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/stubs/substitute.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+namespace {
+// A suffix that will be appended to the file's outer class name if the name
+// conflicts with some other types defined in the file.
+const char* kOuterClassNameSuffix = "OuterClass";
+
+// Strip package name from a descriptor's full name.
+// For example:
+//   Full name   : foo.Bar.Baz
+//   Package name: foo
+//   After strip : Bar.Baz
+string StripPackageName(const string& full_name,
+                        const FileDescriptor* file) {
+  if (file->package().empty()) {
+    return full_name;
+  } else {
+    // Strip package name
+    return full_name.substr(file->package().size() + 1);
+  }
+}
+
+// Get the name of a message's Java class without package name prefix.
+string ClassNameWithoutPackage(const Descriptor* descriptor,
+                               bool immutable) {
+  return StripPackageName(descriptor->full_name(),
+                          descriptor->file());
+}
+
+// Get the name of an enum's Java class without package name prefix.
+string ClassNameWithoutPackage(const EnumDescriptor* descriptor,
+                               bool immutable) {
+  // Doesn't append "Mutable" for enum type's name.
+  const Descriptor* message_descriptor = descriptor->containing_type();
+  if (message_descriptor == NULL) {
+    return descriptor->name();
+  } else {
+    return ClassNameWithoutPackage(message_descriptor, immutable) +
+           "." + descriptor->name();
+  }
+}
+
+// Get the name of a service's Java class without package name prefix.
+string ClassNameWithoutPackage(const ServiceDescriptor* descriptor,
+                               bool immutable) {
+  string full_name = StripPackageName(descriptor->full_name(),
+                                      descriptor->file());
+  // We don't allow nested service definitions.
+  GOOGLE_CHECK(full_name.find('.') == string::npos);
+  return full_name;
+}
+
+// Check whether a given message or its nested types has the given class name.
+bool MessageHasConflictingClassName(const Descriptor* message,
+                                    const string& classname) {
+  if (message->name() == classname) return true;
+  for (int i = 0; i < message->nested_type_count(); ++i) {
+    if (MessageHasConflictingClassName(message->nested_type(i), classname)) {
+      return true;
+    }
+  }
+  for (int i = 0; i < message->enum_type_count(); ++i) {
+    if (message->enum_type(i)->name() == classname) {
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+ClassNameResolver::ClassNameResolver() {
+}
+
+ClassNameResolver::~ClassNameResolver() {
+}
+
+string ClassNameResolver::GetFileDefaultImmutableClassName(
+    const FileDescriptor* file) {
+  string basename;
+  string::size_type last_slash = file->name().find_last_of('/');
+  if (last_slash == string::npos) {
+    basename = file->name();
+  } else {
+    basename = file->name().substr(last_slash + 1);
+  }
+  return UnderscoresToCamelCase(StripProto(basename), true);
+}
+
+string ClassNameResolver::GetFileImmutableClassName(
+    const FileDescriptor* file) {
+  string& class_name = file_immutable_outer_class_names_[file];
+  if (class_name.empty()) {
+    if (file->options().has_java_outer_classname()) {
+      class_name = file->options().java_outer_classname();
+    } else {
+      class_name = GetFileDefaultImmutableClassName(file);
+      if (HasConflictingClassName(file, class_name)) {
+        class_name += kOuterClassNameSuffix;
+      }
+    }
+  }
+  return class_name;
+}
+
+string ClassNameResolver::GetFileClassName(const FileDescriptor* file,
+                                           bool immutable) {
+  if (immutable) {
+    return GetFileImmutableClassName(file);
+  } else {
+    return "Mutable" + GetFileImmutableClassName(file);
+  }
+}
+
+// Check whether there is any type defined in the proto file that has
+// the given class name.
+bool ClassNameResolver::HasConflictingClassName(
+    const FileDescriptor* file, const string& classname) {
+  for (int i = 0; i < file->enum_type_count(); i++) {
+    if (file->enum_type(i)->name() == classname) {
+      return true;
+    }
+  }
+  for (int i = 0; i < file->service_count(); i++) {
+    if (file->service(i)->name() == classname) {
+      return true;
+    }
+  }
+  for (int i = 0; i < file->message_type_count(); i++) {
+    if (MessageHasConflictingClassName(file->message_type(i), classname)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+string ClassNameResolver::GetDescriptorClassName(
+    const FileDescriptor* descriptor) {
+  return GetFileImmutableClassName(descriptor) + "InternalDescriptors";
+}
+
+string ClassNameResolver::GetClassName(const FileDescriptor* descriptor,
+                                       bool immutable) {
+  string result = FileJavaPackage(descriptor, immutable);
+  if (!result.empty()) result += '.';
+  result += GetFileClassName(descriptor, immutable);
+  return result;
+}
+
+// Get the full name of a Java class by prepending the Java package name
+// or outer class name.
+string ClassNameResolver::GetClassFullName(const string& name_without_package,
+                                           const FileDescriptor* file,
+                                           bool immutable,
+                                           bool multiple_files) {
+  string result;
+  if (multiple_files) {
+    result = FileJavaPackage(file, immutable);
+  } else {
+    result = GetClassName(file, immutable);
+  }
+  if (!result.empty()) {
+    result += '.';
+  }
+  result += name_without_package;
+  return result;
+}
+
+string ClassNameResolver::GetClassName(const Descriptor* descriptor,
+                                       bool immutable) {
+  return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
+                          descriptor->file(), immutable,
+                          MultipleJavaFiles(descriptor->file(), immutable));
+}
+
+string ClassNameResolver::GetClassName(const EnumDescriptor* descriptor,
+                                       bool immutable) {
+  return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
+                          descriptor->file(), immutable,
+                          MultipleJavaFiles(descriptor->file(), immutable));
+}
+
+string ClassNameResolver::GetClassName(const ServiceDescriptor* descriptor,
+                                       bool immutable) {
+  return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
+                          descriptor->file(), immutable,
+                          MultipleJavaFiles(descriptor->file(), immutable));
+}
+
+// Get the Java Class style full name of a message.
+string ClassNameResolver::GetJavaClassFullName(
+    const string& name_without_package,
+    const FileDescriptor* file,
+    bool immutable) {
+  string result;
+  if (MultipleJavaFiles(file, immutable)) {
+    result = FileJavaPackage(file, immutable);
+    if (!result.empty()) result += '.';
+  } else {
+    result = GetClassName(file, immutable);
+    if (!result.empty()) result += '$';
+  }
+  result += StringReplace(name_without_package, ".", "$", true);
+  return result;
+}
+
+string ClassNameResolver::GetExtensionIdentifierName(
+    const FieldDescriptor* descriptor, bool immutable) {
+  return GetClassName(descriptor->containing_type(), immutable) + "." +
+         descriptor->name();
+}
+
+
+string ClassNameResolver::GetJavaImmutableClassName(
+    const Descriptor* descriptor) {
+  return GetJavaClassFullName(
+      ClassNameWithoutPackage(descriptor, true),
+      descriptor->file(), true);
+}
+
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_name_resolver.h b/src/google/protobuf/compiler/java/java_name_resolver.h
new file mode 100644
index 00000000..1d3e185c
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_name_resolver.h
@@ -0,0 +1,124 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_NAME_RESOLVER_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_NAME_RESOLVER_H__
+
+#include <map>
+#include <string>
+
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+class Descriptor;
+class EnumDescriptor;
+class FieldDescriptor;
+class FileDescriptor;
+class ServiceDescriptor;
+
+namespace compiler {
+namespace java {
+
+// Used to get the Java class related names for a given descriptor. It caches
+// the results to avoid redundant calculation across multiple name queries.
+// Thread-safety note: This class is *not* thread-safe.
+class ClassNameResolver {
+ public:
+  ClassNameResolver();
+  ~ClassNameResolver();
+
+  // Gets the unqualified outer class name for the file.
+  string GetFileClassName(const FileDescriptor* file, bool immutable);
+  // Gets the unqualified immutable outer class name of a file.
+  string GetFileImmutableClassName(const FileDescriptor* file);
+  // Gets the unqualified default immutable outer class name of a file
+  // (converted from the proto file's name).
+  string GetFileDefaultImmutableClassName(const FileDescriptor* file);
+
+  // Check whether there is any type defined in the proto file that has
+  // the given class name.
+  bool HasConflictingClassName(const FileDescriptor* file,
+                               const string& classname);
+
+  // Gets the name of the outer class that holds descriptor information.
+  // Descriptors are shared between immutable messages and mutable messages.
+  // Since both of them are generated optionally, the descriptors need to be
+  // put in another common place.
+  string GetDescriptorClassName(const FileDescriptor* file);
+
+  // Gets the fully-qualified class name corresponding to the given descriptor.
+  string GetClassName(const Descriptor* descriptor, bool immutable);
+  string GetClassName(const EnumDescriptor* descriptor, bool immutable);
+  string GetClassName(const ServiceDescriptor* descriptor, bool immutable);
+  string GetClassName(const FileDescriptor* descriptor, bool immutable);
+
+  template<class DescriptorType>
+  string GetImmutableClassName(const DescriptorType* descriptor) {
+    return GetClassName(descriptor, true);
+  }
+  template<class DescriptorType>
+  string GetMutableClassName(const DescriptorType* descriptor) {
+    return GetClassName(descriptor, false);
+  }
+
+  // Gets the fully qualified name of an extension identifier.
+  string GetExtensionIdentifierName(const FieldDescriptor* descriptor,
+                                    bool immutable);
+
+  // Gets the fully qualified name for generated classes in Java convention.
+  // Nested classes will be separated using '$' instead of '.'
+  // For example:
+  //   com.package.OuterClass$OuterMessage$InnerMessage
+  string GetJavaImmutableClassName(const Descriptor* descriptor);
+ private:
+  // Get the full name of a Java class by prepending the Java package name
+  // or outer class name.
+  string GetClassFullName(const string& name_without_package,
+                          const FileDescriptor* file,
+                          bool immutable,
+                          bool multiple_files);
+  // Get the Java Class style full name of a message.
+  string GetJavaClassFullName(
+      const string& name_without_package,
+      const FileDescriptor* file,
+      bool immutable);
+  // Caches the result to provide better performance.
+  map<const FileDescriptor*, string> file_immutable_outer_class_names_;
+
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ClassNameResolver);
+};
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_NAME_RESOLVER_H__
diff --git a/src/google/protobuf/compiler/java/java_plugin_unittest.cc b/src/google/protobuf/compiler/java/java_plugin_unittest.cc
index ccc94c9d..52577626 100644
--- a/src/google/protobuf/compiler/java/java_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/java/java_plugin_unittest.cc
@@ -34,6 +34,8 @@
 //   It seemed like parameterizing it would add more complexity than it is
 //   worth.
 
+#include <memory>
+
 #include <google/protobuf/compiler/java/java_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
 #include <google/protobuf/io/zero_copy_stream.h>
@@ -71,7 +73,7 @@ class TestGenerator : public CodeGenerator {
   void TryInsert(const string& filename, const string& insertion_point,
                  GeneratorContext* context) const {
     scoped_ptr<io::ZeroCopyOutputStream> output(
-      context->OpenForInsert(filename, insertion_point));
+        context->OpenForInsert(filename, insertion_point));
     io::Printer printer(output.get(), '$');
     printer.Print("// inserted $name$\n", "name", insertion_point);
   }
@@ -81,16 +83,16 @@ class TestGenerator : public CodeGenerator {
 // not verify that they are correctly-placed; that would require actually
 // compiling the output which is a bit more than I care to do for this test.
 TEST(JavaPluginTest, PluginTest) {
-  File::WriteStringToFileOrDie(
-      "syntax = \"proto2\";\n"
-      "package foo;\n"
-      "option java_package = \"\";\n"
-      "option java_outer_classname = \"Test\";\n"
-      "message Bar {\n"
-      "  message Baz {}\n"
-      "}\n"
-      "enum Qux { BLAH = 1; }\n",
-      TestTempDir() + "/test.proto");
+  GOOGLE_CHECK_OK(File::SetContents(TestTempDir() + "/test.proto",
+                             "syntax = \"proto2\";\n"
+                             "package foo;\n"
+                             "option java_package = \"\";\n"
+                             "option java_outer_classname = \"Test\";\n"
+                             "message Bar {\n"
+                             "  message Baz {}\n"
+                             "}\n"
+                             "enum Qux { BLAH = 1; }\n",
+                             true));
 
   google::protobuf::compiler::CommandLineInterface cli;
   cli.SetInputsAreProtoPathRelative(true);
diff --git a/src/google/protobuf/compiler/java/java_primitive_field.cc b/src/google/protobuf/compiler/java/java_primitive_field.cc
index 0140e23f..031a1293 100644
--- a/src/google/protobuf/compiler/java/java_primitive_field.cc
+++ b/src/google/protobuf/compiler/java/java_primitive_field.cc
@@ -35,10 +35,12 @@
 #include <map>
 #include <string>
 
-#include <google/protobuf/compiler/java/java_primitive_field.h>
-#include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/compiler/java/java_primitive_field.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -73,107 +75,25 @@ const char* PrimitiveTypeName(JavaType type) {
   return NULL;
 }
 
-bool IsReferenceType(JavaType type) {
-  switch (type) {
-    case JAVATYPE_INT    : return false;
-    case JAVATYPE_LONG   : return false;
-    case JAVATYPE_FLOAT  : return false;
-    case JAVATYPE_DOUBLE : return false;
-    case JAVATYPE_BOOLEAN: return false;
-    case JAVATYPE_STRING : return true;
-    case JAVATYPE_BYTES  : return true;
-    case JAVATYPE_ENUM   : return true;
-    case JAVATYPE_MESSAGE: return true;
-
-    // No default because we want the compiler to complain if any new
-    // JavaTypes are added.
-  }
-
-  GOOGLE_LOG(FATAL) << "Can't get here.";
-  return false;
-}
-
-const char* GetCapitalizedType(const FieldDescriptor* field) {
-  switch (GetType(field)) {
-    case FieldDescriptor::TYPE_INT32   : return "Int32"   ;
-    case FieldDescriptor::TYPE_UINT32  : return "UInt32"  ;
-    case FieldDescriptor::TYPE_SINT32  : return "SInt32"  ;
-    case FieldDescriptor::TYPE_FIXED32 : return "Fixed32" ;
-    case FieldDescriptor::TYPE_SFIXED32: return "SFixed32";
-    case FieldDescriptor::TYPE_INT64   : return "Int64"   ;
-    case FieldDescriptor::TYPE_UINT64  : return "UInt64"  ;
-    case FieldDescriptor::TYPE_SINT64  : return "SInt64"  ;
-    case FieldDescriptor::TYPE_FIXED64 : return "Fixed64" ;
-    case FieldDescriptor::TYPE_SFIXED64: return "SFixed64";
-    case FieldDescriptor::TYPE_FLOAT   : return "Float"   ;
-    case FieldDescriptor::TYPE_DOUBLE  : return "Double"  ;
-    case FieldDescriptor::TYPE_BOOL    : return "Bool"    ;
-    case FieldDescriptor::TYPE_STRING  : return "String"  ;
-    case FieldDescriptor::TYPE_BYTES   : return "Bytes"   ;
-    case FieldDescriptor::TYPE_ENUM    : return "Enum"    ;
-    case FieldDescriptor::TYPE_GROUP   : return "Group"   ;
-    case FieldDescriptor::TYPE_MESSAGE : return "Message" ;
-
-    // No default because we want the compiler to complain if any new
-    // types are added.
-  }
-
-  GOOGLE_LOG(FATAL) << "Can't get here.";
-  return NULL;
-}
-
-// For encodings with fixed sizes, returns that size in bytes.  Otherwise
-// returns -1.
-int FixedSize(FieldDescriptor::Type type) {
-  switch (type) {
-    case FieldDescriptor::TYPE_INT32   : return -1;
-    case FieldDescriptor::TYPE_INT64   : return -1;
-    case FieldDescriptor::TYPE_UINT32  : return -1;
-    case FieldDescriptor::TYPE_UINT64  : return -1;
-    case FieldDescriptor::TYPE_SINT32  : return -1;
-    case FieldDescriptor::TYPE_SINT64  : return -1;
-    case FieldDescriptor::TYPE_FIXED32 : return WireFormatLite::kFixed32Size;
-    case FieldDescriptor::TYPE_FIXED64 : return WireFormatLite::kFixed64Size;
-    case FieldDescriptor::TYPE_SFIXED32: return WireFormatLite::kSFixed32Size;
-    case FieldDescriptor::TYPE_SFIXED64: return WireFormatLite::kSFixed64Size;
-    case FieldDescriptor::TYPE_FLOAT   : return WireFormatLite::kFloatSize;
-    case FieldDescriptor::TYPE_DOUBLE  : return WireFormatLite::kDoubleSize;
-
-    case FieldDescriptor::TYPE_BOOL    : return WireFormatLite::kBoolSize;
-    case FieldDescriptor::TYPE_ENUM    : return -1;
-
-    case FieldDescriptor::TYPE_STRING  : return -1;
-    case FieldDescriptor::TYPE_BYTES   : return -1;
-    case FieldDescriptor::TYPE_GROUP   : return -1;
-    case FieldDescriptor::TYPE_MESSAGE : return -1;
-
-    // No default because we want the compiler to complain if any new
-    // types are added.
-  }
-  GOOGLE_LOG(FATAL) << "Can't get here.";
-  return -1;
-}
-
 void SetPrimitiveVariables(const FieldDescriptor* descriptor,
                            int messageBitIndex,
                            int builderBitIndex,
+                           const FieldGeneratorInfo* info,
+                           ClassNameResolver* name_resolver,
                            map<string, string>* variables) {
-  (*variables)["name"] =
-    UnderscoresToCamelCase(descriptor);
-  (*variables)["capitalized_name"] =
-    UnderscoresToCapitalizedCamelCase(descriptor);
-  (*variables)["constant_name"] = FieldConstantName(descriptor);
-  (*variables)["number"] = SimpleItoa(descriptor->number());
+  SetCommonFieldVariables(descriptor, info, variables);
+
   (*variables)["type"] = PrimitiveTypeName(GetJavaType(descriptor));
   (*variables)["boxed_type"] = BoxedPrimitiveTypeName(GetJavaType(descriptor));
   (*variables)["field_type"] = (*variables)["type"];
   (*variables)["field_list_type"] = "java.util.List<" +
       (*variables)["boxed_type"] + ">";
   (*variables)["empty_list"] = "java.util.Collections.emptyList()";
-  (*variables)["default"] = DefaultValue(descriptor);
+  (*variables)["default"] = ImmutableDefaultValue(descriptor, name_resolver);
   (*variables)["default_init"] = IsDefaultValueJavaDefault(descriptor) ?
-      "" : ("= " + DefaultValue(descriptor));
-  (*variables)["capitalized_type"] = GetCapitalizedType(descriptor);
+      "" : ("= " + ImmutableDefaultValue(descriptor, name_resolver));
+  (*variables)["capitalized_type"] =
+      GetCapitalizedType(descriptor, /* immutable = */ true);
   (*variables)["tag"] = SimpleItoa(WireFormat::MakeTag(descriptor));
   (*variables)["tag_size"] = SimpleItoa(
       WireFormat::TagSize(descriptor->number(), GetType(descriptor)));
@@ -196,14 +116,33 @@ void SetPrimitiveVariables(const FieldDescriptor* descriptor,
   (*variables)["on_changed"] =
       HasDescriptorMethods(descriptor->containing_type()) ? "onChanged();" : "";
 
-  // For singular messages and builders, one bit is used for the hasField bit.
-  (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
-  (*variables)["set_has_field_bit_message"] = GenerateSetBit(messageBitIndex);
+  if (SupportFieldPresence(descriptor->file())) {
+    // For singular messages and builders, one bit is used for the hasField bit.
+    (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
+    (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
 
-  (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
-  (*variables)["set_has_field_bit_builder"] = GenerateSetBit(builderBitIndex);
-  (*variables)["clear_has_field_bit_builder"] =
-      GenerateClearBit(builderBitIndex);
+    // Note that these have a trailing ";".
+    (*variables)["set_has_field_bit_message"] =
+        GenerateSetBit(messageBitIndex) + ";";
+    (*variables)["set_has_field_bit_builder"] =
+        GenerateSetBit(builderBitIndex) + ";";
+    (*variables)["clear_has_field_bit_builder"] =
+        GenerateClearBit(builderBitIndex) + ";";
+
+    (*variables)["is_field_present_message"] = GenerateGetBit(messageBitIndex);
+  } else {
+    (*variables)["set_has_field_bit_message"] = "";
+    (*variables)["set_has_field_bit_builder"] = "";
+    (*variables)["clear_has_field_bit_builder"] = "";
+
+    if (descriptor->type() == FieldDescriptor::TYPE_BYTES) {
+      (*variables)["is_field_present_message"] =
+          "!" + (*variables)["name"] + "_.isEmpty()";
+    } else {
+      (*variables)["is_field_present_message"] =
+          (*variables)["name"] + "_ != " + (*variables)["default"];
+    }
+  }
 
   // For repated builders, one bit is used for whether the array is immutable.
   (*variables)["get_mutable_bit_builder"] = GenerateGetBit(builderBitIndex);
@@ -227,46 +166,53 @@ void SetPrimitiveVariables(const FieldDescriptor* descriptor,
 
 // ===================================================================
 
-PrimitiveFieldGenerator::
-PrimitiveFieldGenerator(const FieldDescriptor* descriptor,
-                        int messageBitIndex,
-                        int builderBitIndex)
+ImmutablePrimitiveFieldGenerator::
+ImmutablePrimitiveFieldGenerator(const FieldDescriptor* descriptor,
+                                 int messageBitIndex,
+                                 int builderBitIndex,
+                                 Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
   SetPrimitiveVariables(descriptor, messageBitIndex, builderBitIndex,
-                        &variables_);
+                        context->GetFieldGeneratorInfo(descriptor),
+                        name_resolver_, &variables_);
 }
 
-PrimitiveFieldGenerator::~PrimitiveFieldGenerator() {}
+ImmutablePrimitiveFieldGenerator::~ImmutablePrimitiveFieldGenerator() {}
 
-int PrimitiveFieldGenerator::GetNumBitsForMessage() const {
+int ImmutablePrimitiveFieldGenerator::GetNumBitsForMessage() const {
   return 1;
 }
 
-int PrimitiveFieldGenerator::GetNumBitsForBuilder() const {
+int ImmutablePrimitiveFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$boolean has$capitalized_name$();\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$boolean has$capitalized_name$();\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$$type$ get$capitalized_name$();\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $field_type$ $name$_;\n");
-
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_message$;\n"
-    "}\n");
+  PrintExtraFieldInfo(variables_, printer);
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_message$;\n"
+      "}\n");
+  }
 
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -275,16 +221,18 @@ GenerateMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $field_type$ $name$_ $default_init$;\n");
 
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_builder$;\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_builder$;\n"
+      "}\n");
+  }
 
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -296,7 +244,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "$deprecation$public Builder set$capitalized_name$($type$ value) {\n"
     "$null_check$"
-    "  $set_has_field_bit_builder$;\n"
+    "  $set_has_field_bit_builder$\n"
     "  $name$_ = value;\n"
     "  $on_changed$\n"
     "  return this;\n"
@@ -305,7 +253,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public Builder clear$capitalized_name$() {\n"
-    "  $clear_has_field_bit_builder$;\n");
+    "  $clear_has_field_bit_builder$\n");
   JavaType type = GetJavaType(descriptor_);
   if (type == JAVATYPE_STRING || type == JAVATYPE_BYTES) {
     // The default value is not a simple literal so we want to avoid executing
@@ -322,70 +270,80 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for primitives
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = $default$;\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$name$_ = $default$;\n"
-    "$clear_has_field_bit_builder$;\n");
+    "$clear_has_field_bit_builder$\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "if (other.has$capitalized_name$()) {\n"
-    "  set$capitalized_name$(other.get$capitalized_name$());\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "if (other.has$capitalized_name$()) {\n"
+      "  set$capitalized_name$(other.get$capitalized_name$());\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "if (other.get$capitalized_name$() != $default$) {\n"
+      "  set$capitalized_name$(other.get$capitalized_name$());\n"
+      "}\n");
+  }
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "if ($get_has_field_bit_from_local$) {\n"
+      "  $set_has_field_bit_to_local$;\n"
+      "}\n");
+  }
   printer->Print(variables_,
-    "if ($get_has_field_bit_from_local$) {\n"
-    "  $set_has_field_bit_to_local$;\n"
-    "}\n"
     "result.$name$_ = $name$_;\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "$set_has_field_bit_message$;\n"
+    "$set_has_field_bit_message$\n"
     "$name$_ = input.read$capitalized_type$();\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   // noop for primitives.
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  output.write$capitalized_type$($number$, $name$_);\n"
     "}\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
     "    .compute$capitalized_type$Size($number$, $name$_);\n"
     "}\n");
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   switch (GetJavaType(descriptor_)) {
     case JAVATYPE_INT:
@@ -398,14 +356,18 @@ GenerateEqualsCode(io::Printer* printer) const {
 
     case JAVATYPE_FLOAT:
       printer->Print(variables_,
-        "result = result && (Float.floatToIntBits(get$capitalized_name$())"
-        "    == Float.floatToIntBits(other.get$capitalized_name$()));\n");
+        "result = result && (\n"
+        "    java.lang.Float.floatToIntBits(get$capitalized_name$())\n"
+        "    == java.lang.Float.floatToIntBits(\n"
+        "        other.get$capitalized_name$()));\n");
       break;
 
     case JAVATYPE_DOUBLE:
       printer->Print(variables_,
-        "result = result && (Double.doubleToLongBits(get$capitalized_name$())"
-        "    == Double.doubleToLongBits(other.get$capitalized_name$()));\n");
+        "result = result && (\n"
+        "    java.lang.Double.doubleToLongBits(get$capitalized_name$())\n"
+        "    == java.lang.Double.doubleToLongBits(\n"
+        "        other.get$capitalized_name$()));\n");
       break;
 
     case JAVATYPE_STRING:
@@ -423,7 +385,7 @@ GenerateEqualsCode(io::Printer* printer) const {
   }
 }
 
-void PrimitiveFieldGenerator::
+void ImmutablePrimitiveFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "hash = (37 * hash) + $constant_name$;\n");
@@ -435,24 +397,26 @@ GenerateHashCode(io::Printer* printer) const {
 
     case JAVATYPE_LONG:
       printer->Print(variables_,
-        "hash = (53 * hash) + hashLong(get$capitalized_name$());\n");
+        "hash = (53 * hash) + com.google.protobuf.Internal.hashLong(\n"
+        "    get$capitalized_name$());\n");
       break;
 
     case JAVATYPE_BOOLEAN:
       printer->Print(variables_,
-        "hash = (53 * hash) + hashBoolean(get$capitalized_name$());\n");
+        "hash = (53 * hash) + com.google.protobuf.Internal.hashBoolean(\n"
+        "    get$capitalized_name$());\n");
       break;
 
     case JAVATYPE_FLOAT:
       printer->Print(variables_,
-        "hash = (53 * hash) + Float.floatToIntBits(\n"
+        "hash = (53 * hash) + java.lang.Float.floatToIntBits(\n"
         "    get$capitalized_name$());\n");
       break;
 
     case JAVATYPE_DOUBLE:
       printer->Print(variables_,
-        "hash = (53 * hash) + hashLong(\n"
-        "    Double.doubleToLongBits(get$capitalized_name$()));\n");
+        "hash = (53 * hash) + com.google.protobuf.Internal.hashLong(\n"
+        "    java.lang.Double.doubleToLongBits(get$capitalized_name$()));\n");
       break;
 
     case JAVATYPE_STRING:
@@ -469,33 +433,157 @@ GenerateHashCode(io::Printer* printer) const {
   }
 }
 
-string PrimitiveFieldGenerator::GetBoxedType() const {
+string ImmutablePrimitiveFieldGenerator::GetBoxedType() const {
   return BoxedPrimitiveTypeName(GetJavaType(descriptor_));
 }
 
 // ===================================================================
 
-RepeatedPrimitiveFieldGenerator::
-RepeatedPrimitiveFieldGenerator(const FieldDescriptor* descriptor,
-                                int messageBitIndex,
-                                int builderBitIndex)
+ImmutablePrimitiveOneofFieldGenerator::
+ImmutablePrimitiveOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                 int messageBitIndex,
+                                 int builderBitIndex,
+                                 Context* context)
+    : ImmutablePrimitiveFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+  const OneofGeneratorInfo* info =
+      context->GetOneofGeneratorInfo(descriptor->containing_oneof());
+  SetCommonOneofVariables(descriptor, info, &variables_);
+}
+
+ImmutablePrimitiveOneofFieldGenerator::
+~ImmutablePrimitiveOneofFieldGenerator() {}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  PrintExtraFieldInfo(variables_, printer);
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($boxed_type$) $oneof_name$_;\n"
+    "  }\n"
+    "  return $default$;\n"
+    "}\n");
+}
+
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public $type$ get$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    return ($boxed_type$) $oneof_name$_;\n"
+    "  }\n"
+    "  return $default$;\n"
+    "}\n");
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder set$capitalized_name$($type$ value) {\n"
+    "$null_check$"
+    "  $set_oneof_case_message$;\n"
+    "  $oneof_name$_ = value;\n"
+    "  $on_changed$\n"
+    "  return this;\n"
+    "}\n");
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder clear$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    $clear_oneof_case_message$;\n"
+    "    $oneof_name$_ = null;\n"
+    "    $on_changed$\n"
+    "  }\n"
+    "  return this;\n"
+    "}\n");
+}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  result.$oneof_name$_ = $oneof_name$_;\n"
+    "}\n");
+}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "set$capitalized_name$(other.get$capitalized_name$());\n");
+}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "$set_oneof_case_message$;\n"
+    "$oneof_name$_ = input.read$capitalized_type$();\n");
+}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  output.write$capitalized_type$(\n"
+    "      $number$, ($type$)(($boxed_type$) $oneof_name$_));\n"
+    "}\n");
+}
+
+void ImmutablePrimitiveOneofFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .compute$capitalized_type$Size(\n"
+    "        $number$, ($type$)(($boxed_type$) $oneof_name$_));\n"
+    "}\n");
+}
+
+// ===================================================================
+
+RepeatedImmutablePrimitiveFieldGenerator::
+RepeatedImmutablePrimitiveFieldGenerator(const FieldDescriptor* descriptor,
+                                         int messageBitIndex,
+                                         int builderBitIndex,
+                                         Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
   SetPrimitiveVariables(descriptor, messageBitIndex, builderBitIndex,
-                        &variables_);
+                        context->GetFieldGeneratorInfo(descriptor),
+                        name_resolver_, &variables_);
 }
 
-RepeatedPrimitiveFieldGenerator::~RepeatedPrimitiveFieldGenerator() {}
+RepeatedImmutablePrimitiveFieldGenerator::
+~RepeatedImmutablePrimitiveFieldGenerator() {}
 
-int RepeatedPrimitiveFieldGenerator::GetNumBitsForMessage() const {
+int RepeatedImmutablePrimitiveFieldGenerator::GetNumBitsForMessage() const {
   return 0;
 }
 
-int RepeatedPrimitiveFieldGenerator::GetNumBitsForBuilder() const {
+int RepeatedImmutablePrimitiveFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -509,10 +597,11 @@ GenerateInterfaceMembers(io::Printer* printer) const {
 }
 
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private $field_list_type$ $name$_;\n");
+  PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public java.util.List<$boxed_type$>\n"
@@ -537,7 +626,7 @@ GenerateMembers(io::Printer* printer) const {
   }
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   // One field is the list and the bit field keeps track of whether the
   // list is immutable. If it's immutable, the invariant is that it must
@@ -603,7 +692,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "$deprecation$public Builder addAll$capitalized_name$(\n"
     "    java.lang.Iterable<? extends $boxed_type$> values) {\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  super.addAll(values, $name$_);\n"
+    "  com.google.protobuf.AbstractMessageLite.Builder.addAll(\n"
+    "      values, $name$_);\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -617,24 +707,24 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for primitives
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = $empty_list$;\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$name$_ = $empty_list$;\n"
     "$clear_mutable_bit_builder$;\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   // The code below does two optimizations:
   //   1. If the other list is empty, there's nothing to do. This ensures we
@@ -654,7 +744,7 @@ GenerateMergingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   // The code below ensures that the result has an immutable list. If our
   // list is immutable, we can just reuse it. If not, we make it immutable.
@@ -666,7 +756,7 @@ GenerateBuildingCode(io::Printer* printer) const {
     "result.$name$_ = $name$_;\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (!$get_mutable_bit_parser$) {\n"
@@ -676,7 +766,7 @@ GenerateParsingCode(io::Printer* printer) const {
     "$name$_.add(input.read$capitalized_type$());\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateParsingCodeFromPacked(io::Printer* printer) const {
   printer->Print(variables_,
     "int length = input.readRawVarint32();\n"
@@ -691,7 +781,7 @@ GenerateParsingCodeFromPacked(io::Printer* printer) const {
     "input.popLimit(limit);\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($get_mutable_bit_parser$) {\n"
@@ -699,7 +789,7 @@ GenerateParsingDoneCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   if (descriptor_->options().packed()) {
     printer->Print(variables_,
@@ -718,7 +808,7 @@ GenerateSerializationCode(io::Printer* printer) const {
   }
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "{\n"
@@ -761,14 +851,14 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print("}\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$List()\n"
     "    .equals(other.get$capitalized_name$List());\n");
 }
 
-void RepeatedPrimitiveFieldGenerator::
+void RepeatedImmutablePrimitiveFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (get$capitalized_name$Count() > 0) {\n"
@@ -777,7 +867,7 @@ GenerateHashCode(io::Printer* printer) const {
     "}\n");
 }
 
-string RepeatedPrimitiveFieldGenerator::GetBoxedType() const {
+string RepeatedImmutablePrimitiveFieldGenerator::GetBoxedType() const {
   return BoxedPrimitiveTypeName(GetJavaType(descriptor_));
 }
 
diff --git a/src/google/protobuf/compiler/java/java_primitive_field.h b/src/google/protobuf/compiler/java/java_primitive_field.h
index 1b5b6d95..489e1b20 100644
--- a/src/google/protobuf/compiler/java/java_primitive_field.h
+++ b/src/google/protobuf/compiler/java/java_primitive_field.h
@@ -41,16 +41,26 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
+}
+
+namespace protobuf {
 namespace compiler {
 namespace java {
 
-class PrimitiveFieldGenerator : public FieldGenerator {
+class ImmutablePrimitiveFieldGenerator : public ImmutableFieldGenerator {
  public:
-  explicit PrimitiveFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~PrimitiveFieldGenerator();
+  explicit ImmutablePrimitiveFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutablePrimitiveFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -70,22 +80,47 @@ class PrimitiveFieldGenerator : public FieldGenerator {
 
   string GetBoxedType() const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(PrimitiveFieldGenerator);
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutablePrimitiveFieldGenerator);
+};
+
+class ImmutablePrimitiveOneofFieldGenerator
+    : public ImmutablePrimitiveFieldGenerator {
+ public:
+  ImmutablePrimitiveOneofFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutablePrimitiveOneofFieldGenerator();
+
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutablePrimitiveOneofFieldGenerator);
 };
 
-class RepeatedPrimitiveFieldGenerator : public FieldGenerator {
+class RepeatedImmutablePrimitiveFieldGenerator
+    : public ImmutableFieldGenerator {
  public:
-  explicit RepeatedPrimitiveFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~RepeatedPrimitiveFieldGenerator();
+  explicit RepeatedImmutablePrimitiveFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  virtual ~RepeatedImmutablePrimitiveFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -111,8 +146,10 @@ class RepeatedPrimitiveFieldGenerator : public FieldGenerator {
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedPrimitiveFieldGenerator);
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedImmutablePrimitiveFieldGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_service.cc b/src/google/protobuf/compiler/java/java_service.cc
index bcd80359..aa5c5231 100644
--- a/src/google/protobuf/compiler/java/java_service.cc
+++ b/src/google/protobuf/compiler/java/java_service.cc
@@ -33,8 +33,11 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <google/protobuf/compiler/java/java_service.h>
+
+#include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -49,8 +52,17 @@ ServiceGenerator::ServiceGenerator(const ServiceDescriptor* descriptor)
 
 ServiceGenerator::~ServiceGenerator() {}
 
-void ServiceGenerator::Generate(io::Printer* printer) {
-  bool is_own_file = descriptor_->file()->options().java_multiple_files();
+// ===================================================================
+ImmutableServiceGenerator::ImmutableServiceGenerator(
+    const ServiceDescriptor* descriptor, Context* context)
+    : ServiceGenerator(descriptor), context_(context),
+    name_resolver_(context->GetNameResolver()) {}
+
+ImmutableServiceGenerator::~ImmutableServiceGenerator() {}
+
+void ImmutableServiceGenerator::Generate(io::Printer* printer) {
+  bool is_own_file =
+    MultipleJavaFiles(descriptor_->file(), /* immutable = */ true);
   WriteServiceDocComment(printer, descriptor_);
   printer->Print(
     "public $static$ abstract class $classname$\n"
@@ -77,7 +89,7 @@ void ServiceGenerator::Generate(io::Printer* printer) {
     "    getDescriptor() {\n"
     "  return $file$.getDescriptor().getServices().get($index$);\n"
     "}\n",
-    "file", ClassName(descriptor_->file()),
+    "file", name_resolver_->GetImmutableClassName(descriptor_->file()),
     "index", SimpleItoa(descriptor_->index()));
   GenerateGetDescriptorForType(printer);
 
@@ -98,7 +110,8 @@ void ServiceGenerator::Generate(io::Printer* printer) {
   printer->Print("}\n\n");
 }
 
-void ServiceGenerator::GenerateGetDescriptorForType(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateGetDescriptorForType(
+    io::Printer* printer) {
   printer->Print(
     "public final com.google.protobuf.Descriptors.ServiceDescriptor\n"
     "    getDescriptorForType() {\n"
@@ -106,7 +119,7 @@ void ServiceGenerator::GenerateGetDescriptorForType(io::Printer* printer) {
     "}\n");
 }
 
-void ServiceGenerator::GenerateInterface(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateInterface(io::Printer* printer) {
   printer->Print("public interface Interface {\n");
   printer->Indent();
   GenerateAbstractMethods(printer);
@@ -114,7 +127,7 @@ void ServiceGenerator::GenerateInterface(io::Printer* printer) {
   printer->Print("}\n\n");
 }
 
-void ServiceGenerator::GenerateNewReflectiveServiceMethod(
+void ImmutableServiceGenerator::GenerateNewReflectiveServiceMethod(
     io::Printer* printer) {
   printer->Print(
     "public static com.google.protobuf.Service newReflectiveService(\n"
@@ -141,7 +154,7 @@ void ServiceGenerator::GenerateNewReflectiveServiceMethod(
   printer->Print("}\n\n");
 }
 
-void ServiceGenerator::GenerateNewReflectiveBlockingServiceMethod(
+void ImmutableServiceGenerator::GenerateNewReflectiveBlockingServiceMethod(
     io::Printer* printer) {
   printer->Print(
     "public static com.google.protobuf.BlockingService\n"
@@ -162,7 +175,7 @@ void ServiceGenerator::GenerateNewReflectiveBlockingServiceMethod(
   printer->Print("}\n\n");
 }
 
-void ServiceGenerator::GenerateAbstractMethods(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateAbstractMethods(io::Printer* printer) {
   for (int i = 0; i < descriptor_->method_count(); i++) {
     const MethodDescriptor* method = descriptor_->method(i);
     WriteMethodDocComment(printer, method);
@@ -171,7 +184,7 @@ void ServiceGenerator::GenerateAbstractMethods(io::Printer* printer) {
   }
 }
 
-void ServiceGenerator::GenerateCallMethod(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateCallMethod(io::Printer* printer) {
   printer->Print(
     "\n"
     "public final void callMethod(\n"
@@ -194,8 +207,10 @@ void ServiceGenerator::GenerateCallMethod(io::Printer* printer) {
     map<string, string> vars;
     vars["index"] = SimpleItoa(i);
     vars["method"] = UnderscoresToCamelCase(method);
-    vars["input"] = ClassName(method->input_type());
-    vars["output"] = ClassName(method->output_type());
+    vars["input"] = name_resolver_->GetImmutableClassName(
+        method->input_type());
+    vars["output"] = name_resolver_->GetImmutableClassName(
+        method->output_type());
     printer->Print(vars,
       "case $index$:\n"
       "  this.$method$(controller, ($input$)request,\n"
@@ -217,7 +232,8 @@ void ServiceGenerator::GenerateCallMethod(io::Printer* printer) {
     "\n");
 }
 
-void ServiceGenerator::GenerateCallBlockingMethod(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateCallBlockingMethod(
+    io::Printer* printer) {
   printer->Print(
     "\n"
     "public final com.google.protobuf.Message callBlockingMethod(\n"
@@ -239,8 +255,10 @@ void ServiceGenerator::GenerateCallBlockingMethod(io::Printer* printer) {
     map<string, string> vars;
     vars["index"] = SimpleItoa(i);
     vars["method"] = UnderscoresToCamelCase(method);
-    vars["input"] = ClassName(method->input_type());
-    vars["output"] = ClassName(method->output_type());
+    vars["input"] = name_resolver_->GetImmutableClassName(
+        method->input_type());
+    vars["output"] = name_resolver_->GetImmutableClassName(
+        method->output_type());
     printer->Print(vars,
       "case $index$:\n"
       "  return impl.$method$(controller, ($input$)request);\n");
@@ -259,7 +277,7 @@ void ServiceGenerator::GenerateCallBlockingMethod(io::Printer* printer) {
     "\n");
 }
 
-void ServiceGenerator::GenerateGetPrototype(RequestOrResponse which,
+void ImmutableServiceGenerator::GenerateGetPrototype(RequestOrResponse which,
                                             io::Printer* printer) {
   /*
    * TODO(cpovirk): The exception message says "Service.foo" when it may be
@@ -283,7 +301,7 @@ void ServiceGenerator::GenerateGetPrototype(RequestOrResponse which,
     const MethodDescriptor* method = descriptor_->method(i);
     map<string, string> vars;
     vars["index"] = SimpleItoa(i);
-    vars["type"] = ClassName(
+    vars["type"] = name_resolver_->GetImmutableClassName(
       (which == REQUEST) ? method->input_type() : method->output_type());
     printer->Print(vars,
       "case $index$:\n"
@@ -303,7 +321,7 @@ void ServiceGenerator::GenerateGetPrototype(RequestOrResponse which,
     "\n");
 }
 
-void ServiceGenerator::GenerateStub(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateStub(io::Printer* printer) {
   printer->Print(
     "public static Stub newStub(\n"
     "    com.google.protobuf.RpcChannel channel) {\n"
@@ -312,7 +330,7 @@ void ServiceGenerator::GenerateStub(io::Printer* printer) {
     "\n"
     "public static final class Stub extends $classname$ implements Interface {"
     "\n",
-    "classname", ClassName(descriptor_));
+    "classname", name_resolver_->GetImmutableClassName(descriptor_));
   printer->Indent();
 
   printer->Print(
@@ -335,7 +353,8 @@ void ServiceGenerator::GenerateStub(io::Printer* printer) {
 
     map<string, string> vars;
     vars["index"] = SimpleItoa(i);
-    vars["output"] = ClassName(method->output_type());
+    vars["output"] = name_resolver_->GetImmutableClassName(
+        method->output_type());
     printer->Print(vars,
       "channel.callMethod(\n"
       "  getDescriptor().getMethods().get($index$),\n"
@@ -357,7 +376,7 @@ void ServiceGenerator::GenerateStub(io::Printer* printer) {
     "\n");
 }
 
-void ServiceGenerator::GenerateBlockingStub(io::Printer* printer) {
+void ImmutableServiceGenerator::GenerateBlockingStub(io::Printer* printer) {
   printer->Print(
     "public static BlockingInterface newBlockingStub(\n"
     "    com.google.protobuf.BlockingRpcChannel channel) {\n"
@@ -399,7 +418,8 @@ void ServiceGenerator::GenerateBlockingStub(io::Printer* printer) {
 
     map<string, string> vars;
     vars["index"] = SimpleItoa(i);
-    vars["output"] = ClassName(method->output_type());
+    vars["output"] = name_resolver_->GetImmutableClassName(
+        method->output_type());
     printer->Print(vars,
       "return ($output$) channel.callBlockingMethod(\n"
       "  getDescriptor().getMethods().get($index$),\n"
@@ -417,13 +437,13 @@ void ServiceGenerator::GenerateBlockingStub(io::Printer* printer) {
   printer->Print("}\n");
 }
 
-void ServiceGenerator::GenerateMethodSignature(io::Printer* printer,
+void ImmutableServiceGenerator::GenerateMethodSignature(io::Printer* printer,
                                                const MethodDescriptor* method,
                                                IsAbstract is_abstract) {
   map<string, string> vars;
   vars["name"] = UnderscoresToCamelCase(method);
-  vars["input"] = ClassName(method->input_type());
-  vars["output"] = ClassName(method->output_type());
+  vars["input"] = name_resolver_->GetImmutableClassName(method->input_type());
+  vars["output"] = name_resolver_->GetImmutableClassName(method->output_type());
   vars["abstract"] = (is_abstract == IS_ABSTRACT) ? "abstract" : "";
   printer->Print(vars,
     "public $abstract$ void $name$(\n"
@@ -432,13 +452,13 @@ void ServiceGenerator::GenerateMethodSignature(io::Printer* printer,
     "    com.google.protobuf.RpcCallback<$output$> done)");
 }
 
-void ServiceGenerator::GenerateBlockingMethodSignature(
+void ImmutableServiceGenerator::GenerateBlockingMethodSignature(
     io::Printer* printer,
     const MethodDescriptor* method) {
   map<string, string> vars;
   vars["method"] = UnderscoresToCamelCase(method);
-  vars["input"] = ClassName(method->input_type());
-  vars["output"] = ClassName(method->output_type());
+  vars["input"] = name_resolver_->GetImmutableClassName(method->input_type());
+  vars["output"] = name_resolver_->GetImmutableClassName(method->output_type());
   printer->Print(vars,
     "\n"
     "public $output$ $method$(\n"
diff --git a/src/google/protobuf/compiler/java/java_service.h b/src/google/protobuf/compiler/java/java_service.h
index e07eebf7..0d52325e 100644
--- a/src/google/protobuf/compiler/java/java_service.h
+++ b/src/google/protobuf/compiler/java/java_service.h
@@ -40,8 +40,14 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;            // context.h
+      class ClassNameResolver;  // name_resolver.h
+    }
+  }
   namespace io {
-    class Printer;             // printer.h
+    class Printer;              // printer.h
   }
 }
 
@@ -52,9 +58,27 @@ namespace java {
 class ServiceGenerator {
  public:
   explicit ServiceGenerator(const ServiceDescriptor* descriptor);
-  ~ServiceGenerator();
+  virtual ~ServiceGenerator();
+
+  virtual void Generate(io::Printer* printer) = 0;
+
+  enum RequestOrResponse { REQUEST, RESPONSE };
+  enum IsAbstract { IS_ABSTRACT, IS_CONCRETE };
+
+ protected:
+  const ServiceDescriptor* descriptor_;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ServiceGenerator);
+};
 
-  void Generate(io::Printer* printer);
+class ImmutableServiceGenerator : public ServiceGenerator {
+ public:
+  explicit ImmutableServiceGenerator(const ServiceDescriptor* descriptor,
+                                     Context* context);
+  virtual ~ImmutableServiceGenerator();
+
+  virtual void Generate(io::Printer* printer);
 
  private:
 
@@ -80,7 +104,6 @@ class ServiceGenerator {
   void GenerateCallBlockingMethod(io::Printer* printer);
 
   // Generate the implementations of Service.get{Request,Response}Prototype().
-  enum RequestOrResponse { REQUEST, RESPONSE };
   void GenerateGetPrototype(RequestOrResponse which, io::Printer* printer);
 
   // Generate a stub implementation of the service.
@@ -88,7 +111,6 @@ class ServiceGenerator {
 
   // Generate a method signature, possibly abstract, without body or trailing
   // semicolon.
-  enum IsAbstract { IS_ABSTRACT, IS_CONCRETE };
   void GenerateMethodSignature(io::Printer* printer,
                                const MethodDescriptor* method,
                                IsAbstract is_abstract);
@@ -100,9 +122,9 @@ class ServiceGenerator {
   void GenerateBlockingMethodSignature(io::Printer* printer,
                                        const MethodDescriptor* method);
 
-  const ServiceDescriptor* descriptor_;
-
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ServiceGenerator);
+  Context* context_;
+  ClassNameResolver* name_resolver_;
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableServiceGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/java/java_shared_code_generator.cc b/src/google/protobuf/compiler/java/java_shared_code_generator.cc
new file mode 100644
index 00000000..c9f80abf
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_shared_code_generator.cc
@@ -0,0 +1,223 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: xiaofeng@google.com (Feng Xiao)
+
+#include <google/protobuf/compiler/java/java_shared_code_generator.h>
+
+#include <memory>
+
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/compiler/code_generator.h>
+#include <google/protobuf/io/printer.h>
+#include <google/protobuf/io/zero_copy_stream.h>
+#include <google/protobuf/descriptor.pb.h>
+#include <google/protobuf/descriptor.h>
+#include <google/protobuf/stubs/strutil.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+SharedCodeGenerator::SharedCodeGenerator(const FileDescriptor* file)
+  : name_resolver_(new ClassNameResolver), file_(file) {
+}
+
+SharedCodeGenerator::~SharedCodeGenerator() {
+}
+
+void SharedCodeGenerator::Generate(GeneratorContext* context,
+                                   vector<string>* file_list) {
+  string java_package = FileJavaPackage(file_);
+  string package_dir = JavaPackageToDir(java_package);
+
+  if (HasDescriptorMethods(file_)) {
+    // Generate descriptors.
+    string classname = name_resolver_->GetDescriptorClassName(file_);
+    string filename = package_dir + classname + ".java";
+    file_list->push_back(filename);
+    scoped_ptr<io::ZeroCopyOutputStream> output(context->Open(filename));
+    scoped_ptr<io::Printer> printer(new io::Printer(output.get(), '$'));
+
+    printer->Print(
+      "// Generated by the protocol buffer compiler.  DO NOT EDIT!\n"
+      "// source: $filename$\n"
+      "\n",
+      "filename", file_->name());
+    if (!java_package.empty()) {
+      printer->Print(
+        "package $package$;\n"
+        "\n",
+        "package", java_package);
+    }
+    printer->Print(
+      "public final class $classname$ {\n",
+      "classname", classname);
+    printer->Indent();
+    GenerateDescriptors(printer.get());
+    printer->Outdent();
+    printer->Print(
+      "}\n");
+
+    printer.reset();
+    output.reset();
+  }
+}
+
+
+void SharedCodeGenerator::GenerateDescriptors(io::Printer* printer) {
+  // Embed the descriptor.  We simply serialize the entire FileDescriptorProto
+  // and embed it as a string literal, which is parsed and built into real
+  // descriptors at initialization time.  We unfortunately have to put it in
+  // a string literal, not a byte array, because apparently using a literal
+  // byte array causes the Java compiler to generate *instructions* to
+  // initialize each and every byte of the array, e.g. as if you typed:
+  //   b[0] = 123; b[1] = 456; b[2] = 789;
+  // This makes huge bytecode files and can easily hit the compiler's internal
+  // code size limits (error "code to large").  String literals are apparently
+  // embedded raw, which is what we want.
+  FileDescriptorProto file_proto;
+  file_->CopyTo(&file_proto);
+
+
+  string file_data;
+  file_proto.SerializeToString(&file_data);
+
+  printer->Print(
+    "public static com.google.protobuf.Descriptors.FileDescriptor\n"
+    "    descriptor;\n"
+    "static {\n"
+    "  java.lang.String[] descriptorData = {\n");
+  printer->Indent();
+  printer->Indent();
+
+  // Only write 40 bytes per line.
+  static const int kBytesPerLine = 40;
+  for (int i = 0; i < file_data.size(); i += kBytesPerLine) {
+    if (i > 0) {
+      // Every 400 lines, start a new string literal, in order to avoid the
+      // 64k length limit.
+      if (i % 400 == 0) {
+        printer->Print(",\n");
+      } else {
+        printer->Print(" +\n");
+      }
+    }
+    printer->Print("\"$data$\"",
+      "data", CEscape(file_data.substr(i, kBytesPerLine)));
+  }
+
+  printer->Outdent();
+  printer->Print("\n};\n");
+
+  // -----------------------------------------------------------------
+  // Create the InternalDescriptorAssigner.
+
+  printer->Print(
+    "com.google.protobuf.Descriptors.FileDescriptor."
+    "InternalDescriptorAssigner assigner =\n"
+    "    new com.google.protobuf.Descriptors.FileDescriptor."
+    "    InternalDescriptorAssigner() {\n"
+    "      public com.google.protobuf.ExtensionRegistry assignDescriptors(\n"
+    "          com.google.protobuf.Descriptors.FileDescriptor root) {\n"
+    "        descriptor = root;\n"
+    // Custom options will be handled when immutable messages' outer class is
+    // loaded. Here we just return null and let custom options be unknown
+    // fields.
+    "        return null;\n"
+    "      }\n"
+    "    };\n");
+
+  // -----------------------------------------------------------------
+  // Find out all dependencies.
+  vector<pair<string, string> > dependencies;
+  for (int i = 0; i < file_->dependency_count(); i++) {
+    if (ShouldIncludeDependency(file_->dependency(i))) {
+      string filename = file_->dependency(i)->name();
+      string classname = FileJavaPackage(file_->dependency(i)) + "." +
+                         name_resolver_->GetDescriptorClassName(
+                             file_->dependency(i));
+      dependencies.push_back(make_pair(filename, classname));
+    }
+  }
+
+  // -----------------------------------------------------------------
+  // Invoke internalBuildGeneratedFileFrom() to build the file.
+  printer->Print(
+    "com.google.protobuf.Descriptors.FileDescriptor\n"
+    "  .internalBuildGeneratedFileFrom(descriptorData,\n");
+
+  printer->Print(
+    "    $classname$.class,\n"
+    "    new java.lang.String[] {\n",
+    "classname", name_resolver_->GetDescriptorClassName(file_));
+  for (int i = 0; i < dependencies.size(); i++) {
+    const string& dependency = dependencies[i].second;
+    printer->Print(
+        // Here we load the dependency FileDescriptors lazily via Java
+        // reflection. This is to avoid breaking proto1 targets who have
+        // genproto dependencies for which we can't generate the descriptor
+        // class. They will compile fine but when users try to call reflection
+        // functions upon them it will fail. Users will have to get rid of
+        // genproto dependencies before they can use proto2 reflection on
+        // proto1 messages.
+        "      \"$dependency$\",\n",
+        "dependency", dependency);
+  }
+
+  printer->Print(
+      "    }, new java.lang.String[] {\n");
+
+  for (int i = 0; i < dependencies.size(); i++) {
+    const string& filename = dependencies[i].first;
+    printer->Print(
+        "      \"$filename$\",\n",
+        "filename", filename);
+  }
+
+  printer->Print(
+    "    }, assigner);\n");
+
+  printer->Outdent();
+  printer->Print(
+    "}\n");
+}
+
+bool SharedCodeGenerator::ShouldIncludeDependency(
+    const FileDescriptor* descriptor) {
+  return true;
+}
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_shared_code_generator.h b/src/google/protobuf/compiler/java/java_shared_code_generator.h
new file mode 100644
index 00000000..c5457bf1
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_shared_code_generator.h
@@ -0,0 +1,91 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Author: xiaofeng@google.com (Feng Xiao)
+//
+// Generators that generate shared code between immutable API and mutable API.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_SHARED_CODE_GENERATOR_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_SHARED_CODE_GENERATOR_H__
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <google/protobuf/stubs/common.h>
+
+namespace google {
+namespace protobuf {
+  class FileDescriptor;        // descriptor.h
+  namespace compiler {
+    class GeneratorContext;    // code_generator.h
+    namespace java {
+      class ClassNameResolver;       // name_resolver.h
+    }
+  }
+  namespace io {
+    class Printer;             // printer.h
+  }
+}
+
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+// A generator that generates code that are shared between immutable API
+// and mutable API. Currently only descriptors are shared.
+class SharedCodeGenerator {
+ public:
+  explicit SharedCodeGenerator(const FileDescriptor* file);
+  ~SharedCodeGenerator();
+
+  void Generate(GeneratorContext* generator_context,
+                vector<string>* file_list);
+
+ private:
+  void GenerateDescriptors(io::Printer* printer);
+
+  // Returns whether the dependency should be included in the output file.
+  // Always returns true for opensource, but used internally at Google to help
+  // improve compatibility with version 1 of protocol buffers.
+  bool ShouldIncludeDependency(const FileDescriptor* descriptor);
+
+  scoped_ptr<ClassNameResolver> name_resolver_;
+  const FileDescriptor* file_;
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(SharedCodeGenerator);
+};
+
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_SHARED_CODE_GENERATOR_H__
diff --git a/src/google/protobuf/compiler/java/java_string_field.cc b/src/google/protobuf/compiler/java/java_string_field.cc
index 4815663b..374e1d4e 100644
--- a/src/google/protobuf/compiler/java/java_string_field.cc
+++ b/src/google/protobuf/compiler/java/java_string_field.cc
@@ -36,10 +36,12 @@
 #include <map>
 #include <string>
 
-#include <google/protobuf/compiler/java/java_string_field.h>
-#include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/stubs/common.h>
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_doc_comment.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/compiler/java/java_string_field.h>
 #include <google/protobuf/io/printer.h>
 #include <google/protobuf/wire_format.h>
 #include <google/protobuf/stubs/strutil.h>
@@ -57,17 +59,16 @@ namespace {
 void SetPrimitiveVariables(const FieldDescriptor* descriptor,
                            int messageBitIndex,
                            int builderBitIndex,
+                           const FieldGeneratorInfo* info,
+                           ClassNameResolver* name_resolver,
                            map<string, string>* variables) {
-  (*variables)["name"] =
-    UnderscoresToCamelCase(descriptor);
-  (*variables)["capitalized_name"] =
-    UnderscoresToCapitalizedCamelCase(descriptor);
-  (*variables)["constant_name"] = FieldConstantName(descriptor);
-  (*variables)["number"] = SimpleItoa(descriptor->number());
+  SetCommonFieldVariables(descriptor, info, variables);
+
   (*variables)["empty_list"] = "com.google.protobuf.LazyStringArrayList.EMPTY";
 
-  (*variables)["default"] = DefaultValue(descriptor);
-  (*variables)["default_init"] = ("= " + DefaultValue(descriptor));
+  (*variables)["default"] = ImmutableDefaultValue(descriptor, name_resolver);
+  (*variables)["default_init"] =
+      "= " + ImmutableDefaultValue(descriptor, name_resolver);
   (*variables)["capitalized_type"] = "String";
   (*variables)["tag"] = SimpleItoa(WireFormat::MakeTag(descriptor));
   (*variables)["tag_size"] = SimpleItoa(
@@ -84,16 +85,30 @@ void SetPrimitiveVariables(const FieldDescriptor* descriptor,
   (*variables)["on_changed"] =
       HasDescriptorMethods(descriptor->containing_type()) ? "onChanged();" : "";
 
-  // For singular messages and builders, one bit is used for the hasField bit.
-  (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
-  (*variables)["set_has_field_bit_message"] = GenerateSetBit(messageBitIndex);
+  if (SupportFieldPresence(descriptor->file())) {
+    // For singular messages and builders, one bit is used for the hasField bit.
+    (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
+    (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
+
+    // Note that these have a trailing ";".
+    (*variables)["set_has_field_bit_message"] =
+        GenerateSetBit(messageBitIndex) + ";";
+    (*variables)["set_has_field_bit_builder"] =
+        GenerateSetBit(builderBitIndex) + ";";
+    (*variables)["clear_has_field_bit_builder"] =
+        GenerateClearBit(builderBitIndex) + ";";
 
-  (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
-  (*variables)["set_has_field_bit_builder"] = GenerateSetBit(builderBitIndex);
-  (*variables)["clear_has_field_bit_builder"] =
-      GenerateClearBit(builderBitIndex);
+    (*variables)["is_field_present_message"] = GenerateGetBit(messageBitIndex);
+  } else {
+    (*variables)["set_has_field_bit_message"] = "";
+    (*variables)["set_has_field_bit_builder"] = "";
+    (*variables)["clear_has_field_bit_builder"] = "";
 
-  // For repated builders, one bit is used for whether the array is immutable.
+    (*variables)["is_field_present_message"] =
+        "!get" + (*variables)["capitalized_name"] + "Bytes().isEmpty()";
+  }
+
+  // For repeated builders, one bit is used for whether the array is immutable.
   (*variables)["get_mutable_bit_builder"] = GenerateGetBit(builderBitIndex);
   (*variables)["set_mutable_bit_builder"] = GenerateSetBit(builderBitIndex);
   (*variables)["clear_mutable_bit_builder"] = GenerateClearBit(builderBitIndex);
@@ -111,27 +126,34 @@ void SetPrimitiveVariables(const FieldDescriptor* descriptor,
       GenerateSetBitToLocal(messageBitIndex);
 }
 
+bool CheckUtf8(const FieldDescriptor* descriptor) {
+  return descriptor->file()->options().java_string_check_utf8();
+}
+
 }  // namespace
 
 // ===================================================================
 
-StringFieldGenerator::
-StringFieldGenerator(const FieldDescriptor* descriptor,
-                     int messageBitIndex,
-                     int builderBitIndex)
+ImmutableStringFieldGenerator::
+ImmutableStringFieldGenerator(const FieldDescriptor* descriptor,
+                              int messageBitIndex,
+                              int builderBitIndex,
+                              Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
   SetPrimitiveVariables(descriptor, messageBitIndex, builderBitIndex,
-                        &variables_);
+                        context->GetFieldGeneratorInfo(descriptor),
+                        name_resolver_, &variables_);
 }
 
-StringFieldGenerator::~StringFieldGenerator() {}
+ImmutableStringFieldGenerator::~ImmutableStringFieldGenerator() {}
 
-int StringFieldGenerator::GetNumBitsForMessage() const {
+int ImmutableStringFieldGenerator::GetNumBitsForMessage() const {
   return 1;
 }
 
-int StringFieldGenerator::GetNumBitsForBuilder() const {
+int ImmutableStringFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
@@ -167,11 +189,13 @@ int StringFieldGenerator::GetNumBitsForBuilder() const {
 // For single fields, the logic for this is done inside the generated code. For
 // repeated fields, the logic is done in LazyStringArrayList and
 // UnmodifiableLazyStringList.
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$boolean has$capitalized_name$();\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$boolean has$capitalized_name$();\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$java.lang.String get$capitalized_name$();\n");
@@ -181,15 +205,19 @@ GenerateInterfaceMembers(io::Printer* printer) const {
     "    get$capitalized_name$Bytes();\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private java.lang.Object $name$_;\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_message$;\n"
-    "}\n");
+  PrintExtraFieldInfo(variables_, printer);
+
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_message$;\n"
+      "}\n");
+  }
 
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -200,10 +228,17 @@ GenerateMembers(io::Printer* printer) const {
     "  } else {\n"
     "    com.google.protobuf.ByteString bs = \n"
     "        (com.google.protobuf.ByteString) ref;\n"
-    "    java.lang.String s = bs.toStringUtf8();\n"
-    "    if (bs.isValidUtf8()) {\n"
-    "      $name$_ = s;\n"
-    "    }\n"
+      "    java.lang.String s = bs.toStringUtf8();\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "    $name$_ = s;\n");
+  } else {
+    printer->Print(variables_,
+      "    if (bs.isValidUtf8()) {\n"
+      "      $name$_ = s;\n"
+      "    }\n");
+  }
+  printer->Print(variables_,
     "    return s;\n"
     "  }\n"
     "}\n");
@@ -224,24 +259,36 @@ GenerateMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private java.lang.Object $name$_ $default_init$;\n");
-  WriteFieldDocComment(printer, descriptor_);
-  printer->Print(variables_,
-    "$deprecation$public boolean has$capitalized_name$() {\n"
-    "  return $get_has_field_bit_builder$;\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $get_has_field_bit_builder$;\n"
+      "}\n");
+  }
 
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public java.lang.String get$capitalized_name$() {\n"
     "  java.lang.Object ref = $name$_;\n"
     "  if (!(ref instanceof java.lang.String)) {\n"
-    "    java.lang.String s = ((com.google.protobuf.ByteString) ref)\n"
-    "        .toStringUtf8();\n"
-    "    $name$_ = s;\n"
+    "    com.google.protobuf.ByteString bs =\n"
+    "        (com.google.protobuf.ByteString) ref;\n"
+    "    java.lang.String s = bs.toStringUtf8();\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "    $name$_ = s;\n");
+  } else {
+    printer->Print(variables_,
+      "    if (bs.isValidUtf8()) {\n"
+      "      $name$_ = s;\n"
+      "    }\n");
+  }
+  printer->Print(variables_,
     "    return s;\n"
     "  } else {\n"
     "    return (java.lang.String) ref;\n"
@@ -269,7 +316,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "$deprecation$public Builder set$capitalized_name$(\n"
     "    java.lang.String value) {\n"
     "$null_check$"
-    "  $set_has_field_bit_builder$;\n"
+    "  $set_has_field_bit_builder$\n"
     "  $name$_ = value;\n"
     "  $on_changed$\n"
     "  return this;\n"
@@ -277,7 +324,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public Builder clear$capitalized_name$() {\n"
-    "  $clear_has_field_bit_builder$;\n");
+    "  $clear_has_field_bit_builder$\n");
   // The default value is not a simple literal so we want to avoid executing
   // it multiple times.  Instead, get the default out of the default instance.
   printer->Print(variables_,
@@ -291,89 +338,113 @@ GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "$deprecation$public Builder set$capitalized_name$Bytes(\n"
     "    com.google.protobuf.ByteString value) {\n"
-    "$null_check$"
-    "  $set_has_field_bit_builder$;\n"
+    "$null_check$");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "  checkByteStringIsUtf8(value);\n");
+  }
+  printer->Print(variables_,
+    "  $set_has_field_bit_builder$\n"
     "  $name$_ = value;\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for primitives
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = $default$;\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$name$_ = $default$;\n"
-    "$clear_has_field_bit_builder$;\n");
+    "$clear_has_field_bit_builder$\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
-  // Allow a slight breach of abstraction here in order to avoid forcing
-  // all string fields to Strings when copying fields from a Message.
-  printer->Print(variables_,
-    "if (other.has$capitalized_name$()) {\n"
-    "  $set_has_field_bit_builder$;\n"
-    "  $name$_ = other.$name$_;\n"
-    "  $on_changed$\n"
-    "}\n");
+  if (SupportFieldPresence(descriptor_->file())) {
+    // Allow a slight breach of abstraction here in order to avoid forcing
+    // all string fields to Strings when copying fields from a Message.
+    printer->Print(variables_,
+      "if (other.has$capitalized_name$()) {\n"
+      "  $set_has_field_bit_builder$\n"
+      "  $name$_ = other.$name$_;\n"
+      "  $on_changed$\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "if (!other.get$capitalized_name$().isEmpty()) {\n"
+      "  $name$_ = other.$name$_;\n"
+      "  $on_changed$\n"
+      "}\n");
+  }
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    printer->Print(variables_,
+      "if ($get_has_field_bit_from_local$) {\n"
+      "  $set_has_field_bit_to_local$;\n"
+      "}\n");
+  }
   printer->Print(variables_,
-    "if ($get_has_field_bit_from_local$) {\n"
-    "  $set_has_field_bit_to_local$;\n"
-    "}\n"
     "result.$name$_ = $name$_;\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "$set_has_field_bit_message$;\n"
-    "$name$_ = input.readBytes();\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "String s = input.readStringRequireUtf8();\n"
+      "$set_has_field_bit_message$\n"
+      "$name$_ = s;\n");
+  } else {
+    printer->Print(variables_,
+      "com.google.protobuf.ByteString bs = input.readBytes();\n"
+      "$set_has_field_bit_message$\n"
+      "$name$_ = bs;\n");
+  }
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   // noop for strings.
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  output.writeBytes($number$, get$capitalized_name$Bytes());\n"
     "}\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "if ($get_has_field_bit_message$) {\n"
+    "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
     "    .computeBytesSize($number$, get$capitalized_name$Bytes());\n"
     "}\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$()\n"
     "    .equals(other.get$capitalized_name$());\n");
 }
 
-void StringFieldGenerator::
+void ImmutableStringFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "hash = (37 * hash) + $constant_name$;\n");
@@ -381,39 +452,270 @@ GenerateHashCode(io::Printer* printer) const {
     "hash = (53 * hash) + get$capitalized_name$().hashCode();\n");
 }
 
-string StringFieldGenerator::GetBoxedType() const {
+string ImmutableStringFieldGenerator::GetBoxedType() const {
   return "java.lang.String";
 }
 
+// ===================================================================
+
+ImmutableStringOneofFieldGenerator::
+ImmutableStringOneofFieldGenerator(const FieldDescriptor* descriptor,
+                                   int messageBitIndex,
+                                   int builderBitIndex,
+                                   Context* context)
+    : ImmutableStringFieldGenerator(
+          descriptor, messageBitIndex, builderBitIndex, context) {
+  const OneofGeneratorInfo* info =
+      context->GetOneofGeneratorInfo(descriptor->containing_oneof());
+  SetCommonOneofVariables(descriptor, info, &variables_);
+}
+
+ImmutableStringOneofFieldGenerator::
+~ImmutableStringOneofFieldGenerator() {}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  PrintExtraFieldInfo(variables_, printer);
+
+  if (SupportFieldPresence(descriptor_->file())) {
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public boolean has$capitalized_name$() {\n"
+    "  return $has_oneof_case_message$;\n"
+    "}\n");
+  }
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public java.lang.String get$capitalized_name$() {\n"
+    "  java.lang.Object ref $default_init$;\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    ref = $oneof_name$_;\n"
+    "  }\n"
+    "  if (ref instanceof java.lang.String) {\n"
+    "    return (java.lang.String) ref;\n"
+    "  } else {\n"
+    "    com.google.protobuf.ByteString bs = \n"
+    "        (com.google.protobuf.ByteString) ref;\n"
+    "    java.lang.String s = bs.toStringUtf8();\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+    "    if ($has_oneof_case_message$) {\n"
+    "      $oneof_name$_ = s;\n"
+    "    }\n");
+  } else {
+    printer->Print(variables_,
+    "    if (bs.isValidUtf8() && ($has_oneof_case_message$)) {\n"
+    "      $oneof_name$_ = s;\n"
+    "    }\n");
+  }
+  printer->Print(variables_,
+    "    return s;\n"
+    "  }\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+
+  printer->Print(variables_,
+    "$deprecation$public com.google.protobuf.ByteString\n"
+    "    get$capitalized_name$Bytes() {\n"
+    "  java.lang.Object ref $default_init$;\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    ref = $oneof_name$_;\n"
+    "  }\n"
+    "  if (ref instanceof java.lang.String) {\n"
+    "    com.google.protobuf.ByteString b = \n"
+    "        com.google.protobuf.ByteString.copyFromUtf8(\n"
+    "            (java.lang.String) ref);\n"
+    "    if ($has_oneof_case_message$) {\n"
+    "      $oneof_name$_ = b;\n"
+    "    }\n"
+    "    return b;\n"
+    "  } else {\n"
+    "    return (com.google.protobuf.ByteString) ref;\n"
+    "  }\n"
+    "}\n");
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  if (SupportFieldPresence(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public boolean has$capitalized_name$() {\n"
+      "  return $has_oneof_case_message$;\n"
+      "}\n");
+  }
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public java.lang.String get$capitalized_name$() {\n"
+    "  java.lang.Object ref $default_init$;\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    ref = $oneof_name$_;\n"
+    "  }\n"
+    "  if (!(ref instanceof java.lang.String)) {\n"
+    "    com.google.protobuf.ByteString bs =\n"
+    "        (com.google.protobuf.ByteString) ref;\n"
+    "    java.lang.String s = bs.toStringUtf8();\n"
+    "    if ($has_oneof_case_message$) {\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "      $oneof_name$_ = s;\n");
+  } else {
+    printer->Print(variables_,
+      "      if (bs.isValidUtf8()) {\n"
+      "        $oneof_name$_ = s;\n"
+      "      }\n");
+  }
+  printer->Print(variables_,
+    "    }\n"
+    "    return s;\n"
+    "  } else {\n"
+    "    return (java.lang.String) ref;\n"
+    "  }\n"
+    "}\n");
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public com.google.protobuf.ByteString\n"
+    "    get$capitalized_name$Bytes() {\n"
+    "  java.lang.Object ref $default_init$;\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    ref = $oneof_name$_;\n"
+    "  }\n"
+    "  if (ref instanceof String) {\n"
+    "    com.google.protobuf.ByteString b = \n"
+    "        com.google.protobuf.ByteString.copyFromUtf8(\n"
+    "            (java.lang.String) ref);\n"
+    "    if ($has_oneof_case_message$) {\n"
+    "      $oneof_name$_ = b;\n"
+    "    }\n"
+    "    return b;\n"
+    "  } else {\n"
+    "    return (com.google.protobuf.ByteString) ref;\n"
+    "  }\n"
+    "}\n");
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder set$capitalized_name$(\n"
+    "    java.lang.String value) {\n"
+    "$null_check$"
+    "  $set_oneof_case_message$;\n"
+    "  $oneof_name$_ = value;\n"
+    "  $on_changed$\n"
+    "  return this;\n"
+    "}\n");
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder clear$capitalized_name$() {\n"
+    "  if ($has_oneof_case_message$) {\n"
+    "    $clear_oneof_case_message$;\n"
+    "    $oneof_name$_ = null;\n"
+    "    $on_changed$\n"
+    "  }\n"
+    "  return this;\n"
+    "}\n");
+
+  WriteFieldDocComment(printer, descriptor_);
+  printer->Print(variables_,
+    "$deprecation$public Builder set$capitalized_name$Bytes(\n"
+    "    com.google.protobuf.ByteString value) {\n"
+    "$null_check$");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "  checkByteStringIsUtf8(value);\n");
+  }
+  printer->Print(variables_,
+    "  $set_oneof_case_message$;\n"
+    "  $oneof_name$_ = value;\n"
+    "  $on_changed$\n"
+    "  return this;\n"
+    "}\n");
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  // Allow a slight breach of abstraction here in order to avoid forcing
+  // all string fields to Strings when copying fields from a Message.
+  printer->Print(variables_,
+    "$set_oneof_case_message$;\n"
+    "$oneof_name$_ = other.$oneof_name$_;\n"
+    "$on_changed$\n");
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  result.$oneof_name$_ = $oneof_name$_;\n"
+    "}\n");
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "String s = input.readStringRequireUtf8();\n"
+      "$set_oneof_case_message$;\n"
+      "$oneof_name$_ = s;\n}\n");
+  } else {
+    printer->Print(variables_,
+      "com.google.protobuf.ByteString bs = input.readBytes();\n"
+      "$set_oneof_case_message$;\n"
+      "$oneof_name$_ = bs;\n");
+  }
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  output.writeBytes($number$, get$capitalized_name$Bytes());\n"
+    "}\n");
+}
+
+void ImmutableStringOneofFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(variables_,
+    "if ($has_oneof_case_message$) {\n"
+    "  size += com.google.protobuf.CodedOutputStream\n"
+    "    .computeBytesSize($number$, get$capitalized_name$Bytes());\n"
+    "}\n");
+}
 
 // ===================================================================
 
-RepeatedStringFieldGenerator::
-RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
-                             int messageBitIndex,
-                             int builderBitIndex)
+RepeatedImmutableStringFieldGenerator::
+RepeatedImmutableStringFieldGenerator(const FieldDescriptor* descriptor,
+                                      int messageBitIndex,
+                                      int builderBitIndex,
+                                      Context* context)
   : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
-    builderBitIndex_(builderBitIndex) {
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver()) {
   SetPrimitiveVariables(descriptor, messageBitIndex, builderBitIndex,
-                        &variables_);
+                        context->GetFieldGeneratorInfo(descriptor),
+                        name_resolver_, &variables_);
 }
 
-RepeatedStringFieldGenerator::~RepeatedStringFieldGenerator() {}
+RepeatedImmutableStringFieldGenerator::
+~RepeatedImmutableStringFieldGenerator() {}
 
-int RepeatedStringFieldGenerator::GetNumBitsForMessage() const {
+int RepeatedImmutableStringFieldGenerator::GetNumBitsForMessage() const {
   return 0;
 }
 
-int RepeatedStringFieldGenerator::GetNumBitsForBuilder() const {
+int RepeatedImmutableStringFieldGenerator::GetNumBitsForBuilder() const {
   return 1;
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateInterfaceMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
-    "$deprecation$java.util.List<java.lang.String>\n"
-    "get$capitalized_name$List();\n");
+    "$deprecation$com.google.protobuf.ProtocolStringList\n"
+    "    get$capitalized_name$List();\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$int get$capitalized_name$Count();\n");
@@ -427,13 +729,14 @@ GenerateInterfaceMembers(io::Printer* printer) const {
 }
 
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "private com.google.protobuf.LazyStringList $name$_;\n");
+  PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
-    "$deprecation$public java.util.List<java.lang.String>\n"
+    "$deprecation$public com.google.protobuf.ProtocolStringList\n"
     "    get$capitalized_name$List() {\n"
     "  return $name$_;\n"   // note:  unmodifiable list
     "}\n");
@@ -461,7 +764,7 @@ GenerateMembers(io::Printer* printer) const {
   }
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   // One field is the list and the bit field keeps track of whether the
   // list is immutable. If it's immutable, the invariant is that it must
@@ -489,9 +792,9 @@ GenerateBuilderMembers(io::Printer* printer) const {
     //   immutable.
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
-    "$deprecation$public java.util.List<java.lang.String>\n"
+    "$deprecation$public com.google.protobuf.ProtocolStringList\n"
     "    get$capitalized_name$List() {\n"
-    "  return java.util.Collections.unmodifiableList($name$_);\n"
+    "  return $name$_.getUnmodifiableView();\n"
     "}\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -534,7 +837,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "$deprecation$public Builder addAll$capitalized_name$(\n"
     "    java.lang.Iterable<java.lang.String> values) {\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  super.addAll(values, $name$_);\n"
+    "  com.google.protobuf.AbstractMessageLite.Builder.addAll(\n"
+    "      values, $name$_);\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -551,7 +855,12 @@ GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "$deprecation$public Builder add$capitalized_name$Bytes(\n"
     "    com.google.protobuf.ByteString value) {\n"
-    "$null_check$"
+    "$null_check$");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "  checkByteStringIsUtf8(value);\n");
+  }
+  printer->Print(variables_,
     "  ensure$capitalized_name$IsMutable();\n"
     "  $name$_.add(value);\n"
     "  $on_changed$\n"
@@ -559,24 +868,24 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
   // noop for primitives
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
   printer->Print(variables_, "$name$_ = $empty_list$;\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
     "$name$_ = $empty_list$;\n"
     "$clear_mutable_bit_builder$;\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
   // The code below does two optimizations:
   //   1. If the other list is empty, there's nothing to do. This ensures we
@@ -596,31 +905,43 @@ GenerateMergingCode(io::Printer* printer) const {
     "}\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateBuildingCode(io::Printer* printer) const {
   // The code below ensures that the result has an immutable list. If our
   // list is immutable, we can just reuse it. If not, we make it immutable.
 
   printer->Print(variables_,
     "if ($get_mutable_bit_builder$) {\n"
-    "  $name$_ = new com.google.protobuf.UnmodifiableLazyStringList(\n"
-    "      $name$_);\n"
+    "  $name$_ = $name$_.getUnmodifiableView();\n"
     "  $clear_mutable_bit_builder$;\n"
     "}\n"
     "result.$name$_ = $name$_;\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+    "String s = input.readStringRequireUtf8();\n");
+  } else {
+    printer->Print(variables_,
+    "com.google.protobuf.ByteString bs = input.readBytes();\n");
+  }
   printer->Print(variables_,
     "if (!$get_mutable_bit_parser$) {\n"
     "  $name$_ = new com.google.protobuf.LazyStringArrayList();\n"
     "  $set_mutable_bit_parser$;\n"
-    "}\n"
-    "$name$_.add(input.readBytes());\n");
+    "}\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "$name$_.add(s);\n");
+  } else {
+    printer->Print(variables_,
+      "$name$_.add(bs);\n");
+  }
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateParsingCodeFromPacked(io::Printer* printer) const {
   printer->Print(variables_,
     "int length = input.readRawVarint32();\n"
@@ -629,21 +950,30 @@ GenerateParsingCodeFromPacked(io::Printer* printer) const {
     "  $name$_ = new com.google.protobuf.LazyStringArrayList();\n"
     "  $set_mutable_bit_parser$;\n"
     "}\n"
-    "while (input.getBytesUntilLimit() > 0) {\n"
-    "  $name$.add(input.read$capitalized_type$());\n"
+    "while (input.getBytesUntilLimit() > 0) {\n");
+  if (CheckUtf8(descriptor_)) {
+    printer->Print(variables_,
+      "  String s = input.readStringRequireUtf8();\n");
+  } else {
+    printer->Print(variables_,
+      "  String s = input.readString();\n");
+  }
+  printer->Print(variables_,
+    "  $name$.add(s);\n");
+  printer->Print(variables_,
     "}\n"
     "input.popLimit(limit);\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateParsingDoneCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($get_mutable_bit_parser$) {\n"
-    "  $name$_ = new com.google.protobuf.UnmodifiableLazyStringList($name$_);\n"
+    "  $name$_ = $name$_.getUnmodifiableView();\n"
     "}\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   if (descriptor_->options().packed()) {
     printer->Print(variables_,
@@ -662,7 +992,7 @@ GenerateSerializationCode(io::Printer* printer) const {
   }
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "{\n"
@@ -700,14 +1030,14 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print("}\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
     "result = result && get$capitalized_name$List()\n"
     "    .equals(other.get$capitalized_name$List());\n");
 }
 
-void RepeatedStringFieldGenerator::
+void RepeatedImmutableStringFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (get$capitalized_name$Count() > 0) {\n"
@@ -716,7 +1046,7 @@ GenerateHashCode(io::Printer* printer) const {
     "}\n");
 }
 
-string RepeatedStringFieldGenerator::GetBoxedType() const {
+string RepeatedImmutableStringFieldGenerator::GetBoxedType() const {
   return "String";
 }
 
diff --git a/src/google/protobuf/compiler/java/java_string_field.h b/src/google/protobuf/compiler/java/java_string_field.h
index 4f7532f4..348cbcbd 100644
--- a/src/google/protobuf/compiler/java/java_string_field.h
+++ b/src/google/protobuf/compiler/java/java_string_field.h
@@ -42,16 +42,26 @@
 
 namespace google {
 namespace protobuf {
+  namespace compiler {
+    namespace java {
+      class Context;           // context.h
+      class ClassNameResolver; // name_resolver.h
+    }
+  }
+}
+
+namespace protobuf {
 namespace compiler {
 namespace java {
 
-class StringFieldGenerator : public FieldGenerator {
+class ImmutableStringFieldGenerator : public ImmutableFieldGenerator {
  public:
-  explicit StringFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~StringFieldGenerator();
+  explicit ImmutableStringFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableStringFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -68,24 +78,49 @@ class StringFieldGenerator : public FieldGenerator {
   void GenerateFieldBuilderInitializationCode(io::Printer* printer) const;
   void GenerateEqualsCode(io::Printer* printer) const;
   void GenerateHashCode(io::Printer* printer) const;
+
   string GetBoxedType() const;
 
- private:
+ protected:
   const FieldDescriptor* descriptor_;
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringFieldGenerator);
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableStringFieldGenerator);
 };
 
-class RepeatedStringFieldGenerator : public FieldGenerator {
+class ImmutableStringOneofFieldGenerator
+    : public ImmutableStringFieldGenerator {
  public:
-  explicit RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
-      int messageBitIndex, int builderBitIndex);
-  ~RepeatedStringFieldGenerator();
+  ImmutableStringOneofFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableStringOneofFieldGenerator();
 
-  // implements FieldGenerator ---------------------------------------
+ private:
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableStringOneofFieldGenerator);
+};
+
+class RepeatedImmutableStringFieldGenerator : public ImmutableFieldGenerator {
+ public:
+  explicit RepeatedImmutableStringFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~RepeatedImmutableStringFieldGenerator();
+
+  // implements ImmutableFieldGenerator ---------------------------------------
   int GetNumBitsForMessage() const;
   int GetNumBitsForBuilder() const;
   void GenerateInterfaceMembers(io::Printer* printer) const;
@@ -103,6 +138,7 @@ class RepeatedStringFieldGenerator : public FieldGenerator {
   void GenerateFieldBuilderInitializationCode(io::Printer* printer) const;
   void GenerateEqualsCode(io::Printer* printer) const;
   void GenerateHashCode(io::Printer* printer) const;
+
   string GetBoxedType() const;
 
  private:
@@ -110,8 +146,10 @@ class RepeatedStringFieldGenerator : public FieldGenerator {
   map<string, string> variables_;
   const int messageBitIndex_;
   const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
 
-  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedStringFieldGenerator);
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RepeatedImmutableStringFieldGenerator);
 };
 
 }  // namespace java
diff --git a/src/google/protobuf/compiler/mock_code_generator.cc b/src/google/protobuf/compiler/mock_code_generator.cc
index 0e35ed19..1f91817f 100644
--- a/src/google/protobuf/compiler/mock_code_generator.cc
+++ b/src/google/protobuf/compiler/mock_code_generator.cc
@@ -32,6 +32,8 @@
 
 #include <google/protobuf/compiler/mock_code_generator.h>
 
+#include <memory>
+
 #include <google/protobuf/testing/file.h>
 #include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/descriptor.h>
@@ -53,7 +55,7 @@ string CommaSeparatedList(const vector<const FileDescriptor*> all_files) {
   for (int i = 0; i < all_files.size(); i++) {
     names.push_back(all_files[i]->name());
   }
-  return JoinStrings(names, ",");
+  return Join(names, ",");
 }
 
 static const char* kFirstInsertionPointName = "first_mock_insertion_point";
@@ -77,11 +79,11 @@ void MockCodeGenerator::ExpectGenerated(
     const string& first_parsed_file_name,
     const string& output_directory) {
   string content;
-  ASSERT_TRUE(File::ReadFileToString(
-      output_directory + "/" + GetOutputFileName(name, file), &content));
+  GOOGLE_CHECK_OK(
+      File::GetContents(output_directory + "/" + GetOutputFileName(name, file),
+                        &content, true));
 
-  vector<string> lines;
-  SplitStringUsing(content, "\n", &lines);
+  vector<string> lines = Split(content, "\n", true);
 
   while (!lines.empty() && lines.back().empty()) {
     lines.pop_back();
@@ -95,7 +97,7 @@ void MockCodeGenerator::ExpectGenerated(
     SplitStringUsing(insertions, ",", &insertion_list);
   }
 
-  ASSERT_EQ(lines.size(), 3 + insertion_list.size() * 2);
+  EXPECT_EQ(lines.size(), 3 + insertion_list.size() * 2);
   EXPECT_EQ(GetOutputFileContent(name, parameter, file,
                                  first_parsed_file_name, first_message_name),
             lines[0]);
@@ -155,10 +157,8 @@ bool MockCodeGenerator::Generate(
 
     for (int i = 0; i < insert_into.size(); i++) {
       {
-        scoped_ptr<io::ZeroCopyOutputStream> output(
-            context->OpenForInsert(
-              GetOutputFileName(insert_into[i], file),
-              kFirstInsertionPointName));
+        scoped_ptr<io::ZeroCopyOutputStream> output(context->OpenForInsert(
+            GetOutputFileName(insert_into[i], file), kFirstInsertionPointName));
         io::Printer printer(output.get(), '$');
         printer.PrintRaw(GetOutputFileContent(name_, "first_insert",
                                               file, context));
@@ -170,9 +170,8 @@ bool MockCodeGenerator::Generate(
 
       {
         scoped_ptr<io::ZeroCopyOutputStream> output(
-            context->OpenForInsert(
-              GetOutputFileName(insert_into[i], file),
-              kSecondInsertionPointName));
+            context->OpenForInsert(GetOutputFileName(insert_into[i], file),
+                                   kSecondInsertionPointName));
         io::Printer printer(output.get(), '$');
         printer.PrintRaw(GetOutputFileContent(name_, "second_insert",
                                               file, context));
diff --git a/src/google/protobuf/compiler/parser.cc b/src/google/protobuf/compiler/parser.cc
index 23aa01ce..7e0df7e1 100644
--- a/src/google/protobuf/compiler/parser.cc
+++ b/src/google/protobuf/compiler/parser.cc
@@ -46,7 +46,7 @@
 #include <google/protobuf/io/tokenizer.h>
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/stubs/strutil.h>
-#include <google/protobuf/stubs/map-util.h>
+#include <google/protobuf/stubs/map_util.h>
 
 namespace google {
 namespace protobuf {
@@ -343,6 +343,11 @@ void Parser::LocationRecorder::StartAt(const io::Tokenizer::Token& token) {
   location_->set_span(1, token.column);
 }
 
+void Parser::LocationRecorder::StartAt(const LocationRecorder& other) {
+  location_->set_span(0, other.location_->span(0));
+  location_->set_span(1, other.location_->span(1));
+}
+
 void Parser::LocationRecorder::EndAt(const io::Tokenizer::Token& token) {
   if (token.line != location_->span(0)) {
     location_->add_span(token.line);
@@ -489,15 +494,15 @@ bool Parser::ParseTopLevelStatement(FileDescriptorProto* file,
   } else if (LookingAt("message")) {
     LocationRecorder location(root_location,
       FileDescriptorProto::kMessageTypeFieldNumber, file->message_type_size());
-    return ParseMessageDefinition(file->add_message_type(), location);
+    return ParseMessageDefinition(file->add_message_type(), location, file);
   } else if (LookingAt("enum")) {
     LocationRecorder location(root_location,
       FileDescriptorProto::kEnumTypeFieldNumber, file->enum_type_size());
-    return ParseEnumDefinition(file->add_enum_type(), location);
+    return ParseEnumDefinition(file->add_enum_type(), location, file);
   } else if (LookingAt("service")) {
     LocationRecorder location(root_location,
       FileDescriptorProto::kServiceFieldNumber, file->service_size());
-    return ParseServiceDefinition(file->add_service(), location);
+    return ParseServiceDefinition(file->add_service(), location, file);
   } else if (LookingAt("extend")) {
     LocationRecorder location(root_location,
         FileDescriptorProto::kExtensionFieldNumber);
@@ -505,18 +510,19 @@ bool Parser::ParseTopLevelStatement(FileDescriptorProto* file,
                        file->mutable_message_type(),
                        root_location,
                        FileDescriptorProto::kMessageTypeFieldNumber,
-                       location);
+                       location, file);
   } else if (LookingAt("import")) {
     return ParseImport(file->mutable_dependency(),
                        file->mutable_public_dependency(),
                        file->mutable_weak_dependency(),
-                       root_location);
+                       root_location, file);
   } else if (LookingAt("package")) {
-    return ParsePackage(file, root_location);
+    return ParsePackage(file, root_location, file);
   } else if (LookingAt("option")) {
     LocationRecorder location(root_location,
         FileDescriptorProto::kOptionsFieldNumber);
-    return ParseOption(file->mutable_options(), location, OPTION_STATEMENT);
+    return ParseOption(file->mutable_options(), location, file,
+                       OPTION_STATEMENT);
   } else {
     AddError("Expected top-level statement (e.g. \"message\").");
     return false;
@@ -526,8 +532,10 @@ bool Parser::ParseTopLevelStatement(FileDescriptorProto* file,
 // -------------------------------------------------------------------
 // Messages
 
-bool Parser::ParseMessageDefinition(DescriptorProto* message,
-                                    const LocationRecorder& message_location) {
+bool Parser::ParseMessageDefinition(
+    DescriptorProto* message,
+    const LocationRecorder& message_location,
+    const FileDescriptorProto* containing_file) {
   DO(Consume("message"));
   {
     LocationRecorder location(message_location,
@@ -536,7 +544,7 @@ bool Parser::ParseMessageDefinition(DescriptorProto* message,
         message, DescriptorPool::ErrorCollector::NAME);
     DO(ConsumeIdentifier(message->mutable_name(), "Expected message name."));
   }
-  DO(ParseMessageBlock(message, message_location));
+  DO(ParseMessageBlock(message, message_location, containing_file));
   return true;
 }
 
@@ -575,7 +583,8 @@ void AdjustExtensionRangesWithMaxEndNumber(DescriptorProto* message) {
 }  // namespace
 
 bool Parser::ParseMessageBlock(DescriptorProto* message,
-                               const LocationRecorder& message_location) {
+                               const LocationRecorder& message_location,
+                               const FileDescriptorProto* containing_file) {
   DO(ConsumeEndOfDeclaration("{", &message_location));
 
   while (!TryConsumeEndOfDeclaration("}", NULL)) {
@@ -584,7 +593,7 @@ bool Parser::ParseMessageBlock(DescriptorProto* message,
       return false;
     }
 
-    if (!ParseMessageStatement(message, message_location)) {
+    if (!ParseMessageStatement(message, message_location, containing_file)) {
       // This statement failed to parse.  Skip it, but keep looping to parse
       // other statements.
       SkipStatement();
@@ -598,7 +607,8 @@ bool Parser::ParseMessageBlock(DescriptorProto* message,
 }
 
 bool Parser::ParseMessageStatement(DescriptorProto* message,
-                                   const LocationRecorder& message_location) {
+                                   const LocationRecorder& message_location,
+                                   const FileDescriptorProto* containing_file) {
   if (TryConsumeEndOfDeclaration(";", NULL)) {
     // empty statement; ignore
     return true;
@@ -606,16 +616,18 @@ bool Parser::ParseMessageStatement(DescriptorProto* message,
     LocationRecorder location(message_location,
                               DescriptorProto::kNestedTypeFieldNumber,
                               message->nested_type_size());
-    return ParseMessageDefinition(message->add_nested_type(), location);
+    return ParseMessageDefinition(message->add_nested_type(), location,
+                                  containing_file);
   } else if (LookingAt("enum")) {
     LocationRecorder location(message_location,
                               DescriptorProto::kEnumTypeFieldNumber,
                               message->enum_type_size());
-    return ParseEnumDefinition(message->add_enum_type(), location);
+    return ParseEnumDefinition(message->add_enum_type(), location,
+                               containing_file);
   } else if (LookingAt("extensions")) {
     LocationRecorder location(message_location,
                               DescriptorProto::kExtensionRangeFieldNumber);
-    return ParseExtensions(message, location);
+    return ParseExtensions(message, location, containing_file);
   } else if (LookingAt("extend")) {
     LocationRecorder location(message_location,
                               DescriptorProto::kExtensionFieldNumber);
@@ -623,11 +635,21 @@ bool Parser::ParseMessageStatement(DescriptorProto* message,
                        message->mutable_nested_type(),
                        message_location,
                        DescriptorProto::kNestedTypeFieldNumber,
-                       location);
+                       location, containing_file);
   } else if (LookingAt("option")) {
     LocationRecorder location(message_location,
                               DescriptorProto::kOptionsFieldNumber);
-    return ParseOption(message->mutable_options(), location, OPTION_STATEMENT);
+    return ParseOption(message->mutable_options(), location,
+                       containing_file, OPTION_STATEMENT);
+  } else if (LookingAt("oneof")) {
+    int oneof_index = message->oneof_decl_size();
+    LocationRecorder oneof_location(message_location,
+                                    DescriptorProto::kOneofDeclFieldNumber,
+                                    oneof_index);
+
+    return ParseOneof(message->add_oneof_decl(), message,
+                      oneof_index, oneof_location, message_location,
+                      containing_file);
   } else {
     LocationRecorder location(message_location,
                               DescriptorProto::kFieldFieldNumber,
@@ -636,7 +658,8 @@ bool Parser::ParseMessageStatement(DescriptorProto* message,
                              message->mutable_nested_type(),
                              message_location,
                              DescriptorProto::kNestedTypeFieldNumber,
-                             location);
+                             location,
+                             containing_file);
   }
 }
 
@@ -644,17 +667,30 @@ bool Parser::ParseMessageField(FieldDescriptorProto* field,
                                RepeatedPtrField<DescriptorProto>* messages,
                                const LocationRecorder& parent_location,
                                int location_field_number_for_nested_type,
-                               const LocationRecorder& field_location) {
-  // Parse label and type.
-  io::Tokenizer::Token label_token = input_->current();
+                               const LocationRecorder& field_location,
+                               const FileDescriptorProto* containing_file) {
   {
     LocationRecorder location(field_location,
                               FieldDescriptorProto::kLabelFieldNumber);
     FieldDescriptorProto::Label label;
-    DO(ParseLabel(&label));
+    DO(ParseLabel(&label, containing_file));
     field->set_label(label);
   }
 
+  return ParseMessageFieldNoLabel(field, messages, parent_location,
+                                  location_field_number_for_nested_type,
+                                  field_location,
+                                  containing_file);
+}
+
+bool Parser::ParseMessageFieldNoLabel(
+    FieldDescriptorProto* field,
+    RepeatedPtrField<DescriptorProto>* messages,
+    const LocationRecorder& parent_location,
+    int location_field_number_for_nested_type,
+    const LocationRecorder& field_location,
+    const FileDescriptorProto* containing_file) {
+  // Parse type.
   {
     LocationRecorder location(field_location);  // add path later
     location.RecordLegacyLocation(field, DescriptorPool::ErrorCollector::TYPE);
@@ -693,14 +729,14 @@ bool Parser::ParseMessageField(FieldDescriptorProto* field,
   }
 
   // Parse options.
-  DO(ParseFieldOptions(field, field_location));
+  DO(ParseFieldOptions(field, field_location, containing_file));
 
   // Deal with groups.
   if (field->has_type() && field->type() == FieldDescriptorProto::TYPE_GROUP) {
     // Awkward:  Since a group declares both a message type and a field, we
     //   have to create overlapping locations.
     LocationRecorder group_location(parent_location);
-    group_location.StartAt(label_token);
+    group_location.StartAt(field_location);
     group_location.AddPath(location_field_number_for_nested_type);
     group_location.AddPath(messages->size());
 
@@ -736,7 +772,7 @@ bool Parser::ParseMessageField(FieldDescriptorProto* field,
 
     field->set_type_name(group->name());
     if (LookingAt("{")) {
-      DO(ParseMessageBlock(group, group_location));
+      DO(ParseMessageBlock(group, group_location, containing_file));
     } else {
       AddError("Missing group body.");
       return false;
@@ -749,7 +785,8 @@ bool Parser::ParseMessageField(FieldDescriptorProto* field,
 }
 
 bool Parser::ParseFieldOptions(FieldDescriptorProto* field,
-                               const LocationRecorder& field_location) {
+                               const LocationRecorder& field_location,
+                               const FileDescriptorProto* containing_file) {
   if (!LookingAt("[")) return true;
 
   LocationRecorder location(field_location,
@@ -762,9 +799,10 @@ bool Parser::ParseFieldOptions(FieldDescriptorProto* field,
     if (LookingAt("default")) {
       // We intentionally pass field_location rather than location here, since
       // the default value is not actually an option.
-      DO(ParseDefaultAssignment(field, field_location));
+      DO(ParseDefaultAssignment(field, field_location, containing_file));
     } else {
-      DO(ParseOption(field->mutable_options(), location, OPTION_ASSIGNMENT));
+      DO(ParseOption(field->mutable_options(), location,
+                     containing_file, OPTION_ASSIGNMENT));
     }
   } while (TryConsume(","));
 
@@ -772,8 +810,10 @@ bool Parser::ParseFieldOptions(FieldDescriptorProto* field,
   return true;
 }
 
-bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
-                                    const LocationRecorder& field_location) {
+bool Parser::ParseDefaultAssignment(
+    FieldDescriptorProto* field,
+    const LocationRecorder& field_location,
+    const FileDescriptorProto* containing_file) {
   if (field->has_default_value()) {
     AddError("Already set option \"default\".");
     field->clear_default_value();
@@ -790,8 +830,16 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
 
   if (!field->has_type()) {
     // The field has a type name, but we don't know if it is a message or an
-    // enum yet.  Assume an enum for now.
-    DO(ConsumeIdentifier(default_value, "Expected identifier."));
+    // enum yet. (If it were a primitive type, |field| would have a type set
+    // already.) In this case, simply take the current string as the default
+    // value; we will catch the error later if it is not a valid enum value.
+    // (N.B. that we do not check whether the current token is an identifier:
+    // doing so throws strange errors when the user mistypes a primitive
+    // typename and we assume it's an enum. E.g.: "optional int foo = 1 [default
+    // = 42]". In such a case the fundamental error is really that "int" is not
+    // a type, not that "42" is not an identifier. See b/12533582.)
+    *default_value = input_->current().text;
+    input_->Next();
     return true;
   }
 
@@ -817,7 +865,8 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
       }
       // Parse the integer to verify that it is not out-of-range.
       uint64 value;
-      DO(ConsumeInteger64(max_value, &value, "Expected integer."));
+      DO(ConsumeInteger64(max_value, &value,
+                          "Expected integer for field default value."));
       // And stringify it again.
       default_value->append(SimpleItoa(value));
       break;
@@ -839,7 +888,8 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
       }
       // Parse the integer to verify that it is not out-of-range.
       uint64 value;
-      DO(ConsumeInteger64(max_value, &value, "Expected integer."));
+      DO(ConsumeInteger64(max_value, &value,
+                          "Expected integer for field default value."));
       // And stringify it again.
       default_value->append(SimpleItoa(value));
       break;
@@ -871,7 +921,11 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
       break;
 
     case FieldDescriptorProto::TYPE_STRING:
-      DO(ConsumeString(default_value, "Expected string."));
+      // Note: When file opton java_string_check_utf8 is true, if a
+      // non-string representation (eg byte[]) is later supported, it must
+      // be checked for UTF-8-ness.
+      DO(ConsumeString(default_value, "Expected string for field default "
+                       "value."));
       break;
 
     case FieldDescriptorProto::TYPE_BYTES:
@@ -880,7 +934,8 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
       break;
 
     case FieldDescriptorProto::TYPE_ENUM:
-      DO(ConsumeIdentifier(default_value, "Expected identifier."));
+      DO(ConsumeIdentifier(default_value, "Expected enum identifier for field "
+                                          "default value."));
       break;
 
     case FieldDescriptorProto::TYPE_MESSAGE:
@@ -893,7 +948,8 @@ bool Parser::ParseDefaultAssignment(FieldDescriptorProto* field,
 }
 
 bool Parser::ParseOptionNamePart(UninterpretedOption* uninterpreted_option,
-                                 const LocationRecorder& part_location) {
+                                 const LocationRecorder& part_location,
+                                 const FileDescriptorProto* containing_file) {
   UninterpretedOption::NamePart* name = uninterpreted_option->add_name();
   string identifier;  // We parse identifiers into this string.
   if (LookingAt("(")) {  // This is an extension.
@@ -957,6 +1013,7 @@ bool Parser::ParseUninterpretedBlock(string* value) {
 // UninterpretedOption, to be interpreted later.
 bool Parser::ParseOption(Message* options,
                          const LocationRecorder& options_location,
+                         const FileDescriptorProto* containing_file,
                          OptionStyle style) {
   // Create an entry in the uninterpreted_option field.
   const FieldDescriptor* uninterpreted_option_field = options->GetDescriptor()->
@@ -988,14 +1045,16 @@ bool Parser::ParseOption(Message* options,
     {
       LocationRecorder part_location(name_location,
                                      uninterpreted_option->name_size());
-      DO(ParseOptionNamePart(uninterpreted_option, part_location));
+      DO(ParseOptionNamePart(uninterpreted_option, part_location,
+                             containing_file));
     }
 
     while (LookingAt(".")) {
       DO(Consume("."));
       LocationRecorder part_location(name_location,
                                      uninterpreted_option->name_size());
-      DO(ParseOptionNamePart(uninterpreted_option, part_location));
+      DO(ParseOptionNamePart(uninterpreted_option, part_location,
+                             containing_file));
     }
   }
 
@@ -1088,11 +1147,13 @@ bool Parser::ParseOption(Message* options,
     DO(ConsumeEndOfDeclaration(";", &location));
   }
 
+
   return true;
 }
 
 bool Parser::ParseExtensions(DescriptorProto* message,
-                             const LocationRecorder& extensions_location) {
+                             const LocationRecorder& extensions_location,
+                             const FileDescriptorProto* containing_file) {
   // Parse the declaration.
   DO(Consume("extensions"));
 
@@ -1150,7 +1211,8 @@ bool Parser::ParseExtend(RepeatedPtrField<FieldDescriptorProto>* extensions,
                          RepeatedPtrField<DescriptorProto>* messages,
                          const LocationRecorder& parent_location,
                          int location_field_number_for_nested_type,
-                         const LocationRecorder& extend_location) {
+                         const LocationRecorder& extend_location,
+                         const FileDescriptorProto* containing_file) {
   DO(Consume("extend"));
 
   // Parse the extendee type.
@@ -1192,7 +1254,65 @@ bool Parser::ParseExtend(RepeatedPtrField<FieldDescriptorProto>* extensions,
 
     if (!ParseMessageField(field, messages, parent_location,
                            location_field_number_for_nested_type,
-                           location)) {
+                           location,
+                           containing_file)) {
+      // This statement failed to parse.  Skip it, but keep looping to parse
+      // other statements.
+      SkipStatement();
+    }
+  } while (!TryConsumeEndOfDeclaration("}", NULL));
+
+  return true;
+}
+
+bool Parser::ParseOneof(OneofDescriptorProto* oneof_decl,
+                        DescriptorProto* containing_type,
+                        int oneof_index,
+                        const LocationRecorder& oneof_location,
+                        const LocationRecorder& containing_type_location,
+                        const FileDescriptorProto* containing_file) {
+  DO(Consume("oneof"));
+
+  {
+    LocationRecorder name_location(oneof_location,
+                                   OneofDescriptorProto::kNameFieldNumber);
+    DO(ConsumeIdentifier(oneof_decl->mutable_name(), "Expected oneof name."));
+  }
+
+  DO(ConsumeEndOfDeclaration("{", &oneof_location));
+
+  do {
+    if (AtEnd()) {
+      AddError("Reached end of input in oneof definition (missing '}').");
+      return false;
+    }
+
+    // Print a nice error if the user accidentally tries to place a label
+    // on an individual member of a oneof.
+    if (LookingAt("required") ||
+        LookingAt("optional") ||
+        LookingAt("repeated")) {
+      AddError("Fields in oneofs must not have labels (required / optional "
+               "/ repeated).");
+      // We can continue parsing here because we understand what the user
+      // meant.  The error report will still make parsing fail overall.
+      input_->Next();
+    }
+
+    LocationRecorder field_location(containing_type_location,
+                                    DescriptorProto::kFieldFieldNumber,
+                                    containing_type->field_size());
+
+    FieldDescriptorProto* field = containing_type->add_field();
+    field->set_label(FieldDescriptorProto::LABEL_OPTIONAL);
+    field->set_oneof_index(oneof_index);
+
+    if (!ParseMessageFieldNoLabel(field,
+                                  containing_type->mutable_nested_type(),
+                                  containing_type_location,
+                                  DescriptorProto::kNestedTypeFieldNumber,
+                                  field_location,
+                                  containing_file)) {
       // This statement failed to parse.  Skip it, but keep looping to parse
       // other statements.
       SkipStatement();
@@ -1206,7 +1326,8 @@ bool Parser::ParseExtend(RepeatedPtrField<FieldDescriptorProto>* extensions,
 // Enums
 
 bool Parser::ParseEnumDefinition(EnumDescriptorProto* enum_type,
-                                 const LocationRecorder& enum_location) {
+                                 const LocationRecorder& enum_location,
+                                 const FileDescriptorProto* containing_file) {
   DO(Consume("enum"));
 
   {
@@ -1217,12 +1338,13 @@ bool Parser::ParseEnumDefinition(EnumDescriptorProto* enum_type,
     DO(ConsumeIdentifier(enum_type->mutable_name(), "Expected enum name."));
   }
 
-  DO(ParseEnumBlock(enum_type, enum_location));
+  DO(ParseEnumBlock(enum_type, enum_location, containing_file));
   return true;
 }
 
 bool Parser::ParseEnumBlock(EnumDescriptorProto* enum_type,
-                            const LocationRecorder& enum_location) {
+                            const LocationRecorder& enum_location,
+                            const FileDescriptorProto* containing_file) {
   DO(ConsumeEndOfDeclaration("{", &enum_location));
 
   while (!TryConsumeEndOfDeclaration("}", NULL)) {
@@ -1231,7 +1353,7 @@ bool Parser::ParseEnumBlock(EnumDescriptorProto* enum_type,
       return false;
     }
 
-    if (!ParseEnumStatement(enum_type, enum_location)) {
+    if (!ParseEnumStatement(enum_type, enum_location, containing_file)) {
       // This statement failed to parse.  Skip it, but keep looping to parse
       // other statements.
       SkipStatement();
@@ -1242,7 +1364,8 @@ bool Parser::ParseEnumBlock(EnumDescriptorProto* enum_type,
 }
 
 bool Parser::ParseEnumStatement(EnumDescriptorProto* enum_type,
-                                const LocationRecorder& enum_location) {
+                                const LocationRecorder& enum_location,
+                                const FileDescriptorProto* containing_file) {
   if (TryConsumeEndOfDeclaration(";", NULL)) {
     // empty statement; ignore
     return true;
@@ -1250,16 +1373,17 @@ bool Parser::ParseEnumStatement(EnumDescriptorProto* enum_type,
     LocationRecorder location(enum_location,
                               EnumDescriptorProto::kOptionsFieldNumber);
     return ParseOption(enum_type->mutable_options(), location,
-                       OPTION_STATEMENT);
+                       containing_file, OPTION_STATEMENT);
   } else {
     LocationRecorder location(enum_location,
         EnumDescriptorProto::kValueFieldNumber, enum_type->value_size());
-    return ParseEnumConstant(enum_type->add_value(), location);
+    return ParseEnumConstant(enum_type->add_value(), location, containing_file);
   }
 }
 
 bool Parser::ParseEnumConstant(EnumValueDescriptorProto* enum_value,
-                               const LocationRecorder& enum_value_location) {
+                               const LocationRecorder& enum_value_location,
+                               const FileDescriptorProto* containing_file) {
   // Parse name.
   {
     LocationRecorder location(enum_value_location,
@@ -1284,7 +1408,8 @@ bool Parser::ParseEnumConstant(EnumValueDescriptorProto* enum_value,
     enum_value->set_number(number);
   }
 
-  DO(ParseEnumConstantOptions(enum_value, enum_value_location));
+  DO(ParseEnumConstantOptions(enum_value, enum_value_location,
+                              containing_file));
 
   DO(ConsumeEndOfDeclaration(";", &enum_value_location));
 
@@ -1293,7 +1418,8 @@ bool Parser::ParseEnumConstant(EnumValueDescriptorProto* enum_value,
 
 bool Parser::ParseEnumConstantOptions(
     EnumValueDescriptorProto* value,
-    const LocationRecorder& enum_value_location) {
+    const LocationRecorder& enum_value_location,
+    const FileDescriptorProto* containing_file) {
   if (!LookingAt("[")) return true;
 
   LocationRecorder location(
@@ -1302,7 +1428,8 @@ bool Parser::ParseEnumConstantOptions(
   DO(Consume("["));
 
   do {
-    DO(ParseOption(value->mutable_options(), location, OPTION_ASSIGNMENT));
+    DO(ParseOption(value->mutable_options(), location,
+                   containing_file, OPTION_ASSIGNMENT));
   } while (TryConsume(","));
 
   DO(Consume("]"));
@@ -1312,8 +1439,10 @@ bool Parser::ParseEnumConstantOptions(
 // -------------------------------------------------------------------
 // Services
 
-bool Parser::ParseServiceDefinition(ServiceDescriptorProto* service,
-                                    const LocationRecorder& service_location) {
+bool Parser::ParseServiceDefinition(
+    ServiceDescriptorProto* service,
+    const LocationRecorder& service_location,
+    const FileDescriptorProto* containing_file) {
   DO(Consume("service"));
 
   {
@@ -1324,12 +1453,13 @@ bool Parser::ParseServiceDefinition(ServiceDescriptorProto* service,
     DO(ConsumeIdentifier(service->mutable_name(), "Expected service name."));
   }
 
-  DO(ParseServiceBlock(service, service_location));
+  DO(ParseServiceBlock(service, service_location, containing_file));
   return true;
 }
 
 bool Parser::ParseServiceBlock(ServiceDescriptorProto* service,
-                               const LocationRecorder& service_location) {
+                               const LocationRecorder& service_location,
+                               const FileDescriptorProto* containing_file) {
   DO(ConsumeEndOfDeclaration("{", &service_location));
 
   while (!TryConsumeEndOfDeclaration("}", NULL)) {
@@ -1338,7 +1468,7 @@ bool Parser::ParseServiceBlock(ServiceDescriptorProto* service,
       return false;
     }
 
-    if (!ParseServiceStatement(service, service_location)) {
+    if (!ParseServiceStatement(service, service_location, containing_file)) {
       // This statement failed to parse.  Skip it, but keep looping to parse
       // other statements.
       SkipStatement();
@@ -1349,23 +1479,26 @@ bool Parser::ParseServiceBlock(ServiceDescriptorProto* service,
 }
 
 bool Parser::ParseServiceStatement(ServiceDescriptorProto* service,
-                                   const LocationRecorder& service_location) {
+                                   const LocationRecorder& service_location,
+                                   const FileDescriptorProto* containing_file) {
   if (TryConsumeEndOfDeclaration(";", NULL)) {
     // empty statement; ignore
     return true;
   } else if (LookingAt("option")) {
     LocationRecorder location(
         service_location, ServiceDescriptorProto::kOptionsFieldNumber);
-    return ParseOption(service->mutable_options(), location, OPTION_STATEMENT);
+    return ParseOption(service->mutable_options(), location,
+                       containing_file, OPTION_STATEMENT);
   } else {
     LocationRecorder location(service_location,
         ServiceDescriptorProto::kMethodFieldNumber, service->method_size());
-    return ParseServiceMethod(service->add_method(), location);
+    return ParseServiceMethod(service->add_method(), location, containing_file);
   }
 }
 
 bool Parser::ParseServiceMethod(MethodDescriptorProto* method,
-                                const LocationRecorder& method_location) {
+                                const LocationRecorder& method_location,
+                                const FileDescriptorProto* containing_file) {
   DO(Consume("rpc"));
 
   {
@@ -1402,6 +1535,7 @@ bool Parser::ParseServiceMethod(MethodDescriptorProto* method,
   if (LookingAt("{")) {
     // Options!
     DO(ParseOptions(method_location,
+                    containing_file,
                     MethodDescriptorProto::kOptionsFieldNumber,
                     method->mutable_options()));
   } else {
@@ -1413,6 +1547,7 @@ bool Parser::ParseServiceMethod(MethodDescriptorProto* method,
 
 
 bool Parser::ParseOptions(const LocationRecorder& parent_location,
+                          const FileDescriptorProto* containing_file,
                           const int optionsFieldNumber,
                           Message* mutable_options) {
   // Options!
@@ -1428,7 +1563,8 @@ bool Parser::ParseOptions(const LocationRecorder& parent_location,
     } else {
       LocationRecorder location(parent_location,
                                 optionsFieldNumber);
-      if (!ParseOption(mutable_options, location, OPTION_STATEMENT)) {
+      if (!ParseOption(mutable_options, location, containing_file,
+                       OPTION_STATEMENT)) {
         // This statement failed to parse.  Skip it, but keep looping to
         // parse other statements.
         SkipStatement();
@@ -1441,7 +1577,8 @@ bool Parser::ParseOptions(const LocationRecorder& parent_location,
 
 // -------------------------------------------------------------------
 
-bool Parser::ParseLabel(FieldDescriptorProto::Label* label) {
+bool Parser::ParseLabel(FieldDescriptorProto::Label* label,
+                        const FileDescriptorProto* containing_file) {
   if (TryConsume("optional")) {
     *label = FieldDescriptorProto::LABEL_OPTIONAL;
     return true;
@@ -1510,7 +1647,8 @@ bool Parser::ParseUserDefinedType(string* type_name) {
 // ===================================================================
 
 bool Parser::ParsePackage(FileDescriptorProto* file,
-                          const LocationRecorder& root_location) {
+                          const LocationRecorder& root_location,
+                          const FileDescriptorProto* containing_file) {
   if (file->has_package()) {
     AddError("Multiple package definitions.");
     // Don't append the new package to the old one.  Just replace it.  Not
@@ -1544,7 +1682,8 @@ bool Parser::ParsePackage(FileDescriptorProto* file,
 bool Parser::ParseImport(RepeatedPtrField<string>* dependency,
                          RepeatedField<int32>* public_dependency,
                          RepeatedField<int32>* weak_dependency,
-                         const LocationRecorder& root_location) {
+                         const LocationRecorder& root_location,
+                         const FileDescriptorProto* containing_file) {
   DO(Consume("import"));
   if (LookingAt("public")) {
     LocationRecorder location(
diff --git a/src/google/protobuf/compiler/parser.h b/src/google/protobuf/compiler/parser.h
index cfd3649b..6bca7fa7 100644
--- a/src/google/protobuf/compiler/parser.h
+++ b/src/google/protobuf/compiler/parser.h
@@ -40,7 +40,6 @@
 #include <map>
 #include <string>
 #include <utility>
-#include <google/protobuf/stubs/common.h>
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/descriptor.pb.h>
 #include <google/protobuf/repeated_field.h>
@@ -233,6 +232,9 @@ class LIBPROTOBUF_EXPORT Parser {
     // location to the given token instead.
     void StartAt(const io::Tokenizer::Token& token);
 
+    // Start at the same location as some other LocationRecorder.
+    void StartAt(const LocationRecorder& other);
+
     // By default the location is considered to end at the previous token at
     // the time the LocationRecorder is destroyed.  EndAt() sets the end
     // location to the given token instead.
@@ -284,38 +286,50 @@ class LIBPROTOBUF_EXPORT Parser {
 
   // Parse various language high-level language construrcts.
   bool ParseMessageDefinition(DescriptorProto* message,
-                              const LocationRecorder& message_location);
+                              const LocationRecorder& message_location,
+                              const FileDescriptorProto* containing_file);
   bool ParseEnumDefinition(EnumDescriptorProto* enum_type,
-                           const LocationRecorder& enum_location);
+                           const LocationRecorder& enum_location,
+                           const FileDescriptorProto* containing_file);
   bool ParseServiceDefinition(ServiceDescriptorProto* service,
-                              const LocationRecorder& service_location);
+                              const LocationRecorder& service_location,
+                              const FileDescriptorProto* containing_file);
   bool ParsePackage(FileDescriptorProto* file,
-                    const LocationRecorder& root_location);
+                    const LocationRecorder& root_location,
+                    const FileDescriptorProto* containing_file);
   bool ParseImport(RepeatedPtrField<string>* dependency,
                    RepeatedField<int32>* public_dependency,
                    RepeatedField<int32>* weak_dependency,
-                   const LocationRecorder& root_location);
+                   const LocationRecorder& root_location,
+                   const FileDescriptorProto* containing_file);
   bool ParseOption(Message* options,
-                   const LocationRecorder& options_location);
+                   const LocationRecorder& options_location,
+                   const FileDescriptorProto* containing_file);
 
   // These methods parse the contents of a message, enum, or service type and
   // add them to the given object.  They consume the entire block including
   // the beginning and ending brace.
   bool ParseMessageBlock(DescriptorProto* message,
-                         const LocationRecorder& message_location);
+                         const LocationRecorder& message_location,
+                         const FileDescriptorProto* containing_file);
   bool ParseEnumBlock(EnumDescriptorProto* enum_type,
-                      const LocationRecorder& enum_location);
+                      const LocationRecorder& enum_location,
+                      const FileDescriptorProto* containing_file);
   bool ParseServiceBlock(ServiceDescriptorProto* service,
-                         const LocationRecorder& service_location);
+                         const LocationRecorder& service_location,
+                         const FileDescriptorProto* containing_file);
 
   // Parse one statement within a message, enum, or service block, inclunding
   // final semicolon.
   bool ParseMessageStatement(DescriptorProto* message,
-                             const LocationRecorder& message_location);
+                             const LocationRecorder& message_location,
+                             const FileDescriptorProto* containing_file);
   bool ParseEnumStatement(EnumDescriptorProto* message,
-                          const LocationRecorder& enum_location);
+                          const LocationRecorder& enum_location,
+                          const FileDescriptorProto* containing_file);
   bool ParseServiceStatement(ServiceDescriptorProto* message,
-                             const LocationRecorder& service_location);
+                             const LocationRecorder& service_location,
+                             const FileDescriptorProto* containing_file);
 
   // Parse a field of a message.  If the field is a group, its type will be
   // added to "messages".
@@ -329,11 +343,22 @@ class LIBPROTOBUF_EXPORT Parser {
                          RepeatedPtrField<DescriptorProto>* messages,
                          const LocationRecorder& parent_location,
                          int location_field_number_for_nested_type,
-                         const LocationRecorder& field_location);
+                         const LocationRecorder& field_location,
+                         const FileDescriptorProto* containing_file);
+
+  // Like ParseMessageField() but expects the label has already been filled in
+  // by the caller.
+  bool ParseMessageFieldNoLabel(FieldDescriptorProto* field,
+                                RepeatedPtrField<DescriptorProto>* messages,
+                                const LocationRecorder& parent_location,
+                                int location_field_number_for_nested_type,
+                                const LocationRecorder& field_location,
+                                const FileDescriptorProto* containing_file);
 
   // Parse an "extensions" declaration.
   bool ParseExtensions(DescriptorProto* message,
-                       const LocationRecorder& extensions_location);
+                       const LocationRecorder& extensions_location,
+                       const FileDescriptorProto* containing_file);
 
   // Parse an "extend" declaration.  (See also comments for
   // ParseMessageField().)
@@ -341,30 +366,46 @@ class LIBPROTOBUF_EXPORT Parser {
                    RepeatedPtrField<DescriptorProto>* messages,
                    const LocationRecorder& parent_location,
                    int location_field_number_for_nested_type,
-                   const LocationRecorder& extend_location);
+                   const LocationRecorder& extend_location,
+                   const FileDescriptorProto* containing_file);
+
+  // Parse a "oneof" declaration.  The caller is responsible for setting
+  // oneof_decl->label() since it will have had to parse the label before it
+  // knew it was parsing a oneof.
+  bool ParseOneof(OneofDescriptorProto* oneof_decl,
+                  DescriptorProto* containing_type,
+                  int oneof_index,
+                  const LocationRecorder& oneof_location,
+                  const LocationRecorder& containing_type_location,
+                  const FileDescriptorProto* containing_file);
 
   // Parse a single enum value within an enum block.
   bool ParseEnumConstant(EnumValueDescriptorProto* enum_value,
-                         const LocationRecorder& enum_value_location);
+                         const LocationRecorder& enum_value_location,
+                         const FileDescriptorProto* containing_file);
 
   // Parse enum constant options, i.e. the list in square brackets at the end
   // of the enum constant value definition.
   bool ParseEnumConstantOptions(EnumValueDescriptorProto* value,
-                                const LocationRecorder& enum_value_location);
+                                const LocationRecorder& enum_value_location,
+                                const FileDescriptorProto* containing_file);
 
   // Parse a single method within a service definition.
   bool ParseServiceMethod(MethodDescriptorProto* method,
-                          const LocationRecorder& method_location);
+                          const LocationRecorder& method_location,
+                          const FileDescriptorProto* containing_file);
 
 
   // Parse options of a single method or stream.
   bool ParseOptions(const LocationRecorder& parent_location,
+                    const FileDescriptorProto* containing_file,
                     const int optionsFieldNumber,
                     Message* mutable_options);
 
   // Parse "required", "optional", or "repeated" and fill in "label"
   // with the value.
-  bool ParseLabel(FieldDescriptorProto::Label* label);
+  bool ParseLabel(FieldDescriptorProto::Label* label,
+                  const FileDescriptorProto* containing_file);
 
   // Parse a type name and fill in "type" (if it is a primitive) or
   // "type_name" (if it is not) with the type parsed.
@@ -377,12 +418,14 @@ class LIBPROTOBUF_EXPORT Parser {
   // Parses field options, i.e. the stuff in square brackets at the end
   // of a field definition.  Also parses default value.
   bool ParseFieldOptions(FieldDescriptorProto* field,
-                         const LocationRecorder& field_location);
+                         const LocationRecorder& field_location,
+                         const FileDescriptorProto* containing_file);
 
   // Parse the "default" option.  This needs special handling because its
   // type is the field's type.
   bool ParseDefaultAssignment(FieldDescriptorProto* field,
-                              const LocationRecorder& field_location);
+                              const LocationRecorder& field_location,
+                              const FileDescriptorProto* containing_file);
 
   enum OptionStyle {
     OPTION_ASSIGNMENT,  // just "name = value"
@@ -394,6 +437,7 @@ class LIBPROTOBUF_EXPORT Parser {
   // is set to the parsed value.
   bool ParseOption(Message* options,
                    const LocationRecorder& options_location,
+                   const FileDescriptorProto* containing_file,
                    OptionStyle style);
 
   // Parses a single part of a multipart option name. A multipart name consists
@@ -401,7 +445,8 @@ class LIBPROTOBUF_EXPORT Parser {
   // of identifiers separated by dots and enclosed in parentheses. E.g.,
   // "foo.(bar.baz).qux".
   bool ParseOptionNamePart(UninterpretedOption* uninterpreted_option,
-                           const LocationRecorder& part_location);
+                           const LocationRecorder& part_location,
+                           const FileDescriptorProto* containing_file);
 
   // Parses a string surrounded by balanced braces.  Strips off the outer
   // braces and stores the enclosed string in *value.
diff --git a/src/google/protobuf/compiler/parser_unittest.cc b/src/google/protobuf/compiler/parser_unittest.cc
index c61ac60e..847370a8 100644
--- a/src/google/protobuf/compiler/parser_unittest.cc
+++ b/src/google/protobuf/compiler/parser_unittest.cc
@@ -32,6 +32,7 @@
 //  Based on original Protocol Buffers design by
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
+#include <memory>
 #include <vector>
 #include <algorithm>
 #include <map>
@@ -47,7 +48,7 @@
 #include <google/protobuf/unittest_custom_options.pb.h>
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
-#include <google/protobuf/stubs/map-util.h>
+#include <google/protobuf/stubs/map_util.h>
 
 #include <google/protobuf/testing/googletest.h>
 #include <gtest/gtest.h>
@@ -436,6 +437,69 @@ TEST_F(ParseMessageTest, FieldOptions) {
     "}");
 }
 
+TEST_F(ParseMessageTest, Oneof) {
+  ExpectParsesTo(
+    "message TestMessage {\n"
+    "  oneof foo {\n"
+    "    int32 a = 1;\n"
+    "    string b = 2;\n"
+    "    TestMessage c = 3;\n"
+    "    group D = 4 { optional int32 i = 5; }\n"
+    "  }\n"
+    "}\n",
+
+    "message_type {"
+    "  name: \"TestMessage\""
+    "  field { name:\"a\" label:LABEL_OPTIONAL type:TYPE_INT32 number:1 "
+    "          oneof_index:0 }"
+    "  field { name:\"b\" label:LABEL_OPTIONAL type:TYPE_STRING number:2 "
+    "          oneof_index:0 }"
+    "  field { name:\"c\" label:LABEL_OPTIONAL type_name:\"TestMessage\" "
+    "          number:3 oneof_index:0 }"
+    "  field { name:\"d\" label:LABEL_OPTIONAL type:TYPE_GROUP "
+    "          type_name:\"D\" number:4 oneof_index:0 }"
+    "  oneof_decl {"
+    "    name: \"foo\""
+    "  }"
+    "  nested_type {"
+    "    name: \"D\""
+    "    field { name:\"i\" label:LABEL_OPTIONAL type:TYPE_INT32 number:5 }"
+    "  }"
+    "}");
+}
+
+TEST_F(ParseMessageTest, MultipleOneofs) {
+  ExpectParsesTo(
+    "message TestMessage {\n"
+    "  oneof foo {\n"
+    "    int32 a = 1;\n"
+    "    string b = 2;\n"
+    "  }\n"
+    "  oneof bar {\n"
+    "    int32 c = 3;\n"
+    "    string d = 4;\n"
+    "  }\n"
+    "}\n",
+
+    "message_type {"
+    "  name: \"TestMessage\""
+    "  field { name:\"a\" label:LABEL_OPTIONAL type:TYPE_INT32 number:1 "
+    "          oneof_index:0 }"
+    "  field { name:\"b\" label:LABEL_OPTIONAL type:TYPE_STRING number:2 "
+    "          oneof_index:0 }"
+    "  field { name:\"c\" label:LABEL_OPTIONAL type:TYPE_INT32 number:3 "
+    "          oneof_index:1 }"
+    "  field { name:\"d\" label:LABEL_OPTIONAL type:TYPE_STRING number:4 "
+    "          oneof_index:1 }"
+    "  oneof_decl {"
+    "    name: \"foo\""
+    "  }"
+    "  oneof_decl {"
+    "    name: \"bar\""
+    "  }"
+    "}");
+}
+
 TEST_F(ParseMessageTest, Group) {
   ExpectParsesTo(
     "message TestMessage {\n"
@@ -575,6 +639,7 @@ TEST_F(ParseMessageTest, MultipleExtensionsOneExtendee) {
     "            type_name:\"TestMessage\" extendee: \"Extendee1\" }");
 }
 
+
 // ===================================================================
 
 typedef ParserTest ParseEnumTest;
@@ -681,6 +746,8 @@ TEST_F(ParseServiceTest, MethodsAndStreams) {
     "}");
 }
 
+
+
 // ===================================================================
 // imports and packages
 
@@ -870,7 +937,7 @@ TEST_F(ParseErrorTest, DefaultValueTypeMismatch) {
     "message TestMessage {\n"
     "  optional uint32 foo = 1 [default=true];\n"
     "}\n",
-    "1:35: Expected integer.\n");
+    "1:35: Expected integer for field default value.\n");
 }
 
 TEST_F(ParseErrorTest, DefaultValueNotBoolean) {
@@ -886,7 +953,7 @@ TEST_F(ParseErrorTest, DefaultValueNotString) {
     "message TestMessage {\n"
     "  optional string foo = 1 [default=1];\n"
     "}\n",
-    "1:35: Expected string.\n");
+    "1:35: Expected string for field default value.\n");
 }
 
 TEST_F(ParseErrorTest, DefaultValueUnsignedNegative) {
@@ -934,7 +1001,7 @@ TEST_F(ParseErrorTest, DefaultValueMissing) {
     "message TestMessage {\n"
     "  optional uint32 foo = 1 [default=];\n"
     "}\n",
-    "1:35: Expected integer.\n");
+    "1:35: Expected integer for field default value.\n");
 }
 
 TEST_F(ParseErrorTest, DefaultValueForGroup) {
@@ -953,6 +1020,27 @@ TEST_F(ParseErrorTest, DuplicateDefaultValue) {
     "1:37: Already set option \"default\".\n");
 }
 
+TEST_F(ParseErrorTest, MissingOneofName) {
+  ExpectHasErrors(
+    "message TestMessage {\n"
+    "  oneof {\n"
+    "    int32 bar = 1;\n"
+    "  }\n"
+    "}\n",
+    "1:8: Expected oneof name.\n");
+}
+
+TEST_F(ParseErrorTest, LabelInOneof) {
+  ExpectHasErrors(
+    "message TestMessage {\n"
+    "  oneof foo {\n"
+    "    optional int32 bar = 1;\n"
+    "  }\n"
+    "}\n",
+    "2:4: Fields in oneofs must not have labels (required / optional "
+      "/ repeated).\n");
+}
+
 TEST_F(ParseErrorTest, GroupNotCapitalized) {
   ExpectHasErrors(
     "message TestMessage {\n"
@@ -1244,17 +1332,93 @@ TEST_F(ParserValidationErrorTest, MethodOutputTypeError) {
 }
 
 
+TEST_F(ParserValidationErrorTest, ResovledUndefinedError) {
+  // Create another file which defines symbol ".base.bar".
+  FileDescriptorProto other_file;
+  other_file.set_name("base.proto");
+  other_file.set_package("base");
+  other_file.add_message_type()->set_name("bar");
+  EXPECT_TRUE(pool_.BuildFile(other_file) != NULL);
+
+  // Define "foo.base" and try "base.bar".
+  // "base.bar" is resolved to "foo.base.bar" which is not defined.
+  ExpectHasValidationErrors(
+    "package foo.base;\n"
+    "import \"base.proto\";\n"
+    "message qux {\n"
+    "  optional base.bar baz = 1;\n"
+    "  optional .base.bar quz = 2;\n"
+    "}\n",
+    "3:11: \"base.bar\" is resolved to \"foo.base.bar\","
+    " which is not defined. The innermost scope is searched first "
+    "in name resolution. Consider using a leading '.'(i.e., \".base.bar\")"
+    " to start from the outermost scope.\n");
+}
+
+TEST_F(ParserValidationErrorTest, ResovledUndefinedOptionError) {
+  // Build descriptor message in test pool
+  FileDescriptorProto descriptor_proto;
+  DescriptorProto::descriptor()->file()->CopyTo(&descriptor_proto);
+  ASSERT_TRUE(pool_.BuildFile(descriptor_proto) != NULL);
+
+  // base2.proto:
+  //   package baz
+  //   import google/protobuf/descriptor.proto
+  //   message Bar { optional int32 foo = 1; }
+  //   extend FileOptions { optional Bar bar = 7672757; }
+  FileDescriptorProto other_file;
+  other_file.set_name("base2.proto");
+  other_file.set_package("baz");
+  other_file.add_dependency();
+  other_file.set_dependency(0, descriptor_proto.name());
+
+  DescriptorProto* message(other_file.add_message_type());
+  message->set_name("Bar");
+  FieldDescriptorProto* field(message->add_field());
+  field->set_name("foo");
+  field->set_number(1);
+  field->set_label(FieldDescriptorProto_Label_LABEL_OPTIONAL);
+  field->set_type(FieldDescriptorProto_Type_TYPE_INT32);
+
+  FieldDescriptorProto* extension(other_file.add_extension());
+  extension->set_name("bar");
+  extension->set_number(7672757);
+  extension->set_label(FieldDescriptorProto_Label_LABEL_OPTIONAL);
+  extension->set_type(FieldDescriptorProto_Type_TYPE_MESSAGE);
+  extension->set_type_name("Bar");
+  extension->set_extendee("google.protobuf.FileOptions");
+
+  EXPECT_TRUE(pool_.BuildFile(other_file) != NULL);
+
+  // qux.proto:
+  //   package qux.baz
+  //   option (baz.bar).foo = 1;
+  //
+  // Although "baz.bar" is already defined, the lookup code will try
+  // "qux.baz.bar", since it's the match from the innermost scope,
+  // which will cause a symbol not defined error.
+  ExpectHasValidationErrors(
+      "package qux.baz;\n"
+      "import \"base2.proto\";\n"
+      "option (baz.bar).foo = 1;\n",
+      "2:7: Option \"(baz.bar)\" is resolved to \"(qux.baz.bar)\","
+      " which is not defined. The innermost scope is searched first "
+      "in name resolution. Consider using a leading '.'(i.e., \"(.baz.bar)\")"
+      " to start from the outermost scope.\n");
+}
+
 // ===================================================================
 // Test that the output from FileDescriptor::DebugString() (and all other
 // descriptor types) is parseable, and results in the same Descriptor
-// definitions again afoter parsing (not, however, that the order of messages
+// definitions again afoter parsing (note, however, that the order of messages
 // cannot be guaranteed to be the same)
 
 typedef ParserTest ParseDecriptorDebugTest;
 
 class CompareDescriptorNames {
  public:
-  bool operator()(const DescriptorProto* left, const DescriptorProto* right) {
+  bool operator()(const DescriptorProto* left,
+                  const DescriptorProto* right) const {
     return left->name() < right->name();
   }
 };
@@ -1298,7 +1462,8 @@ TEST_F(ParseDecriptorDebugTest, TestAllDescriptorTypes) {
   FileDescriptorProto parsed;
   parser_->Parse(input_.get(), &parsed);
   EXPECT_EQ(io::Tokenizer::TYPE_END, input_->current().type);
-  ASSERT_EQ("", error_collector_.text_);
+  ASSERT_EQ("", error_collector_.text_)
+      << "Failed to parse:\n" << debug_string;
 
   // We now have a FileDescriptorProto, but to compare with the expected we
   // need to link to a FileDecriptor, then output back to a proto. We'll
@@ -1317,6 +1482,8 @@ TEST_F(ParseDecriptorDebugTest, TestAllDescriptorTypes) {
   ASSERT_TRUE(pool_.BuildFile(import_proto) != NULL);
   const FileDescriptor* actual = pool_.BuildFile(parsed);
   parsed.Clear();
+  ASSERT_TRUE(actual != NULL)
+      << "Failed to validate:\n" << debug_string;
   actual->CopyTo(&parsed);
   ASSERT_TRUE(actual != NULL);
 
@@ -1871,6 +2038,31 @@ TEST_F(SourceInfoTest, ExtensionRanges) {
   EXPECT_TRUE(HasSpan(file_.message_type(0), "name"));
 }
 
+TEST_F(SourceInfoTest, Oneofs) {
+  EXPECT_TRUE(Parse(
+      "message Foo {\n"
+      "  $a$oneof $c$foo$d$ {\n"
+      "    $e$int32$f$ $g$a$h$ = $i$1$j$;$k$\n"
+      "  }$r$\n"
+      "}\n"));
+
+  const OneofDescriptorProto& oneof_decl = file_.message_type(0).oneof_decl(0);
+  const FieldDescriptorProto& field = file_.message_type(0).field(0);
+
+  EXPECT_TRUE(HasSpan('a', 'r', oneof_decl));
+  EXPECT_TRUE(HasSpan('c', 'd', oneof_decl, "name"));
+
+  EXPECT_TRUE(HasSpan('e', 'k', field));
+  EXPECT_TRUE(HasSpan('e', 'f', field, "type"));
+  EXPECT_TRUE(HasSpan('g', 'h', field, "name"));
+  EXPECT_TRUE(HasSpan('i', 'j', field, "number"));
+
+  // Ignore these.
+  EXPECT_TRUE(HasSpan(file_));
+  EXPECT_TRUE(HasSpan(file_.message_type(0)));
+  EXPECT_TRUE(HasSpan(file_.message_type(0), "name"));
+}
+
 TEST_F(SourceInfoTest, NestedMessages) {
   EXPECT_TRUE(Parse(
       "message Foo {\n"
@@ -2029,6 +2221,7 @@ TEST_F(SourceInfoTest, MethodsAndStreams) {
   EXPECT_TRUE(HasSpan(file_.service(0), "name"));
 }
 
+
 TEST_F(SourceInfoTest, Options) {
   EXPECT_TRUE(Parse(
       "$a$option $b$foo$c$.$d$($e$bar.baz$f$)$g$ = "
@@ -2365,6 +2558,51 @@ TEST_F(SourceInfoTest, DocComments3) {
       bar.options().uninterpreted_option(0), "aggregate_value"));
 }
 
+TEST_F(SourceInfoTest, DocCommentsOneof) {
+  EXPECT_TRUE(Parse(
+      "// ignored\n"
+      "syntax = \"proto2\";\n"
+      "// Foo leading\n"
+      "$a$message Foo {\n"
+      "  /* Foo trailing\n"
+      "   */\n"
+      "  // ignored\n"
+      "  /* bar leading\n"
+      "   * line 2 */\n"
+      "  $b$oneof bar {\n"
+      "  /* bar trailing\n"
+      "   * line 2 */\n"
+      "  // ignored\n"
+      "  /* bar_int leading\n"
+      "   */\n"
+      "  $c$int32 bar_int = 1;$d$  // bar_int trailing\n"
+      "  // ignored\n"
+      "  }$e$\n"
+      "}$f$\n"));
+
+  const DescriptorProto& foo = file_.message_type(0);
+  const OneofDescriptorProto& bar = foo.oneof_decl(0);
+  const FieldDescriptorProto& bar_int = foo.field(0);
+
+  EXPECT_TRUE(HasSpanWithComment('a', 'f', foo,
+      " Foo leading\n",
+      " Foo trailing\n"));
+  EXPECT_TRUE(HasSpanWithComment('b', 'e', bar,
+      " bar leading\n line 2 ",
+      " bar trailing\n line 2 "));
+  EXPECT_TRUE(HasSpanWithComment('c', 'd', bar_int,
+      " bar_int leading\n",
+      " bar_int trailing\n"));
+
+  // Ignore these.
+  EXPECT_TRUE(HasSpan(file_));
+  EXPECT_TRUE(HasSpan(foo, "name"));
+  EXPECT_TRUE(HasSpan(bar, "name"));
+  EXPECT_TRUE(HasSpan(bar_int, "type"));
+  EXPECT_TRUE(HasSpan(bar_int, "name"));
+  EXPECT_TRUE(HasSpan(bar_int, "number"));
+}
+
 // ===================================================================
 
 }  // anonymous namespace
diff --git a/src/google/protobuf/compiler/plugin.pb.cc b/src/google/protobuf/compiler/plugin.pb.cc
index 6525d15c..b5cd01b5 100644
--- a/src/google/protobuf/compiler/plugin.pb.cc
+++ b/src/google/protobuf/compiler/plugin.pb.cc
@@ -171,6 +171,7 @@ const int CodeGeneratorRequest::kProtoFileFieldNumber;
 CodeGeneratorRequest::CodeGeneratorRequest()
   : ::google::protobuf::Message() {
   SharedCtor();
+  // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorRequest)
 }
 
 void CodeGeneratorRequest::InitAsDefaultInstance() {
@@ -180,20 +181,23 @@ CodeGeneratorRequest::CodeGeneratorRequest(const CodeGeneratorRequest& from)
   : ::google::protobuf::Message() {
   SharedCtor();
   MergeFrom(from);
+  // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorRequest)
 }
 
 void CodeGeneratorRequest::SharedCtor() {
+  ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+  parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
 CodeGeneratorRequest::~CodeGeneratorRequest() {
+  // @@protoc_insertion_point(destructor:google.protobuf.compiler.CodeGeneratorRequest)
   SharedDtor();
 }
 
 void CodeGeneratorRequest::SharedDtor() {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete parameter_;
   }
   if (this != default_instance_) {
@@ -222,11 +226,9 @@ CodeGeneratorRequest* CodeGeneratorRequest::New() const {
 }
 
 void CodeGeneratorRequest::Clear() {
-  if (_has_bits_[1 / 32] & (0xffu << (1 % 32))) {
-    if (has_parameter()) {
-      if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
-        parameter_->clear();
-      }
+  if (has_parameter()) {
+    if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
+      parameter_->clear();
     }
   }
   file_to_generate_.Clear();
@@ -237,23 +239,27 @@ void CodeGeneratorRequest::Clear() {
 
 bool CodeGeneratorRequest::MergePartialFromCodedStream(
     ::google::protobuf::io::CodedInputStream* input) {
-#define DO_(EXPRESSION) if (!(EXPRESSION)) return false
+#define DO_(EXPRESSION) if (!(EXPRESSION)) goto failure
   ::google::protobuf::uint32 tag;
-  while ((tag = input->ReadTag()) != 0) {
+  // @@protoc_insertion_point(parse_start:google.protobuf.compiler.CodeGeneratorRequest)
+  for (;;) {
+    ::std::pair< ::google::protobuf::uint32, bool> p = input->ReadTagWithCutoff(127);
+    tag = p.first;
+    if (!p.second) goto handle_unusual;
     switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {
       // repeated string file_to_generate = 1;
       case 1: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 10) {
          parse_file_to_generate:
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->add_file_to_generate()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->file_to_generate(this->file_to_generate_size() - 1).data(),
             this->file_to_generate(this->file_to_generate_size() - 1).length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "file_to_generate");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(10)) goto parse_file_to_generate;
         if (input->ExpectTag(18)) goto parse_parameter;
@@ -262,16 +268,16 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
 
       // optional string parameter = 2;
       case 2: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 18) {
          parse_parameter:
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->mutable_parameter()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->parameter().data(), this->parameter().length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "parameter");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(122)) goto parse_proto_file;
         break;
@@ -279,24 +285,24 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
 
       // repeated .google.protobuf.FileDescriptorProto proto_file = 15;
       case 15: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 122) {
          parse_proto_file:
           DO_(::google::protobuf::internal::WireFormatLite::ReadMessageNoVirtual(
                 input, add_proto_file()));
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(122)) goto parse_proto_file;
-        if (input->ExpectAtEnd()) return true;
+        if (input->ExpectAtEnd()) goto success;
         break;
       }
 
       default: {
-      handle_uninterpreted:
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
+      handle_unusual:
+        if (tag == 0 ||
+            ::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
             ::google::protobuf::internal::WireFormatLite::WIRETYPE_END_GROUP) {
-          return true;
+          goto success;
         }
         DO_(::google::protobuf::internal::WireFormat::SkipField(
               input, tag, mutable_unknown_fields()));
@@ -304,27 +310,35 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
       }
     }
   }
+success:
+  // @@protoc_insertion_point(parse_success:google.protobuf.compiler.CodeGeneratorRequest)
   return true;
+failure:
+  // @@protoc_insertion_point(parse_failure:google.protobuf.compiler.CodeGeneratorRequest)
+  return false;
 #undef DO_
 }
 
 void CodeGeneratorRequest::SerializeWithCachedSizes(
     ::google::protobuf::io::CodedOutputStream* output) const {
+  // @@protoc_insertion_point(serialize_start:google.protobuf.compiler.CodeGeneratorRequest)
   // repeated string file_to_generate = 1;
   for (int i = 0; i < this->file_to_generate_size(); i++) {
-  ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+  ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
     this->file_to_generate(i).data(), this->file_to_generate(i).length(),
-    ::google::protobuf::internal::WireFormat::SERIALIZE);
+    ::google::protobuf::internal::WireFormat::SERIALIZE,
+    "file_to_generate");
     ::google::protobuf::internal::WireFormatLite::WriteString(
       1, this->file_to_generate(i), output);
   }
 
   // optional string parameter = 2;
   if (has_parameter()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->parameter().data(), this->parameter().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
-    ::google::protobuf::internal::WireFormatLite::WriteString(
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "parameter");
+    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       2, this->parameter(), output);
   }
 
@@ -338,24 +352,28 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
+  // @@protoc_insertion_point(serialize_end:google.protobuf.compiler.CodeGeneratorRequest)
 }
 
 ::google::protobuf::uint8* CodeGeneratorRequest::SerializeWithCachedSizesToArray(
     ::google::protobuf::uint8* target) const {
+  // @@protoc_insertion_point(serialize_to_array_start:google.protobuf.compiler.CodeGeneratorRequest)
   // repeated string file_to_generate = 1;
   for (int i = 0; i < this->file_to_generate_size(); i++) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->file_to_generate(i).data(), this->file_to_generate(i).length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "file_to_generate");
     target = ::google::protobuf::internal::WireFormatLite::
       WriteStringToArray(1, this->file_to_generate(i), target);
   }
 
   // optional string parameter = 2;
   if (has_parameter()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->parameter().data(), this->parameter().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "parameter");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         2, this->parameter(), target);
@@ -372,6 +390,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
+  // @@protoc_insertion_point(serialize_to_array_end:google.protobuf.compiler.CodeGeneratorRequest)
   return target;
 }
 
@@ -451,9 +470,7 @@ void CodeGeneratorRequest::CopyFrom(const CodeGeneratorRequest& from) {
 
 bool CodeGeneratorRequest::IsInitialized() const {
 
-  for (int i = 0; i < proto_file_size(); i++) {
-    if (!this->proto_file(i).IsInitialized()) return false;
-  }
+  if (!::google::protobuf::internal::AllAreInitialized(this->proto_file())) return false;
   return true;
 }
 
@@ -488,6 +505,7 @@ const int CodeGeneratorResponse_File::kContentFieldNumber;
 CodeGeneratorResponse_File::CodeGeneratorResponse_File()
   : ::google::protobuf::Message() {
   SharedCtor();
+  // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorResponse.File)
 }
 
 void CodeGeneratorResponse_File::InitAsDefaultInstance() {
@@ -497,28 +515,31 @@ CodeGeneratorResponse_File::CodeGeneratorResponse_File(const CodeGeneratorRespon
   : ::google::protobuf::Message() {
   SharedCtor();
   MergeFrom(from);
+  // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorResponse.File)
 }
 
 void CodeGeneratorResponse_File::SharedCtor() {
+  ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
-  insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
-  content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+  name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
 CodeGeneratorResponse_File::~CodeGeneratorResponse_File() {
+  // @@protoc_insertion_point(destructor:google.protobuf.compiler.CodeGeneratorResponse.File)
   SharedDtor();
 }
 
 void CodeGeneratorResponse_File::SharedDtor() {
-  if (name_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete name_;
   }
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete insertion_point_;
   }
-  if (content_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete content_;
   }
   if (this != default_instance_) {
@@ -547,19 +568,19 @@ CodeGeneratorResponse_File* CodeGeneratorResponse_File::New() const {
 }
 
 void CodeGeneratorResponse_File::Clear() {
-  if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
+  if (_has_bits_[0 / 32] & 7) {
     if (has_name()) {
-      if (name_ != &::google::protobuf::internal::GetEmptyString()) {
+      if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
         name_->clear();
       }
     }
     if (has_insertion_point()) {
-      if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
+      if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
         insertion_point_->clear();
       }
     }
     if (has_content()) {
-      if (content_ != &::google::protobuf::internal::GetEmptyString()) {
+      if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
         content_->clear();
       }
     }
@@ -570,21 +591,25 @@ void CodeGeneratorResponse_File::Clear() {
 
 bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
     ::google::protobuf::io::CodedInputStream* input) {
-#define DO_(EXPRESSION) if (!(EXPRESSION)) return false
+#define DO_(EXPRESSION) if (!(EXPRESSION)) goto failure
   ::google::protobuf::uint32 tag;
-  while ((tag = input->ReadTag()) != 0) {
+  // @@protoc_insertion_point(parse_start:google.protobuf.compiler.CodeGeneratorResponse.File)
+  for (;;) {
+    ::std::pair< ::google::protobuf::uint32, bool> p = input->ReadTagWithCutoff(127);
+    tag = p.first;
+    if (!p.second) goto handle_unusual;
     switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {
       // optional string name = 1;
       case 1: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 10) {
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->mutable_name()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->name().data(), this->name().length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "name");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(18)) goto parse_insertion_point;
         break;
@@ -592,16 +617,16 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
 
       // optional string insertion_point = 2;
       case 2: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 18) {
          parse_insertion_point:
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->mutable_insertion_point()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->insertion_point().data(), this->insertion_point().length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "insertion_point");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(122)) goto parse_content;
         break;
@@ -609,26 +634,27 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
 
       // optional string content = 15;
       case 15: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 122) {
          parse_content:
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->mutable_content()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->content().data(), this->content().length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "content");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
-        if (input->ExpectAtEnd()) return true;
+        if (input->ExpectAtEnd()) goto success;
         break;
       }
 
       default: {
-      handle_uninterpreted:
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
+      handle_unusual:
+        if (tag == 0 ||
+            ::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
             ::google::protobuf::internal::WireFormatLite::WIRETYPE_END_GROUP) {
-          return true;
+          goto success;
         }
         DO_(::google::protobuf::internal::WireFormat::SkipField(
               input, tag, mutable_unknown_fields()));
@@ -636,36 +662,45 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
       }
     }
   }
+success:
+  // @@protoc_insertion_point(parse_success:google.protobuf.compiler.CodeGeneratorResponse.File)
   return true;
+failure:
+  // @@protoc_insertion_point(parse_failure:google.protobuf.compiler.CodeGeneratorResponse.File)
+  return false;
 #undef DO_
 }
 
 void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::io::CodedOutputStream* output) const {
+  // @@protoc_insertion_point(serialize_start:google.protobuf.compiler.CodeGeneratorResponse.File)
   // optional string name = 1;
   if (has_name()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->name().data(), this->name().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
-    ::google::protobuf::internal::WireFormatLite::WriteString(
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "name");
+    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       1, this->name(), output);
   }
 
   // optional string insertion_point = 2;
   if (has_insertion_point()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->insertion_point().data(), this->insertion_point().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
-    ::google::protobuf::internal::WireFormatLite::WriteString(
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "insertion_point");
+    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       2, this->insertion_point(), output);
   }
 
   // optional string content = 15;
   if (has_content()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->content().data(), this->content().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
-    ::google::protobuf::internal::WireFormatLite::WriteString(
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "content");
+    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       15, this->content(), output);
   }
 
@@ -673,15 +708,18 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
+  // @@protoc_insertion_point(serialize_end:google.protobuf.compiler.CodeGeneratorResponse.File)
 }
 
 ::google::protobuf::uint8* CodeGeneratorResponse_File::SerializeWithCachedSizesToArray(
     ::google::protobuf::uint8* target) const {
+  // @@protoc_insertion_point(serialize_to_array_start:google.protobuf.compiler.CodeGeneratorResponse.File)
   // optional string name = 1;
   if (has_name()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->name().data(), this->name().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "name");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         1, this->name(), target);
@@ -689,9 +727,10 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
 
   // optional string insertion_point = 2;
   if (has_insertion_point()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->insertion_point().data(), this->insertion_point().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "insertion_point");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         2, this->insertion_point(), target);
@@ -699,9 +738,10 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
 
   // optional string content = 15;
   if (has_content()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->content().data(), this->content().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "content");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         15, this->content(), target);
@@ -711,6 +751,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
+  // @@protoc_insertion_point(serialize_to_array_end:google.protobuf.compiler.CodeGeneratorResponse.File)
   return target;
 }
 
@@ -826,6 +867,7 @@ const int CodeGeneratorResponse::kFileFieldNumber;
 CodeGeneratorResponse::CodeGeneratorResponse()
   : ::google::protobuf::Message() {
   SharedCtor();
+  // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorResponse)
 }
 
 void CodeGeneratorResponse::InitAsDefaultInstance() {
@@ -835,20 +877,23 @@ CodeGeneratorResponse::CodeGeneratorResponse(const CodeGeneratorResponse& from)
   : ::google::protobuf::Message() {
   SharedCtor();
   MergeFrom(from);
+  // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorResponse)
 }
 
 void CodeGeneratorResponse::SharedCtor() {
+  ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+  error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
 CodeGeneratorResponse::~CodeGeneratorResponse() {
+  // @@protoc_insertion_point(destructor:google.protobuf.compiler.CodeGeneratorResponse)
   SharedDtor();
 }
 
 void CodeGeneratorResponse::SharedDtor() {
-  if (error_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete error_;
   }
   if (this != default_instance_) {
@@ -877,11 +922,9 @@ CodeGeneratorResponse* CodeGeneratorResponse::New() const {
 }
 
 void CodeGeneratorResponse::Clear() {
-  if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
-    if (has_error()) {
-      if (error_ != &::google::protobuf::internal::GetEmptyString()) {
-        error_->clear();
-      }
+  if (has_error()) {
+    if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
+      error_->clear();
     }
   }
   file_.Clear();
@@ -891,21 +934,25 @@ void CodeGeneratorResponse::Clear() {
 
 bool CodeGeneratorResponse::MergePartialFromCodedStream(
     ::google::protobuf::io::CodedInputStream* input) {
-#define DO_(EXPRESSION) if (!(EXPRESSION)) return false
+#define DO_(EXPRESSION) if (!(EXPRESSION)) goto failure
   ::google::protobuf::uint32 tag;
-  while ((tag = input->ReadTag()) != 0) {
+  // @@protoc_insertion_point(parse_start:google.protobuf.compiler.CodeGeneratorResponse)
+  for (;;) {
+    ::std::pair< ::google::protobuf::uint32, bool> p = input->ReadTagWithCutoff(127);
+    tag = p.first;
+    if (!p.second) goto handle_unusual;
     switch (::google::protobuf::internal::WireFormatLite::GetTagFieldNumber(tag)) {
       // optional string error = 1;
       case 1: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 10) {
           DO_(::google::protobuf::internal::WireFormatLite::ReadString(
                 input, this->mutable_error()));
-          ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+          ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->error().data(), this->error().length(),
-            ::google::protobuf::internal::WireFormat::PARSE);
+            ::google::protobuf::internal::WireFormat::PARSE,
+            "error");
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(122)) goto parse_file;
         break;
@@ -913,24 +960,24 @@ bool CodeGeneratorResponse::MergePartialFromCodedStream(
 
       // repeated .google.protobuf.compiler.CodeGeneratorResponse.File file = 15;
       case 15: {
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
-            ::google::protobuf::internal::WireFormatLite::WIRETYPE_LENGTH_DELIMITED) {
+        if (tag == 122) {
          parse_file:
           DO_(::google::protobuf::internal::WireFormatLite::ReadMessageNoVirtual(
                 input, add_file()));
         } else {
-          goto handle_uninterpreted;
+          goto handle_unusual;
         }
         if (input->ExpectTag(122)) goto parse_file;
-        if (input->ExpectAtEnd()) return true;
+        if (input->ExpectAtEnd()) goto success;
         break;
       }
 
       default: {
-      handle_uninterpreted:
-        if (::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
+      handle_unusual:
+        if (tag == 0 ||
+            ::google::protobuf::internal::WireFormatLite::GetTagWireType(tag) ==
             ::google::protobuf::internal::WireFormatLite::WIRETYPE_END_GROUP) {
-          return true;
+          goto success;
         }
         DO_(::google::protobuf::internal::WireFormat::SkipField(
               input, tag, mutable_unknown_fields()));
@@ -938,18 +985,25 @@ bool CodeGeneratorResponse::MergePartialFromCodedStream(
       }
     }
   }
+success:
+  // @@protoc_insertion_point(parse_success:google.protobuf.compiler.CodeGeneratorResponse)
   return true;
+failure:
+  // @@protoc_insertion_point(parse_failure:google.protobuf.compiler.CodeGeneratorResponse)
+  return false;
 #undef DO_
 }
 
 void CodeGeneratorResponse::SerializeWithCachedSizes(
     ::google::protobuf::io::CodedOutputStream* output) const {
+  // @@protoc_insertion_point(serialize_start:google.protobuf.compiler.CodeGeneratorResponse)
   // optional string error = 1;
   if (has_error()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->error().data(), this->error().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
-    ::google::protobuf::internal::WireFormatLite::WriteString(
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "error");
+    ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       1, this->error(), output);
   }
 
@@ -963,15 +1017,18 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
+  // @@protoc_insertion_point(serialize_end:google.protobuf.compiler.CodeGeneratorResponse)
 }
 
 ::google::protobuf::uint8* CodeGeneratorResponse::SerializeWithCachedSizesToArray(
     ::google::protobuf::uint8* target) const {
+  // @@protoc_insertion_point(serialize_to_array_start:google.protobuf.compiler.CodeGeneratorResponse)
   // optional string error = 1;
   if (has_error()) {
-    ::google::protobuf::internal::WireFormat::VerifyUTF8String(
+    ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->error().data(), this->error().length(),
-      ::google::protobuf::internal::WireFormat::SERIALIZE);
+      ::google::protobuf::internal::WireFormat::SERIALIZE,
+      "error");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         1, this->error(), target);
@@ -988,6 +1045,7 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
+  // @@protoc_insertion_point(serialize_to_array_end:google.protobuf.compiler.CodeGeneratorResponse)
   return target;
 }
 
diff --git a/src/google/protobuf/compiler/plugin.pb.h b/src/google/protobuf/compiler/plugin.pb.h
index d26a135e..b590d8df 100644
--- a/src/google/protobuf/compiler/plugin.pb.h
+++ b/src/google/protobuf/compiler/plugin.pb.h
@@ -89,7 +89,6 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
   void SharedDtor();
   void SetCachedSize(int size) const;
   public:
-
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -143,13 +142,11 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
 
   ::google::protobuf::UnknownFieldSet _unknown_fields_;
 
+  ::google::protobuf::uint32 _has_bits_[1];
+  mutable int _cached_size_;
   ::google::protobuf::RepeatedPtrField< ::std::string> file_to_generate_;
   ::std::string* parameter_;
   ::google::protobuf::RepeatedPtrField< ::google::protobuf::FileDescriptorProto > proto_file_;
-
-  mutable int _cached_size_;
-  ::google::protobuf::uint32 _has_bits_[(3 + 31) / 32];
-
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_ShutdownFile_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -206,7 +203,6 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   void SharedDtor();
   void SetCachedSize(int size) const;
   public:
-
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -260,13 +256,11 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
 
   ::google::protobuf::UnknownFieldSet _unknown_fields_;
 
+  ::google::protobuf::uint32 _has_bits_[1];
+  mutable int _cached_size_;
   ::std::string* name_;
   ::std::string* insertion_point_;
   ::std::string* content_;
-
-  mutable int _cached_size_;
-  ::google::protobuf::uint32 _has_bits_[(3 + 31) / 32];
-
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_ShutdownFile_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -323,7 +317,6 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
   void SharedDtor();
   void SetCachedSize(int size) const;
   public:
-
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -363,12 +356,10 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
 
   ::google::protobuf::UnknownFieldSet _unknown_fields_;
 
+  ::google::protobuf::uint32 _has_bits_[1];
+  mutable int _cached_size_;
   ::std::string* error_;
   ::google::protobuf::RepeatedPtrField< ::google::protobuf::compiler::CodeGeneratorResponse_File > file_;
-
-  mutable int _cached_size_;
-  ::google::protobuf::uint32 _has_bits_[(2 + 31) / 32];
-
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_ShutdownFile_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -391,39 +382,49 @@ inline void CodeGeneratorRequest::clear_file_to_generate() {
   file_to_generate_.Clear();
 }
 inline const ::std::string& CodeGeneratorRequest::file_to_generate(int index) const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
   return file_to_generate_.Get(index);
 }
 inline ::std::string* CodeGeneratorRequest::mutable_file_to_generate(int index) {
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
   return file_to_generate_.Mutable(index);
 }
 inline void CodeGeneratorRequest::set_file_to_generate(int index, const ::std::string& value) {
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
   file_to_generate_.Mutable(index)->assign(value);
 }
 inline void CodeGeneratorRequest::set_file_to_generate(int index, const char* value) {
   file_to_generate_.Mutable(index)->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
 }
 inline void CodeGeneratorRequest::set_file_to_generate(int index, const char* value, size_t size) {
   file_to_generate_.Mutable(index)->assign(
     reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
 }
 inline ::std::string* CodeGeneratorRequest::add_file_to_generate() {
   return file_to_generate_.Add();
 }
 inline void CodeGeneratorRequest::add_file_to_generate(const ::std::string& value) {
   file_to_generate_.Add()->assign(value);
+  // @@protoc_insertion_point(field_add:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
 }
 inline void CodeGeneratorRequest::add_file_to_generate(const char* value) {
   file_to_generate_.Add()->assign(value);
+  // @@protoc_insertion_point(field_add_char:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
 }
 inline void CodeGeneratorRequest::add_file_to_generate(const char* value, size_t size) {
   file_to_generate_.Add()->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_add_pointer:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
 }
 inline const ::google::protobuf::RepeatedPtrField< ::std::string>&
 CodeGeneratorRequest::file_to_generate() const {
+  // @@protoc_insertion_point(field_list:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
   return file_to_generate_;
 }
 inline ::google::protobuf::RepeatedPtrField< ::std::string>*
 CodeGeneratorRequest::mutable_file_to_generate() {
+  // @@protoc_insertion_point(field_mutable_list:google.protobuf.compiler.CodeGeneratorRequest.file_to_generate)
   return &file_to_generate_;
 }
 
@@ -438,54 +439,59 @@ inline void CodeGeneratorRequest::clear_has_parameter() {
   _has_bits_[0] &= ~0x00000002u;
 }
 inline void CodeGeneratorRequest::clear_parameter() {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     parameter_->clear();
   }
   clear_has_parameter();
 }
 inline const ::std::string& CodeGeneratorRequest::parameter() const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorRequest.parameter)
   return *parameter_;
 }
 inline void CodeGeneratorRequest::set_parameter(const ::std::string& value) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     parameter_ = new ::std::string;
   }
   parameter_->assign(value);
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 inline void CodeGeneratorRequest::set_parameter(const char* value) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     parameter_ = new ::std::string;
   }
   parameter_->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 inline void CodeGeneratorRequest::set_parameter(const char* value, size_t size) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     parameter_ = new ::std::string;
   }
   parameter_->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 inline ::std::string* CodeGeneratorRequest::mutable_parameter() {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     parameter_ = new ::std::string;
   }
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorRequest.parameter)
   return parameter_;
 }
 inline ::std::string* CodeGeneratorRequest::release_parameter() {
   clear_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     return NULL;
   } else {
     ::std::string* temp = parameter_;
-    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
     return temp;
   }
 }
 inline void CodeGeneratorRequest::set_allocated_parameter(::std::string* parameter) {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete parameter_;
   }
   if (parameter) {
@@ -493,8 +499,9 @@ inline void CodeGeneratorRequest::set_allocated_parameter(::std::string* paramet
     parameter_ = parameter;
   } else {
     clear_has_parameter();
-    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 
 // repeated .google.protobuf.FileDescriptorProto proto_file = 15;
@@ -505,20 +512,25 @@ inline void CodeGeneratorRequest::clear_proto_file() {
   proto_file_.Clear();
 }
 inline const ::google::protobuf::FileDescriptorProto& CodeGeneratorRequest::proto_file(int index) const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorRequest.proto_file)
   return proto_file_.Get(index);
 }
 inline ::google::protobuf::FileDescriptorProto* CodeGeneratorRequest::mutable_proto_file(int index) {
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorRequest.proto_file)
   return proto_file_.Mutable(index);
 }
 inline ::google::protobuf::FileDescriptorProto* CodeGeneratorRequest::add_proto_file() {
+  // @@protoc_insertion_point(field_add:google.protobuf.compiler.CodeGeneratorRequest.proto_file)
   return proto_file_.Add();
 }
 inline const ::google::protobuf::RepeatedPtrField< ::google::protobuf::FileDescriptorProto >&
 CodeGeneratorRequest::proto_file() const {
+  // @@protoc_insertion_point(field_list:google.protobuf.compiler.CodeGeneratorRequest.proto_file)
   return proto_file_;
 }
 inline ::google::protobuf::RepeatedPtrField< ::google::protobuf::FileDescriptorProto >*
 CodeGeneratorRequest::mutable_proto_file() {
+  // @@protoc_insertion_point(field_mutable_list:google.protobuf.compiler.CodeGeneratorRequest.proto_file)
   return &proto_file_;
 }
 
@@ -537,54 +549,59 @@ inline void CodeGeneratorResponse_File::clear_has_name() {
   _has_bits_[0] &= ~0x00000001u;
 }
 inline void CodeGeneratorResponse_File::clear_name() {
-  if (name_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     name_->clear();
   }
   clear_has_name();
 }
 inline const ::std::string& CodeGeneratorResponse_File::name() const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.name)
   return *name_;
 }
 inline void CodeGeneratorResponse_File::set_name(const ::std::string& value) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     name_ = new ::std::string;
   }
   name_->assign(value);
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 inline void CodeGeneratorResponse_File::set_name(const char* value) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     name_ = new ::std::string;
   }
   name_->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 inline void CodeGeneratorResponse_File::set_name(const char* value, size_t size) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     name_ = new ::std::string;
   }
   name_->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_name() {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     name_ = new ::std::string;
   }
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.name)
   return name_;
 }
 inline ::std::string* CodeGeneratorResponse_File::release_name() {
   clear_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     return NULL;
   } else {
     ::std::string* temp = name_;
-    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
     return temp;
   }
 }
 inline void CodeGeneratorResponse_File::set_allocated_name(::std::string* name) {
-  if (name_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete name_;
   }
   if (name) {
@@ -592,8 +609,9 @@ inline void CodeGeneratorResponse_File::set_allocated_name(::std::string* name)
     name_ = name;
   } else {
     clear_has_name();
-    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 
 // optional string insertion_point = 2;
@@ -607,54 +625,59 @@ inline void CodeGeneratorResponse_File::clear_has_insertion_point() {
   _has_bits_[0] &= ~0x00000002u;
 }
 inline void CodeGeneratorResponse_File::clear_insertion_point() {
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     insertion_point_->clear();
   }
   clear_has_insertion_point();
 }
 inline const ::std::string& CodeGeneratorResponse_File::insertion_point() const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
   return *insertion_point_;
 }
 inline void CodeGeneratorResponse_File::set_insertion_point(const ::std::string& value) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     insertion_point_ = new ::std::string;
   }
   insertion_point_->assign(value);
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 inline void CodeGeneratorResponse_File::set_insertion_point(const char* value) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     insertion_point_ = new ::std::string;
   }
   insertion_point_->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 inline void CodeGeneratorResponse_File::set_insertion_point(const char* value, size_t size) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     insertion_point_ = new ::std::string;
   }
   insertion_point_->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_insertion_point() {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     insertion_point_ = new ::std::string;
   }
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
   return insertion_point_;
 }
 inline ::std::string* CodeGeneratorResponse_File::release_insertion_point() {
   clear_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     return NULL;
   } else {
     ::std::string* temp = insertion_point_;
-    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
     return temp;
   }
 }
 inline void CodeGeneratorResponse_File::set_allocated_insertion_point(::std::string* insertion_point) {
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete insertion_point_;
   }
   if (insertion_point) {
@@ -662,8 +685,9 @@ inline void CodeGeneratorResponse_File::set_allocated_insertion_point(::std::str
     insertion_point_ = insertion_point;
   } else {
     clear_has_insertion_point();
-    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 
 // optional string content = 15;
@@ -677,54 +701,59 @@ inline void CodeGeneratorResponse_File::clear_has_content() {
   _has_bits_[0] &= ~0x00000004u;
 }
 inline void CodeGeneratorResponse_File::clear_content() {
-  if (content_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     content_->clear();
   }
   clear_has_content();
 }
 inline const ::std::string& CodeGeneratorResponse_File::content() const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.content)
   return *content_;
 }
 inline void CodeGeneratorResponse_File::set_content(const ::std::string& value) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     content_ = new ::std::string;
   }
   content_->assign(value);
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 inline void CodeGeneratorResponse_File::set_content(const char* value) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     content_ = new ::std::string;
   }
   content_->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 inline void CodeGeneratorResponse_File::set_content(const char* value, size_t size) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     content_ = new ::std::string;
   }
   content_->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_content() {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     content_ = new ::std::string;
   }
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.content)
   return content_;
 }
 inline ::std::string* CodeGeneratorResponse_File::release_content() {
   clear_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     return NULL;
   } else {
     ::std::string* temp = content_;
-    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
     return temp;
   }
 }
 inline void CodeGeneratorResponse_File::set_allocated_content(::std::string* content) {
-  if (content_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete content_;
   }
   if (content) {
@@ -732,8 +761,9 @@ inline void CodeGeneratorResponse_File::set_allocated_content(::std::string* con
     content_ = content;
   } else {
     clear_has_content();
-    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 
 // -------------------------------------------------------------------
@@ -751,54 +781,59 @@ inline void CodeGeneratorResponse::clear_has_error() {
   _has_bits_[0] &= ~0x00000001u;
 }
 inline void CodeGeneratorResponse::clear_error() {
-  if (error_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     error_->clear();
   }
   clear_has_error();
 }
 inline const ::std::string& CodeGeneratorResponse::error() const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.error)
   return *error_;
 }
 inline void CodeGeneratorResponse::set_error(const ::std::string& value) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     error_ = new ::std::string;
   }
   error_->assign(value);
+  // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 inline void CodeGeneratorResponse::set_error(const char* value) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     error_ = new ::std::string;
   }
   error_->assign(value);
+  // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 inline void CodeGeneratorResponse::set_error(const char* value, size_t size) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     error_ = new ::std::string;
   }
   error_->assign(reinterpret_cast<const char*>(value), size);
+  // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 inline ::std::string* CodeGeneratorResponse::mutable_error() {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     error_ = new ::std::string;
   }
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.error)
   return error_;
 }
 inline ::std::string* CodeGeneratorResponse::release_error() {
   clear_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     return NULL;
   } else {
     ::std::string* temp = error_;
-    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
     return temp;
   }
 }
 inline void CodeGeneratorResponse::set_allocated_error(::std::string* error) {
-  if (error_ != &::google::protobuf::internal::GetEmptyString()) {
+  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
     delete error_;
   }
   if (error) {
@@ -806,8 +841,9 @@ inline void CodeGeneratorResponse::set_allocated_error(::std::string* error) {
     error_ = error;
   } else {
     clear_has_error();
-    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyString());
+    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 
 // repeated .google.protobuf.compiler.CodeGeneratorResponse.File file = 15;
@@ -818,20 +854,25 @@ inline void CodeGeneratorResponse::clear_file() {
   file_.Clear();
 }
 inline const ::google::protobuf::compiler::CodeGeneratorResponse_File& CodeGeneratorResponse::file(int index) const {
+  // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.file)
   return file_.Get(index);
 }
 inline ::google::protobuf::compiler::CodeGeneratorResponse_File* CodeGeneratorResponse::mutable_file(int index) {
+  // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.file)
   return file_.Mutable(index);
 }
 inline ::google::protobuf::compiler::CodeGeneratorResponse_File* CodeGeneratorResponse::add_file() {
+  // @@protoc_insertion_point(field_add:google.protobuf.compiler.CodeGeneratorResponse.file)
   return file_.Add();
 }
 inline const ::google::protobuf::RepeatedPtrField< ::google::protobuf::compiler::CodeGeneratorResponse_File >&
 CodeGeneratorResponse::file() const {
+  // @@protoc_insertion_point(field_list:google.protobuf.compiler.CodeGeneratorResponse.file)
   return file_;
 }
 inline ::google::protobuf::RepeatedPtrField< ::google::protobuf::compiler::CodeGeneratorResponse_File >*
 CodeGeneratorResponse::mutable_file() {
+  // @@protoc_insertion_point(field_mutable_list:google.protobuf.compiler.CodeGeneratorResponse.file)
   return &file_;
 }
 
diff --git a/src/google/protobuf/compiler/python/python_generator.cc b/src/google/protobuf/compiler/python/python_generator.cc
index 211ac70c..067d856b 100644
--- a/src/google/protobuf/compiler/python/python_generator.cc
+++ b/src/google/protobuf/compiler/python/python_generator.cc
@@ -28,6 +28,8 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+//#PY25 compatible generated code for GAE.
+// Copyright 2007 Google Inc. All Rights Reserved.
 // Author: robinson@google.com (Will Robinson)
 //
 // This module outputs pure-Python protocol message classes that will
@@ -45,6 +47,7 @@
 #include <limits>
 #include <map>
 #include <utility>
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -128,6 +131,7 @@ void PrintTopBoilerplate(
   printer->Print(
       "# Generated by the protocol buffer compiler.  DO NOT EDIT!\n"
       "# source: $filename$\n"
+      "\nimport sys\n_b=sys.version_info[0]<3 and (lambda x:x) or (lambda x:x.encode('latin1'))"  //##PY25
       "\n",
       "filename", file->name());
   if (HasTopLevelEnums(file)) {
@@ -138,7 +142,8 @@ void PrintTopBoilerplate(
       "from google.protobuf import descriptor as _descriptor\n"
       "from google.protobuf import message as _message\n"
       "from google.protobuf import reflection as _reflection\n"
-      );
+      "from google.protobuf import symbol_database as "
+      "_symbol_database\n");
   if (HasGenericServices(file)) {
     printer->Print(
         "from google.protobuf import service as _service\n"
@@ -151,7 +156,8 @@ void PrintTopBoilerplate(
         "from google.protobuf import descriptor_pb2\n");
   }
   printer->Print(
-    "# @@protoc_insertion_point(imports)\n");
+      "# @@protoc_insertion_point(imports)\n\n"
+      "_sym_db = _symbol_database.Default()\n");
   printer->Print("\n\n");
 }
 
@@ -217,14 +223,14 @@ string StringifyDefaultValue(const FieldDescriptor& field) {
     case FieldDescriptor::CPPTYPE_ENUM:
       return SimpleItoa(field.default_value_enum()->number());
     case FieldDescriptor::CPPTYPE_STRING:
-      if (field.type() == FieldDescriptor::TYPE_STRING) {
-        return "unicode(\"" + CEscape(field.default_value_string()) +
-                        "\", \"utf-8\")";
-      } else {
-        return "\"" + CEscape(field.default_value_string()) + "\"";
-      }
-      case FieldDescriptor::CPPTYPE_MESSAGE:
-          return "None";
+//##!PY25      return "b\"" + CEscape(field.default_value_string()) +
+//##!PY25             (field.type() != FieldDescriptor::TYPE_STRING ? "\"" :
+//##!PY25               "\".decode('utf-8')");
+      return "_b(\"" + CEscape(field.default_value_string()) +  //##PY25
+             (field.type() != FieldDescriptor::TYPE_STRING ? "\")" :  //##PY25
+               "\").decode('utf-8')");  //##PY25
+    case FieldDescriptor::CPPTYPE_MESSAGE:
+      return "None";
   }
   // (We could add a default case above but then we wouldn't get the nice
   // compiler warning when a new type is added.)
@@ -330,14 +336,25 @@ void Generator::PrintFileDescriptor() const {
   printer_->Print(m, file_descriptor_template);
   printer_->Indent();
   printer_->Print(
-      "serialized_pb='$value$'",
+//##!PY25      "serialized_pb=b'$value$'\n",
+      "serialized_pb=_b('$value$')\n",  //##PY25
       "value", strings::CHexEscape(file_descriptor_serialized_));
+  if (file_->dependency_count() != 0) {
+    printer_->Print(",\ndependencies=[");
+    for (int i = 0; i < file_->dependency_count(); ++i) {
+      string module_name = ModuleName(file_->dependency(i)->name());
+      printer_->Print("$module_name$.DESCRIPTOR,", "module_name", module_name);
+    }
+    printer_->Print("]");
+  }
 
   // TODO(falk): Also print options and fix the message_type, enum_type,
   //             service and extension later in the generation.
 
   printer_->Outdent();
   printer_->Print(")\n");
+  printer_->Print("_sym_db.RegisterFileDescriptor($name$)\n", "name",
+                  kDescriptorKey);
   printer_->Print("\n");
 }
 
@@ -382,7 +399,9 @@ void Generator::PrintAllNestedEnumsInFile() const {
 // enum_descriptor.
 void Generator::PrintEnum(const EnumDescriptor& enum_descriptor) const {
   map<string, string> m;
-  m["descriptor_name"] = ModuleLevelDescriptorName(enum_descriptor);
+  string module_level_descriptor_name =
+      ModuleLevelDescriptorName(enum_descriptor);
+  m["descriptor_name"] = module_level_descriptor_name;
   m["name"] = enum_descriptor.name();
   m["full_name"] = enum_descriptor.full_name();
   m["file"] = kDescriptorKey;
@@ -412,6 +431,8 @@ void Generator::PrintEnum(const EnumDescriptor& enum_descriptor) const {
   PrintSerializedPbInterval(enum_descriptor, edp);
   printer_->Outdent();
   printer_->Print(")\n");
+  printer_->Print("_sym_db.RegisterEnumDescriptor($name$)\n", "name",
+                  module_level_descriptor_name);
   printer_->Print("\n");
 }
 
@@ -522,27 +543,36 @@ void Generator::PrintServiceDescriptor(
 
 void Generator::PrintServiceClass(const ServiceDescriptor& descriptor) const {
   // Print the service.
-  printer_->Print("class $class_name$(_service.Service):\n",
+  printer_->Print("$class_name$ = service_reflection.GeneratedServiceType("
+                  "'$class_name$', (_service.Service,), dict(\n",
                   "class_name", descriptor.name());
   printer_->Indent();
   printer_->Print(
-      "__metaclass__ = service_reflection.GeneratedServiceType\n"
-      "$descriptor_key$ = $descriptor_name$\n",
+      "$descriptor_key$ = $descriptor_name$,\n",
       "descriptor_key", kDescriptorKey,
       "descriptor_name", ModuleLevelServiceDescriptorName(descriptor));
+  printer_->Print(
+      "__module__ = '$module_name$'\n",
+      "module_name", ModuleName(file_->name()));
+  printer_->Print("))\n\n");
   printer_->Outdent();
 }
 
 void Generator::PrintServiceStub(const ServiceDescriptor& descriptor) const {
   // Print the service stub.
-  printer_->Print("class $class_name$_Stub($class_name$):\n",
+  printer_->Print("$class_name$_Stub = "
+                  "service_reflection.GeneratedServiceStubType("
+                  "'$class_name$_Stub', ($class_name$,), dict(\n",
                   "class_name", descriptor.name());
   printer_->Indent();
   printer_->Print(
-      "__metaclass__ = service_reflection.GeneratedServiceStubType\n"
-      "$descriptor_key$ = $descriptor_name$\n",
+      "$descriptor_key$ = $descriptor_name$,\n",
       "descriptor_key", kDescriptorKey,
       "descriptor_name", ModuleLevelServiceDescriptorName(descriptor));
+  printer_->Print(
+      "__module__ = '$module_name$'\n",
+      "module_name", ModuleName(file_->name()));
+  printer_->Print("))\n\n");
   printer_->Outdent();
 }
 
@@ -635,7 +665,12 @@ void Generator::PrintNestedDescriptors(
 // Prints all messages in |file|.
 void Generator::PrintMessages() const {
   for (int i = 0; i < file_->message_type_count(); ++i) {
-    PrintMessage(*file_->message_type(i));
+    vector<string> to_register;
+    PrintMessage(*file_->message_type(i), "", &to_register);
+    for (int j = 0; j < to_register.size(); ++j) {
+      printer_->Print("_sym_db.RegisterMessage($name$)\n", "name",
+                      to_register[j]);
+    }
     printer_->Print("\n");
   }
 }
@@ -647,33 +682,40 @@ void Generator::PrintMessages() const {
 // reflection.py will use to construct the meat of the class itself.
 //
 // Mutually recursive with PrintNestedMessages().
-void Generator::PrintMessage(
-    const Descriptor& message_descriptor) const {
-  printer_->Print("class $name$(_message.Message):\n", "name",
-                  message_descriptor.name());
+// Collect nested message names to_register for the symbol_database.
+void Generator::PrintMessage(const Descriptor& message_descriptor,
+                             const string& prefix,
+                             vector<string>* to_register) const {
+  string qualified_name(prefix + message_descriptor.name());
+  to_register->push_back(qualified_name);
+  printer_->Print(
+      "$name$ = _reflection.GeneratedProtocolMessageType('$name$', "
+      "(_message.Message,), dict(\n",
+      "name", message_descriptor.name());
   printer_->Indent();
-  printer_->Print("__metaclass__ = _reflection.GeneratedProtocolMessageType\n");
-  PrintNestedMessages(message_descriptor);
+
+  PrintNestedMessages(message_descriptor, qualified_name + ".", to_register);
   map<string, string> m;
   m["descriptor_key"] = kDescriptorKey;
   m["descriptor_name"] = ModuleLevelDescriptorName(message_descriptor);
-  printer_->Print(m, "$descriptor_key$ = $descriptor_name$\n");
-
-  printer_->Print(
-    "\n"
-    "# @@protoc_insertion_point(class_scope:$full_name$)\n",
-    "full_name", message_descriptor.full_name());
-
+  printer_->Print(m, "$descriptor_key$ = $descriptor_name$,\n");
+  printer_->Print("__module__ = '$module_name$'\n",
+                  "module_name", ModuleName(file_->name()));
+  printer_->Print("# @@protoc_insertion_point(class_scope:$full_name$)\n",
+                  "full_name", message_descriptor.full_name());
+  printer_->Print("))\n");
   printer_->Outdent();
 }
 
 // Prints all nested messages within |containing_descriptor|.
 // Mutually recursive with PrintMessage().
-void Generator::PrintNestedMessages(
-    const Descriptor& containing_descriptor) const {
+void Generator::PrintNestedMessages(const Descriptor& containing_descriptor,
+                                    const string& prefix,
+                                    vector<string>* to_register) const {
   for (int i = 0; i < containing_descriptor.nested_type_count(); ++i) {
     printer_->Print("\n");
-    PrintMessage(*containing_descriptor.nested_type(i));
+    PrintMessage(*containing_descriptor.nested_type(i), prefix, to_register);
+    printer_->Print(",\n");
   }
 }
 
@@ -714,6 +756,29 @@ void Generator::AddMessageToFileDescriptor(const Descriptor& descriptor) const {
   printer_->Print(m, file_descriptor_template);
 }
 
+void Generator::AddEnumToFileDescriptor(
+    const EnumDescriptor& descriptor) const {
+  map<string, string> m;
+  m["descriptor_name"] = kDescriptorKey;
+  m["enum_name"] = descriptor.name();
+  m["enum_descriptor_name"] = ModuleLevelDescriptorName(descriptor);
+  const char file_descriptor_template[] =
+      "$descriptor_name$.enum_types_by_name['$enum_name$'] = "
+      "$enum_descriptor_name$\n";
+  printer_->Print(m, file_descriptor_template);
+}
+
+void Generator::AddExtensionToFileDescriptor(
+    const FieldDescriptor& descriptor) const {
+  map<string, string> m;
+  m["descriptor_name"] = kDescriptorKey;
+  m["field_name"] = descriptor.name();
+  const char file_descriptor_template[] =
+      "$descriptor_name$.extensions_by_name['$field_name$'] = "
+      "$field_name$\n";
+  printer_->Print(m, file_descriptor_template);
+}
+
 // Sets any necessary message_type and enum_type attributes
 // for the Python version of |field|.
 //
@@ -778,7 +843,7 @@ void Generator::FixContainingTypeInDescriptor(
     const string parent_name = ModuleLevelDescriptorName(
         *containing_descriptor);
     printer_->Print(
-        "$nested_name$.containing_type = $parent_name$;\n",
+        "$nested_name$.containing_type = $parent_name$\n",
         "nested_name", nested_name,
         "parent_name", parent_name);
   }
@@ -795,6 +860,12 @@ void Generator::FixForeignFieldsInDescriptors() const {
   for (int i = 0; i < file_->message_type_count(); ++i) {
     AddMessageToFileDescriptor(*file_->message_type(i));
   }
+  for (int i = 0; i < file_->enum_type_count(); ++i) {
+    AddEnumToFileDescriptor(*file_->enum_type(i));
+  }
+  for (int i = 0; i < file_->extension_count(); ++i) {
+    AddExtensionToFileDescriptor(*file_->extension(i));
+  }
   printer_->Print("\n");
 }
 
@@ -875,8 +946,10 @@ string Generator::OptionsValue(
     return "None";
   } else {
     string full_class_name = "descriptor_pb2." + class_name;
-    return "_descriptor._ParseOptions(" + full_class_name + "(), '"
-        + CEscape(serialized_options)+ "')";
+//##!PY25    return "_descriptor._ParseOptions(" + full_class_name + "(), b'"
+//##!PY25        + CEscape(serialized_options)+ "')";
+    return "_descriptor._ParseOptions(" + full_class_name + "(), _b('"  //##PY25
+        + CEscape(serialized_options)+ "'))";  //##PY25
   }
 }
 
diff --git a/src/google/protobuf/compiler/python/python_generator.h b/src/google/protobuf/compiler/python/python_generator.h
index a3f22cee..40dfddf3 100644
--- a/src/google/protobuf/compiler/python/python_generator.h
+++ b/src/google/protobuf/compiler/python/python_generator.h
@@ -94,8 +94,11 @@ class LIBPROTOC_EXPORT Generator : public CodeGenerator {
   void PrintNestedDescriptors(const Descriptor& containing_descriptor) const;
 
   void PrintMessages() const;
-  void PrintMessage(const Descriptor& message_descriptor) const;
-  void PrintNestedMessages(const Descriptor& containing_descriptor) const;
+  void PrintMessage(const Descriptor& message_descriptor, const string& prefix,
+                    vector<string>* to_register) const;
+  void PrintNestedMessages(const Descriptor& containing_descriptor,
+                           const string& prefix,
+                           vector<string>* to_register) const;
 
   void FixForeignFieldsInDescriptors() const;
   void FixForeignFieldsInDescriptor(
@@ -105,6 +108,8 @@ class LIBPROTOC_EXPORT Generator : public CodeGenerator {
                                const FieldDescriptor& field,
                                const string& python_dict_name) const;
   void AddMessageToFileDescriptor(const Descriptor& descriptor) const;
+  void AddEnumToFileDescriptor(const EnumDescriptor& descriptor) const;
+  void AddExtensionToFileDescriptor(const FieldDescriptor& descriptor) const;
   string FieldReferencingExpression(const Descriptor* containing_type,
                                     const FieldDescriptor& field,
                                     const string& python_dict_name) const;
diff --git a/src/google/protobuf/compiler/python/python_plugin_unittest.cc b/src/google/protobuf/compiler/python/python_plugin_unittest.cc
index da619ad3..77da8a87 100644
--- a/src/google/protobuf/compiler/python/python_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/python/python_plugin_unittest.cc
@@ -34,6 +34,8 @@
 //   It seemed like parameterizing it would add more complexity than it is
 //   worth.
 
+#include <memory>
+
 #include <google/protobuf/compiler/python/python_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
 #include <google/protobuf/io/zero_copy_stream.h>
@@ -68,7 +70,7 @@ class TestGenerator : public CodeGenerator {
   void TryInsert(const string& filename, const string& insertion_point,
                  GeneratorContext* context) const {
     scoped_ptr<io::ZeroCopyOutputStream> output(
-      context->OpenForInsert(filename, insertion_point));
+        context->OpenForInsert(filename, insertion_point));
     io::Printer printer(output.get(), '$');
     printer.Print("// inserted $name$\n", "name", insertion_point);
   }
@@ -78,13 +80,13 @@ class TestGenerator : public CodeGenerator {
 // not verify that they are correctly-placed; that would require actually
 // compiling the output which is a bit more than I care to do for this test.
 TEST(PythonPluginTest, PluginTest) {
-  File::WriteStringToFileOrDie(
-      "syntax = \"proto2\";\n"
-      "package foo;\n"
-      "message Bar {\n"
-      "  message Baz {}\n"
-      "}\n",
-      TestTempDir() + "/test.proto");
+  GOOGLE_CHECK_OK(File::SetContents(TestTempDir() + "/test.proto",
+                             "syntax = \"proto2\";\n"
+                             "package foo;\n"
+                             "message Bar {\n"
+                             "  message Baz {}\n"
+                             "}\n",
+                             true));
 
   google::protobuf::compiler::CommandLineInterface cli;
   cli.SetInputsAreProtoPathRelative(true);
diff --git a/src/google/protobuf/compiler/subprocess.cc b/src/google/protobuf/compiler/subprocess.cc
index 67da120d..ca4b874d 100644
--- a/src/google/protobuf/compiler/subprocess.cc
+++ b/src/google/protobuf/compiler/subprocess.cc
@@ -449,7 +449,7 @@ bool Subprocess::Communicate(const Message& input, Message* output,
   }
 
   if (!output->ParseFromString(output_data)) {
-    *error = "Plugin output is unparseable.";
+    *error = "Plugin output is unparseable: " + CEscape(output_data);
     return false;
   }