Support custom options in C#

This consists of:
- Changing the codegen for the fixed set of options protos, to parse unknown fields instead of skipping them
- Add a new CustomOptions type in the C# support library
- Expose CustomOptions properties from the immutable proto wrappers in the support library

Only single-value options are currently supported, and fetching options values requires getting the type right
and knowing the field number. Both of these can be addressed at a later time.

Fixes #2143, at least as a first pass.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/google/protobuf/compiler/csharp/csharp_helpers.h b/src/google/protobuf/compiler/csharp/csharp_helpers.h
index 1563ca7e..c317ad0e 100644
--- a/src/google/protobuf/compiler/csharp/csharp_helpers.h
+++ b/src/google/protobuf/compiler/csharp/csharp_helpers.h
@@ -120,6 +120,22 @@ inline bool IsDescriptorProto(const FileDescriptor* descriptor) {
   return descriptor->name() == "google/protobuf/descriptor.proto";
 }
 
+// Determines whether the given message is an options message within descriptor.proto.
+inline bool IsDescriptorOptionMessage(const Descriptor* descriptor) {
+  if (!IsDescriptorProto(descriptor->file())) {
+    return false;
+  }
+  const string name = descriptor->full_name();
+  return name == "google.protobuf.FileOptions" ||
+      name == "google.protobuf.MessageOptions" ||
+      name == "google.protobuf.FieldOptions" ||
+      name == "google.protobuf.OneofOptions" ||
+      name == "google.protobuf.EnumOptions" ||
+      name == "google.protobuf.EnumValueOptions" ||
+      name == "google.protobuf.ServiceOptions" ||
+      name == "google.protobuf.MethodOptions";
+}
+
 inline bool IsWrapperType(const FieldDescriptor* descriptor) {
   return descriptor->type() == FieldDescriptor::TYPE_MESSAGE &&
       descriptor->message_type()->file()->name() == "google/protobuf/wrappers.proto";