Fix bug with large extension field numbers.

Previously, extensions with field numbers greater than 268435455 would
result in a compile time error in generated code that looks something
like this:

Foo.java:3178: error: integer number too large: 3346754610
                3346754610);

This is because we were trying to represent the tag number (an
unsigned int) using a java int constant, but java int constants are
signed, and can't exceed Integer.MAX_VALUE.

Fixed by declaring it as a long instead, and casting it down to an
int in the implementation. This is safe, because the tag value always
fits in 32 bis.

Change-Id: If2017bacb4e20af667eaeaf9b65ddc2c30a7709f

3 files changed, 30 insertions, 8 deletions

diff --git a/javanano/src/main/java/com/google/protobuf/nano/Extension.java b/javanano/src/main/java/com/google/protobuf/nano/Extension.java
index c29b030f..2d091f01 100644
--- a/javanano/src/main/java/com/google/protobuf/nano/Extension.java
+++ b/javanano/src/main/java/com/google/protobuf/nano/Extension.java
@@ -74,6 +74,11 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
     public static final int TYPE_SINT32   = InternalNano.TYPE_SINT32;
     public static final int TYPE_SINT64   = InternalNano.TYPE_SINT64;
 
+    // Note: these create...() methods take a long for the tag parameter,
+    // because tags are represented as unsigned longs, and these values exist
+    // in generated code as long values. However, they can fit in 32-bits, so
+    // it's safe to cast them to int without loss of precision.
+
     /**
      * Creates an {@code Extension} of the given message type and tag number.
      * Should be used by the generated code only.
@@ -81,8 +86,8 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
      * @param type {@link #TYPE_MESSAGE} or {@link #TYPE_GROUP}
      */
     public static <M extends ExtendableMessageNano<M>, T extends MessageNano>
-            Extension<M, T> createMessageTyped(int type, Class<T> clazz, int tag) {
-        return new Extension<M, T>(type, clazz, tag, false);
+            Extension<M, T> createMessageTyped(int type, Class<T> clazz, long tag) {
+        return new Extension<M, T>(type, clazz, (int) tag, false);
     }
 
     /**
@@ -92,8 +97,8 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
      * @param type {@link #TYPE_MESSAGE} or {@link #TYPE_GROUP}
      */
     public static <M extends ExtendableMessageNano<M>, T extends MessageNano>
-            Extension<M, T[]> createRepeatedMessageTyped(int type, Class<T[]> clazz, int tag) {
-        return new Extension<M, T[]>(type, clazz, tag, true);
+            Extension<M, T[]> createRepeatedMessageTyped(int type, Class<T[]> clazz, long tag) {
+        return new Extension<M, T[]>(type, clazz, (int) tag, true);
     }
 
     /**
@@ -104,8 +109,8 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
      * @param clazz the boxed Java type of this extension
      */
     public static <M extends ExtendableMessageNano<M>, T>
-            Extension<M, T> createPrimitiveTyped(int type, Class<T> clazz, int tag) {
-        return new PrimitiveExtension<M, T>(type, clazz, tag, false, 0, 0);
+            Extension<M, T> createPrimitiveTyped(int type, Class<T> clazz, long tag) {
+        return new PrimitiveExtension<M, T>(type, clazz, (int) tag, false, 0, 0);
     }
 
     /**
@@ -117,8 +122,9 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
      */
     public static <M extends ExtendableMessageNano<M>, T>
             Extension<M, T> createRepeatedPrimitiveTyped(
-                    int type, Class<T> clazz, int tag, int nonPackedTag, int packedTag) {
-        return new PrimitiveExtension<M, T>(type, clazz, tag, true, nonPackedTag, packedTag);
+                    int type, Class<T> clazz, long tag, long nonPackedTag, long packedTag) {
+        return new PrimitiveExtension<M, T>(type, clazz, (int) tag, true,
+            (int) nonPackedTag, (int) packedTag);
     }
 
     /**
diff --git a/javanano/src/main/java/com/google/protobuf/nano/Extension.java.rej b/javanano/src/main/java/com/google/protobuf/nano/Extension.java.rej
new file mode 100644
index 00000000..465495a7
--- /dev/null
+++ b/javanano/src/main/java/com/google/protobuf/nano/Extension.java.rej
@@ -0,0 +1,13 @@
+diff a/javanano/src/main/java/com/google/protobuf/nano/Extension.java b/javanano/src/main/java/com/google/protobuf/nano/Extension.java	(rejected hunks)
+@@ -74,6 +74,11 @@ public class Extension<M extends ExtendableMessageNano<M>, T> {
+     public static final int TYPE_SINT32   = 17;
+     public static final int TYPE_SINT64   = 18;
+ 
++    // Note: these create...() methods take a long for the tag parameter,
++    // because tags are represented as unsigned longs, and these values exist
++    // in generated code as long values. However, they can fit in 32-bits, so
++    // it's safe to cast them to int without loss of precision.
++
+     /**
+      * Creates an {@code Extension} of the given message type and tag number.
+      * Should be used by the generated code only.
diff --git a/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto b/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
index 2a678a80..d1c5766d 100644
--- a/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
+++ b/javanano/src/test/java/com/google/protobuf/nano/unittest_extension_nano.proto
@@ -21,6 +21,9 @@ message AnotherMessage {
 message ContainerMessage {
   extend ExtendableMessage {
     optional bool another_thing = 100;
+    // The largest permitted field number, per
+    // https://developers.google.com/protocol-buffers/docs/proto#simple
+    optional bool large_field_number = 536870911;
   }
 }