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, 18 insertions, 9 deletions

diff --git a/java/src/main/java/com/google/protobuf/nano/Extension.java b/java/src/main/java/com/google/protobuf/nano/Extension.java
index a851daf..728f0dc 100644
--- a/java/src/main/java/com/google/protobuf/nano/Extension.java
+++ b/java/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   = 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.
@@ -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/src/google/protobuf/compiler/javanano/javanano_extension.cc b/src/google/protobuf/compiler/javanano/javanano_extension.cc
index 754ed55..0b9d1d8 100644
--- a/src/google/protobuf/compiler/javanano/javanano_extension.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_extension.cc
@@ -140,7 +140,7 @@ void ExtensionGenerator::Generate(io::Printer* printer) const {
     "        com.google.protobuf.nano.Extension.create$repeated$$ext_type$(\n"
     "            com.google.protobuf.nano.Extension.$type$,\n"
     "            $class$.class,\n"
-    "            $tag_params$);\n");
+    "            $tag_params$L);\n");
 }
 
 }  // namespace javanano
diff --git a/src/google/protobuf/unittest_extension_nano.proto b/src/google/protobuf/unittest_extension_nano.proto
index 2a678a8..d1c5766 100644
--- a/src/google/protobuf/unittest_extension_nano.proto
+++ b/src/google/protobuf/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;
   }
 }