Breaking Change: fixed json_encode/json_decode to use the message's pool.

This bug arises only in the uncommon case where there is more than one
DescriptorPool.  In such a case, JSON encode/decode should always use
the pool of the message being encoded/decoded, not the generated pool.

ruby/ext/google/protobuf_c/message.c

@@ -975,9 +975,6 @@ static VALUE Message_decode_json(int argc, VALUE* argv, VALUE klass) {
   int options = 0;
   upb_Status status;
 
-  // TODO: use this message's pool instead.
-  const upb_DefPool* symtab = DescriptorPool_GetSymtab(generated_pool);
-
   if (argc < 1 || argc > 2) {
     rb_raise(rb_eArgError, "Expected 1 or 2 arguments.");
   }
@@ -1011,8 +1008,9 @@ static VALUE Message_decode_json(int argc, VALUE* argv, VALUE klass) {
   }
 
   upb_Status_Clear(&status);
+  const upb_DefPool* pool = upb_FileDef_Pool(upb_MessageDef_File(msg->msgdef));
   if (!upb_JsonDecode(RSTRING_PTR(data), RSTRING_LEN(data),
-                      (upb_Message*)msg->msg, msg->msgdef, symtab, options,
+                      (upb_Message*)msg->msg, msg->msgdef, pool, options,
                       Arena_get(msg->arena), &status)) {
     rb_raise(cParseError, "Error occurred during parsing: %s",
              upb_Status_ErrorMessage(&status));
@@ -1091,9 +1089,6 @@ static VALUE Message_encode_json(int argc, VALUE* argv, VALUE klass) {
   size_t size;
   upb_Status status;
 
-  // TODO: use this message's pool instead.
-  const upb_DefPool* symtab = DescriptorPool_GetSymtab(generated_pool);
-
   if (argc < 1 || argc > 2) {
     rb_raise(rb_eArgError, "Expected 1 or 2 arguments.");
   }
@@ -1128,7 +1123,8 @@ static VALUE Message_encode_json(int argc, VALUE* argv, VALUE klass) {
   }
 
   upb_Status_Clear(&status);
-  size = upb_JsonEncode(msg->msg, msg->msgdef, symtab, options, buf,
+  const upb_DefPool* pool = upb_FileDef_Pool(upb_MessageDef_File(msg->msgdef));
+  size = upb_JsonEncode(msg->msg, msg->msgdef, pool, options, buf,
                         sizeof(buf), &status);
 
   if (!upb_Status_IsOk(&status)) {
@@ -1139,7 +1135,7 @@ static VALUE Message_encode_json(int argc, VALUE* argv, VALUE klass) {
   VALUE ret;
   if (size >= sizeof(buf)) {
     char* buf2 = malloc(size + 1);
-    upb_JsonEncode(msg->msg, msg->msgdef, symtab, options, buf2, size + 1,
+    upb_JsonEncode(msg->msg, msg->msgdef, pool, options, buf2, size + 1,
                    &status);
     ret = rb_str_new(buf2, size);
     free(buf2);

ruby/tests/basic_proto2.rb

@@ -263,6 +263,30 @@ module BasicTestProto2
       assert_equal 42, extension.get(message)
     end
 
+    def test_extension_json
+      message = TestExtensions.decode_json '{"[basic_test_proto2.optional_int32_extension]": 123}'
+      extension = Google::Protobuf::DescriptorPool.generated_pool.lookup 'basic_test_proto2.optional_int32_extension'
+      assert_instance_of Google::Protobuf::FieldDescriptor, extension
+      assert_equal 123, extension.get(message)
+    end
+
+    def test_extension_json_separate_pool
+      pool = Google::Protobuf::DescriptorPool.new
+
+      # This serialized descriptor is a subset of basic_test_proto2.proto that
+      # contains only the TestExtensions message, but no actual extensions.
+      descriptor_data = "\n\x17\x62\x61sic_test_proto2.proto\x12\x11\x62\x61sic_test_proto2\"\x1a\n\x0eTestExtensions*\x08\x08\x01\x10\x80\x80\x80\x80\x02:M\n\"different_optional_int32_extension\x12!.basic_test_proto2.TestExtensions\x18\x01 \x01(\x05"
+      pool.add_serialized_file(descriptor_data)
+      message_class = pool.lookup("basic_test_proto2.TestExtensions").msgclass
+      extension = pool.lookup 'basic_test_proto2.different_optional_int32_extension'
+
+      message = message_class.decode_json '{"[basic_test_proto2.different_optional_int32_extension]": 123}'
+      assert_equal 123, extension.get(message)
+
+      message2 = message_class.decode_json(message_class.encode_json(message))
+      assert_equal 123, extension.get(message2)
+    end
+
     def test_nested_extension
       message = TestExtensions.new
       extension = Google::Protobuf::DescriptorPool.generated_pool.lookup 'basic_test_proto2.TestNestedExtension.test'