Nested message with repeated field not in to_json when mutated after initialization

[dallagi]

Summary

Possibly related to #199

Given a message with a nested message field containing a repeated field, if the field is mutated (eg. via list.append) after initialization, to_dict will not include it.

Reproduction Steps

Given a proto schema like this

syntax = "proto3";

message RootMessage {
  NestedMessage nested = 1;
}

message NestedMessage {
  repeated string content = 1;
}

Running the following script

message = RootMessage()

message.nested.content.append("test-content")

print("Including default values: True")
pprint(message.to_dict(include_default_values=True))

print("Including default values: False")
pprint(message.to_dict(include_default_values=False))

will result in:

Including default values: True
{'nested': {'content': ['test-content']}}

Including default values: False
{}

Expected Results

I would expect the content field of the nested message to appear in the returned dict also when include_default_values is set to False, as its content was mutated and it's no longer the default value.

Actual Results

to_dict returns an empty dict

System Information

libprotoc 3.21.6
Python 3.10.13
Name: betterproto
Version: 2.0.0b6
Summary: A better Protobuf / gRPC generator & library
Home-page: https://github.com/danielgtaylor/python-betterproto
Author: Daniel G. Taylor
Author-email: danielgtaylor@gmail.com
License: MIT
Location: /home/marco/.local/share/rtx/installs/python/3.10.13/lib/python3.10/site-packages
Requires: grpclib, python-dateutil
Required-by: 

Checklist

• I have searched the issues for duplicates.
• I have shown the entire traceback, if possible.
• I have verified this issue occurs on the latest prelease of betterproto which can be installed using pip install -U --pre betterproto, if possible.