Deepcopy incorrectly sets the 'active' oneof field to last field in structure (breaking which_one_of)

[sshumaker]

Summary

When calling deepcopy on a proto, the oneOf field state gets overwritten.

Reproduction Steps

1. Create a simple proto with two one_of fields.
2. set the first field
3. Call which_one_of which will return the first field
4. Call deepcopy on the proto
5. check which_one_of again.
6. The second field is returned.

The implementation of deepcopy does this:

        for name in self._betterproto.sorted_field_names:
            value = self.__raw_get(name)
            if value is not PLACEHOLDER:
                kwargs[name] = deepcopy(value)

And of course, setattr sets the current group by field, which overwrites this.

one option is to simply make deepcopy one_of aware, using oneof_field_by_group, default initializing the nonset fields and adding them to a set, and then only iterating over the names that aren't in the set using the overall loop above.

Expected Results

We preserve the correct one_of field

Actual Results

The second one_of field is set.

System Information

libprotoc 3.21.12
Python 3.11.9
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: /usr/local/lib/python3.11/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.