python: Segfault comparing default message fields with protobuf 4.21.x

[villainy]

What version of protobuf and what language are you using?
Version: v21.2
Language: Python

What operating system (Linux, Windows, ...) and version?
Ubuntu Linux 20.04.4 LTS

What runtime / compiler are you using (e.g., python version or gcc version)
Python 3.10.5/3.9.13/3.8.13

What did you do?
Steps to reproduce the behavior:

1. Create a protobuf outer message with an inner submessage field
2. Build python module with protoc v21.2
3. Compare (==) the default value of the outer message's field with a standalone instance of the inner message
4. See Python segfault

What did you expect to see

Not a segfault

What did you see instead?

A segfault

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

Versions:

$ lsb_release -d
Description:    Ubuntu 20.04 LTS

$ protoc --version
libprotoc 3.21.2

$ python --version
Python 3.10.5

$ pip show protobuf|grep Version
Version: 4.21.2

Minimal reproducible protobuf repro.proto:

syntax = "proto3";

package repro;

message OuterMessage {
    uint32 id = 1;
    InnerMessage msg = 2;
}

message InnerMessage {
    uint32 id = 1;
}

Minimal reproducible python repro.py:

from repro_pb2 import OuterMessage, InnerMessage

outer = OuterMessage(id=1)
inner = InnerMessage(id=2)

outer.msg == inner

print("Segfault before we get here.")

Example output:

$ ls
repro.proto  repro.py

$ protoc --python_out . repro.proto

$ ls
repro.proto  repro.py  repro_pb2.py

$ python repro.py
Segmentation fault

Anything else we should know about your project / environment

[ericsalo]

This looks identical to #10208, which I fixed three days ago. Please confirm whether this bug still exists after a fresh sync.

[villainy]

Confirmed cannot reproduce from main. Thanks for the quick reply and sorry for the noise.