[[deprecated]] attribute additions break compilation of protobuf-generated files

[pitrou]

What version of protobuf and what language are you using?
Version: 29.0.0
Language: C++

What operating system (Linux, Windows, ...) and version?
All.

What runtime / compiler are you using (e.g., python version or gcc version)
Multiple (gcc, clang, MSVC... depending on platform)

What did you do?
Compiling Apache Arrow.
See apache/arrow#44954

What did you expect to see
I expect protobuf-generated files to compile fine.

What did you see instead?
Compiling protobuf-generated files with -Werror -Wdeprecated fails because protobuf's own generated C++ code is not safe to compile with these options.

This is because of #18036 . I commented there, but the author/submitter is a bot (are contributions to protobuf anonymous now?).

[pitrou]

@emkornfield FYI :)

[tonyliaoss]

This seems to be related to #18205

[zhangskz]

We're rolling this back in f05e51c (and cherry-picking this for a patch to v29.2)