use_fast_cpp_protos=true on MacOS Arm64

[rstz]

Hi,

I'm trying to restore MacOS support for Yggdrasil Decision Forests, which proves more challenging than expected. As a first step, I tried running the tests in this repository under MacOS 14.5 (Arm64 architecture).

However, simply adding build --define=use_fast_cpp_protos=true to the project's .bazelrc makes tests fail with

# Configuration: 0d5ebff10b22bfda3f3ae92bd192687fc16f9a19af7749ad3686c9e0dd13d0b1
# Execution platform: @@platforms//host:host

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
Undefined symbols for architecture arm64:
  "_PyModule_AddIntConstant", referenced from:
      _PyInit__api_implementation in api_implementation.o
  "_PyModule_Create2", referenced from:
      _PyInit__api_implementation in api_implementation.o
  "__Py_Dealloc", referenced from:
      _Py_DECREF(_object*) in api_implementation.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

The issue happens with all Python versions. Is this a known issue on MacOS?

[rwgk]

--define=use_fast_cpp_protos=true

AFAIK the protobuf team is working towards completely removing OSS support for that feature. The feature was never really supported in pybind11_protobuf OSS.

See also: #161 (comment)

The linker error looks more general, macOS has general issues around undefined symbols from the Python runtime library. I don't have full context there, just saying it's not surprising at first sight.

What happens if you simply don't try to use use_fast_cpp_protos? (Does that sidestep the linker error?)

[rstz]

Thank you for explaining. Removing use_fast_cpp_protos sidesteps the error, so I'll see if I can also remove the flag from our library.