Feature or enhancement

See discussion: https://discuss.python.org/t/module-slot-for-checking-abi-compatibility/96443/

The checks we can do using C API are limited, but would still be useful, e.g. for the case of mixing up GIL-ful and free-threaded extensions/builds.

I propose adding:

• PyABIInfo struct with:
  • abiinfo_major_version
  • abiinfo_minor_version
  • flags which can be set to:
    • PyABIInfo_DEFAULT_FLAGS
    • PyABIInfo_STABLE
    • PyABIInfo_INTERNAL
    • PyABIInfo_FREETHREADED
    • PyABIInfo_GIL
  • build_version
  • abi_version
• int PyABIInfo_Check(PyABIInfo *info, const char *module_name)
• PyABIInfo_VAR(NAME) macro that defines a suitable PyABIInfo variable
• Py_mod_abi, a module slot that causes a PyABIInfo_Check call

C API WG vote pending: capi-workgroup/decisions#72

Linked PRs

• gh-137210: Add a struct, slot & function for checking an extension's ABI #137212
• gh-137210: Move PYTHON_API_VERSION & PYTHON_ABI_VERSION to patchlevel.h #138545