Issue with `PYTHONCAPI_COMPAT_SPEC ` on macOS

[cdce8p]

This issue seems to be specific to MacOS. Encountered while testing with mypy / mypyc.

The traceback below is with Python 3.13.1 (v3.13.1:06714517797, Dec 3 2024, 14:00:22) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin, however a slightly different error is also reproducible in CI with Python 3.9. See link below.

In file included from /.../mypyc/lib-rt/pythonsupport.h:11:
/.../mypyc/lib-rt/pythoncapi_compat.h:2086:9: error: no member named 'use_system_logger' in 'PyConfig'
        PYTHONCAPI_COMPAT_SPEC(use_system_logger, BOOL, _Py_NULL),
        ^                      ~~~~~~~~~~~~~~~~~
/.../mypyc/lib-rt/pythoncapi_compat.h:2000:15: note: expanded from macro 'PYTHONCAPI_COMPAT_SPEC'
    {#MEMBER, offsetof(PyConfig, MEMBER), \
              ^                  ~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/15.0.0/include/stddef.h:105:24: note: expanded from macro 'offsetof'
#define offsetof(t, d) __builtin_offsetof(t, d)
                       ^                     ~
In file included from /.../mypyc/lib-rt/pythonsupport.h:11:
/.../mypyc/lib-rt/pythoncapi_compat.h:2098:26: error: invalid application of 'sizeof' to an incomplete type 'const PyConfigSpec[]'
    for (size_t i=0; i < Py_ARRAY_LENGTH(config_spec); i++) {
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Library/Frameworks/Python.framework/Versions/3.13/include/python3.13/pymacro.h:100:12: note: expanded from macro 'Py_ARRAY_LENGTH'
    (sizeof(array) / sizeof((array)[0]) \

python/mypy#18535
https://github.com/python/mypy/actions/runs/12973783593/job/36182870602?pr=18535#step:9:118

[vstinner]

Oh right, PyConfig.use_system_logger will only be available on Python 3.13.2 which is not available yet! I just removed the member in 03043e3. I modified the CI to test more Python versions on macOS.

however a slightly different error is also reproducible in CI with Python 3.9. See link below.

I cannot reproduce the Python 3.9 error. Can you please retry with updated pythoncapi_compat.h?

If you still have the bug, you may try to replace Py_ARRAY_LENGTH(config_spec) with sizeof(config_spec) / sizeof(config_spec[0]).

---

By the way, I'm curious, why do you update pythoncapi_compat.h?

[vstinner]

Oh, I see that Py_ARRAY_LENGTH() is still causing troubles after PyConfig.use_system_logger removal. I wrote 4c53701 to replace Py_ARRAY_LENGTH() with sizeof().

[cdce8p]

Looks good now. Thanks for the quick fixes!

By the way, I'm curious, why do you update pythoncapi_compat.h?

Did you mean the fix I applied manually in the PR? That was just #130.
Aside from that another maybe better name for the mypy PR would be "Sync pythoncapi_compat.h" :)

[vstinner]

If you don't need new functions, you don't have to update pythoncapi_compat.h.

But I'm glad that you did it, to report regressions :-)

Looks good now. Thanks for the quick fixes!

Good. You're welcome.

[cdce8p]

If you don't need new functions, you don't have to update pythoncapi_compat.h.

True.

But I'm glad that you did it, to report regressions :-)

Always good to stay on top of it. Especially with mypyc you never know when you're going to need one of these ;)