gh-141671: PyMODINIT_FUNC: apply __declspec(dllexport) on Windows

[encukou]

• Issue: PyMODINIT_FUNC does not apply __declspec(dllexport) on Windows #141671

[encukou]

cc @jaraco / @pfmoore: what are your thoughts on removing /EXPORT from setuptools/distutils on Python 3.15+?

[zooba]

I'm not 100% sure about this... don't we need it for our own exports?

[encukou]

Only for Py_ENABLE_SHARED -- see #99888 that added the #else.

[zooba]

Ah, I see we do these checks again everywhere else we use the macros. No problem them.

[pfmoore]

TBH, I have no view. My knowledge of C is very out of date, so I wouldn't trust anything I might say anyway...

[da-woods]

The /EXPORT from setuptools has definitely caused Cython an amount of pain before (although some of that was self-inflicted....). It'd be nice not to have to define PyInit_ just to to make the name exist. Although I suspect we can't really avoid it in a realistic timeline.

(Edit: admittedly we also aren't the people that it's designed to help either)

[encukou]

Here's a version that removes some redundant defines (setting things to defaults).

[vstinner]

LGTM. This change mostly moves code around, and just add __declspec(dllexport) on Windows.

[vstinner]

Supporting an already defined PyMODINIT_FUNC/PyMODEXPORT_FUNC is a new feature. Is it really worth it? I'm not against it, just curious.

[encukou]

It's an escape hatch: if there's an unexpected problem with this PR, this can allow people to hotfix it without patching or waiting for a new release.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @encukou for commit 5091b79 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F141672%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[AraHaan]

I think a better option instead is to define Py_EXPORTED_SYMBOL here and then use that.

Also I feel like an escape hatch like Py_EMBED_MODULE where it basically uses Py_LOCAL_SYMBOL instead could be an option as well for when one does not want the module init function exported due to intending to use PyImport_AppendInitTab within the exe that they directly build the module into.

[encukou]

I don't want to change the meaning of Py_EXPORTED_SYMBOL.

For the inittab, you can avoid PyMODINIT_FUNC/PyMODEXPORT_FUNC, and just use a normal declaration.