Provide aarch64 wheel for windows

[saschanaz]

It would be nice to set up CI for aarch64 windows wheel.

[saschanaz]

Looks like it'll take a few months to openly access windows arm64 runner: https://github.blog/news-insights/product-news/arm64-on-github-actions-powering-faster-more-efficient-build-systems/

[glandium]

I tried cross-compiling with cibuildwheel, but that didn't work. I ended up with an arm64 wheel containing an amd64 module. Compiling natively works (except for #240), but arm64 GHA workers are only available on Enterprise.

[saschanaz]

Might be related to pypa/cibuildwheel#1942 ?

[glandium]

So, it turns out it's properly cross compiling... but the files "just" have the wrong name:

$ file zstandard/*.pyd 
zstandard/_cffi.cp311-win_amd64.pyd:     PE32+ executable (DLL) (GUI) Aarch64, for MS Windows, 6 sections
zstandard/backend_c.cp311-win_amd64.pyd: PE32+ executable (DLL) (GUI) Aarch64, for MS Windows, 6 sections

[glandium]

So, the VSCMD_ARG_TGT_ARCH mentioned in the cibuildwheel issue is taken into account here:
https://github.com/python/cpython/blob/v3.11.11/Lib/distutils/util.py#L101-L106

which... doesn't support arm64.
So let's look at its fallback, get_host_platform... which allows to set _PYTHON_HOST_PLATFORM:
https://github.com/python/cpython/blob/v3.11.11/Lib/distutils/util.py#L48-L50

But guess what... this is what comes before that block:
https://github.com/python/cpython/blob/v3.11.11/Lib/distutils/util.py#L39-L46

The replacement for that, sysconfig.get_platform has the same problem:
https://github.com/python/cpython/blob/v3.13.1/Lib/sysconfig/__init__.py#L603-L618

[saschanaz]

FWIW, as python 3.12 removed distutils, it's been maintained as part of setuptools, including the fix for get_platform: pypa/distutils@f15f814

Perhaps we should make sure cibuildwheel doesn't depend on python distutils?

[glandium]

So, turns out the file name for modules ultimately comes from sysconfig.get_config_var("EXT_SUFFIX") in https://github.com/pypa/setuptools/blob/v75.6.0/setuptools/_distutils/command/build_ext.py#L711-L720

The equivalent setuptools code has an escape hatch via an environment variable:
https://github.com/pypa/setuptools/blob/v75.6.0/setuptools/command/build_ext.py#L161-L186

But that also means we can probably trick it from setup.py.

[glandium]

I got something to work.