feat: use SPEC 0 schedule for cibuildwheel

[mayeut]

As discussed in various issues, I think that cibuildwheel is in position where it might make sense to follow SPEC 0 schedule rather than the CPython schedule. This would allow to take advantage of new Python features faster (or without/ with less back ports).

This draft PR is:

• to gather feedback on such a change
• to check that indeed, every CI we support is ready.
• preview what would change
• if we want to follow-up with this, then, it might be a good thing to warn users ahead to let them update there workflows if need be (mostly for CI that do not come with python pre-installed).

The idea would be to switch to SPEC 0 in 2024Q4 after Python 3.8 EOL & Python 3.13 GA, thus dropping 3.8, 3.9 & 3.10.

[joerick]

I support this change. There is very little reason to hang on to older Pythons on the host side, when we can benefit from new features.

To be clear to anyone coming across this, we're talking about the version of Python that is used to run cibuildwheel. That is distinct from the versions of Python that we build wheels for, which would be unchanged by this.

[EwoutH]

I think it's very logical for a project like cibuildwheel to follow SPEC 0 on the host side.

[henryiii]

Let's get 3.13.0 in, make a patch release, then I think this will be ready to merge?

[mayeut]

then I think this will be ready to merge?

I was waiting for 3.13.0 final availability in GHA but maybe we don't care that much about that (or removing the allow-prereleases: true in tests)

[henryiii]

Don't necessarily need to remove the allow-prereleases. The only time Python pre-releases is for upcoming Python versions, which you opt-into anyway. Maybe "3.x" or version ranges could be confused, but otherwise there's no harm in keeping it around. And it's really only our tests, users don't care or need GHA's 3.13.

[henryiii]

(and, 3.13.0 is available AFAICT, it's just not shipped in manifests or runner images yet. But also I'm not talking about merging the instant we release, either ;) )

[Czaki]

looks good to me

[henryiii]

Should we add a warning to cibuildwheel running on Python 3.8-3.10 stating that the host Python needs to be upgraded to keep working with the next version of cibuildwheel? Unlike a normal Python package, you don't want to get silently stuck on an older version of cibuildwheel.

[joerick]

Yeah, that's a good idea. I just checked and a decent number of projects just write pip install cibuildwheel into their build scripts - those people would miss out on cibuildwheel upgrades if their python is oldish.

[joerick]

We're talking in #2047 about holding this until a v3.0 release, but we'll want to get #2052 and perhaps other changes in before then, so I've added a label to that effect.