feat: add CPython 3.15 support for iOS

[henryiii]

Missing support files; either should be vendored or added to xbuild.

Assisted-by: OpenCode:Kimi-K2.6
Assisted-by: Copilot:claude-sonnet-4.6

[agriyakhetarpal]

Thanks @henryiii! LGTM on the other code, but some small corrections needed on the README.

[freakboy3742]

@henryiii Thanks for picking this up. We've already spoken about the target_python assertion; looking at the current CI failures, I forgot about the make_cross_venv script as well.

That script isn't part of the offical package either (and shouldn't be); my intention was to break that out into xbuild. xbuild needs a little bit of work before that's possible, plus the changes in cibuildwheel to hook it in.

Alternatively, (and/or as a stop-gap measure) we could include the make_cross_venv script (et al) as a resource in cibuildwheel.

[freakboy3742]

This all makes sense to me, and works great in my manual testing. A couple of notes inline. Not sure what's going on with the macOS test failures in CI, though.

I've taken an initial look at doing this with xbuild; it doesn't look too difficult, but there's a couple of fixes needed to xbuild to finalise that. I'm unlikely to get a chance to look at this until post-PyCon; what is in this PR seems like a very workable stop-gap.

[Copilot]

Pull request overview

Adds CPython 3.15 iOS support by wiring official python.org iOS XCFramework downloads into cibuildwheel and vendoring support files needed to create iOS cross-compilation virtual environments.

Changes:

• Adds CPython 3.15 iOS configurations and updates expected wheel/readme support metadata.
• Adds cibuildwheel-managed iOS cross-venv support scripts and resource path constants.
• Updates iOS setup logic to inject missing platform config files for python.org 3.15+ XCFrameworks.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/utils.py	Extends expected iOS wheels to include CPython 3.15 when prerelease builds are enabled.
README.md	Marks CPython 3.15 as supported for iOS.
pyproject.toml	Adjusts wheel-content checks for new iOS support resources.
cibuildwheel/util/resources.py	Adds a resource path for vendored iOS support files.
cibuildwheel/resources/ios-support/x86_64-iphonesimulator/sitecustomize.py	Adds x86_64 simulator startup customization.
cibuildwheel/resources/ios-support/x86_64-iphonesimulator/_cross_x86_64_iphonesimulator.py	Adds x86_64 simulator platform/sysconfig patching.
cibuildwheel/resources/ios-support/make_cross_venv.py	Adds cross-venv conversion helper for iOS support files.
cibuildwheel/resources/ios-support/arm64-iphonesimulator/sitecustomize.py	Adds arm64 simulator startup customization.
cibuildwheel/resources/ios-support/arm64-iphonesimulator/_cross_arm64_iphonesimulator.py	Adds arm64 simulator platform/sysconfig patching.
cibuildwheel/resources/ios-support/arm64-iphoneos/sitecustomize.py	Adds arm64 device startup customization.
cibuildwheel/resources/ios-support/arm64-iphoneos/_cross_arm64_iphoneos.py	Adds arm64 device platform/sysconfig patching.
cibuildwheel/resources/ios-support/_cross_venv.py	Adds build-environment import hook to preserve cross-venv files.
cibuildwheel/resources/build-platforms.toml	Adds CPython 3.15 iOS target configurations.
cibuildwheel/platforms/ios.py	Injects platform config data for 3.15+ and uses vendored cross-venv resources.
bin/update_pythons.py	Updates iOS version refresh logic for python.org 3.15+ releases.
.pre-commit-config.yaml	Excludes vendored iOS support files from pre-commit checks except the helper script.

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[joerick]

This looks okay to me! I guess we expect these support files to be included in the next CPython XCframework release? So we'll only be vendoring this stuff for a little while?

[freakboy3742]

This looks okay to me! I guess we expect these support files to be included in the next CPython XCframework release? So we'll only be vendoring this stuff for a little while?

I don't expect they'll ever be in the XCframework - but they will (and are already) in xbuild. That set of tools should be able to remove the duplication of "cross platform venv" stuff in Android, iOS and Emscripten - but it needs a little more work before it's ready for serious consideration.

However, once it is ready for consideration, we'll be able to remove the vendoring in cibuildwheel.

[freakboy3742]

This doesn't seem quite right yet - the _inject_support_files call shouldn't be needed at all.

I think the problem is that the platform_config_path that is being passed in for the 3.15 case doesn't actually exist - and the path to the stdlib (which is where sysconfigdata comes from) isn't being provided.

[henryiii]

@freakboy3742 have you had a chance to look at the latest changes? (also waiting on PyPy)

[freakboy3742]

@freakboy3742 have you had a chance to look at the latest changes? (also waiting on PyPy)

My apologies - I wasn't as productive on my flight home as I was hoping. I'm taking a look now.

[freakboy3742]

I've pushed a couple of minor tweaks - mostly clarifying the naming of the paths being referenced in the make_cross_venv script. It doesn't change the actual work being done, but the variable/argument names correspond a little closer to the actual purpose of the script. It also tweaks the message printed describing the conversion taking place - previously, it was printing the location of the sysconfig data, not the target platform type.

Otherwise, this looks good to me. I'll be able to revisit this once I've got xbuild to a more stable state. That will remove the need to vendor these scripts; but in the meantime, this should work. Thanks @henryiii for pushing this forward.