ci: add android test

[henryiii]

Description

Testing pypa/cibuildwheel#2349.

Suggested changelog entry:

• Add CI testing Android

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📚 Documentation preview 📚: https://pybind11--5714.org.readthedocs.build/

[henryiii]

@mhsmith Had to install wheel and patchelf, and now it's failing at the test step on all three systems.

[mhsmith]

The current failures are because KVM hasn't been enabled on Linux, and GitHub Actions isn't able to run the Android emulator on macOS. Both of these are discussed in pypa/cibuildwheel#2349.

It also looks like somehow the merge of henryiii#23 has missed a couple of the files. Correction: they've already been merged in #5733.

But this PR-against-PR workflow is confusing, so would it be simpler if I created my own PR to replace this one? Since you're a member of the pybind11 project, we would both be able to push to it.

[henryiii]

I'm fine if you make a PR, but I'm fine to give you access to my fork.

[mhsmith]

Thanks, that works too.

[mhsmith]

OK, I've updated the GitHub Actions configuration as discussed in my previous comment, and the Android jobs are passing now.

To enable local testing, I also moved the ANDROID_API_LEVEL environment variable from tests-cibw.yml to pyproject.toml. But this breaks the iOS and Pyodide jobs, because the stable cibuildwheel version doesn't recognize the android namespace. I guess you aren't planning to merge this PR until after the next cibuildwheel release anyway, so I've put a TODO comment in tests-cibw.yml to indicate that.

[henryiii]

Android: can't find wheel in path?

The iOS 3.14 failure is expected (pypa/cibuildwheel#2494).

[mhsmith]

I've added wheel back to this PR so it can work with cibuildwheel 3.1, and fixed it properly for the next cibuildwheel version in pypa/cibuildwheel#2515.

I think this PR is now ready to merge.

[henryiii]

Suggested change

	# TODO: remove "wheel" once we're using a cibuildwheel version that includes
	# https://github.com/pypa/cibuildwheel/pull/2515.
	- run: pipx install wheel patchelf
	- run: pipx install patchelf

I guess we still need patchelf? Is that something cibuildwheel should install?

[mhsmith]

Actually, I see it's on PyPI for both Linux and macOS, so maybe we could make it a dependency of cibuildwheel.

[henryiii]

Does it have to be co-installed with cibuildwheel? cibuildwheel shouldn't depend on compiled dependencies. But in an environment is fine. I haven't looked at where it's used.

[mhsmith]

Actually on Linux cibuildwheel already depended on patchelf via auditwheel, but neither of them needed to be declared as a Python-level dependency because they're installed in the manylinux Docker image.

On Android, cibuildwheel uses patchelf in a more limited way to deal with linking against the C++ library. I'm planning to eventually move that functionality into auditwheel, and then cibuildwheel will be able to use the same auditwheel "repair" command on both Linux and Android.

Does it have to be co-installed with cibuildwheel? cibuildwheel shouldn't depend on compiled dependencies.

We could use environment markers to limit the dependency to the Linux or Mac platforms that support the Android build tools. patchelf appears to have all the necessary wheels.