chore: try using scikit-build-core

[henryiii]

This is an experiment using scikit-build-core for the example. Several things are handled by scikit-build-core automatically, like auto downloading cmake/ninja if needed, backporting FindPython 3.26.1 if an older CMake is used, auto-discovery of properly placed cmake Config files (which nanobind seems to do!), release types (which technically were always handled by scikit-build), and better SDist & wheel directory handling.

How is ABI3 specified? I didn't see it set for the old setup.py. There's a setting in scikit-build-core for it; like every setting, it can be in pyproject.toml, as a --config-settings option, or via an environment variable.. I can work on implementing an overrides system to control settings based on the Python being used, would that be enough? I can also provide a nice way to communicate to CMakeLists.txt if ABI3 is requested. Just need to know what the expectation here is.

Closes #19.

[wjakob]

This looks amazing! To me it looks like a nice improvement without any downside. Are there potential gotchas/limitations that I am not aware of?

Regarding ABI3 builds: Ideally, the normal pip install should target the current Python version, while the GHA wheel action additionally makes an ABI3 wheel to be future-proof.

However, nanobind's ABI3 support depends on Python 3.12, and that wasn't officially supported by cibuildwheel yet. (But it might be soon, with the Python3.12b1 having been released 2 days ago). Anyways, that's why ABI3 isn't mentioned in this example project (yet!)

Minor: I saw that you reduced the minimum CMake version to 3.15. I am not 100% sure that this will be compatible with the nanobind CMake scripts (have not tested it though.). Is there a particular reason for this change?

[henryiii]

It's not as hackable as something based on setuptools (which is not really a downside...). Features are carefully being added as needed. Otherwise, I think it should be a solid upgrade.

A way to detect ABI 3 should be available in the next release (though I might change the in-main version before release, there is something there now). I think overrides will be coming soon too, hopefully 0.5.

I checked nanobind and it puts 3.15 (or was it 3.14?) as the minimum version - if that's the case, scikit-build-core supports and is tested on 3.15+. Since it backports FindPython from 3.26.1 (configurable), you actually can use the features required for making wheels, like Development.Module, ABI3, etc. in CMake 3.15+.

I didn't run a test on 3.15 though.

[henryiii]

(I could PR that later)

[henryiii]

Going to try it without the require statement. It’s a cibuildwheel bug if it doesn’t work.

[henryiii]

Looks good to me:

6 wheels produced in 10 minutes:
  nanobind_example-0.0.1-cp310-cp310-win_amd64.whl        34 kB
  nanobind_example-0.0.1-cp311-cp311-win_amd64.whl        34 kB
  nanobind_example-0.0.1-cp312-abi3-win_amd64.whl         33 kB
  nanobind_example-0.0.1-cp38-cp38-win_amd64.whl          34 kB
  nanobind_example-0.0.1-cp39-cp39-win_amd64.whl          34 kB
  nanobind_example-0.0.1-pp39-pypy39_pp73-win_amd64.whl   32 kB

[wjakob]

Amazing 🎊. Thank you very much, Henry!