Python Build

[johannes-spies]

This PR adds the infrastructure needed to build the metatomic_core Python wheel. Essentially, it's a port of the same functionality in metatensor (setup.py, CMakeLists.txt, and package-core.sh). The only difference is that we import metatensor in cmake_ext's run method to get the cmake_prefix_path which is required to build the native library.

The PR also makes an important change to the CI setup: now, containers for testing are built with Rust, similar to what metatensor does.

📚 Download documentation for this pull-request

⚙️ Download Python wheels for this pull-request (you can install these with pip)

[Luthaf]

Looks good overall, I'm not convinced we should switch to uv in CI, and we should for sure do it in a separate PR anyway

[johannes-spies]

Thank you for the review! You're right, the switch to uv was not necessary and I will revert it. I just tried to make the CI as similar as possible to track down the failure in the windows tests.

[Luthaf]

The wheel (as created by python -m build python/metatomic_core) contains configuration files to find nlohmann::json, which I don't think we want to make available through the to external users here.

[...]
adding 'metatomic/share/cmake/nlohmann_json/nlohmann_jsonConfig.cmake'
adding 'metatomic/share/cmake/nlohmann_json/nlohmann_jsonConfigVersion.cmake'
adding 'metatomic/share/cmake/nlohmann_json/nlohmann_jsonTargets.cmake'
adding 'metatomic/share/pkgconfig/nlohmann_json.pc'
[...]

Ideally they should not even be installed by the main metatomic CMakeLists.txt (this is not specific to Python) when we fetch the code from github ourself.

Can you have a look?

[johannes-spies]

Yes, you're right. 27675fd sets JSON_Install to OFF.

[Luthaf]

We still need to install the headers, just not the cmake config / .pc files

[johannes-spies]

I added the headers in 8dc3972. Also, I tried making the build-wheels.yml pipelines as close as possible to metatensor's pipeline! I hope everything is now very similar, minus uv.