How do I get the limited API version from wheel.py-api into USE_SABI?

[minrk]

I am exploring limited API wheel suport in the Cython 3.1 alpha, and I am trying to figure out the simplest way to set the right API version to match the wheel tag. There are valuable features (I think) for my case in the 3.11 and 3.12 Limited APIs, so I am considering building one 3.8 wheel and at least one or both of 3.11 and 3.12.

I expected setting wheel.pyapi=cp38 to set the equivalent of USE_SABI 3.8, but it doesn't (I'm sure there's a good reason). And I can't seem to find the cp38 string anywhere in the cmake variables. What is the simplest way to set the SABI to match the version specified in wheel.py-api and/or set both from the same place?

[minrk]

For more detail, I'm exploring building limited API wheels for pyzmq with Cython 3.1 and cibuildwheel in zeromq/pyzmq#2051

A key point is that I can't just switch to a single stable api wheel and be done, because I need the buffer APIs added to the stable API in 3.11, but still support older Python than that. So I need to at least build wheels for <=3.10, 313t, pypy, and then a stable wheel for cp311. I'm trying to figure out the best way to do that where I want some stable API wheels targeting specific versions and other regular wheels in the most maintainable way I can.

[jcfr]

When setting wheel.py-api¹², the CMake variable SKBUILD_SABI_COMPONENT is set to Development.SABIModule³ so that it can be conveniently used when calling `find_package(Python ...). For example:

find_package(Python REQUIRED COMPONENTS Interpreter Development.Module ${SKBUILD_SABI_COMPONENT})`

Improving scikit-build-core so that it also conveniently set a variable called SKBUILD_SABI_VERSION set that it can be used when calling Python3_add_library would be sensible. That way we could do the following:

if(NOT "${SKBUILD_SABI_COMPONENT}" STREQUAL "")
  python_add_library(some_ext MODULE WITH_SOABI USE_SABI ${SKBUILD_SABI_VERSION} ...)
else()
  python_add_library(some_ext MODULE WITH_SOABI ...)
endif()

In the meantime, the approach you implemented in the pull request linked above is sensible.

Related issues & pull-requests:

• Introduce SKBUILD_SABI_VERSION CMake variable scikit-build-core#958
• SKBUILD_USE_SABI scikit-build-core#743
• docs: Fix instructions to check if Development.SABIModule was requested scikit-build-core#957

cc: @henryiii

Footnotes

1. https://scikit-build-core.readthedocs.io/en/latest/cmakelists.html#limited-api-stable-abi ↩

2. https://scikit-build-core.readthedocs.io/en/latest/configuration.html#customizing-the-output-wheel ↩

3. https://cmake.org/cmake/help/latest/module/FindPython3.html#findpython3 ↩

[minrk]

Yeah, my approach assumes that if building with the stable ABI, the wheel tag is the build-time Python's version. But that's not necessarily the case, and can easily result in invalid wheels without any checks. I think scikit-build/scikit-build-core#958 would be a great help to make sure the output matches the input.

It would probably also be nice if I could specify with a boolean flag to use the stable ABI with the build-time Python as the target. I think that would help integration with cibuildhweel, so I wouldn't need a separate overrides entry for every combination, only one expressing when stable abi wheels should be built.