Make it easier to support multiple versions

[Narsil]

Idea

in safetensors, we can leverage the PyBuffer stabilisation in abi3 in order to make some performance optimizations. However, the official support for safetensors the support goes back to py38.

Currently I'm solving this by making a feature to check which abi3 we're supposed to build.

Currently it's quite inconvenient to choose which abi3 to enable directly from pip install command, huggingface/safetensors#567
I'm mostly switching the flags using MATURIN_PEP517_ARGS which is not super simple for newcomers to know. Using pip install . was quite convenient.

I tried to find some kind of mecanism to choose the feature set based on python_version but couldn't find any.
I could make one feature be default and let knowing users be able to build for older python version, but for them the error message is also not great currently (the thing builds, but when running the library missing symbols are declared)

Did I miss it ?
If not, do you think it would be something doable and interesting ?

Implementation

My pyproject knowledge seems limited by the marker notations is specified here: https://peps.python.org/pep-0508/ https://peps.python.org/pep-0496/

I'm not sure how we would implement, or even if there is no major counter indication to it.

[messense]

Have you tried https://pyo3.rs/latest/building-and-distribution/multiple-python-versions.html?

[Narsil]

Thanks, but that doesn't apply to the abi3-pyxx features, does it ?

Here it would something like that, but more a way to switch features in pyproject.toml based on the python version.