Pass pyo3/abi3-pyXX feature to pyo3 automatically

[messense]

No description provided.

[davidhewitt]

Thank you for all of these PRs! I have some time later this afternoon so will review all of them then.

[davidhewitt]

Thanks! I took a long time to think about this, and decided to create a PR to add some extra functionality on top of this commit. See https://github.com/messense/setuptools-rust/pull/1

I made it a separate PR onto your branch because I wanted to give you a chance to review it.

Once that is merged into this branch, I'm happy to push a CHANGELOG entry and more docs here.

[davidhewitt]

@alex based off #132 (comment), I'd be interested in hearing what you think of this PR.

Essentially if you set py_limited_api to True or False, the behaviour will be backwards-compatible and continue to match setuptools - you'll need to define the features as currently done.

With the new default "auto" mode, the command-line --py-limited-api option to bdist_wheel will be used to infer the build mode for the extension too, and will pass the correct feature to pyo3. I'd be curious if you'd want to use this in cryptography.

IMO it seems like a win for everyone: package maintainers can still build and distribute abi3 wheels, and users installing the package directly can build a version-specific extension. (PyO3 already uses a few optimizations when building version-specific, and I'd consider adding more.)

[alex]

I think we'd probably use this in pyca/cryptography, sure.

One note: I think you'll want to have auto -> not try to enable abi3 on PyPy still.

[davidhewitt]

Great!

One note: I think you'll want to have auto -> not try to enable abi3 on PyPy still.

Given that PyPy is sounding like it'll support a "stable api" for PyPy 3.8, my thought was that we should allow this in setuptools-rust so that it's future-compatible with when PyPy does add support.

PyO3 0.14 will emit a warning when abi3 is enabled for PyPy; we opted to do that so that it wouldn't cause a hard error in builds if the feature is set. PyO3 0.13.2 will silently complete the build, which imo is still fine because it'll be a working build. Setuptools just won't actually package it as an abi3 wheel.