Remove dependency of pyo3-macros-backend on pyo3-build-config

[davidhewitt]

Looks like this cuts a few minutes off the clippy CI jobs - see #5809 (comment)

This will also fix #4579

This changes the macros to emit the same code regardless of Python version, leaving the implementation in pyo3 to decide what to do with the code.

I suspect that this will also improve the situation for users who are experiencing rebuilds as per #1708 (by making rebuilds less expensive)

[codspeed-hq]

Merging this PR will not alter performance

✅ 103 untouched benchmarks
⏩ 1 skipped benchmark¹

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_{Comparing davidhewitt:macros-no-config (05e6a40) with main (c442049)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[davidhewitt]

Nice, looks like this cut the runtimes of the clippy jobs by 2-3 minutes each, which will add up when the pipelines are busy. Seems worth pushing forward with this for multiple reasons, I'll come back to this soon and see if I can figure out how to abstract the CallingConvention choice away.

[davidhewitt]

This is ready for review; I'm pretty pleased with this, it seems to improve a couple of painful issues with the build system with only a small bump in complexity.

[Tpt]

Nice to see improved compile times 🥳

[Tpt]

pedantic-nit: could this shorter version be enough?

                const _: () = {
                    assert!(#pyo3_path::impl_::pyclass::DICT_SUPPORTED, "{}", #pyo3_path::impl_::pyclass::DICT_UNSUPPORTED_ERROR);
                };

and maybe even wrap it in a function like:

#[track_caller]
const fn assert_dict_supported() {
    assert!(cfg!(any(not(Py_LIMITED_API), Py_3_9)),
    "`dict` requires Python >= 3.9 when using the `abi3` feature");
}

and just have

const _: () = { assert_dict_supported() };

[davidhewitt]

Thanks, I did try functions but I missed the #[track_caller] attribute and without that the error messages show the function source, which I didn't like as much.

With #[track_caller], this works perfectly. Pushed, will merge 👍

[davidhewitt]

Ooops this is from local testing, will merge release notes merge first! 🙈