Re: [PR PATCH] [Closed]: [RFC] Support for PEP517 build systems with new build style

[ahesford <ahesford@users.noreply.github.com>]

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There's a closed pull request on the void-packages repository

[RFC] Support for PEP517 build systems with new build style
https://github.com/void-linux/void-packages/pull/26883

Description:
I [have been told](https://github.com/pypa/packaging/issues/363) that PEP517 build systems are the way of the future for Python package building and installation, and `setuptools` will become (or is now) disfavored. `python3-packaging` is the first of our packages to drop `setuptools` and specifically require a PEP517 builder.

This is an attempt to support PEP517 builds in our `python3-module` build style. For now, the preferred (only?) way to do PEP517 builds is to rely on `pip` to do the work. Fortunately, because no PEP517 builder supports compiled extensions, we can avoid the pain of trying to force `pip` to behave with cross compilers (for now).

Use of the PEP517 build procedure in a template is enabled by setting `python_pep517=yes`. If this is adopted, we'll have to modify `xlint` as well.

`pip` can do a one-pass build and install, but I figured it was better to split into a build-wheel stage and an install-wheel stage so people can do `./xbps-src build` and investigate the artifacts.

I am not thrilled with the use of globs in `do_install` when setting a default `$python_pep517_wheel` but, according to [PEP 427](https://www.python.org/dev/peps/pep-0427/#file-name-convention) and its referenced [PEP 425](https://www.python.org/dev/peps/pep-0425), the filename components I'm trying to match with the globs are not easily predicted. In any case, if this produces undesirable behavior in specific templates, the author can manually set that variable. Any other ideas are welcome.

Finally, the build process produces `direct_url.json` in the Python `dist-info` directory to comply with [PEP 610](https://www.python.org/dev/peps/pep-0610), which replaces a simple version number in `pip freeze` output with a `file://` URL pointing to the location of the wheel used for installation. (In our case, this will be `/builddir/$wrksrc/$build_wrksrc/$python_pep517_wheel`.) For distribution packages, I do not believe this is desirable. We can manually remove the file, for example in `do_install`, assuming the `dist-info` directory is predictable. Comments about doing this are welcome.

cc: any @void-linux/pkg-committers with a stake in Python packages