Add pyproject.toml build file

[xxyzz]

This fixes the pip install error when adding Lupa source code as dependency in other packages' pyproject.toml file because Lupa's setup.py doesn't install Cython automatically.

Example pyproject.toml:

[build-system]
requires = ["setuptools"]
build-backend = "setuptools.build_meta"

[project]
name = "mypackage"
version = "0.0.1"
dependencies = [
    "lupa @ git+https://github.com/scoder/lupa.git"
]

[xxyzz]

Hi @scoder, could you please review this minor change if you have the time?

[scoder]

Note that setup.py now has a build_requires line. And there's also a requirements.txt. I'd rather not triplicate the dependencies across even more files.

[xxyzz]

But setuptools doesn't recognize the build_requires keyword. It has setup_requires and install_requires, but that would install Cython as normal dependency instead of build dependency package and Cython is not installed when prepare_extensions() is running according to the build log.

[scoder]

But setuptools doesn't recognize the build_requires keyword.

Understood. so that can probably be removed. Still, the GHA and appveyor scripts both use requirements.txt, so that is the single point of truth. Is there a way to make pyproject.toml use requirements.txt?

[xxyzz]

Is there a way to make pyproject.toml use requirements.txt?

Probably not, project.dependencies can use dynamic metadata to set a file but not for build-system.requires.

[xxyzz]

I removed the pyproject.toml file and replaced the invalid build_requires keyword with setup_requires. Now Cython can be installed with pip install's --use-pep517 option.

[scoder]

Thanks