Move build requirements from setup.cfg to pyproject.toml.

[danxmoran]

Using setup_requires in setup.cfg is deprecated in newer verisons of setuptools, in favor of PEP517-style [build-system].requires in pyproject.toml.

More concretely, I believe moving to the newer style will fix an issue my team is hitting in our monorepo, where we've occasionally been seeing failures to install cairocffi because of "file already exists" errors when building the underlying cffi. I found a discussion in another project where the cffi maintainer said the issue arises when the same dependency is listed in both setup_requires and install_requires (pypa/cibuildwheel#813 (comment)) and then confirmed that switching to a PEP517-style build fixed things (pypa/cibuildwheel#813 (comment)).

[liZe]

Thanks for your proposal.

It could be great to move everything that’s in setup.cfg into pyproject.toml. Would you like to do this and check that the build still works for you?

[danxmoran]

@liZe I figured out porting most things over, but hit a few blockers:

• flake8 doesn't support pyproject.toml config (pyproject.toml (PEP 518) support PyCQA/flake8#234).
• sphinx doesn't natively support pyproject.toml config. I found this project as a way to shim in support, but it doesn't seem to be maintained or cover all the configs used by this project.
• coverage can use pyproject.toml, but only if installed with the toml extra (see docs here). Looking through the code I don't even see where coverage is installed - is that config just unused?

Based on the above, I think we have some options:

1. Leave things at my latest commit, with some leftover config in setup.cfg
2. Move the remaining setup.cfg configs into tool-specific config files
3. Revert back to my original commit in this branch, so pyproject.toml is minimal and setup.cfg keeps the bulk of config

What do you think between those? I'd vote 2 or 3

[liZe]

Thank you!

What do you think between those? I'd vote 2 or 3

4: remove default options for tools that don’t support pyproject.toml and update documentation accordingly 😁. We’ve done this before for other projects, we’ll use the same trick for CairoCFFI.

[danxmoran]

@liZe done! I updated the flake8 invocation in CI now that the config is gone. I couldn't find any actual usage of sphinx to update in CI / in docs.

[liZe]

Thanks, everything seems to work well!