[FR] Support a standalone config file .cython-lint.yml

[webknjaz]

Hi, I'd like to request a feature that is a missing bit for a specific use case.

For projects that use mass maintenance techniques similar to https://github.com/jaraco/skeleton (where there's an upstream Git skeleton that is periodically git merged into downstream), it's important for tools to have their own config files that are auto-detected. The reason is that this maintenance approach causes lower number of merge conflicts compared to having many tool configs in one file.

Examples of modern tools supporting separate non-pyproject config locations (even in the post-PEP 518 world) in the TOML format are Hatch, pip-tools, Poetry, Ruff, Towncrier.

Having experience taking part in implementing this for pip-tools, and leading the review/debates, I want to point out one implementation detail that may come up. It's the naming and the presence of the tool section in a non-pyproject config.
We debated the following options:

1. Only having it in pyproject.toml as [tool.<tool-name>] and bare keys in the .<tool>.toml one.
2. Having [<tool-name>] in .<tool>.toml.
3. Having [tool.<tool-name>] in .<tool>.toml.

We chose the third option. This allows copying the config section across files without changes. It also allows co-existing with other tools. It's also consistent, so the config reader doesn't have to implement multiple fallbacks for reading the config.

This I why I propose having .cython-lint.yml, which would take precedence over pyproject.toml (even when it's empty!). The section header for this file would be the same — [tool.cython-lint].

Here are some of our earlier discussions: jazzband/pip-tools#1863 (comment).

P.S. Many tools also have a --config CLI flag for passing arbitrary file paths. It's not necessary for my use case, but some people may want it at some point.

[MarcoGorelli]

hey @webknjaz - thanks for the request. I'm quite tight on time at the moment, but happy to review / approve a PR if anyone fancied raising one

[webknjaz]

Thanks for greenlighting it!