Enable mypy on CI

[Avasam]

Summary of changes

Follow-up to #3979. Extracted from #4192. Enables mypy type-checking in the CI.

Example failure: https://github.com/pypa/setuptools/actions/runs/8158516102/job/22300634747?pr=4257#step:9:69

Pull Request Checklist

• Changes have tests (this is enabling the tests! 😄 )
• News fragment added in newsfragments/. (no user-facing change)
  (See documentation for details)

[abravalheri]

I suppose that this is to cover

setuptools/setuptools/tests/integration/test_pip_install_sdist.py

Line 203 in 0435c72

import tomli as toml

?

If we are going for that approach, would it make more sense to remove the testing-integration extra and just use testing for everything?

[Avasam]

I suppose that this is to cover ... ?

Yes, same reason as importlib_metadata, with tomli not directly required by any dependency on 3.11

I don't see an issue with having less dependencies in testing-integration. And if you wanna merge them together that's up to you.

If you want to reduce duplication, then I think my latest commit should help with that (assuming it works)

[abravalheri]

Hi @Avasam, I was just asking your option about the matter, sorry if it prompted a change.

I think what we do in the PR is to just leave as you wrote it before: not touching testing-integration and just adding the extras in testing.

In a separated PR, I think we just remove the testing-integration and use testing everywhere...

Although it might add a bit of overhead for the integration tests, it will simplify and streamline the setup... This way we reduce the divergence with skeleton. The additional overhead in the integration tests should not be too much, and the integration tests just run before the releases anyway.

[Avasam]

sorry if it prompted a change.

I actually had the deduplication commit ready already, so it's more of a coincidence ^^

I think what we do in the PR is to just leave as you wrote it before

np, I'll revert that change and leave modifications to setup.cfg that are not absolutely necessary to another PR.

The additional overhead in the integration tests should not be too much

Especially if the pypi downloads are cached anyway (are they?)

[abravalheri]

Especially if the pypi downloads are cached anyway (are they?)

I don't remember now if the CI is keeping the pip cache 😅. But it should not matter that much.

I just hope someone is not installing setuptools[testing-integration]. But that is unlikely in my opinion.

[abravalheri]

Thank you very much @Avasam!