Add a pre-commit hook

[GideonBear]

Feature

Add a pre-commit hook to mypy (see mirrors-mypy/.pre-commit-hooks.yaml).
The only major roadblock is building it using mypyc, but that could use mypy_mypyc-wheels.

Pitch

Currently, to use mypy as a pre-commit hook, you need to use mirrors-mypy. It works fine, the only problem is you're not able to use arbitrary commits or branches (including master), just versions released on PyPI. If mypy were to add pre-commit hooks to the repo itself, it would be possible.

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Also see pre-commit/mirrors-mypy#80

[hauntsaninja]

Thanks for the suggestion, but we won't be doing this. In addition to the wheels issue (which is very important to resolve, compilation makes mypy 4x faster), pre-commit just often is not a great fit for running mypy. It results in enough issues that I wouldn't feel comfortable having an official setup for it. See #13916

[GideonBear]

Hi @hauntsaninja,
Thanks for the reply! I completely understand why you don't want to add it. Any chance there can be alpha/beta/dev releases released once in a while, especially when there's a long time before the next update? I don't know if it's necessary before 1.0, seems like it'll get released soon, but it's something that will help with using mypy with pre-commit.

[hauntsaninja]

Yeah, mypy's release frequency is a painpoint :-(

I think more releases, and more prereleases would be great! See #12210 (comment)

(In fairness to the Dropbox folks, who are in charge of new version releases, we were much better about release frequency for parts of 2022. I think the big "1.0" number has put some pressure on this release)

It sounds like you're aware of https://github.com/mypyc/mypy_mypyc-wheels ; you can specify URLs in requirements, so maybe there's a way to get pre-commit to use one of those wheels too.