Check for PEP 604 usage in CI - #5903

I'd rather put this in flake8-pyi, I'm happy to do the merging and releasing on a PR on that repo.

Also, | doesn't work in type aliases yet, so we can't check for it, at the moment.

PyCQA/flake8-pyi#45

@srittau This script doesn't check type aliases (just annotated assignments, function args, function returns), so should be fine to merge if we wanted to.
@JelleZijlstra that's a good point, I'll take a look. flake8-pyi won't be able to use ast.unparse for friendly errors, but should otherwise be workable.

Sounds good!

Relatedly would either of you be interested in becoming a maintainer on flake8-pyi? I don't have the power to add more maintainers but I'm sure Lukasz would be OK with that.

Sure!

I'd be glad to help out.

@ambv would you mind giving @hauntsaninja and @srittau commit access to https://github.com/ambv/flake8-pyi ?

@JelleZijlstra, done! Welcome, @srittau and @hauntsaninja.

Re-opening; feels like a good idea to have this for now, and add the check to flake8-pyi when we can use PEP 604 in type aliases cc @srittau

👍 Since the next mypy release is not in sight, creating a flake8-pyi check is not really useful at the moment. As a stopgap, this will do for now. Cc @JelleZijlstra

@hoefling Before I saw this PR, I pinged you on another merged PR asking you to do this, but now I can't find that PR. Sorry about that.