PEP 695: Add detection and error reporting for the use of incorrect expressions within the scope of a type parameter and a type alias

[Eclips4]

This fixes part of #15238:

Add detection and error reporting for use of assignment expressions, yield, yield from, and await expressions within the type parameter scope; see this section of PEP for details

[JelleZijlstra]

This seems incomplete because it detects these cases only at the top level, not anywhere within the expression. For example, def f[x: (T + (yield 42))](): pass should also be flagged.

[sobolevn]

Yes, you need a recursive visitor for this.

[sobolevn]

Thank you, one last nit :)

[sobolevn]

Thanks! Congrats on your first mypy PR :)

I will leave it open for a couple of days for others to have a potential feedback.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅