[branchv]

This enables PEP 563 and PEP 585 🔥

Blocked by #5055
Relates-To: #4997

[neersighted]

I think this might be a bit too aggressive -- is the new union syntax really available? I see all the tests pass, but according to PEP 604 this wasn't added til 3.10. My memory is a bit rusty however.

[branchv]

Yea, you're right technically x: int | str is a syntax error for <3.10. However, with from __future__ import annotations this becomes equivalent to x: "int | str". So by default it's not evaluated at run-time, but mypy knows how to interpret it.

I should have noted that pyupgrade handled this migration, the only other change here was removing unused imports (for which I used pycln).

[neersighted]

A second PR adding pycln to the pre-commit config would be welcome, I think.

Consensus seems to be that the new Union syntax is harmless and nicer to write. Let's go ahead with this.

[neersighted]

Approved, but I'd like to wait for at least one other maintainer to eyeball this before we merge.

[danieleades]

I don't hate this. I've got a feeling that the pyupgrade hook can also add the from __future__ import annotations line, but perhaps only on later targets (maybe 3.9?). Not sure if anyone can confirm or deny that.

[branchv]

pyupgrade hook can also add the from __future__ import annotations line

I checked, it can definitely remove them, but I can't find any indication of it adding them. See asottile/pyupgrade#255 (comment) for an explanation of why it doesn't support that

[branchv]

rebased due to conflicts

[github-actions]

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