[flake8-return] Recognize functions returning Never as non-returning (RET503)

[viccie30]

Summary

This pull request makes flake8-return recognize functions annotated to return typing.Never as non-returning.

Test Plan

I have duplicated the existing tests for functions returning NoReturn.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

Your code changes look correct, but they seem to have no effect. I'd expect that the rule wouldn't flag this specific line because there's no implicit return (it never returns). I added a ton of debug statements to is_noreturn_func and I suspect the problem is that the semantic model hasn't seen bar at the moment we try to resolve its name. My suspicious gets confirmed when changing the example to

import typing

def bar() -> typing.Never:
    abort()

def foo(x: int) -> int:
    if x == 5:
        return 5
    bar()

which raises a violation before your change but now doesn't.

I suggest that you change your examples (including the existing NoReturn) to not use a nested function. We can add a dedicated test with a nested function with a doc comment explaining that this is currently not supported.

[viccie30]

I have changed the current tests to no longer use nested functions and have added a currently ignored test checking nested functions.