PLR6301 doesn't detect @override from TYPE_CHECKING

[ItsDrike]

Summary

The preview rule PLR6301 is meant to detect when a method should instead become a staticmethod, class method or a fucntion, and triggering when the self argument in the function body is unused.

The documentation for this rule explains that it doesn't trigger for methods decorated with @typing.override, which is good, however, this detection doesn't work when the override symbol is imported within a TYPE_CHECKING block, and has a fallback in the else block after to just a no-op decorator.

This pattern is pretty important for libraries that need to handle backwards compatibility and don't want to have typing_extensions become a runtime dependency.

E.g.

if TYPE_CHECKING:
    from typing_extensions import override
else:
    override = lambda f: f

# Ruff doesn't seem to understand that `override` in here is actually the `typing.override`
# and when PLR6301 violation is detected, even if decorated with `@override`, it triggers.

Playground link: https://play.ruff.rs/45ead6a4-9511-49be-bf76-010f6d325a80

Version

ruff 0.15.9

[ntBre]

Thanks for the report!

I don't think this is an issue with PLR6301 or with our TYPE_CHECKING handling, at least directly. Instead, this is caused by the else branch of the if TYPE_CHECKING block. That seems to be shadowing the first definition in a way that our semantic model can't follow.

If you invert the condition and order, it works as expected:

if not TYPE_CHECKING:
    override = lambda f: f  # noqa: E731
else:
    from typing_extensions import override

or if you import override from one of the known typing-modules, but those are both workarounds.

This may be pretty tricky to fix without introducing other issues, but it does feel like a bug to me.

[MichaReiser]

I don't know if this is an option for you but you could have your own typing modules that only exportes override (and any other typing symbols) from within TYPE_CHECKING, then use typing_modules to teach ruff that said model should be treated like the built in typing module