Add warning for tuple type hint with single entry (e.g. tuple[int])

[pohlt]

Maybe it started as a list of integers and at some point you realized that a tuple makes more sense, so what you have now is this:
nums: tuple[int] # maybe was a list[int] once

You just forgot to add the ellipsis. A warning would have saved me a few head-scratching minutes.

Cheers,
Tom

[dhruvmanila]

Thanks, I think this kind of violation will be caught easily by a type checker where if nums has more then a single element, the type checker would highlight that. We're currently working on a type checker (code named "Red Knot") which should catch this.

[pohlt]

Thanks for the input.
In my use case, I'm using cattrs to structure incoming messages (from msgpack to attrs data classes), so a type checker wouldn't help here. That's why I personally would prefer a warning from ruff itself, but I can see how this is a very special use case.

[Daverball]

There is an existing rule for this in flake8-pyi, although it is disabled by default, since it has a relatively high rate of false positives, and has not been ported to ruff: https://github.com/PyCQA/flake8-pyi/blob/main/ERRORCODES.md#Y090

Generally a lot of the flake8-pyi rules have not been ported, since they're so opinionated and specific to typeshed's guidelines.

[pohlt]

That's exactly the warning I'm proposing. I don't know about the rest of the rules, but this rule in particular makes a lot of sense to me and I would not expect a high rate of false positives.
Anyway, thanks for the pointer.