bad-exit-annotation (PYI036) triggers on typing.overload definitions

[tjkuson]

Keywords searched in the issue tracker: PYI036, overload

Running ruff check --select PYI036 --isolated using Ruff version 0.4.0 on the file

import typing
from types import TracebackType


class Foo:
    def __enter__(self) -> typing.Self:
        return self

    @typing.overload
    def __exit__(self, exc_type: None, exc_val: None, exc_tb: None) -> None: ...

    @typing.overload
    def __exit__(
        self,
        exc_type: type[BaseException],
        exc_val: BaseException,
        exc_tb: TracebackType,
    ) -> None: ...

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_val: BaseException | None,
        exc_tb: TracebackType | None,
    ) -> None:
        pass

produces six PYI036 errors (three for each overload definition). The expected behaviour is that no PYI036 errors are raised, as these are overloads that describe legal calls rather than the complete implementation. This approach was recommended on this blog post.

[charliermarsh]

@AlexWaygood - do you mind taking this one?

[AlexWaygood]

Yeah, good call — I think we should just skip any functions decorated with @overload for this check. Thanks for the report!

[AlexWaygood]

On second thought, we can provide some validation for overloaded functions. Slightly more fiddly, but definitely doable.

[charliermarsh]

Thanks Alex!

[bswck]

Some "related off-topic" from me, since I recently went through a similar thing.

There should be no need to write overloads if we return None in either case.
That's the thing for a PEP to propose the ability of unpacking unions of same-sized tuples:

from __future__ import annotations

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from _typeshed import OptExcInfo  # tuple[None, None, None] | tuple[type[BaseException], BaseException, TracebackType]
    from typing_extensions import Unpack


class Foo:
    def __exit__(self, *args: Unpack[OptExcInfo]) -> None:  # should be legal, but isn't
        pass

What Ruff might or might not want to do is allow unpacking _typeshed.ExcInfo in the annotations of the __exit__ signature, not require either object or full signature. But that would only make sense if we always expect an error to occur 🤷‍♀️