Context manager types

[last-partizan]

This is another case from django-types, where I'm not sure this is error, or I should fix my types.

from types import TracebackType
from typing import Any


class TestContextManager():
    def __enter__(self) -> Any | None: ...
    def __exit__(
        self,
        exc_type: type[Exception] | None,
        exc_value: Exception | None,
        traceback: TracebackType | None,
    ) -> None: ...


with TestContextManager():
    ...

ERROR Cannot use `TestContextManager` as a context manager [bad-context-manager]
  --> /home/serg/typing-repro-contextmanager/repro_plain.py:15:6
   |
15 | with TestContextManager():
   |      ^^^^^^^^^^^^^^^^^^^^
   |
  Argument `type[BaseException] | None` is not assignable to parameter `exc_type` with type `type[Exception] | None` in function `TestContextManager.__exit__`
ERROR Cannot use `TestContextManager` as a context manager [bad-context-manager]
  --> /home/serg/typing-repro-contextmanager/repro_plain.py:15:6
   |
15 | with TestContextManager():
   |      ^^^^^^^^^^^^^^^^^^^^
   |
  Argument `BaseException | None` is not assignable to parameter `exc_value` with type `Exception | None` in function `TestContextManager.__exit__`
 INFO 2 errors

https://pyrefly.org/sandbox/?code=GYJw9gtgBALgngBwKYGcoEsILCGUAqIAhgMZIBGpA1vokgFCiSyLoB2A5hljngIJs49YSQA2RFGnyoYAYTBsYSAB4wAskTZEOSEAAoAlAC56UM1AAmSYFAD6tpIt329KJKOAGoAWgB8UATgoAB8oADkFJCMoADo403MrG3sVdBgXBPNzNw8AGkysqBUSW3hkaLKkAG0AUWUyBBh0BQBdEPDI-MLzYtsANyJRAFcoqDqGpoV2iLYkLu7YYjJKEipowlIKalpkac6Crz8O2ei4mOF6AHc0gAsCGXknVQ0tHX1jArOgA&version=3.12

Technically, pyrefly is correct here. But, other type-checkers don't mind.

I think we should just update our django-types, to be more correct, and also use BaseException there.

[rchen152]

I believe pyrefly is correct here; I can construct an example where, at runtime, the context manager's __exit__ method receives a BaseException, not an Exception: https://codapi.org/embed/?sandbox=python&code=data%3A%3Bbase64%2CZZCxTsMwEIZ3P8VPJ0cKPEAGpA4MLHTphpDluBewSG3Ld4FE4uGRU5om4ra7%2B%2BT7fvtzilnAE6suxzNkSsTwl%2BkxW0etdZ%2FHKZFSyvWWGftGAcCJOhhDQSgbo5n6rrosSmWSIQeUqVrToxdj9IKVfb10NDpT7jezxevT6CiJj%2BENP3iJgbbkl%2B0HarBQ%2FyC52jfbIBuwwv3j3N7cfYcQBZ55aOfE%2BipW366tspZK2QfRu0NMfIdn0JjICZ1gw0qwHQTvUZpdvUStlFLfXj6w138v8sQP5Zt09Qs%3D.

Mypy does't appear to do any check at all on the type signature of __exit__. I can change the Exception annotations to something totally wrong like int and there's still no error: playground.

[last-partizan]

Thanks! fixed this one in django-types.