Subclass of Generic containing Any doesn't work with TypeVar

[Dreamsorcerer]

I'm not sure if this is a bug, or I'm just misunderstanding it. But, any tips on how to make it pass correctly would be great.

class Application(MutableMapping[Union[str, AppKey[Any]], Any]):
    @overload
    def __getitem__(self, key: AppKey[_T]) -> _T: ...
    @overload
    def __getitem__(self, key: str) -> Any: ...
    def __getitem__(self, key: Union[str, AppKey[_T]]) -> Any:
        return self._state[key]

Outputs:

aiohttp/web_app.py:145: error: Signature of "__getitem__" incompatible with supertype "Mapping"  [override]
aiohttp/web_app.py:145: note:      Superclass:
aiohttp/web_app.py:145: note:          def __getitem__(self, Union[str, AppKey[Any]]) -> Any
aiohttp/web_app.py:145: note:      Subclass:
aiohttp/web_app.py:145: note:          @overload
aiohttp/web_app.py:145: note:          def [_T] __getitem__(self, AppKey[_T]) -> _T
aiohttp/web_app.py:145: note:          @overload
aiohttp/web_app.py:145: note:          def __getitem__(self, str) -> Any

My assumption is that Any in the MutableMapping declaration means that it shouldn't care about the type in the subclass. But, also, _T is unbounded, so it accepts anything anyway.

Full code located at: https://github.com/aio-libs/aiohttp/pull/6498/files#diff-864083f9cc0dd7f38b50564bb430ddb33cf9123064b42b50decac1f9d7eca18c

[Dreamsorcerer]

Not needed anymore, even if it is a bug.