Fix typing, mostly related to async_generator

[laundmo]

While running the "advanced" example from the readme with pyright, i noticed it was alerting me to some typing issues, relating to asynccontextmanager and Client.__aexit__.

Pyright errors

Argument of type "Client" cannot be assigned to parameter "cm" of type "AsyncContextManager[_T@enter_async_context]" in function "enter_async_context"
  "Client" is incompatible with protocol "AsyncContextManager[_T@enter_async_context]"
    "__aexit__" is an incompatible type
      Type "(exc_type: Type[Exception], exc: Exception, tb: TracebackType) -> Coroutine[Any, Any, None]" cannot be assigned to type "(__exc_type: Type[BaseException] | None, __exc_value: BaseException | None, __traceback: TracebackType | None) -> Awaitable[bool | None]"
        Parameter 1: type "Type[BaseException] | None" cannot be assigned to type "Type[Exception]"
          Type "Type[BaseException] | None" cannot be assigned to type "Type[Exception]"
        Parameter 2: type "BaseException | None" cannot be assigned to type "Exception"
          Type "BaseException | None" cannot be assigned to type "Exception"
        Parameter 3: type "TracebackType | None" cannot be assigned to type "TracebackType"

Argument of type "AsyncIterator[AsyncGenerator[MQTTMessage, None]]" cannot be assigned to parameter "cm" of type "AsyncContextManager[_T@enter_async_context]" in function "enter_async_context"
  "AsyncIterator[AsyncGenerator[MQTTMessage, None]]" is incompatible with protocol "AsyncContextManager[_T@enter_async_context]"
    "__aenter__" is not present
    "__aexit__" is not present

Argument of type "AsyncIterator[AsyncGenerator[MQTTMessage, None]]" cannot be assigned to parameter "cm" of type "AsyncContextManager[_T@enter_async_context]" in function "enter_async_context"
  "AsyncIterator[AsyncGenerator[MQTTMessage, None]]" is incompatible with protocol "AsyncContextManager[_T@enter_async_context]"
    "__aenter__" is not present
    "__aexit__" is not present

The issue with Client.__aexit__ was simple, the arguments were missing the Optional[] around their type hint, and also need to use BaseException instead of Exception.

After a LOT of time trying to figure out what the issue wth asynccontextmanager was, i noticed that the compatibility import async_generator was missing type information, which caused pyright to fail at inferring the AsyncContextManager type for Client.filtered_messages and Client.unfiltered_messages.

I solved this by redefining the asynccontextmanager imported from async_generator with the proper typehints, and ignoring the type issues on those lines. This could potentially be moved to a type stub, though im not very comfortable working with them yet.

After these changes there are no more issues running pyright on the advanced readme example.
MyPy still throws a few errors relating to SocketOption, but this is behaviour that has not changed.
I have tested running the advanced readme example on python 3.6 and with modifications to the example due to missing features it runs fine.

[sdwilsh]

#87 has a less-verbose fix for this for python3.7+

I suspect some combination of the two is desired for support for 3.6 with type information.

[laundmo]

i did test this with 3.6, though not with a 3.6 pyright (I don't think it would make a difference)

this basically just copies the exact signature that the contextlib version has, so theres no need for pyright to understand sys.version, I don't think.

maybe it would still be better to use sys.version instead of the try-except though.

i might just merge your PR into my fork, when i have some time.

[frederikaalund]

Hi @laundmo and @sdwilsh. Thanks for opening these pull requests. I'll tackle both #86 and #87 in here since they cover the same underlying issue.

Good catch on the type errors in general. 👍 I'm happy to merge this as-is.

I guess the only open question is how to deal with the untyped async_generator.asynccontextmanager in python 3.6. Again, I'll happily accept either of the approaches that you propose. Do you guys agree on a specific approach or do you need a BDFL decision? :)

[laundmo]

@frederikaalund why not both? replace the try/except with the version if that @sdwilsh proposed, and leave my type overwrite in that. That way, 3.6 has correct typing and pyright can still understand it won't ever get to use async_generator.asynccontextmanager on versions > 3.6

[frederikaalund]

You're right, we need both. 👍 I'll merge this as soon as that last change lands in this PR.

[frederikaalund]

I'll credit you both in CHANGELOG.md by the way. :)

[laundmo]

@frederikaalund i don't have any more changes planned. Feel free to merge, or do you want me to merge the other PR into this one first?

[frederikaalund]

Well, one of the PRs are going to be in conflict. I'll merge this one first. 👍 Then @sdwilsh can update his PR accordingly.

Thanks for your contribution to asyncio-mqtt. :)