Use covariant type Mapping instead of invariant type Dict in arguments and let's wait for mypy upstream issue about nested Union

[achimnol]

Describe the bug

I see some typecheck failures in my code using aioredis v2,
which are related to python/mypy#8554
where the arguments with generics should use covariant type Mapping instead of Dict to allow aioredis user codes to be properly typechecked.

To Reproduce

    async def produce_event(
        self,
        event: AbstractEvent,
        *,
        source: str = 'manager',
    ) -> None:
        raw_event: Dict[bytes, bytes] = {
            b'name': event.name.encode(),
            b'source': source.encode(),
            b'args': msgpack.packb(event.serialize()),
        }
        await redis.execute(
            self.redis_client,
            lambda r: r.xadd('events', raw_event),  # <-- type error
        )

Type error:

error: Argument 2 to "xadd" of "Redis" has incompatible type "Dict[bytes, bytes]";
expected "Dict[Union[Union[bytes, memoryview], Union[str, int, float]], Union[Union[bytes, memoryview], Union[str, int, float]]]"

Expected behavior

There should be no type error. At the runtime the code runs fine.

Logs/tracebacks

Nothing for here.

Python Version

$ python --version
Python 3.9.6

aioredis Version

$ python -m pip show aioredis
Name: aioredis
Version: 2.0.0
Summary: asyncio (PEP 3156) Redis support
Home-page: https://github.com/aio-libs/aioredis
Author:
Author-email:
License: MIT
Location: /Users/joongi/.pyenv/versions/3.9.6/envs/venv-edge-common/lib/python3.9/site-packages
Requires: async-timeout, typing-extensions
Required-by: backend.ai-common

Additional context

No response

Code of Conduct

• I agree to follow the aio-libs Code of Conduct

[achimnol]

Manually modifying aioredis source code to use Mapping still seems not to resolve the issue.
Maybe it's something to do with nested Unions? 🤔

error: Argument 2 to "xadd" of "Redis" has incompatible type "Dict[bytes, bytes]";
expected "Mapping[Union[Union[bytes, memoryview], Union[str, int, float]], Union[Union[bytes, memoryview], Union[str, int, float]]]"

[achimnol]

Maybe... it's another mypy issue: python/mypy#10764 😭

[Andrew-Chen-Wang]

heads up: I have not been checking many mypy issues in #1156 which may be a downfall to the repository. Any help for #1156 would be greatly appreciated!