Assorted issues with context managers

[mikeshardmind]

Describe the bug

Context manager handling is inconsistent, and where issues with it are detected, the error messages do not correctly identify the root cause

Code or Screenshots

Code sample in pyright playground

import asyncio

class WorkingExample:

    async def __aenter__(self) -> None:  ...
    async def __aexit__(self, *dont_care: object) -> None:  ...
    def __enter__(self) -> None:  ...
    def __exit__(self, *dont_care: object) -> None:  ...


class AsyncInvisiblyBrokenExample:
    async def __aenter__(self) -> None:  ...
    def __aexit__(self, *dont_care: object) -> None:  ...  # Ideally, this should be an error too, incompatible with data model
    def __enter__(self) -> None:  ...
    def __exit__(self) -> None:  ...  # Ideally, this should be an error too, incompatible with data model


class VisiblyBrokenExample:
    def __aenter__(self) -> None:  ...  # Ideally, this should be an error too, incompatible with data model
    def __aexit__(self, *dont_care: object) -> None:  ...  # Ideally, this should be an error too, incompatible with data model
    def __enter__(self) -> None:  ...
    def __exit__(self) -> None:  ...

class AlsoInVisiblyBroken:
    def __enter__(self) -> None:  ...



if __name__ == "__main__":
    
    works = WorkingExample()
    visibly_broken = VisiblyBrokenExample()
    async_invisbly_broken = AsyncInvisiblyBrokenExample()

    async def amain() -> None:
        async with works:
            ...
        async with visibly_broken:
            # pyright detects None is not Awaitable (correctly identified issue)
            # however the error message is incorrect, as it claims `__await__` isn't present
            ...
        async with async_invisbly_broken:
            # pyright does not detect that `__aexit__` has the wrong type
            ...

    with works:
        with visibly_broken:  # pyright detects this, but the error message is misleading
            # claims AsyncInvisiblyBroken does not implement `__exit__`, when it does, just incorrectly
            # it does not satisfy the runtime requirements of being a context manager as a result,
            # so the error is correct, but the message doesn't identify the actual issue.
            with async_invisbly_broken:  # same as above
                # in addition though, this shows the asymmetery with the async with above
                # not being caught. 
                asyncio.run(amain())

This was discovered while typing some previously private code for public use with N:M concurrency for use with freethreading python builds.

edit: ignore the definition of AlsoInVisiblyBroken, it was there to demonstrate things that ended up redundant and couldd have been removed.