Missing warning for unawaited coroutine when invoking method in superclass

[mschurr]

Bug Report

An edge-case where warn-unawaited-coroutine does not work.

To Reproduce

class Parent:
    async def func(self) -> bool:
        return True


class Child(Parent):
    async def func(self) -> bool:
        # no warn-unawaited-coroutine emitted here?
        if not super().func():
            return False
        return True

Expected Behavior

Should warn about unawaited coroutine/incompatible type.

Actual Behavior

No warning.

Your Environment

mypy 0.971

[erictraut]

I don't think mypy has a feature to detect unawaited coroutines. In general, it's not a bug to return a coroutine without awaiting it. Using a coroutine in a conditional expression (especially when applying a not unary operator) is probably an unintended bug, so maybe that's something mypy could detect. I think that would be a new feature though.

[mschurr]

https://mypy.readthedocs.io/en/stable/error_code_list.html#check-that-coroutine-return-value-is-used-unused-coroutine

I was probably thinking of this.

Maybe truthy-function handles this, though, and I should be turning that on.

[mschurr]

I've confirmed truthy-function also does not catch this, so maybe this is still a bug?

[JelleZijlstra]

The super() calls are a red herring, here's a simpler repro:

async def func() -> bool:
    return True

async def func2() -> None:
    if func():
        print("hi")

I think this should be a new feature detecting that func() returns a Coroutine object, which is always true. This is similar to but distinct from truthy-function.

[mschurr-extrahop]

Worth noting that truthy-bool does catch both these cases. So maybe that's sufficient?

"mypy-test.func" returns "Coroutine[Any, Any, bool]" which does not implement __bool__ or __len__ so it could always be true in boolean context  [truthy-bool]

[JelleZijlstra]

Thanks, I didn't try that code. I think that's enough.

[ikonst]

I believe truthy-bool is still not default, and might not ever be, which is why we added truthy-function. Should we add a truthy-coroutine?

[JukkaL]

Should we add a truthy-coroutine?

This sounds reasonable to me. It seems unlikely to produce a false positive, at least if strict optional checking is enabled.

[ikonst]

Created #16069.