Functions annotated to return None can't return function calls returning None

[TRManderson]

Minimal example:

def fn1() -> None:
    return None

def fn2() -> None:
    return fn1() # test.py:5: error: No return value expected

Sorry for the poor issue naming, not sure how else to describe this.

[TRManderson]

One of the tests explicitly disallows this, which is the cause for my PR #2829 failing. I've removed it in the PR, but is there a reason to have it there in the first place?

[JukkaL]

I have a feeling that this has been discussed earlier. Anyway, it's a matter of style -- the code is clearly correct. I wonder if @gvanrossum has an opinion whether fn2 should be accepted.

[gvanrossum]

I'm torn, since I sometimes do this myself, but I do think it's a (very slight) code smell. I also think that fn1() and fn2() should either both be errors or both pass (both have a -> None and a return EXPR where EXPR is known to have the value None).

[ddfisher]

For what it's worth, this is allowed with --strict-optional.

[JukkaL]

If it's only a very slight code smell, mypy should perhaps not complain about it.

[gvanrossum]

Agreed.

[msullivan]

This is fixed