Always complain if returning a value if annotated to return None

[JukkaL]

Mypy doesn't complain about this code that returns a value in a function declared to return None, since the return value is Any:

def f() -> None:
    return g()   # oops, but no error

def g():
    return 1

I think that mypy could complain about the return statement even if the value has type Any. The current behavior is not inconsistent or incorrect, but probably not optimal.

[gvanrossum]

If you're saying that in a function declared as -> None, any return statement with an expression should always be flagged as an error, I agree with you, though it's technically a style choice, and I've occasionally seen code that uses this knowing the function being called is also returning None, just as a shorthand for

g()
return

IIRC there was also some discussion with @ddfisher about the opposite -- whether in a function declared to return an Optional type, a bare return (or falling off the end) is acceptable style or not.

[gnprice]

Added label depends-on/strict-optional because I think anything we do here will probably look different in the strict-optional world from the no-strict-optional world, and any discussion should probably be in the context of the strict-optional world which we intend to be the only world in the future.

[AlexWaygood]

Mypy now correctly emits an error if --warn-return-any and/or --strict are specified (though the default behavior is still that it emits no errors).

Is this sufficient? — can this issue now be closed?