truthy-bool check does not check the not operator

[komodovaran]

class Foo:
    @property
    def prop(self) -> bool:
        return False


def bools_only(value: bool) -> bool:
    return value


bools_only(Foo().prop) # Standard behavior of properties
bools_only(Foo.prop) # Expected type 'bool', got 'property' instead 
bools_only(not Foo.prop) # no error after casting with `not`!

Python interprets not object as not bool(object) which doesn't seem to be covered by any checks.

Tested with Mypy 1.11.2 and Python 3.12

https://mypy-play.net/?mypy=latest&python=3.12&gist=1c5f3510b686dd0e2e04e0a9ef191a96

[JelleZijlstra]

This falls conceptually within the https://mypy.readthedocs.io/en/stable/error_code_list2.html#check-that-expression-is-not-implicitly-true-in-boolean-context-truthy-bool code. However, it doesn't appear mypy checks for this at all in the not operator.

To fix this,

mypy/mypy/checkexpr.py

Line 4258 in 72c413d

result: Type = self.bool_type()

needs to be changed to call a variation of

mypy/mypy/checker.py

Line 5654 in 72c413d

def _check_for_truthy_type(self, t: Type, expr: Expression) -> None:

.