Un-narrowing optional type when defining nested function within a conditional

[mishok13]

Bug Report

When defining a nested function under a branch that accesses argument passed to outer function, the type narrowing resets to the original type.

To Reproduce

See the playground. Code posted here as well.

from functools import wraps
from typing import Any, Callable

def d(f: Callable[..., Any] | None) -> None:
    if f is not None: # <-- narrowed to Callable
        def inner() -> Any:
            return f() # <-- resolved as Callable | None
    return None

Expected Behavior

Inner function retains narrowed type.

Actual Behavior

Function f's type is resolved as Callable | None leading to this error:

main.py:9: error: "None" not callable  [misc]

Your Environment

• Mypy version used: 1.2, 1.3
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): no additional config
• Python version used: 3.11, 3.10

[AlexWaygood]

Duplicate of #2608

[AlexWaygood]

(Your code type checks fine on mypy master. The fix for #2608 will be available in the next release of mypy :)