Variable with narrowed type does not get carried into nested function

[alexkoay]

Bug Report

Variables with narrowed types do not seem to be transferred into a nested function.

To Reproduce

from typing import Optional

def foo(value: Optional[int]) -> int:
    if value is None:
        return 0

    def bar() -> int:
        # value should be inferred to int here, but mypy detects it as Optional[int] and throws an error
        return value
    return value

def spam(value: Union[int, str]) -> str:
    if isinstance(value, str):
        def baz() -> str:
            return value
        return value

    else:
        def baz() -> int:
            return value
        return value

Expected Behavior

value should be narrowed in the nested function.

Actual Behavior

mypy raises errors in the nested function

Your Environment

Tested this on Windows in WSL with Python 3.8, and on Windows with Python 3.10

• Mypy version used: 0.991

• Mypy command-line flags: None

• Mypy configuration options from mypy.ini (and other config files): warn_no_return = true warn_redundant_casts = true warn_return_any = true warn_unreachable = true warn_unused_ignores = true ignore_missing_imports = true

• Python version used: 3.8 / 3.10