UnboundLocalError in nested function is not detected by mypy

[ltworf]

Bug Report

Mypy does not detect invalid usage within nested functions. This might be a duplicate of #8746 but I thought it's a different issue.

To Reproduce

def a() -> None:
    val = 0
    def b() -> None:
        val += 1
    b()
a()

Expected Behavior

I'd like mypy to mark val += 1 as an error, as the runtime does

Actual Behavior

Code is considered correct.

Your Environment

• Mypy version used: 0.982
• Mypy command-line flags: None
• Python version used: 3.10.8

[hauntsaninja]

mypy mostly doesn't complain about UnboundLocalErrors, this is being actively worked on. Duplicate of #2400 , #686 , etc