Mypy not detecting referenced before assignment

[stephan-nordnes-eriksen]

Bug Report

Not catching reference before assignment.

To Reproduce

The following code results in UnboundLocalError: local variable 'result' referenced before assignment if run, but mypy does not report an issue.

def foo(input: bool):
    if input:
        result = "value"
        print('result set')
    else:
        print('result is not assigned')

    return result

a = foo(False)

Expected Behavior

I would expect mypy to complain about result being referenced before assignment.

Actual Behavior

Success: no issues found in 1 source file

Your Environment

• Mypy version used: 0.980+dev.61a9b92297e1363b5bd99855df51e9a84be8da69 (current master)
• Mypy command-line flags: (none)
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.5 and 3.9.7 (both with pyenv)
• Operating system and version: Ubuntu 20.04.4 LTS

Notes
This is my firt bug report to mypy, so I'm sorry if this issue is already reported (I was not able to find it), or if this is out of scope for mypy. I do also realize that this is halting-problem-esque, but I believe this category of problem should be possible to resolve with static analysis.

[hauntsaninja]

Duplicate of #686 / #4019 / #2400