Please just change something. Weird combination of dead code and inferred None

Feature

foo = None

def bar() -> str:
    global foo
    if foo is not None:
        print("Hello")
    else:
        foo = "bar"
        return "lol"

This program type-checks, even though it's obviously wrong. It's not a bug, it's a feature:

• Inferred type of foo is None, even though Optional[str] was intended.
• Because foo has type None, the if foo is not None: part is eliminated as dead code, and therefore the missing return isn't detected.
• After setting foo = "bar", reveal_type(foo) shows str. Perhaps the assignment should be an error?

Pitch

A friend submitted a PR like this and thought it was fine.

Il payload non indica file, test o punti di ingresso. Inizia eseguendo lo snippet fornito con mypy e verificando come vengono gestiti None inferito, la riassegnazione globale, i rami irraggiungibili e i return mancanti. Prima di poter definire l’ambito dell’implementazione è necessaria una decisione dei maintainer sulla semantica prevista e sulla copertura delle regressioni.