Walrus narrowing not propagated from inside expression

[hauntsaninja]

def main(cond: bool) -> None:
    woo = None
    if cond and (woo := 5) in range(10):
        reveal_type(woo)  # should reveal int, reveals int | None

[sterliakov]

I improved walrus propagation in #19038, this problem reproduces equally well without any assignment exprs in view:

def main(cond: bool) -> None:
    woo: int | None = None
    if cond and woo in range(10):
        reveal_type(woo)  # should reveal int, reveals int | None

However, there are still walrus-related issues too, apparently:

def check(cond: bool) -> None:
    woo: int | None = None
    if cond and isinstance(woo, int):
        reveal_type(woo)  # int

def assign(cond: bool) -> None:
    woo: int | None
    if cond and isinstance(woo := 4, int):
        reveal_type(woo)  # int | None

[sterliakov]

Ah, yes, because I only added support for top-level walrus (as in if cond and (woo := val): ...), and implementation flexibility expanded that to attribute and index access scenarios. Either isinstance should also be special-cased, or a proper WalrusAssignerVisitor should be implemented to propagate nested assignments in arbitrary positions.

[hauntsaninja]

Ah sorry, the contains narrowing thing is different, that would be #3229

The issue isn't about narrowing introduced by additional checks via contains or isinstance, more the narrowing produced by assignment (when it occurs on every code path into the if branch, i.e. relevant for and but not for or). Maybe the following example is clearer:

def main(cond: bool, n: int) -> None:
    woo = None
    if cond and (woo := 5) + n:
        reveal_type(woo)  # should reveal int (or Literal[5]), reveals int | None

[sterliakov]

#19038 added support for narrowing foo in (foo := val).attr and (foo := val)[key] in such scenarios (but not like "and but not or" exactly, there's more: in if cond or (foo := 1) we can narrow foo by assignment in else branch). Walrus nested in any other exprs is still not handled. I was just too lazy to write a full visitor, that would probably be the best solution...