Type narrowing in while loop

Feature

example.py

from __future__ import annotations
import typing as t

class Node:
    parent: Node | None = None

N = t.TypeVar("N", bound=Node)

def find_ancestor(node: Node, node_type: t.Type[N]) -> N | None:
    ancestor = node.parent
    while ancestor and not isinstance(ancestor, node_type):
        ancestor = ancestor.parent
    return ancestor

mypy 1.0.1 errors with:

example.py:13: error: Incompatible return value type (got "Optional[Node]", expected "Optional[N]")  [return-value]

Would be great to narrow the type to N here and avoid the spurious error.

Pitch

Type narrowing in a while loop would improve inference. pyright already does this.

Start by running mypy against the provided example.py and reproducing the return-value error. Then inspect the type-narrowing control flow for while loops and compare the behavior with pyright. Done means the loop narrows the value to N after isinstance and the example no longer reports the error.