type inference is fragile for protocols like SupportsKeysAndGetItem

Repro: https://mypy-play.net/?mypy=latest&python=3.11&gist=d2f8dfa1fdfda5c0c286f1a73f5e39eb

Pasted below for convenience:

import typing as t

from _typeshed import SupportsKeysAndGetItem


KT = t.TypeVar("KT")
VT = t.TypeVar("VT")


def version1(obj: SupportsKeysAndGetItem[KT, VT] | t.Iterable[tuple[KT, VT]]):
    if hasattr(obj, "keys") and hasattr(obj, "__getitem__"):
        reveal_type(obj)  # SupportsKeysAndGetItem[KT, VT] | Iterable[tuple[KT, VT]] (as expected)
    else:
        reveal_type(obj)  # narrowed to Iterable[tuple[KT, VT]] as expected


def version2(obj: SupportsKeysAndGetItem[KT, VT] | t.Iterable[tuple[KT, VT]]):
    if hasattr(obj, "keys") and hasattr(obj, "__getitem__") and (obj_getitem := obj.__getitem__):
        reveal_type(obj)  # SupportsKeysAndGetItem[KT, VT] | Iterable[tuple[KT, VT]] (as expected)
    else:
        reveal_type(obj)  # NOT narrowed

I would expect version 2 to behave the same as version 1. Is that an improvement mypy could reasonably make?

I searched for relevant docs and existing issues, but didn't find anything specifically about this. Apologies if I missed something.

Esegui la riproduzione collegata di mypy-play e confronta i risultati di reveal_type in version1 e version2. Traccia la logica del restringimento dei tipi per i controlli combinati hasattr e l’assegnazione con walrus; il lavoro è completo quando version2 restringe il ramo else in modo coerente con version1, con una copertura di regressione per l’esempio.