Mypy fails to solve `tuple[int, *Ts, int]` as an `Iterable[T]`.

from typing import Iterable

def upcast[T](arg: Iterable[T]) -> Iterable[T]: return arg

def f[*Ts](padded_tuple: tuple[int, *Ts, int]) -> None:
    as_iterable = upcast(padded_tuple)  # Argument 1 to "upcast" has incompatible type
    reveal_type(as_iterable)  # "typing.Iterable[builtins.int]" ❌

https://mypy-play.net/?mypy=latest&python=3.12&enable-incomplete-feature=PreciseTupleTypes&gist=ed0d06b3234441ebf6f31b98224618fc

For comparison, pyright predicts Code sample in pyright playground Iterable[int | Union[*Ts@demo]].

Since Union of TypeVarTuple is not specced yet, mypy should nevertheless probably fall back to something like Iterable[object] or Iterable[Any], but Iterable[int] is just wrong.

If the tuple is not padded, then mypy still falsely issues [arg-type], but at least the reveal_type is Iterable[Any]. https://mypy-play.net/?mypy=latest&python=3.12&enable-incomplete-feature=PreciseTupleTypes&gist=b3429973142b9a329d0fcc1dda8aabb2

Inizia dalle riproduzioni collegate di mypy-play e confronta i casi di tuple con e senza padding. Traccia l’inferenza di TypeVarTuple per la chiamata a Iterable[T] e verifica il risultato rispetto al comportamento segnalato di pyright; il lavoro è completato quando non si verifica alcun errore arg-type errato e non viene ristretto erroneamente alcun tipo Iterable[int].