PEP-646 generic with self annotated function gives incorrect result

Bug Report

When a class is generic over a PEP-646/TypeVarTuple/varadic generic and uses that outer generic in a self annotated function, the result of calling that function is incorrect.

To Reproduce

https://mypy-play.net/?gist=e1eb19d739dd5cdc55e99e1ead4fc55c

from typing import reveal_type

class A[*TS]:
    def __init__(self, *state: *TS):
        self.state: tuple[*TS] = state

    def add(self: A[*TS, int, int]) -> A[*TS, int]:
        return A(*self.state[:-2], self.state[-2] + self.state[-1])

# Expected type: "A[1, int]" or "A[1, 5]" or similar
# Actual: Revealed type is "__main__.A[Literal[1]?, Literal[2]?, Literal[3]?, int]"
reveal_type(A(1, 2, 3).add())

Expected Behavior

Mypy should either give the correct type for A(1, 2, 3).add(), or give an error somewhere.

Actual Behavior

Mypy silently gives the wrong type for A(1, 2, 3).add()

Your Environment

• Mypy version used: Playground 2.3.1

Riproduci l’esempio mypy-play collegato, iniziando con reveal_type(A(1, 2, 3).add()) e l’annotazione self PEP-646 mostrata nell’issue. Traccia l’inferenza generica per il metodo add; il lavoro è completato quando mypy segnala il risultato corretto o un errore invece di rivelare silenziosamente il tipo errato, verificato con la riproduzione.