PEP-646 generic with self annotated function gives incorrect result

[MeGaGiGaGon]

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

[A5rocks]

Hmm my interpretation is this should error, like you mention. I don't think we should allow a typevar within the same scope to have two different values... Sounds confusing! Ideally we would error at definition time but IMO the easiest thing is probably just saying that .add cannot be used on A(1,2,3) because A[1,2,3] is not assignable to A[1,2,3,int,int] (which is probably just a bug in self-types).

[MeGaGiGaGon]

I think you're right that this is an issue with self type and not typevartuple specific, since trying this code all checkers besides mypy error on all three transform calls
https://mypy-play.net/?gist=3d9aa38b47834e0da1fd9e879805cb3d