False positive: "overloaded signature will never be matched" with Self

[sterliakov]

Bug Report

When combining Self and base class overloads, mypy incorrectly warns about the former being "the same or broader" as the latter. However, those overloads are both actually used.

I do know that this can be solved with a single TypeVar - the case is extracted from a more complicated code where similar TypeVar solution doesn't seem to apply.

To Reproduce

playground

from __future__ import annotations

from typing import Self, overload

class Base:
    @overload
    def fn(self, other: Self) -> Self: ...
    @overload
    def fn(self, other: Base) -> Base: ...
    def fn(self, other: Base) -> Base:
        return other


class X(Base): ...
class Y(Base): ...

reveal_type(X().fn(X()))
reveal_type(X().fn(Y()))
reveal_type(Y().fn(X()))
reveal_type(Y().fn(Y()))

Expected Behavior

No errors reported

Actual Behavior

main.py:10: error: Overloaded function signature 2 will never be matched: signature 1's parameter type(s) are the same or broader  [misc]
main.py:18: note: Revealed type is "__main__.X"
main.py:19: note: Revealed type is "__main__.Base"
main.py:20: note: Revealed type is "__main__.Base"
main.py:21: note: Revealed type is "__main__.Y"
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.11.1 and master (playground)
• Mypy command-line flags: none and --strict - both reproduce
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11, 3.12 - does not affect