Weird error message for incompatible override when using a `TypeVar` for `self`

Bug Report

Minimal repro:

from typing import TypeVar

Self = TypeVar("Self")

class Flag:
    def __or__(self: Self, other: Self) -> Self: ...
    __ror__ = __or__

class IntFlag(int, Flag):
    def __or__(self: Self, other: int) -> Self: ...
    def __ror__(self: Self, other: int) -> Self: ...

mypy output:

main.py:11: error: Signature of "__ror__" incompatible with supertype "Flag"
main.py:11: note:      Superclass:
main.py:11: note:          def [Self] __or__(self, Self, Self) -> Self
main.py:11: note:      Subclass:
main.py:11: note:          def __ror__(self, int) -> IntFlag

Mypy playground link here: https://mypy-play.net/?mypy=latest&python=3.10&gist=26b60881cd02e608bb9e555db4c3f627

Expected Behavior

I'm not sure an error is even appropriate here: no incompatible override is reported for __or__.

Even if an error is appropriate here, however, the error message is weird and garbled. According to the error message, mypy seems to think that __ror__ in the superclass expects three arguments (it only expects two). It also seems to think the method in the subclass will return IntFlag (not necessarily true; the return type will be whatever self is, and self could be any subtype of IntFlag).

The function that creates this error message is here: https://github.com/python/mypy/blob/9b4bce9065cbef6185fbc77f2849b63dc9e5e293/mypy/messages.py#L824

Mypy version used

• 0.950.
• This doesn't seem to be a recent regression: I can reproduce as far back as 0.920, which is the earliest mypy version that has the verbose error messages.
• I've also reproduced the bug on mypy master.

Beginne mit der minimalen Python-Reproduktion und untersuche die Erstellung der Diagnose in mypy/messages.py um Zeile 824. Vergleiche die gemeldeten Signaturen der Ober- und Unterklasse mit den auf TypeVar basierenden Self-Typen und bestimme anschließend, ob das Überschreiben akzeptiert werden sollte oder wie seine Meldung dargestellt werden sollte. Als erledigt gilt die Aufgabe, wenn das Verhalten korrigiert und die Reproduktion durch einen Regressionstest abgedeckt ist.