Issue with Narrowing

[George-Ogden]

This is a duplicate of #20600, although I cannot reopen it. Here is an example to reproduce. I believe it was introduced in v1.20.0.

from dataclasses import dataclass
from typing import TypeGuard, Self


@dataclass
class ErrorCase:
    x: int

    def __eq__(self, other: object) -> TypeGuard[Self]:
        return (
            type(other)
            is type(self)
        ) and (
                self.x # error: "object" has no attribute "x"
                == other.x
        )

The error on line 14 is a false-positive.

[George-Ogden]

@hauntsaninja - I think you're the best person to investigate this.

[hauntsaninja]

Thanks for the issue! This is related to Self type.

This is not a bad regression, as mypy 1.19 and earlier will complain about this code too, just at a different place.

[hauntsaninja]

Fix in #21174