`@classmethod` forces `Self` to coerce to a specific type

[eigenein]

The issue split from: #14650 (comment)

To Reproduce

from typing import Self


class Foo:
    foo: Self

    # This fails:
    @classmethod
    def bar(cls) -> Self:
        reveal_type(cls.foo)  # note: Revealed type is "__main__.Foo"
        return cls.foo  # error: Incompatible return value type (got "Foo", expected "Self")  [return-value]

    # This works well:
    def qux(self) -> Self:
        reveal_type(self.foo)  # note: Revealed type is "Self`0"
        return self.foo

Gist: https://mypy-play.net/?mypy=latest&python=3.11&gist=b9c80d80d0d6c8c80c9c4029da34c8e2

Expected Behavior

reveal_type() inside the bar() function should show Self`0, and the code should pass the linting check, just like the qux() function does.

Actual Behavior

Somehow @classmethod forces Mypy to coerce Self to the specific type, hence the incompatible return value type.

Your Environment

• Mypy version used: 1.3.0 & 1.2.0
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11.3