`Self` and `self` are not bound until after class definition, becoming `Any`/`Never` when passed through a decorator

Bug Report

There is occasional use for a method that exhibits different behaviours when accessed via an instance vs the class. SQLAlchemy has one such example named hybrid_method (code). I was experimenting with a generic decorator for this pattern and found what appear to be two bugs in Mypy 1.7.0. The code works at runtime and passes type validation in Pyright 1.1.337 (barring a no-redef error).

First problem, given the following code pattern:

class Host:
    # T = TypeVar, P = ParamSpec, R = TypeVar
    @Decorator  # (Callable[Concatenate[T, P], R]) -> Decorator[Generic[T, P, R]]
    def method(self) -> Self:
        return self

    reveal_type(method)  #  T=Never, R=Any

Type T is self and R is Self, and both should be the same. The decorator has to be Generic[P, R] to return Callable[P, R] in __get__, but R then turns into Any. If the decorator is Generic[T, P, R], then R becomes Never and Host().method() errors on the self parameter: expected Never, got Host. reveal_type shows that self's type is lost within the class definition itself. Pyright processes it correctly.

Second problem, when the decorator implements the @prop.setter pattern to replace itself with a new object with different generic binds. Mypy raises a no-redef error, which can be type-ignored, but the revealed type continues to show the old generic binds. This problem goes away when the second method is given a different name.

To Reproduce

Here's sample code with a functioning decorator and three ways to use it. This code works at runtime and passes Pyright (barring one redef), but each of these versions has different errors or loss of type information in Mypy.

https://mypy-play.net/?mypy=latest&python=3.11&gist=03abdb6bef5ae78eea51d6ae07a0e778

Tested in Mypy 1.7, Pyright 1.1, Python 3.9 and 3.11

Inizia con la riproduzione collegata di mypy-play usando Python 3.11 e confronta i tipi rivelati e gli errori con i risultati di Pyright. Traccia il modo in cui mypy associa Self, self e i parametri generici del decoratore durante l’analisi del corpo della classe, quindi verifica che entrambe le forme di decoratore conservino i tipi attesi e che il pattern del setter non segnali più associazioni obsolete o una ridefinizione errata.