Overloaded generic constructors can cause spurious errors in class methods

This fails, while it shouldn't:

from typing import TypeVar, Generic, overload

T = TypeVar('T')

class C(Generic[T]):
    @overload
    def __new__(cls) -> C[None]: ...
    @overload
    def __new__(cls, item: T) -> C[T]: ...
    def __new__(cls, item=None):
        ...
    @classmethod
    def f(cls, x: T) -> T:
        return x

C.f(42)  # Argument 1 to "f" of "C" has incompatible type "int"; expected "None"

I think the same also will happen with __init__(). The problem is because the return type of the first overload is always passed as an instance type to analyze_class_attribute_access().

Note: enabling test case testGenericClassInGenericFunctionOverloadedConstructor is blocked on this.

Inizia da analyze_class_attribute_access() e riproduci il caso del costruttore generico sovraccarico mostrato nell’issue. Analizza perché il tipo restituito dal primo overload viene utilizzato come tipo dell’istanza, quindi controlla il comportamento correlato di init. Abilita testGenericClassInGenericFunctionOverloadedConstructor e conferma che l’errore spurio relativo al metodo di classe non si verifica più.