Using classmethod of generic alias of a generic type and --disallow-any-generics #16982

from typing import TypeVar, Generic, reveal_type

T = TypeVar('T')
N = TypeVar('N')

class My(Generic[T]):
    def __init__(self, arg: T) -> None:
        self.arg = arg
    @classmethod
    def from_arg(cls, arg: N) -> 'My[N]':
        return My(arg)
        

Alias = My[T]
        
reveal_type(My.from_arg(1)) 
# note: Revealed type is "__main__.My[builtins.int]"

reveal_type(Alias.from_arg(1))
# error: Missing type parameters for generic type "Alias"  [type-arg]
# note: Revealed type is "__main__.My[builtins.int]"