type of class member can be a free type variable

[rwbarton]

This doesn't make sense:

from typing import TypeVar

T = TypeVar('T')

class A:
    def __init__(self, x: T) -> None:
        self.x = x

a = A(1)
reveal_type(a.x)  # E: Revealed type is 'T`-1'

I guess we need to check that the types of class attributes don't contain free type variables. (Type variables that are bound by the class declaration, i.e. deriving from Generic[T], are okay of course.)

[ilevkivskyi]

Tracking this is now moved to #6520