Incorrect mypy behaviour when inheriting a generic with List[T] field

[Fatal1ty]

I have the following sample of code:

from dataclasses import dataclass
from typing import Generic, List, TypeVar


T = TypeVar('T', int, str)


@dataclass
class A(Generic[T]):
    x: List[T]


@dataclass
class B(A[int]):
    pass


B(x=[1])  # error: List item 0 has incompatible type "int"; expected "T"

mypy 0.910 gives error: List item 0 has incompatible type "int"; expected "T" that is not what I expected since I declared x as List[int] with generic inheritance.

• Mypy version used: 0.910
• Python version used: 3.9.1

[ilevkivskyi]

FWIW this works correctly on the current master.