Error when inheriting from a generic dataclass with a generic attribute

[drewm1980]

Bug Report

When typechecking the following code:

from typing import Generic, TypeVar
from dataclasses import dataclass

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

class C(Generic[T]):
    pass

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

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

B(x=C[int]())  # error: Argument "x" to "B" has incompatible type "C[int]"; expected "C[T]"

The equivalent code with the parent class NOT a data class:

class A_(Generic[T]):        
    x: C[T]

    def __init__(self, x: C[T]):   
        self.x = x

@dataclass
class B_(A_[int]):           
    pass                     

B_(x=C[int]())

Does not error.
If A_ is a normal class and B_ is marked as a dataclass, it also does not error. In other words it is the parent class that must be "un-dataclassed" as a workaround.

Your Environment

I have reproduced this on a recent version of mypy and python, but encountered it first in a python 3.6 environment, so it is not a new regression.

• Mypy version used: Reproduced in mypy 0.910
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.9.7
• Operating system and version: Ubuntu, but this was reproduced in a conda environment, not with the system intepreter.

[drewm1980]

First reported at the end of related issue that is already fixed and closed:

#7520

[drewm1980]

@natemcmaster thank you for resolving the previous similar bug, and thanks for your work on mypy. Life in python is so much better with static types.

[AlexWaygood]

Closing as a duplicate of #10986