(regression: 0.960) Generic[Protocol] fails with dataclass

[JSS95]

Bug Report

The following code uses Generic with Protocol for dataclass. It passes with mypy 0.950, but fails with 0.960.

from dataclasses import dataclass
from typing import Protocol, Dict, TypeVar, Generic


class DataclassProtocol(Protocol):
    __dataclass_fields__: Dict


T = TypeVar("T", bound=DataclassProtocol)


@dataclass
class MyDataclass:
    x: int = 1


class MyGeneric(Generic[T]):
    ...


class MyClass(MyGeneric[MyDataclass]):
    ...

Error messge:

error: Type argument "MyDataclass" of "MyGeneric" must be a subtype of "DataclassProtocol"

Your Environment

• Mypy version used: 0.960
• Mypy command-line flags: no flag
• Mypy configuration options from mypy.ini (and other config files): no config
• Python version used: 3.10
• Operating system and version: Ubuntu 20.04

(Edit)

Using typing.ClassVar fixes this.

from dataclasses import Field
from typing import Protocol, ClassVar, Dict

class DataclassProtocol(Protocol):
    __dataclass_fields__: ClassVar[Dict[str, Field]]

[hauntsaninja]

Thanks for opening a new issue with repro! mypy_primer bisects this to #12762

[JSS95]

@JukkaL

Hello. I am encountering the same issue again.
Until mypy v0.982 the Generic[Protocol] worked fine, but from v0.990 to the latest v1.0.1 the test fails with the same error message.

[hauntsaninja]

Add ClassVar to the Protocol, I think

[JSS95]

@hauntsaninja Thanks! It worked.