Invalid Frozen Dataclass Subclass

What it does

Checks for dataclasses with invalid frozen inheritance:

• A frozen dataclass cannot inherit from a non-frozen dataclass.
• A non-frozen dataclass cannot inherit from a frozen dataclass.

Why is this bad?

Python raises a TypeError at runtime when either of these inheritance patterns occurs.

Example

from dataclasses import dataclass


@dataclass
class Base:
    x: int


@dataclass(frozen=True)
class Child(Base):  # error
    y: int


@dataclass(frozen=True)
class FrozenBase:
    x: int


@dataclass
class NonFrozenChild(FrozenBase):  # error
    y: int