mypy crashes on callable frozen dataclass

[alexei]

Crash Report

mypy crashes on callable frozen dataclass

Traceback

➜ mypy-bug poetry run mypy mypy_bug/case_3.py --show-traceback
mypy_bug/case_3.py:14: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.931
Traceback (most recent call last):
 File "mypy/semanal.py", line 5142, in accept
 File "mypy/nodes.py", line 1005, in accept
 File "mypy/semanal.py", line 1105, in visit_class_def
 File "mypy/semanal.py", line 1184, in analyze_class
 File "mypy/semanal.py", line 1193, in analyze_class_body_common
 File "mypy/semanal.py", line 1239, in apply_class_plugin_hooks
 File "mypy/plugins/dataclasses.py", line 489, in dataclass_class_maker_callback
 File "mypy/plugins/dataclasses.py", line 194, in transform
 File "mypy/plugins/dataclasses.py", line 431, in _freeze
AssertionError: 
mypy_bug/case_3.py:14: : note: use --pdb to drop into pdb

To Reproduce

from dataclasses import dataclass
from typing import Any, Callable

# here both `Parent` and `Child` are frozen dataclasses

@dataclass(frozen=True)
class Parent:
 __call__: Callable[..., None]

 def __call__(self, *args: Any, **kwargs: Any) -> None: # type: ignore
 raise NotImplementedError


@dataclass(frozen=True)
class Child(Parent):
 def __call__(self, value: int) -> None:
 ...

Your Environment

• Mypy version used: 0.931
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10.0
• Operating system and version: macOS Catalina (10.15)

---

I'm using "Guido's hack" from #9560 (comment) which does work in other circumstances:

from typing import Any, Callable

# here both `Parent` and `Child` are "regular" classes

class Parent:
 __call__: Callable[..., None]

 def __call__(self, *args: Any, **kwargs: Any) -> None: # type: ignore
 raise NotImplementedError


class Child(Parent):
 def __call__(self, value: int) -> None:
 ...

from dataclasses import dataclass
from typing import Any, Callable

# here `Parent` is a frozen dataclass, but `Child` is not

@dataclass(frozen=True)
class Parent:
 __call__: Callable[..., None]

 def __call__(self, *args: Any, **kwargs: Any) -> None: # type: ignore
 raise NotImplementedError


class Child(Parent):
 def __call__(self, value: int) -> None:
 ...

from dataclasses import dataclass
from typing import Any, Callable

# here both `Parent` and `Child` are dataclasses, but not frozen

@dataclass
class Parent:
 __call__: Callable[..., None]

 def __call__(self, *args: Any, **kwargs: Any) -> None: # type: ignore
 raise NotImplementedError


@dataclass
class Child(Parent):
 def __call__(self, value: int) -> None:
 ...

[JukkaL]

This no longer crashes. It seems to have been fixed in 0.950.

[alexei]

👍