Overridden untyped ClassVar get an error_untyped_fields with mypy plugin

[vincent-hachin-wmx]

Initial Checks

• I confirm that I'm using Pydantic V2

Description

Untyped overridden fields are forbidden and an error is thrown on execution and in mypy. However, untyped ClassVar are allowed in a BaseModel, but it seems that this case is not properly handeled by the mypy plugin here .

The example code below run fine, but a mypy error error: Untyped fields disallowed is thrown.

Example Code

from typing import ClassVar
from pydantic import BaseModel

class Abstract(BaseModel):
    class_id: ClassVar

class Foo(Abstract):
    class_id = 1

print(Foo())

Python, Pydantic & OS Version

pydantic version: 2.5.0
        pydantic-core version: 2.14.1
          pydantic-core build: profile=release pgo=true
                 install path: /Users/vincent.hachin/.pyenv/versions/3.11.6/lib/python3.11/site-packages/pydantic
               python version: 3.11.6 (main, Oct  9 2023, 17:58:53) [Clang 15.0.0 (clang-1500.0.40.1)]
                     platform: macOS-14.0-arm64-arm-64bit
             related packages: typing_extensions-4.8.0 mypy-1.7.0

[sydney-runkle]

Hi @vincent-hachin-wmx,

Thanks for reporting this. This does look like a bug. Looks like you may have found the source of the problem. Are you interested in contributing a PR with a fix?

[vincent-hachin-wmx]

Hi,
Sure I'll do a PR.

[vincent-hachin-wmx]

Hi @sydney-runkle,

I made a PR but I couldn't figure out how to add unit tests for the mypy plugin.
I guess the test should be added around here:

pydantic/tests/mypy/modules/plugin_fail_baseConfig.py

Lines 95 to 108 in eb90b59

	class DefaultTestingModel(BaseModel):
	# Required
	a: int
	b: int = ...
	c: int = Field(...)
	d: Union[int, str]
	e = ...
	# Not required
	f: Optional[int]
	g: int = 1
	h: int = Field(1)
	i: int = Field(None)
	j = 1

How to specify that a line should pass or throw a specific mypy error ?