mypy complains about pre=True root validators

[bochecha]

Bug

Please complete:

• OS: Ubuntu 19.04
• Python version import sys; print(sys.version): 3.7.3
• Pydantic version import pydantic; print(pydantic.VERSION): 1.0

With the code found in the root validators documentation:

from pydantic import BaseModel, root_validator


class UserModel(BaseModel):
    username: str
    password1: str
    password2: str

    @root_validator(pre=True)
    def check_card_number_omitted(cls, values):  # type: ignore
        assert 'card_number' not in values, 'card_number should not be included'
        return values

Mypy has the following to say:

9: error: "classmethod" not callable

The following change pleases mypy, but of course that changes the semantics:

-    @root_validator(pre=True)
+    @root_validator

[samuelcolvin]

Thanks for reporting. Fixed by #985