fix mypy complaint on @root_validator(pre=True) (#985)

* fix mypy complaint on @root_validator(pre=True)

* fix internal mypy

* use overload on root_validator

changes/984-samuelcolvin.md

@@ -0,0 +1 @@
+Fix mypy complaint about `@root_validator(pre=True)`

pydantic/class_validators.py

@@ -4,7 +4,7 @@ from functools import wraps
 from inspect import Signature, signature
 from itertools import chain
 from types import FunctionType
-from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, Union
+from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, Union, overload
 
 from .errors import ConfigError
 from .typing import AnyCallable
@@ -90,9 +90,23 @@ def validator(
     return dec
 
 
+@overload
+def root_validator(_func: AnyCallable) -> classmethod:
+    ...
+
+
+@overload
+def root_validator(*, pre: bool = False) -> Callable[[AnyCallable], classmethod]:
+    ...
+
+
 def root_validator(
     _func: Optional[AnyCallable] = None, *, pre: bool = False
 ) -> Union[classmethod, Callable[[AnyCallable], classmethod]]:
+    """
+    Decorate methods on a model indicating that they should be used to validate (and perhaps modify) data either
+    before or after standard model parsing/validation is performed.
+    """
     if _func:
         _check_validator_name(_func)
         f_cls = classmethod(_func)

tests/mypy/modules/success.py

@@ -6,9 +6,9 @@ Do a little skipping about with types to demonstrate its usage.
 import json
 import sys
 from datetime import datetime
-from typing import Generic, List, Optional, TypeVar
+from typing import Any, Dict, Generic, List, Optional, TypeVar
 
-from pydantic import BaseModel, NoneStr, StrictBool
+from pydantic import BaseModel, NoneStr, StrictBool, root_validator, validator
 from pydantic.dataclasses import dataclass
 from pydantic.fields import Field
 from pydantic.generics import GenericModel
@@ -25,6 +25,19 @@ class Model(BaseModel):
     signup_ts: Optional[datetime] = None
     list_of_ints: List[int]
 
+    @validator('age')
+    def check_age(cls, value: int) -> int:
+        assert value < 100, 'too old'
+        return value
+
+    @root_validator
+    def root_check(cls, values: Dict[str, Any]) -> Dict[str, Any]:
+        return values
+
+    @root_validator(pre=True)
+    def pre_root_check(cls, values: Dict[str, Any]) -> Dict[str, Any]:
+        return values
+
 
 def dog_years(age: int) -> int:
     return age * 7