Fix error message for invalid validator signatures

Backport of: #12366

Author: Viicos

pydantic/_internal/_decorators.py

@@ -522,14 +522,17 @@ def update_from_config(self, config_wrapper: ConfigWrapper) -> None:
             computed_field_dec.info._update_from_config(config_wrapper, name)
 
 
-def inspect_validator(validator: Callable[..., Any], mode: FieldValidatorModes) -> bool:
+def inspect_validator(
+    validator: Callable[..., Any], *, mode: FieldValidatorModes, type: Literal['field', 'model']
+) -> bool:
     """Look at a field or model validator function and determine whether it takes an info argument.
 
     An error is raised if the function has an invalid signature.
 
     Args:
         validator: The validator function to inspect.
         mode: The proposed validator mode.
+        type: The type of validator, either 'field' or 'model'.
 
     Returns:
         Whether the validator takes an info argument.
@@ -554,7 +557,7 @@ def inspect_validator(validator: Callable[..., Any], mode: FieldValidatorModes)
             return False
 
     raise PydanticUserError(
-        f'Unrecognized field_validator function signature for {validator} with `mode={mode}`:{sig}',
+        f'Unrecognized {type} validator function signature for {validator} with `mode={mode}`: {sig}',
         code='validator-signature',
     )
 

pydantic/_internal/_generate_schema.py

@@ -2508,7 +2508,9 @@ def apply_validators(
         The updated schema.
     """
     for validator in validators:
-        info_arg = inspect_validator(validator.func, validator.info.mode)
+        # Actually, type could be 'field' or 'model', but this is only used for deprecated
+        # decorators, so let's not worry about it.
+        info_arg = inspect_validator(validator.func, mode=validator.info.mode, type='field')
         val_type = 'with-info' if info_arg else 'no-info'
 
         schema = _VALIDATOR_F_MATCH[(validator.info.mode, val_type)](validator.func, schema)
@@ -2565,7 +2567,7 @@ def apply_model_validators(
             continue
         if mode == 'outer' and validator.info.mode == 'before':
             continue
-        info_arg = inspect_validator(validator.func, validator.info.mode)
+        info_arg = inspect_validator(validator.func, mode=validator.info.mode, type='model')
         if validator.info.mode == 'wrap':
             if info_arg:
                 schema = core_schema.with_info_wrap_validator_function(function=validator.func, schema=schema)

pydantic/functional_validators.py

@@ -73,7 +73,7 @@ class Model(BaseModel):
 
     def __get_pydantic_core_schema__(self, source_type: Any, handler: GetCoreSchemaHandler) -> core_schema.CoreSchema:
         schema = handler(source_type)
-        info_arg = _inspect_validator(self.func, 'after')
+        info_arg = _inspect_validator(self.func, mode='after', type='field')
         if info_arg:
             func = cast(core_schema.WithInfoValidatorFunction, self.func)
             return core_schema.with_info_after_validator_function(func, schema=schema)
@@ -131,7 +131,7 @@ def __get_pydantic_core_schema__(self, source_type: Any, handler: GetCoreSchemaH
             else handler.generate_schema(self.json_schema_input_type)
         )
 
-        info_arg = _inspect_validator(self.func, 'before')
+        info_arg = _inspect_validator(self.func, mode='before', type='field')
         if info_arg:
             func = cast(core_schema.WithInfoValidatorFunction, self.func)
             return core_schema.with_info_before_validator_function(
@@ -229,7 +229,7 @@ def __get_pydantic_core_schema__(self, source_type: Any, handler: GetCoreSchemaH
 
         input_schema = handler.generate_schema(self.json_schema_input_type)
 
-        info_arg = _inspect_validator(self.func, 'plain')
+        info_arg = _inspect_validator(self.func, mode='plain', type='field')
         if info_arg:
             func = cast(core_schema.WithInfoValidatorFunction, self.func)
             return core_schema.with_info_plain_validator_function(
@@ -304,7 +304,7 @@ def __get_pydantic_core_schema__(self, source_type: Any, handler: GetCoreSchemaH
             else handler.generate_schema(self.json_schema_input_type)
         )
 
-        info_arg = _inspect_validator(self.func, 'wrap')
+        info_arg = _inspect_validator(self.func, mode='wrap', type='field')
         if info_arg:
             func = cast(core_schema.WithInfoWrapValidatorFunction, self.func)
             return core_schema.with_info_wrap_validator_function(

tests/test_decorators.py

@@ -41,7 +41,7 @@ def _one_pos_required_arg_one_optional(a, b=1):
     ],
 )
 def test_inspect_validator(obj, mode, expected):
-    assert inspect_validator(obj, mode=mode) == expected
+    assert inspect_validator(obj, mode=mode, type='field') == expected
 
 
 def test_inspect_validator_error_wrap():
@@ -52,12 +52,12 @@ def validator4(arg1, arg2, arg3, arg4):
         pass
 
     with pytest.raises(PydanticUserError) as e:
-        inspect_validator(validator1, mode='wrap')
+        inspect_validator(validator1, mode='wrap', type='field')
 
     assert e.value.code == 'validator-signature'
 
     with pytest.raises(PydanticUserError) as e:
-        inspect_validator(validator4, mode='wrap')
+        inspect_validator(validator4, mode='wrap', type='field')
 
     assert e.value.code == 'validator-signature'
 
@@ -71,12 +71,12 @@ def validator3(arg1, arg2, arg3):
         pass
 
     with pytest.raises(PydanticUserError) as e:
-        inspect_validator(validator, mode=mode)
+        inspect_validator(validator, mode=mode, type='field')
 
     assert e.value.code == 'validator-signature'
 
     with pytest.raises(PydanticUserError) as e:
-        inspect_validator(validator3, mode=mode)
+        inspect_validator(validator3, mode=mode, type='field')
 
     assert e.value.code == 'validator-signature'