ValidationException.errors() are ErrorDetails

Update the documentation to explain that `RequestValidationError` isn't
literally a subclass since Pydantic V2.

docs/en/docs/tutorial/handling-errors.md

@@ -163,7 +163,7 @@ path -> item_id
 !!! warning
     These are technical details that you might skip if it's not important for you now.
 
-`RequestValidationError` is a sub-class of Pydantic's <a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a>.
+`RequestValidationError` is morally a sub-class of Pydantic's <a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a>.
 
 **FastAPI** uses it so that, if you use a Pydantic model in `response_model`, and your data has an error, you will see the error in your log.
 

fastapi/_compat.py

@@ -17,7 +17,7 @@
     Union,
 )
 
-from fastapi.exceptions import RequestErrorModel
+from fastapi.exceptions import ErrorDetails, RequestErrorModel
 from fastapi.types import IncEx, ModelNameMap, UnionType
 from pydantic import BaseModel, create_model
 from pydantic.version import VERSION as P_VERSION
@@ -121,7 +121,7 @@ def validate(
             values: Dict[str, Any] = {},  # noqa: B006
             *,
             loc: Tuple[Union[int, str], ...] = (),
-        ) -> Tuple[Any, Union[List[Dict[str, Any]], None]]:
+        ) -> Tuple[Any, Union[List[ErrorDetails], None]]:
             try:
                 return (
                     self._type_adapter.validate_python(value, from_attributes=True),
@@ -167,9 +167,6 @@ def get_annotation_from_field_info(
     ) -> Any:
         return annotation
 
-    def _normalize_errors(errors: Sequence[Any]) -> List[Dict[str, Any]]:
-        return errors  # type: ignore[return-value]
-
     def _model_rebuild(model: Type[BaseModel]) -> None:
         model.model_rebuild()
 
@@ -265,12 +262,12 @@ def serialize_sequence_value(*, field: ModelField, value: Any) -> Sequence[Any]:
         assert issubclass(origin_type, sequence_types)  # type: ignore[arg-type]
         return sequence_annotation_to_type[origin_type](value)  # type: ignore[no-any-return]
 
-    def get_missing_field_error(loc: Tuple[str, ...]) -> Dict[str, Any]:
+    def get_missing_field_error(loc: Tuple[str, ...]) -> ErrorDetails:
         error = ValidationError.from_exception_data(
             "Field required", [{"type": "missing", "loc": loc, "input": {}}]
         ).errors(include_url=False)[0]
         error["input"] = None
-        return error  # type: ignore[return-value]
+        return error
 
     def create_body_model(
         *, fields: Sequence[ModelField], model_name: str
@@ -418,20 +415,6 @@ def is_pv1_scalar_sequence_field(field: ModelField) -> bool:
             return True
         return False
 
-    def _normalize_errors(errors: Sequence[Any]) -> List[Dict[str, Any]]:
-        use_errors: List[Any] = []
-        for error in errors:
-            if isinstance(error, ErrorWrapper):
-                new_errors = ValidationError(  # type: ignore[call-arg]
-                    errors=[error], model=RequestErrorModel
-                ).errors()
-                use_errors.extend(new_errors)
-            elif isinstance(error, list):
-                use_errors.extend(_normalize_errors(error))
-            else:
-                use_errors.append(error)
-        return use_errors
-
     def _model_rebuild(model: Type[BaseModel]) -> None:
         model.update_forward_refs()
 
@@ -500,10 +483,10 @@ def copy_field_info(*, field_info: FieldInfo, annotation: Any) -> FieldInfo:
     def serialize_sequence_value(*, field: ModelField, value: Any) -> Sequence[Any]:
         return sequence_shape_to_type[field.shape](value)  # type: ignore[no-any-return,attr-defined]
 
-    def get_missing_field_error(loc: Tuple[str, ...]) -> Dict[str, Any]:
+    def get_missing_field_error(loc: Tuple[str, ...]) -> ErrorDetails:
         missing_field_error = ErrorWrapper(MissingError(), loc=loc)  # type: ignore[call-arg]
         new_error = ValidationError([missing_field_error], RequestErrorModel)
-        return new_error.errors()[0]  # type: ignore[return-value]
+        return new_error.errors()[0]
 
     def create_body_model(
         *, fields: Sequence[ModelField], model_name: str
@@ -515,14 +498,9 @@ def create_body_model(
 
 
 def _regenerate_error_with_loc(
-    *, errors: Sequence[Any], loc_prefix: Tuple[Union[str, int], ...]
-) -> List[Dict[str, Any]]:
-    updated_loc_errors: List[Any] = [
-        {**err, "loc": loc_prefix + err.get("loc", ())}
-        for err in _normalize_errors(errors)
-    ]
-
-    return updated_loc_errors
+    *, errors: Sequence[ErrorDetails], loc_prefix: Tuple[Union[str, int], ...]
+) -> List[ErrorDetails]:
+    return [{**err, "loc": loc_prefix + err.get("loc", ())} for err in errors]
 
 
 def _annotation_is_sequence(annotation: Union[Type[Any], None]) -> bool:

fastapi/dependencies/utils.py

@@ -50,6 +50,7 @@
     contextmanager_in_threadpool,
 )
 from fastapi.dependencies.models import Dependant, SecurityRequirement
+from fastapi.exceptions import ErrorDetails
 from fastapi.logger import logger
 from fastapi.security.base import SecurityBase
 from fastapi.security.oauth2 import OAuth2, SecurityScopes
@@ -654,7 +655,7 @@ def request_params_to_args(
     received_params: Union[Mapping[str, Any], QueryParams, Headers],
 ) -> Tuple[Dict[str, Any], List[Any]]:
     values = {}
-    errors = []
+    errors: list[ErrorDetails] = []
     for field in required_params:
         if is_scalar_sequence_field(field) and isinstance(
             received_params, (QueryParams, Headers)
@@ -687,9 +688,9 @@ def request_params_to_args(
 async def request_body_to_args(
     required_params: List[ModelField],
     received_body: Optional[Union[Dict[str, Any], FormData]],
-) -> Tuple[Dict[str, Any], List[Dict[str, Any]]]:
+) -> Tuple[Dict[str, Any], List[ErrorDetails]]:
     values = {}
-    errors: List[Dict[str, Any]] = []
+    errors: List[ErrorDetails] = []
     if required_params:
         field = required_params[0]
         field_info = field.field_info

fastapi/exceptions.py

@@ -1,9 +1,22 @@
-from typing import Any, Dict, Optional, Sequence, Type, Union
+from typing import Any, Dict, Optional, Sequence, Tuple, Type, Union
 
 from pydantic import BaseModel, create_model
 from starlette.exceptions import HTTPException as StarletteHTTPException
 from starlette.exceptions import WebSocketException as StarletteWebSocketException
-from typing_extensions import Annotated, Doc
+from typing_extensions import Annotated, Doc, TypedDict
+
+
+class ErrorDetails(TypedDict):
+    """
+    The common subset shared by `ErrorDict` in Pydantic V1[0] and `ErrorDetails` in Pydantic V2[1].
+
+    [0] https://github.com/pydantic/pydantic/blob/4d7bef62aeff10985fe67d13477fe666b13ba070/pydantic/v1/error_wrappers.py#L21-L22
+    [1] https://github.com/pydantic/pydantic-core/blob/e1fc99dd3207157aad77defc20ab6873fd268b5b/python/pydantic_core/__init__.py#L73-L91
+    """
+
+    loc: Tuple[Union[int, str], ...]
+    msg: str
+    type: str
 
 
 class HTTPException(StarletteHTTPException):
@@ -147,15 +160,15 @@ class FastAPIError(RuntimeError):
 
 
 class ValidationException(Exception):
-    def __init__(self, errors: Sequence[Any]) -> None:
+    def __init__(self, errors: Sequence[ErrorDetails]) -> None:
         self._errors = errors
 
-    def errors(self) -> Sequence[Any]:
+    def errors(self) -> Sequence[ErrorDetails]:
         return self._errors
 
 
 class RequestValidationError(ValidationException):
-    def __init__(self, errors: Sequence[Any], *, body: Any = None) -> None:
+    def __init__(self, errors: Sequence[ErrorDetails], *, body: Any = None) -> None:
         super().__init__(errors)
         self.body = body
 
@@ -165,7 +178,7 @@ class WebSocketRequestValidationError(ValidationException):
 
 
 class ResponseValidationError(ValidationException):
-    def __init__(self, errors: Sequence[Any], *, body: Any = None) -> None:
+    def __init__(self, errors: Sequence[ErrorDetails], *, body: Any = None) -> None:
         super().__init__(errors)
         self.body = body
 

fastapi/routing.py

@@ -25,7 +25,6 @@
     Undefined,
     _get_model_config,
     _model_dump,
-    _normalize_errors,
     lenient_issubclass,
 )
 from fastapi.datastructures import Default, DefaultPlaceholder
@@ -39,6 +38,7 @@
 )
 from fastapi.encoders import jsonable_encoder
 from fastapi.exceptions import (
+    ErrorDetails,
     FastAPIError,
     RequestValidationError,
     ResponseValidationError,
@@ -132,7 +132,7 @@ async def serialize_response(
     is_coroutine: bool = True,
 ) -> Any:
     if field:
-        errors = []
+        errors: list[ErrorDetails] = []
         if not hasattr(field, "serialize"):
             # pydantic v1
             response_content = _prepare_response_content(
@@ -147,14 +147,10 @@ async def serialize_response(
             value, errors_ = await run_in_threadpool(
                 field.validate, response_content, {}, loc=("response",)
             )
-        if isinstance(errors_, list):
+        if errors_ is not None:
             errors.extend(errors_)
-        elif errors_:
-            errors.append(errors_)
         if errors:
-            raise ResponseValidationError(
-                errors=_normalize_errors(errors), body=response_content
-            )
+            raise ResponseValidationError(errors=errors, body=response_content)
 
         if hasattr(field, "serialize"):
             return field.serialize(
@@ -251,7 +247,7 @@ async def app(request: Request) -> Response:
                             "msg": "JSON decode error",
                             "input": {},
                             "ctx": {"error": e.msg},
-                        }
+                        }  # type: ignore [typeddict-unknown-key]
                     ],
                     body=e.doc,
                 )
@@ -309,9 +305,7 @@ async def app(request: Request) -> Response:
                             response.body = b""
                         response.headers.raw.extend(sub_response.headers.raw)
             if errors:
-                validation_error = RequestValidationError(
-                    _normalize_errors(errors), body=body
-                )
+                validation_error = RequestValidationError(errors=errors, body=body)
                 raise validation_error
         if response is None:
             raise FastAPIError(
@@ -343,7 +337,7 @@ async def app(websocket: WebSocket) -> None:
             )
             values, errors, _, _2, _3 = solved_result
             if errors:
-                raise WebSocketRequestValidationError(_normalize_errors(errors))
+                raise WebSocketRequestValidationError(errors)
             assert dependant.call is not None, "dependant.call must be a function"
             await dependant.call(**values)