♻️ Tweak implementation and tests for coverage

fastapi/_compat/main.py

@@ -99,11 +99,11 @@ def _is_error_wrapper(exc: Exception) -> bool:
 def copy_field_info(*, field_info: FieldInfo, annotation: Any) -> FieldInfo:
     if isinstance(field_info, v1.FieldInfo):
         return v1.copy_field_info(field_info=field_info, annotation=annotation)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.copy_field_info(field_info=field_info, annotation=annotation)
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def create_body_model(
@@ -111,11 +111,11 @@ def create_body_model(
 ) -> Type[BaseModel]:
     if fields and isinstance(fields[0], v1.ModelField):
         return v1.create_body_model(fields=fields, model_name=model_name)  # type: ignore[return-value]
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.create_body_model(fields=fields, model_name=model_name)  # type: ignore[return-value]
-    raise TypeError("fields must be a sequence of ModelField instances")
 
 
 def get_annotation_from_field_info(
@@ -125,73 +125,73 @@ def get_annotation_from_field_info(
         return v1.get_annotation_from_field_info(
             annotation=annotation, field_info=field_info, field_name=field_name
         )
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.get_annotation_from_field_info(
             annotation=annotation, field_info=field_info, field_name=field_name
         )
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def is_bytes_field(field: ModelField) -> bool:
     if isinstance(field, v1.ModelField):
         return v1.is_bytes_field(field)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.is_bytes_field(field)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def is_bytes_sequence_field(field: ModelField) -> bool:
     if isinstance(field, v1.ModelField):
         return v1.is_bytes_sequence_field(field)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.is_bytes_sequence_field(field)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def is_scalar_field(field: ModelField) -> bool:
     if isinstance(field, v1.ModelField):
         return v1.is_scalar_field(field)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.is_scalar_field(field)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def is_scalar_sequence_field(field: ModelField) -> bool:
     if isinstance(field, v1.ModelField):
         return v1.is_scalar_sequence_field(field)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.is_scalar_sequence_field(field)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def is_sequence_field(field: ModelField) -> bool:
     if isinstance(field, v1.ModelField):
         return v1.is_sequence_field(field)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.is_sequence_field(field)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def serialize_sequence_value(*, field: ModelField, value: Any) -> Sequence[Any]:
     if isinstance(field, v1.ModelField):
         return v1.serialize_sequence_value(field=field, value=value)
-    elif PYDANTIC_V2:
+    else:
+        assert PYDANTIC_V2
         from . import v2
 
         return v2.serialize_sequence_value(field=field, value=value)  # type: ignore[return-value]
-    raise TypeError("field_info must be an instance of FieldInfo")
 
 
 def _model_rebuild(model: Type[BaseModel]) -> None:
@@ -281,16 +281,6 @@ def _is_model_field(value: Any) -> bool:
     return False
 
 
-def _is_field_info(value: Any) -> bool:
-    if isinstance(value, v1.FieldInfo):
-        return True
-    elif PYDANTIC_V2:
-        from . import v2
-
-        return isinstance(value, v2.FieldInfo)
-    return False
-
-
 def _is_model_class(value: Any) -> bool:
     if lenient_issubclass(value, v1.BaseModel):
         return True

fastapi/_compat/model_field.py

@@ -1,4 +1,3 @@
-from dataclasses import dataclass
 from typing import (
     Any,
     Dict,
@@ -9,49 +8,28 @@ from typing import (
 
 from fastapi.types import IncEx
 from pydantic.fields import FieldInfo
-from typing_extensions import Literal
+from typing_extensions import Literal, Protocol
 
 
-@dataclass
-class ModelField:
+class ModelField(Protocol):
     field_info: "FieldInfo"
     name: str
     mode: Literal["validation", "serialization"] = "validation"
     _version: Literal["v1", "v2"] = "v1"
 
     @property
-    def alias(self) -> str:
-        return self._model_field.alias
+    def alias(self) -> str: ...
 
     @property
-    def required(self) -> bool:
-        return self._model_field.required
+    def required(self) -> bool: ...
 
     @property
-    def default(self) -> Any:
-        return self._model_field.default
+    def default(self) -> Any: ...
 
     @property
-    def type_(self) -> Any:
-        return self._model_field.type_
+    def type_(self) -> Any: ...
 
-    def __post_init__(self) -> None:
-        if self._version == "v1":
-            from . import v1
-
-            self._model_field = v1.ModelField(
-                field_info=self.field_info, name=self.name
-            )
-        else:
-            assert self._version == "v2"
-            from . import v2
-
-            self._model_field = v2.ModelField(
-                field_info=self.field_info, name=self.name, mode=self.mode
-            )
-
-    def get_default(self) -> Any:
-        return self._model_field.get_default()
+    def get_default(self) -> Any: ...
 
     def validate(
         self,
@@ -59,8 +37,7 @@ class ModelField:
         values: Dict[str, Any] = {},  # noqa: B006
         *,
         loc: Tuple[Union[int, str], ...] = (),
-    ) -> Tuple[Any, Union[List[Dict[str, Any]], None]]:
-        return self._model_field.validate(value=value, values=values, loc=loc)
+    ) -> Tuple[Any, Union[List[Dict[str, Any]], None]]: ...
 
     def serialize(
         self,
@@ -73,19 +50,4 @@ class ModelField:
         exclude_unset: bool = False,
         exclude_defaults: bool = False,
         exclude_none: bool = False,
-    ) -> Any:
-        return self._model_field.serialize(
-            value=value,
-            mode=mode,
-            include=include,
-            exclude=exclude,
-            by_alias=by_alias,
-            exclude_unset=exclude_unset,
-            exclude_defaults=exclude_defaults,
-            exclude_none=exclude_none,
-        )
-
-    def __hash__(self) -> int:
-        # Each ModelField is unique for our purposes, to allow making a dict from
-        # ModelField to its JSON Schema.
-        return id(self)
+    ) -> Any: ...

tests/test_compat.py

@@ -2,7 +2,6 @@ from typing import Any, Dict, List, Union
 
 from fastapi import FastAPI, UploadFile
 from fastapi._compat import (
-    ModelField,
     Undefined,
     _get_model_config,
     get_cached_model_fields,
@@ -10,12 +9,12 @@ from fastapi._compat import (
     is_uploadfile_sequence_annotation,
     v1,
 )
-from fastapi._compat.shared import is_bytes_sequence_annotation
+from fastapi._compat.shared import is_bytes_sequence_annotation, lenient_issubclass
 from fastapi.testclient import TestClient
-from pydantic import BaseConfig, BaseModel, ConfigDict
+from pydantic import BaseModel, ConfigDict
 from pydantic.fields import FieldInfo
 
-from .utils import needs_pydanticv1, needs_pydanticv2
+from .utils import needs_pydanticv2
 
 
 @needs_pydanticv2
@@ -28,29 +27,25 @@ def test_model_field_default_required():
     assert field.default is Undefined
 
 
-@needs_pydanticv1
-def test_upload_file_dummy_with_info_plain_validator_function():
+def test_v1_plain_validator_function():
     # For coverage
-    assert UploadFile.__get_pydantic_core_schema__(str, lambda x: None) == {}
+    def func(v):  # pragma: no cover
+        return v
 
+    result = v1.with_info_plain_validator_function(func)
+    assert result == {}
 
-@needs_pydanticv1
-def test_union_scalar_list():
+
+def test_lenient_is_subclass():
     # For coverage
-    # TODO: there might not be a current valid code path that uses this, it would
-    # potentially enable query parameters defined as both a scalar and a list
-    # but that would require more refactors, also not sure it's really useful
-    from fastapi._compat.v1 import is_pv1_scalar_field
-
-    field_info = FieldInfo()
-    field = ModelField(
-        name="foo",
-        field_info=field_info,
-        type_=Union[str, List[int]],
-        class_validators={},
-        model_config=BaseConfig,
-    )
-    assert not is_pv1_scalar_field(field)
+    assert lenient_issubclass(Union[str, int], str) is False
+
+
+def test_is_model_field():
+    # For coverage
+    from fastapi._compat import _is_model_field
+
+    assert not _is_model_field(str)
 
 
 @needs_pydanticv2

tests/test_pydantic_v1_v2_list.py

@@ -185,6 +185,18 @@ def test_list_to_item_filter():
     assert "internal_id" not in result
 
 
+def test_list_to_item_filter_no_data():
+    response = client.post("/item-list-filter", json=[])
+    assert response.status_code == 200, response.text
+    assert response.json() == {
+        "title": "",
+        "size": 0,
+        "description": None,
+        "sub": {"name": ""},
+        "multi": [],
+    }
+
+
 def test_list_to_list():
     input_items = [
         {"title": "Item 1", "size": 10, "sub": {"name": "Sub1"}},
@@ -250,6 +262,15 @@ def test_list_to_list_filter():
         assert "internal_id" not in item
 
 
+def test_list_to_list_filter_no_data():
+    response = client.post(
+        "/item-list-to-list-filter",
+        json=[],
+    )
+    assert response.status_code == 200, response.text
+    assert response.json() == []
+
+
 def test_list_validation_error():
     response = client.post(
         "/item-list",

tests/test_response_model_as_return_annotation.py

@@ -2,6 +2,7 @@ from typing import List, Union
 
 import pytest
 from fastapi import FastAPI
+from fastapi._compat import v1
 from fastapi.exceptions import FastAPIError, ResponseValidationError
 from fastapi.responses import JSONResponse, Response
 from fastapi.testclient import TestClient
@@ -509,6 +510,23 @@ def test_invalid_response_model_field():
     assert "parameter response_model=None" in e.value.args[0]
 
 
+# TODO: remove when dropping Pydantic v1 support
+def test_invalid_response_model_field_pv1():
+    app = FastAPI()
+
+    class Model(v1.BaseModel):
+        foo: str
+
+    with pytest.raises(FastAPIError) as e:
+
+        @app.get("/")
+        def read_root() -> Union[Response, Model, None]:
+            return Response(content="Foo")  # pragma: no cover
+
+    assert "valid Pydantic field type" in e.value.args[0]
+    assert "parameter response_model=None" in e.value.args[0]
+
+
 def test_openapi_schema():
     response = client.get("/openapi.json")
     assert response.status_code == 200, response.text