Use lenient ForwardRef resolution as fallback

fastapi/dependencies/utils.py

@@ -245,19 +245,23 @@ def get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
 
 class _LenientTypeResolutionDict(dict[str, Any]):
     def __missing__(self, key: str) -> Any:
-        value = vars(builtins).get(key, ForwardRef(key))
-        self[key] = value
-        return value
+        return vars(builtins).get(key, ForwardRef(key))
 
 
 def get_typed_annotation(annotation: Any, globalns: dict[str, Any]) -> Any:
     if isinstance(annotation, str):
         annotation = ForwardRef(annotation)
     if isinstance(annotation, ForwardRef):
-        lenient_globalns = _LenientTypeResolutionDict(globalns)
         annotation = evaluate_forwardref(  # ty: ignore[deprecated]
-            annotation, lenient_globalns, lenient_globalns
+            annotation, globalns, globalns
         )
+        if isinstance(annotation, ForwardRef):
+            try:
+                annotation = eval(  # noqa: S307
+                    annotation.__forward_arg__, _LenientTypeResolutionDict(globalns)
+                )
+            except Exception:
+                pass
         if annotation is type(None):
             return None
     return annotation

tests/test_dependencies_utils.py

@@ -1,3 +1,6 @@
+from typing import Annotated, ForwardRef, get_args, get_origin
+
+from fastapi import Depends, params
 from fastapi.dependencies.utils import get_typed_annotation
 
 
@@ -6,3 +9,20 @@ def test_get_typed_annotation():
     annotation = "None"
     typed_annotation = get_typed_annotation(annotation, globals())
     assert typed_annotation is None
+
+
+def test_get_typed_annotation_falls_back_to_lenient_forwardref_resolution():
+    def dependency() -> None:
+        return None
+
+    annotation = "Annotated[Potato, Depends(dependency)]"
+    typed_annotation = get_typed_annotation(
+        annotation,
+        {"Annotated": Annotated, "Depends": Depends, "dependency": dependency},
+    )
+
+    assert get_origin(typed_annotation) is Annotated
+    type_annotation, depends = get_args(typed_annotation)
+    assert isinstance(type_annotation, ForwardRef)
+    assert type_annotation.__forward_arg__ == "Potato"
+    assert isinstance(depends, params.Depends)