Fix stringified Annotated dependency forward refs

fastapi/dependencies/utils.py

@@ -1,3 +1,4 @@
+import ast
 import dataclasses
 import inspect
 import sys
@@ -60,7 +61,7 @@ from fastapi.logger import logger
 from fastapi.security.oauth2 import SecurityScopes
 from fastapi.types import DependencyCacheKey
 from fastapi.utils import create_model_field, get_path_param_names
-from pydantic import BaseModel, Json
+from pydantic import BaseModel, Json, PydanticUndefinedAnnotation
 from pydantic.fields import FieldInfo
 from starlette.background import BackgroundTasks as StarletteBackgroundTasks
 from starlette.concurrency import run_in_threadpool
@@ -242,7 +243,63 @@ def get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
     return typed_signature
 
 
+def _evaluate_typed_forwardref(annotation: str, globalns: dict[str, Any]) -> Any:
+    forward_ref = ForwardRef(annotation)
+    try:
+        return evaluate_forwardref(forward_ref, globalns, globalns)  # ty: ignore[deprecated]
+    except (NameError, PydanticUndefinedAnnotation):
+        return forward_ref
+
+
+def _get_stringified_annotated(annotation: str, globalns: dict[str, Any]) -> Any | None:
+    try:
+        expression = ast.parse(annotation, mode="eval").body
+    except SyntaxError:
+        return None
+
+    if not isinstance(expression, ast.Subscript):
+        return None
+
+    annotated_target = expression.value
+    is_annotated = (
+        isinstance(annotated_target, ast.Name)
+        and annotated_target.id == "Annotated"
+    ) or (
+        isinstance(annotated_target, ast.Attribute)
+        and annotated_target.attr == "Annotated"
+    )
+    if not is_annotated:
+        return None
+
+    annotated_items = (
+        expression.slice.elts
+        if isinstance(expression.slice, ast.Tuple)
+        else [expression.slice]
+    )
+    if len(annotated_items) < 2:
+        return None
+
+    first_annotation = ast.unparse(annotated_items[0])
+    annotated_args = [
+        get_typed_annotation(first_annotation, globalns)
+        if "Annotated[" in first_annotation
+        else _evaluate_typed_forwardref(first_annotation, globalns)
+    ]
+    annotated_args.extend(
+        eval(
+            compile(ast.Expression(item), "<fastapi_annotation>", "eval"),
+            globalns,
+            globalns,
+        )
+        for item in annotated_items[1:]
+    )
+    return Annotated[tuple(annotated_args)]  # ty: ignore[invalid-type-form]
+
+
 def get_typed_annotation(annotation: Any, globalns: dict[str, Any]) -> Any:
+    if isinstance(annotation, str):
+        if "Annotated[" in annotation:
+            annotation = _get_stringified_annotated(annotation, globalns) or annotation
         if isinstance(annotation, str):
             annotation = ForwardRef(annotation)
             annotation = evaluate_forwardref(annotation, globalns, globalns)  # ty: ignore[deprecated]

tests/test_stringified_annotation_dependency.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Annotated
+from typing import TYPE_CHECKING, Any, Annotated
 
 import pytest
 from fastapi import Depends, FastAPI
@@ -77,3 +77,45 @@ def test_openapi_schema(client: TestClient):
             },
         }
     )
+
+
+def test_openapi_schema_for_dependency_with_forward_ref_defined_later():
+    namespace: dict[str, Any] = {}
+    exec(
+        """
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Annotated
+
+from fastapi import Depends, FastAPI
+
+app = FastAPI()
+
+
+def get_potato() -> Potato:
+    return Potato(color="red", size=10)
+
+
+@app.get("/")
+async def read_root(potato: Annotated[Potato, Depends(get_potato)]):
+    return {"color": potato.color, "size": potato.size}
+
+
+@dataclass
+class Potato:
+    color: str
+    size: int
+""",
+        namespace,
+    )
+
+    client = TestClient(namespace["app"])
+
+    response = client.get("/")
+    assert response.status_code == 200, response.text
+    assert response.json() == {"color": "red", "size": 10}
+
+    response = client.get("/openapi.json")
+    assert response.status_code == 200, response.text
+    assert "requestBody" not in response.json()["paths"]["/"]["get"]