🐛 Fix "default" extra response with extra status codes (#489)

* 🐛 Fix lowercase "default" extra response

* 🐛 Fix model for responses, to allow "default" plus status codes

* ✅ Add test for "default" extra response

fastapi/openapi/models.py

@@ -210,10 +210,6 @@ class Response(BaseModel):
     links: Optional[Dict[str, Union[Link, Reference]]] = None
 
 
-class Responses(BaseModel):
-    default: Response
-
-
 class Operation(BaseModel):
     tags: Optional[List[str]] = None
     summary: Optional[str] = None
@@ -222,7 +218,7 @@ class Operation(BaseModel):
     operationId: Optional[str] = None
     parameters: Optional[List[Union[Parameter, Reference]]] = None
     requestBody: Optional[Union[RequestBody, Reference]] = None
-    responses: Union[Responses, Dict[str, Response]]
+    responses: Dict[str, Response]
     # Workaround OpenAPI recursive reference
     callbacks: Optional[Dict[str, Union[Dict[str, Any], Reference]]] = None
     deprecated: Optional[bool] = None

fastapi/openapi/utils.py

@@ -49,7 +49,7 @@ status_code_ranges: Dict[str, str] = {
     "3XX": "Redirection",
     "4XX": "Client Error",
     "5XX": "Server Error",
-    "default": "Default Response",
+    "DEFAULT": "Default Response",
 }
 
 
@@ -205,9 +205,10 @@ def get_openapi_path(
                     response.setdefault(
                         "description", status_text or "Additional Response"
                     )
-                    operation.setdefault("responses", {})[
-                        str(additional_status_code).upper()
-                    ] = response
+                    status_code_key = str(additional_status_code).upper()
+                    if status_code_key == "DEFAULT":
+                        status_code_key = "default"
+                    operation.setdefault("responses", {})[status_code_key] = response
             status_code = str(route.status_code)
             response_schema = {"type": "string"}
             if lenient_issubclass(route.response_class, JSONResponse):