Fixed the EndpointMetadata population

Author: mkArtakMSFT

src/Mvc/Mvc.ApiExplorer/src/ApiResponseTypeProvider.cs

@@ -364,9 +364,8 @@ internal static void CalculateResponseFormatForType(ApiResponseType apiResponse,
 
         // If the method is declared to return IActionResult, IResult or a derived class, that information
         // isn't valuable to the formatter, unless it implements IEndpointMetadataProvider interface.
-        bool isIResultOrIActionResult = typeof(IActionResult).IsAssignableFrom(unwrappedType) ||
-            typeof(IResult).IsAssignableFrom(unwrappedType);
-        if (isIResultOrIActionResult && !typeof(IEndpointMetadataProvider).IsAssignableFrom(unwrappedType))
+        if (typeof(IActionResult).IsAssignableFrom(unwrappedType) ||
+            typeof(IResult).IsAssignableFrom(unwrappedType))
         {
             return null;
         }

src/Mvc/Mvc.Core/src/ApplicationModels/DefaultApplicationModelProvider.cs

@@ -353,13 +353,13 @@ internal PropertyModel CreatePropertyModel(PropertyInfo propertyInfo)
         applicableAttributes.AddRange(routeAttributes);
         AddRange(actionModel.Selectors, CreateSelectors(applicableAttributes));
 
-        // There may be additional metadata for the action that is associated with the return type.
-        AddEndpointMetadata(actionModel, methodInfo);
+        AddReturnTypeMetadata(actionModel.Selectors, methodInfo);
+
 
         return actionModel;
     }
 
-    private static void AddEndpointMetadata(ActionModel actionModel, MethodInfo methodInfo)
+    private static void AddReturnTypeMetadata(IList<SelectorModel> selectors, MethodInfo methodInfo)
     {
         // Get metadata from return type
         var returnType = methodInfo.ReturnType;
@@ -376,6 +376,16 @@ private static void AddEndpointMetadata(ActionModel actionModel, MethodInfo meth
             invokeArgs[0] = methodInfo;
             invokeArgs[1] = builder;
             PopulateMetadataForEndpointMethod.MakeGenericMethod(returnType).Invoke(null, invokeArgs);
+
+            // The metadata is added to the builder's metadata collection.
+            // We need to populate the selectors with that metadata.
+            foreach (var metadata in builder.Metadata)
+            {
+                foreach (var selector in selectors)
+                {
+                    selector.EndpointMetadata.Add(metadata);
+                }
+            }
         }
     }