Update ApiExplorer logic to never infer Task or ValueTask as the responseType

Author: halter73

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

@@ -332,10 +332,9 @@ private static void AddSupportedResponseTypes(
         var defaultErrorType = errorMetadata?.Type ?? typeof(void);
         var contentTypes = new MediaTypeCollection();
 
-        // If the return type is an IResult or an awaitable IResult, then we should treat it as a void return type
-        // since we can't infer anything without additional metadata.
-        if (typeof(IResult).IsAssignableFrom(responseType) ||
-            producesResponseMetadata.Any(metadata => typeof(IResult).IsAssignableFrom(metadata.Type)))
+        // If the return type is an IResult or wrapped in a Task or ValueTask, then we should treat it as a void return type
+        // since we can't infer anything without additional metadata or requiring unreferenced code.
+        if (IsTaskOrValueTask(responseType) || typeof(IResult).IsAssignableFrom(responseType))
         {
             responseType = typeof(void);
         }
@@ -427,6 +426,23 @@ static bool TypesAreCompatible(Type? apiResponseType, Type? metadataType)
             return apiResponseType == metadataType ||
                 metadataType?.IsAssignableFrom(apiResponseType) == true;
         }
+
+        static bool IsTaskOrValueTask(Type returnType)
+        {
+            // If this method did not need to be trim-safe, we would use CoercedAwaitableInfo.IsTypeAwaitable, but we cannot.
+            if (returnType.IsAssignableFrom(typeof(Task)) || returnType.IsAssignableFrom(typeof(ValueTask)))
+            {
+                return true;
+            }
+
+            if (returnType.FullName is null)
+            {
+                return false;
+            }
+
+            return returnType.FullName.StartsWith("System.Threading.Tasks.Task`1[", StringComparison.Ordinal) ||
+                returnType.FullName.StartsWith("System.Threading.Tasks.ValueTask`1[", StringComparison.Ordinal);
+        }
     }
 
     private static ApiResponseType CreateDefaultApiResponseType(Type responseType)