[Fixes #4960] Action results returned from controller actions rendered as json instead of executed

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvoker.cs

@@ -641,7 +641,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                         else if (!_executor.IsMethodAsync)
                         {
                             var resultAsObject = _executor.Execute(_controller, arguments);
-                            result = new ObjectResult(resultAsObject)
+                            result = resultAsObject as IActionResult ?? new ObjectResult(resultAsObject)
                             {
                                 DeclaredType = returnType,
                             };
@@ -649,7 +649,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                         else if (_executor.TaskGenericType != null)
                         {
                             var resultAsObject = await _executor.ExecuteAsync(_controller, arguments);
-                            result = new ObjectResult(resultAsObject)
+                            result = resultAsObject as IActionResult ?? new ObjectResult(resultAsObject)
                             {
                                 DeclaredType = _executor.TaskGenericType,
                             };

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ControllerActionInvokerTest.cs

@@ -2357,6 +2357,58 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             Assert.IsType<EmptyResult>(result);
         }
 
+        [Fact]
+        public async Task InvokeAction_AsyncActionWithTaskOfObjectReturnType_AndReturningTaskOfActionResult()
+        {
+            // Arrange
+            var actionParameters = new Dictionary<string, object> { ["value"] = 3 };
+            IActionResult result = null;
+
+            var filter = new Mock<IActionFilter>(MockBehavior.Strict);
+            filter.Setup(f => f.OnActionExecuting(It.IsAny<ActionExecutingContext>())).Verifiable();
+            filter
+                .Setup(f => f.OnActionExecuted(It.IsAny<ActionExecutedContext>()))
+                .Callback<ActionExecutedContext>(c => result = c.Result);
+
+            var invoker = CreateInvoker(
+                new[] { filter.Object },
+                nameof(TestController.AsyncActionMethodReturningActionResultWithTaskOfObjectAsReturnType),
+                actionParameters);
+
+            // Act
+            await invoker.InvokeAsync();
+
+            // Assert
+            var testResult = Assert.IsType<TestActionResult>(result);
+            Assert.Equal(3, testResult.Value);
+        }
+
+        [Fact]
+        public async Task InvokeAction_ActionWithObjectReturnType_AndReturningActionResult()
+        {
+            // Arrange
+            var actionParameters = new Dictionary<string, object> { ["value"] = 3 };
+            IActionResult result = null;
+
+            var filter = new Mock<IActionFilter>(MockBehavior.Strict);
+            filter.Setup(f => f.OnActionExecuting(It.IsAny<ActionExecutingContext>())).Verifiable();
+            filter
+                .Setup(f => f.OnActionExecuted(It.IsAny<ActionExecutedContext>()))
+                .Callback<ActionExecutedContext>(c => result = c.Result);
+
+            var invoker = CreateInvoker(
+                new[] { filter.Object },
+                nameof(TestController.ActionMethodReturningActionResultWithObjectAsReturnType),
+                actionParameters);
+
+            // Act
+            await invoker.InvokeAsync();
+
+            // Assert
+            var testResult = Assert.IsType<TestActionResult>(result);
+            Assert.Equal(3, testResult.Value);
+        }
+
         [Fact]
         public async Task InvokeAction_AsyncMethod_ParametersInRandomOrder()
         {
@@ -2914,6 +2966,16 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 return null;
             }
 
+            public object ActionMethodReturningActionResultWithObjectAsReturnType(int value = 5)
+            {
+                return new TestActionResult { Value = value };
+            }
+
+            public async Task<object> AsyncActionMethodReturningActionResultWithTaskOfObjectAsReturnType(int value = 5)
+            {
+                return await Task.FromResult(new TestActionResult { Value = value });
+            }
+
             public TestActionResult TestActionMethodWithNullActionResult()
             {
                 return null;

test/WebSites/BasicWebSite/Controllers/HomeController.cs

@@ -16,7 +16,9 @@ namespace BasicWebSite.Controllers
             return View();
         }
 
-        public IActionResult PlainView()
+        // Keep the return type as object to ensure that we don't
+        // wrap IActionResult instances into ObjectResults.
+        public object PlainView()
         {
             return View();
         }