Modify TemplateRenderer to use ThrowIfFaulted instead of Task.Wait

Fixes aspnet#782

src/Microsoft.AspNet.Mvc.Core/Internal/TaskHelper.cs

@@ -0,0 +1,25 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNet.Mvc.Internal
+{
+    /// <summary>
+    /// Utility methods for dealing with <see cref="Task"/>.
+    /// </summary>
+    public static class TaskHelper
+    {
+        /// <summary>
+        /// Throws the first faulting exception for a task which is faulted. It preserves the original stack trace when
+        /// throwing the exception.
+        /// </summary>
+        /// <remarks>
+        /// Invoking this method is equivalent to calling Wait() on the <paramref name="task" /> if it is not completed.
+        /// </remarks>
+        public static void ThrowIfFaulted(Task task)
+        {
+            task.GetAwaiter().GetResult();
+        }
+    }
+}

src/Microsoft.AspNet.Mvc.Core/Rendering/Html/TemplateRenderer.cs

@@ -8,6 +8,7 @@
 using System.IO;
 using System.Linq;
 using Microsoft.AspNet.Mvc.Core;
+using Microsoft.AspNet.Mvc.Internal;
 using Microsoft.Framework.DependencyInjection;
 
 namespace Microsoft.AspNet.Mvc.Rendering
@@ -99,7 +100,8 @@ public string Render()
                         using (view as IDisposable)
                         {
                             var viewContext = new ViewContext(_viewContext, viewEngineResult.View, _viewData, writer);
-                            viewEngineResult.View.RenderAsync(viewContext).Wait();
+                            var renderTask = viewEngineResult.View.RenderAsync(viewContext);
+                            TaskHelper.ThrowIfFaulted(renderTask);
                             return writer.ToString();
                         }
                     }

test/Microsoft.AspNet.Mvc.Core.Test/Internal/TaskHelperTest.cs

@@ -0,0 +1,58 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.Internal
+{
+    public class TaskHelperTest
+    {
+        [Fact]
+        public void ThrowIfFaulted_DoesNotThrowIfTaskIsNotFaulted()
+        {
+            // Arrange
+            var task = Task.FromResult(0);
+
+            // Act and Assert
+            Assert.DoesNotThrow(() => TaskHelper.ThrowIfFaulted(task));
+        }
+
+        [Fact]
+        public void ThrowIfFaulted_ThrowsIfTaskIsFaulted()
+        {
+            // Arrange
+            var message = "Exception message";
+            var task = CreatingFailingTask(message);
+
+            // Act and Assert
+            var ex = Assert.Throws<Exception>(() => TaskHelper.ThrowIfFaulted(task));
+            Assert.Equal(message, ex.Message);
+        }
+
+        [Fact]
+        public void ThrowIfFaulted_ThrowsFirstExceptionWhenAggregateTaskFails()
+        {
+            // Arrange
+            var message = "Exception message";
+            var task = Task.Run(async () =>
+            {
+                await Task.WhenAll(CreatingFailingTask(message), 
+                                   CreatingFailingTask("different message"));
+            });
+
+            // Act and Assert
+            var ex = Assert.Throws<Exception>(() => TaskHelper.ThrowIfFaulted(task));
+            Assert.Equal(message, ex.Message);
+        }
+
+        private static Task CreatingFailingTask(string message)
+        {
+            return Task.Run(() =>
+            {
+                throw new Exception(message);
+            });
+        }
+    }
+}

test/Microsoft.AspNet.Mvc.Core.Test/Rendering/DefaultDisplayTemplatesTests.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.Mvc.Rendering;
 using Moq;
@@ -235,5 +236,29 @@ public void DisplayFor_FindsModel_EvenIfNullOrEmpty(string propertyValue)
             // Assert
             Assert.Empty(result.ToString());
         }
+
+        [Fact]
+        public void DisplayFor_DoesNotWrapExceptionThrowsDuringViewRendering()
+        {
+            // Arrange
+            var expectedMessage = "my exception message";
+            var model = new DefaultTemplatesUtilities.ObjectTemplateModel { Property1 = "Test string", };
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Returns(Task.Run(() =>
+                {
+                    throw new ArgumentException(expectedMessage);
+                }));
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine
+                .Setup(v => v.FindPartialView(It.IsAny<ActionContext>(), It.IsAny<string>()))
+                .Returns(ViewEngineResult.Found("test-view", view.Object));
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(model, viewEngine.Object);
+            helper.ViewData["Property1"] = "ViewData string";
+
+            // Act and Assert
+            var ex = Assert.Throws<ArgumentException>(() => helper.DisplayFor(m => m.Property1));
+            Assert.Equal(expectedMessage, ex.Message);
+        }
     }
 }

test/Microsoft.AspNet.Mvc.Core.Test/Rendering/DefaultEditorTemplatesTests.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.Mvc.Rendering;
 using Microsoft.AspNet.Testing;
@@ -386,5 +387,29 @@ public void EditorFor_FindsModel_EvenIfNullOrEmpty(string propertyValue)
                 "<input class=\"text-box single-line\" id=\"Property1\" name=\"Property1\" type=\"text\" value=\"\" />",
                 result.ToString());
         }
+
+        [Fact]
+        public void EditorFor_DoesNotWrapExceptionThrowsDuringViewRendering()
+        {
+            // Arrange
+            var expectedMessage = "my exception message";
+            var model = new DefaultTemplatesUtilities.ObjectTemplateModel { Property1 = "Test string", };
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Returns(Task.Run(() =>
+                {
+                    throw new FormatException(expectedMessage);
+                }));
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine
+                .Setup(v => v.FindPartialView(It.IsAny<ActionContext>(), It.IsAny<string>()))
+                .Returns(ViewEngineResult.Found("test-view", view.Object));
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(model, viewEngine.Object);
+            helper.ViewData["Property1"] = "ViewData string";
+
+            // Act and Assert
+            var ex = Assert.Throws<FormatException>(() => helper.EditorFor(m => m.Property1));
+            Assert.Equal(expectedMessage, ex.Message);
+        }
     }
 }