RenderSection \ RenderSectionAsync does not work in sections

Fixes #1509

src/Microsoft.AspNet.Mvc.Razor/RazorPage.cs

@@ -451,7 +451,11 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// In layout pages, renders the content of the section named <paramref name="name"/>.
         /// </summary>
         /// <param name="name">The name of the section to render.</param>
-        /// <returns>Returns a HtmlString that contains the rendered HTML.</returns>
+        /// <returns>Returns <see cref="HtmlString.Empty"/> to allow the <see cref="Write(object)"/> call to
+        /// succeed.</returns>
+        /// <remarks>The method writes to the <see cref="Output"/> and the value returned is a token
+        /// value that allows the Write (produced due to @RenderSection(..)) to succeed. However the
+        /// value does not represent the rendered content.</remarks>
         public HtmlString RenderSection([NotNull] string name)
         {
             return RenderSection(name, required: true);
@@ -462,7 +466,11 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// </summary>
         /// <param name="name">The section to render.</param>
         /// <param name="required">Indicates if this section must be rendered.</param>
-        /// <returns>Returns a HtmlString that contains the rendered HTML.</returns>
+        /// <returns>Returns <see cref="HtmlString.Empty"/> to allow the <see cref="Write(object)"/> call to
+        /// succeed.</returns>
+        /// <remarks>The method writes to the <see cref="Output"/> and the value returned is a token
+        /// value that allows the Write (produced due to @RenderSection(..)) to succeed. However the
+        /// value does not represent the rendered content.</remarks>
         public HtmlString RenderSection([NotNull] string name, bool required)
         {
             EnsureMethodCanBeInvoked(nameof(RenderSection));
@@ -475,8 +483,11 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// In layout pages, asynchronously renders the content of the section named <paramref name="name"/>.
         /// </summary>
         /// <param name="name">The section to render.</param>
-        /// <returns>A <see cref="Task{TResult}"/> that on completion returns a <see cref="HtmlString"/> containing
+        /// <returns>A <see cref="Task{HtmlString}"/> that on completion returns <see cref="HtmlString.Empty"/> that
-        /// the rendered HTML.</returns>
+        /// allows the <see cref="Write(object)"/> call to succeed.</returns>
+        /// <remarks>The method writes to the <see cref="Output"/> and the value returned is a token
+        /// value that allows the Write (produced due to @RenderSection(..)) to succeed. However the
+        /// value does not represent the rendered content.</remarks>
         public Task<HtmlString> RenderSectionAsync([NotNull] string name)
         {
             return RenderSectionAsync(name, required: true);
@@ -486,8 +497,11 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// In layout pages, asynchronously renders the content of the section named <paramref name="name"/>.
         /// </summary>
         /// <param name="name">The section to render.</param>
-        /// <returns>A <see cref="Task{TResult}"/> that on completion returns a <see cref="HtmlString"/> containing
+        /// <returns>A <see cref="Task{HtmlString}"/> that on completion returns <see cref="HtmlString.Empty"/> that
-        /// the rendered HTML.</returns>
+        /// allows the <see cref="Write(object)"/> call to succeed.</returns>
+        /// <remarks>The method writes to the <see cref="Output"/> and the value returned is a token
+        /// value that allows the Write (produced due to @RenderSection(..)) to succeed. However the
+        /// value does not represent the rendered content.</remarks>
         /// <exception cref="InvalidOperationException">if <paramref name="required"/> is <c>true</c> and the section
         /// was not registered using the <c>@section</c> in the Razor page.</exception>
         public async Task<HtmlString> RenderSectionAsync([NotNull] string name, bool required)
@@ -508,14 +522,11 @@ namespace Microsoft.AspNet.Mvc.Razor
             if (PreviousSectionWriters.TryGetValue(sectionName, out renderDelegate))
             {
                 _renderedSections.Add(sectionName);
+                await renderDelegate(Output);
 
-                using (var writer = new StringCollectionTextWriter(Output.Encoding))
+                // Return a token value that allows the Write call that wraps the RenderSection \ RenderSectionAsync
-                {
+                // to succeed.
-                    await renderDelegate(writer);
+                return HtmlString.Empty;
-
-                    // Returning a disposed StringCollectionTextWriter is safe.
-                    return new HtmlString(writer);
-                }
             }
             else if (required)
             {

test/Microsoft.AspNet.Mvc.FunctionalTests/FlushPointTest.cs

@@ -67,8 +67,10 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             Assert.Equal("Final content", GetTrimmedString(stream));
         }
 
-        [Fact]
+        [Theory]
-        public async Task FlushPointsAreExecutedForPagesWithComponentsAndPartials()
+        [InlineData("PageWithPartialsAndViewComponents", "FlushAsync invoked inside RenderSection")]
+        [InlineData("PageWithRenderSectionAsync", "FlushAsync invoked inside RenderSectionAsync")]
+        public async Task FlushPointsAreExecutedForPagesWithComponentsPartialsAndSections(string action, string title)
         {
             var waitService = new WaitService();
             var serviceProvider = GetServiceProvider(waitService);
@@ -77,23 +79,31 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             var client = server.CreateClient();
 
             // Act
-            var stream = await client.GetStreamAsync("http://localhost/FlushPoint/PageWithPartialsAndViewComponents");
+            var stream = await client.GetStreamAsync("http://localhost/FlushPoint/" + action);
 
             // Assert - 1
-            Assert.Equal(
+            Assert.Equal(string.Join(Environment.NewLine,
-@"<title>Page With Components and Partials</title>
+                                     "<title>" + title + "</title>",
-
+                                     "",
-RenderBody content", GetTrimmedString(stream));
+                                     "RenderBody content"), GetTrimmedString(stream));
             waitService.WaitForServer();
 
             // Assert - 2
-            Assert.Equal("partial-content", GetTrimmedString(stream));
+            Assert.Equal(string.Join(
+                Environment.NewLine,
+                "partial-content",
+                "",
+                "Value from TaskReturningString",
+                "<p>section-content</p>"), GetTrimmedString(stream));
             waitService.WaitForServer();
 
             // Assert - 3
-            Assert.Equal(
+            Assert.Equal(string.Join(
-@"component-content
+                Environment.NewLine,
-    <span>Content that takes time to produce</span>", GetTrimmedString(stream));
+                "component-content",
+                "    <span>Content that takes time to produce</span>",
+                "",
+                "More content from layout"), GetTrimmedString(stream));
         }
 
         private IServiceProvider GetServiceProvider(WaitService waitService)

test/WebSites/RazorWebSite/Controllers/FlushPoint.cs

@@ -17,9 +17,16 @@ namespace RazorWebSite
             return View();
         }
 
+        // This uses RenderSection to render the section that contains a FlushAsync call
         public ViewResult PageWithPartialsAndViewComponents()
         {
             return View();
         }
+
+        // This uses RenderSectionAsync to render the section that contains a FlushAsync call
+        public ViewResult PageWithRenderSectionAsync()
+        {
+            return View("PageWithSectionInvokedViaRenderSectionAsync");
+        }
     }
 }

test/WebSites/RazorWebSite/Services/TaskReturningService.cs

@@ -0,0 +1,16 @@
+// 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 RazorWebSite
+{
+    public class TaskReturningService
+    {
+        public async Task<string> GetValueAsync()
+        {
+            await Task.Delay(100);
+            return "Value from TaskReturningString";
+        }
+    }
+}

test/WebSites/RazorWebSite/Startup.cs

@@ -17,6 +17,7 @@ namespace RazorWebSite
                 // Add MVC services to the services container
                 services.AddMvc(configuration);
                 services.AddTransient<InjectedHelper>();
+                services.AddTransient<TaskReturningService>();
                 services.Configure<RazorViewEngineOptions>(options =>
                 {
                     var expander = new LanguageViewLocationExpander(

test/WebSites/RazorWebSite/Views/FlushPoint/PageWithPartialsAndViewComponents.cshtml

@@ -1,15 +1,19 @@
 @inject WaitService WaitService
+@inject TaskReturningService TaskReturningService
+
 @{
     Layout = "/Views/Shared/_LayoutWithPartialAndFlush.cshtml";
-    ViewBag.Title = "Page With Components and Partials";
+    ViewBag.Title = "FlushAsync invoked inside RenderSection";
 }
 RenderBody content
 @section content
 {
+@await TaskReturningService.GetValueAsync()
+<p>section-content</p>
     @{
         await FlushAsync();
         WaitService.WaitForClient();
     }
     @await Component.InvokeAsync("ComponentThatSetsTitle")
     <span>Content that takes time to produce</span>
-}
+}

test/WebSites/RazorWebSite/Views/FlushPoint/PageWithSectionInvokedViaRenderSectionAsync.cshtml

@@ -0,0 +1,19 @@
+@inject WaitService WaitService
+@inject TaskReturningService TaskReturningService
+
+@{
+    Layout = "/Views/Shared/_LayoutWithRenderSectionAsync.cshtml";
+    ViewBag.Title = "FlushAsync invoked inside RenderSectionAsync";
+}
+RenderBody content
+@section content
+{
+@await TaskReturningService.GetValueAsync()
+<p>section-content</p>
+    @{
+        await FlushAsync();
+        WaitService.WaitForClient();
+    }
+    @await Component.InvokeAsync("ComponentThatSetsTitle")
+    <span>Content that takes time to produce</span>
+}

test/WebSites/RazorWebSite/Views/Shared/_LayoutWithFlush.cshtml

@@ -6,6 +6,3 @@
 }
 @RenderBody()
 @await RenderSectionAsync("content")
-@{ 
-    WaitService.NotifyClient();
-}

test/WebSites/RazorWebSite/Views/Shared/_LayoutWithPartialAndFlush.cshtml

@@ -7,6 +7,4 @@
 }
 @await Html.PartialAsync("_PartialThatSetsTitle")
 @await RenderSectionAsync("content")
-@{ 
+More content from layout
-    WaitService.NotifyClient();
-}

test/WebSites/RazorWebSite/Views/Shared/_LayoutWithRenderSectionAsync.cshtml

@@ -0,0 +1,10 @@
+@inject WaitService WaitService
+<title>@ViewBag.Title</title>
+@RenderBody()
+@{
+    await FlushAsync();
+    WaitService.WaitForClient();
+}
+@await Html.PartialAsync("_PartialThatSetsTitle")
+@await RenderSectionAsync("content")
+More content from layout