Add `HtmlEncoder` parameter to `RazorPage.StartTagHelperWritingScope()`

- aspnet/Razor#643 part 2: react to aspnet/Razor#653
 - change test calls and delegates to include new parameter
 - add tests specifically of the new feature
 - add tag helpers using new feature to `TagHelpersTest` functional test
- note `HtmlEncoder`s used elsewhere e.g. in other `RazorPage` instances are unaffected
 - i.e. changing one `RazorPage.HtmlEncoder` property only affects C# expressions in that page

Also simplify scope management, removing bizarre assertion when user does something odd.

nits:
- correct `// Act` and `//  Act & Assert` content
- remove #YOLO wrapping

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

@@ -30,8 +30,7 @@ namespace Microsoft.AspNet.Mvc.Razor
     public abstract class RazorPage : IRazorPage
     {
         private readonly HashSet<string> _renderedSections = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-        private readonly Stack<HtmlContentWrapperTextWriter> _writerScopes;
+        private readonly Stack<TagHelperScopeInfo> _tagHelperScopes = new Stack<TagHelperScopeInfo>();
-        private TextWriter _originalWriter;
         private IUrlHelper _urlHelper;
         private ITagHelperActivator _tagHelperActivator;
         private ITypeActivatorCache _typeActivatorCache;
@@ -44,7 +43,6 @@ namespace Microsoft.AspNet.Mvc.Razor
         public RazorPage()
         {
             SectionWriters = new Dictionary<string, RenderAsyncDelegate>(StringComparer.OrdinalIgnoreCase);
-            _writerScopes = new Stack<HtmlContentWrapperTextWriter>();
         }
 
         /// <summary>
@@ -62,7 +60,8 @@ namespace Microsoft.AspNet.Mvc.Razor
         public string Layout { get; set; }
 
         /// <summary>
-        /// Gets the <see cref="HtmlEncoder"/> to be used for encoding HTML.
+        /// Gets the <see cref="System.Text.Encodings.Web.HtmlEncoder"/> to use when this <see cref="RazorPage"/>
+        /// handles non-<see cref="IHtmlContent"/> C# expressions.
         /// </summary>
         [RazorInject]
         public HtmlEncoder HtmlEncoder { get; set; }
@@ -116,7 +115,7 @@ namespace Microsoft.AspNet.Mvc.Razor
         public IDictionary<string, RenderAsyncDelegate> PreviousSectionWriters { get; set; }
 
         /// <inheritdoc />
-        public IDictionary<string, RenderAsyncDelegate> SectionWriters { get; private set; }
+        public IDictionary<string, RenderAsyncDelegate> SectionWriters { get; }
 
         /// <inheritdoc />
         public abstract Task ExecuteAsync();
@@ -201,28 +200,31 @@ namespace Microsoft.AspNet.Mvc.Razor
         }
 
         /// <summary>
-        /// Starts a new writing scope.
+        /// Starts a new writing scope and optionally overrides <see cref="HtmlEncoder"/> within that scope.
         /// </summary>
+        /// <param name="encoder">
+        /// The <see cref="System.Text.Encodings.Web.HtmlEncoder"/> to use when this <see cref="RazorPage"/> handles
+        /// non-<see cref="IHtmlContent"/> C# expressions. If <c>null</c>, does not change <see cref="HtmlEncoder"/>.
+        /// </param>
         /// <remarks>
         /// All writes to the <see cref="Output"/> or <see cref="ViewContext.Writer"/> after calling this method will
         /// be buffered until <see cref="EndTagHelperWritingScope"/> is called.
         /// </remarks>
-        public void StartTagHelperWritingScope()
+        public void StartTagHelperWritingScope(HtmlEncoder encoder)
         {
-            // If there isn't a base writer take the ViewContext.Writer
+            _tagHelperScopes.Push(new TagHelperScopeInfo(HtmlEncoder, ViewContext.Writer));
-            if (_originalWriter == null)
-            {
-                _originalWriter = ViewContext.Writer;
-            }
 
-            var buffer = new ViewBuffer(BufferScope, Path);
+            // If passed an HtmlEncoder, override the property.
-            var writer = new HtmlContentWrapperTextWriter(buffer, _originalWriter.Encoding);
+            if (encoder != null)
+            {
+                HtmlEncoder = encoder;
+            }
 
             // We need to replace the ViewContext's Writer to ensure that all content (including content written
             // from HTML helpers) is redirected.
+            var buffer = new ViewBuffer(BufferScope, Path);
+            var writer = new HtmlContentWrapperTextWriter(buffer, ViewContext.Writer.Encoding);
             ViewContext.Writer = writer;
-
-            _writerScopes.Push(writer);
         }
 
         /// <summary>
@@ -231,28 +233,21 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// <returns>The buffered <see cref="TagHelperContent"/>.</returns>
         public TagHelperContent EndTagHelperWritingScope()
         {
-            if (_writerScopes.Count == 0)
+            if (_tagHelperScopes.Count == 0)
             {
                 throw new InvalidOperationException(Resources.RazorPage_ThereIsNoActiveWritingScopeToEnd);
             }
 
-            var writer = _writerScopes.Pop();
+            // Get the content written during the current scope.
-            Debug.Assert(writer == ViewContext.Writer);
+            var writer = ViewContext.Writer as HtmlContentWrapperTextWriter;
-
-            if (_writerScopes.Count > 0)
-            {
-                ViewContext.Writer = _writerScopes.Peek();
-            }
-            else
-            {
-                ViewContext.Writer = _originalWriter;
-
-                // No longer a base writer
-                _originalWriter = null;
-            }
-
             var tagHelperContent = new DefaultTagHelperContent();
-            tagHelperContent.AppendHtml(writer.ContentBuilder);
+            tagHelperContent.AppendHtml(writer?.ContentBuilder);
+
+            // Restore previous scope.
+            var scopeInfo = _tagHelperScopes.Pop();
+            HtmlEncoder = scopeInfo.Encoder;
+            ViewContext.Writer = scopeInfo.Writer;
+
             return tagHelperContent;
         }
 
@@ -290,7 +285,9 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// Writes the specified <paramref name="value"/> with HTML encoding to given <paramref name="writer"/>.
         /// </summary>
         /// <param name="writer">The <see cref="TextWriter"/> instance to write to.</param>
-        /// <param name="encoder">The <see cref="HtmlEncoder"/> to use when encoding <paramref name="value"/>.</param>
+        /// <param name="encoder">
+        /// The <see cref="System.Text.Encodings.Web.HtmlEncoder"/> to use when encoding <paramref name="value"/>.
+        /// </param>
         /// <param name="value">The <see cref="object"/> to write.</param>
         /// <remarks>
         /// <paramref name="value"/>s of type <see cref="IHtmlContent"/> are written using
@@ -825,9 +822,8 @@ namespace Microsoft.AspNet.Mvc.Razor
         /// </remarks>
         public async Task<HtmlString> FlushAsync()
         {
-            // If there are active writing scopes then we should throw. Cannot flush content that has the potential to
+            // If there are active scopes, then we should throw. Cannot flush content that has the potential to change.
-            // change.
+            if (_tagHelperScopes.Count > 0)
-            if (_writerScopes.Count > 0)
             {
                 throw new InvalidOperationException(
                     Resources.FormatRazorPage_CannotFlushWhileInAWritingScope(nameof(FlushAsync), Path));
@@ -1000,5 +996,18 @@ namespace Microsoft.AspNet.Mvc.Razor
 
             public bool Suppressed { get; set; }
         }
+
+        private struct TagHelperScopeInfo
+        {
+            public TagHelperScopeInfo(HtmlEncoder encoder, TextWriter writer)
+            {
+                Encoder = encoder;
+                Writer = writer;
+            }
+
+            public HtmlEncoder Encoder { get; }
+
+            public TextWriter Writer { get; }
+        }
     }
 }

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

@@ -253,6 +253,33 @@ page:<root>root-content</root>"
                 PlatformNormalizer.NormalizeContent(expectedContent),
                 responseContent,
                 ignoreLineEndingDifferences: true);
+#endif
+        }
+
+        [Theory]
+        [InlineData("Index")]
+        [InlineData("CustomEncoder")]
+        [InlineData("NullEncoder")]
+        [InlineData("TwoEncoders")]
+        [InlineData("ThreeEncoders")]
+        public async Task EncodersPages_ReturnExpectedContent(string actionName)
+        {
+            // Arrange
+            var outputFile = $"compiler/resources/TagHelpersWebSite.Encoders.{ actionName }.html";
+            var expectedContent =
+                await ResourceFile.ReadResourceAsync(_resourcesAssembly, outputFile, sourceFile: false);
+
+            // Act
+            var response = await Client.GetAsync($"/Encoders/{ actionName }");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            var responseContent = await response.Content.ReadAsStringAsync();
+
+#if GENERATE_BASELINES
+            ResourceFile.UpdateFile(_resourcesAssembly, outputFile, expectedContent, responseContent);
+#else
+            Assert.Equal(expectedContent, responseContent, ignoreLineEndingDifferences: true);
 #endif
         }
     }

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/TagHelpersWebSite.Encoders.CustomEncoder.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Using a custom HTML encoder - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - Using a custom HTML encoder</h1>
+        <div>
+            
+
+<pre>Custom encoder: Custom[[Outer knows <b>1 < 4</b>]]
+<inner>Custom[[Inner knows <b>1 < 4</b>]]</inner><br />Outer knows &lt;b&gt;2 &lt; 4&lt;/b&gt;
+<inner>Inner knows &lt;b&gt;2 &lt; 4&lt;/b&gt;</inner></pre>
+        </div>
+    </body>
+</html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/TagHelpersWebSite.Encoders.Index.html

@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Using the default HTML encoder - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - Using the default HTML encoder</h1>
+        <div>
+            
+
+<pre>Default encoder: Outer knows &lt;b&gt;1 &lt; 4&lt;/b&gt;
+<pre>Default encoder: Inner knows &lt;b&gt;1 &lt; 4&lt;/b&gt;</pre></pre>
+        </div>
+    </body>
+</html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/TagHelpersWebSite.Encoders.NullEncoder.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Using the null HTML encoder - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - Using the null HTML encoder</h1>
+        <div>
+            
+
+<pre>Outer knows &lt;b&gt;2 &lt; 4&lt;/b&gt;
+<inner>Inner knows &lt;b&gt;2 &lt; 4&lt;/b&gt;</inner><br />Null encoder: Outer knows <b>1 < 4</b>
+<inner>Inner knows <b>1 < 4</b></inner></pre>
+        </div>
+    </body>
+</html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/TagHelpersWebSite.Encoders.ThreeEncoders.html

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Using three HTML encoders - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - Using three HTML encoders</h1>
+        <div>
+            
+
+<pre>Custom encoder: Custom[[Outer knows <b>1 < 4</b>]]
+<pre>Default encoder: Custom[[Inner knows <b>1 < 4</b>]]</pre><br />Default encoder: Outer knows &lt;b&gt;2 &lt; 4&lt;/b&gt;
+<pre>Default encoder: Inner knows &lt;b&gt;2 &lt; 4&lt;/b&gt;</pre><br />Null encoder: Outer knows <b>3 < 4</b>
+<pre>Default encoder: Inner knows <b>3 < 4</b></pre></pre>
+        </div>
+    </body>
+</html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/TagHelpersWebSite.Encoders.TwoEncoders.html

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Using two HTML encoders - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - Using two HTML encoders</h1>
+        <div>
+            
+
+<pre>Custom encoder: Custom[[Outer knows <b>1 < 4</b>]]
+<inner>Custom[[Inner knows <b>1 < 4</b>]]</inner><br />Outer knows &lt;b&gt;3 &lt; 4&lt;/b&gt;
+<inner>Inner knows &lt;b&gt;3 &lt; 4&lt;/b&gt;</inner><br />Null encoder: Outer knows <b>2 < 4</b>
+<inner>Inner knows <b>2 < 4</b></inner></pre>
+        </div>
+    </body>
+</html>

test/Microsoft.AspNet.Mvc.Razor.Test/RazorPageTest.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Text.Encodings.Web;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Html;
 using Microsoft.AspNet.Http.Internal;
@@ -41,7 +42,7 @@ namespace Microsoft.AspNet.Mvc.Razor
             {
                 v.HtmlEncoder = new HtmlTestEncoder();
                 v.Write("Hello Prefix");
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 v.Write("Hello from Output");
                 v.ViewContext.Writer.Write("Hello from view context writer");
                 var scopeValue = v.EndTagHelperWritingScope();
@@ -54,8 +55,10 @@ namespace Microsoft.AspNet.Mvc.Razor
             var pageOutput = page.Output.ToString();
 
             // Assert
-            Assert.Equal("HtmlEncode[[Hello Prefix]]HtmlEncode[[From Scope: ]]HtmlEncode[[Hello from Output]]" +
+            Assert.Equal(
-                "Hello from view context writer", pageOutput);
+                "HtmlEncode[[Hello Prefix]]HtmlEncode[[From Scope: ]]HtmlEncode[[Hello from Output]]" +
+                "Hello from view context writer",
+                pageOutput);
         }
 
         [Fact]
@@ -67,7 +70,7 @@ namespace Microsoft.AspNet.Mvc.Razor
             {
                 v.HtmlEncoder = new HtmlTestEncoder();
                 v.Write("Hello Prefix");
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 v.Write("Hello In Scope");
                 var scopeValue = v.EndTagHelperWritingScope();
                 v.Write("From Scope: ");
@@ -91,10 +94,10 @@ namespace Microsoft.AspNet.Mvc.Razor
             {
                 v.HtmlEncoder = new HtmlTestEncoder();
                 v.Write("Hello Prefix");
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 v.Write("Hello In Scope Pre Nest");
 
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 v.Write("Hello In Nested Scope");
                 var scopeValue1 = v.EndTagHelperWritingScope();
 
@@ -108,36 +111,85 @@ namespace Microsoft.AspNet.Mvc.Razor
 
             // Act
             await page.ExecuteAsync();
-            var pageOutput = page.Output.ToString();
 
             // Assert
-            Assert.Equal("HtmlEncode[[Hello Prefix]]HtmlEncode[[From Scopes: ]]HtmlEncode[[Hello In Scope Pre Nest]]" +
+            var pageOutput = page.Output.ToString();
-                "HtmlEncode[[Hello In Scope Post Nest]]HtmlEncode[[Hello In Nested Scope]]", pageOutput);
+            Assert.Equal(
+                "HtmlEncode[[Hello Prefix]]HtmlEncode[[From Scopes: ]]HtmlEncode[[Hello In Scope Pre Nest]]" +
+                "HtmlEncode[[Hello In Scope Post Nest]]HtmlEncode[[Hello In Nested Scope]]",
+                pageOutput);
         }
 
         [Fact]
-        public async Task StartNewWritingScope_CannotFlushInWritingScope()
+        public async Task StartTagHelperWritingScope_CannotFlushInWritingScope()
         {
             // Arrange
             var viewContext = CreateViewContext();
             var page = CreatePage(async v =>
             {
                 v.Path = "/Views/TestPath/Test.cshtml";
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 await v.FlushAsync();
             });
 
+            // Act & Assert
+            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => page.ExecuteAsync());
+            Assert.Equal(
+                "The FlushAsync operation cannot be performed while " +
+                "inside a writing scope in '/Views/TestPath/Test.cshtml'.",
+                ex.Message);
+        }
+
+        public static TheoryData<HtmlEncoder> HtmlEncoderData
+        {
+            get
+            {
+                return new TheoryData<HtmlEncoder>
+                {
+                    HtmlEncoder.Default,
+                    NullHtmlEncoder.Default,
+                    new HtmlTestEncoder(),
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(HtmlEncoderData))]
+        public async Task StartTagHelperWritingScope_SetsHtmlEncoder(HtmlEncoder encoder)
+        {
+            // Arrange
+            var page = CreatePage(v =>
+            {
+                v.StartTagHelperWritingScope(encoder);
+            });
+
             // Act
-            var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            await page.ExecuteAsync();
-                                () => page.ExecuteAsync());
 
             // Assert
-            Assert.Equal("The FlushAsync operation cannot be performed while " +
+            Assert.Same(encoder, page.HtmlEncoder);
-                "inside a writing scope in '/Views/TestPath/Test.cshtml'.", ex.Message);
         }
 
         [Fact]
-        public async Task StartNewWritingScope_CannotEndWritingScopeWhenNoWritingScope()
+        public async Task StartTagHelperWritingScope_DoesNotSetHtmlEncoderToNull()
+        {
+            // Arrange
+            var page = CreatePage(v =>
+            {
+                v.StartTagHelperWritingScope(encoder: null);
+            });
+            var originalEncoder = page.HtmlEncoder;
+
+            // Act
+            await page.ExecuteAsync();
+
+            // Assert
+            Assert.NotNull(originalEncoder);
+            Assert.Same(originalEncoder, page.HtmlEncoder);
+        }
+
+        [Fact]
+        public async Task EndTagHelperWritingScope_CannotEndWritingScopeWhenNoWritingScope()
         {
             // Arrange
             var viewContext = CreateViewContext();
@@ -146,11 +198,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 v.EndTagHelperWritingScope();
             });
 
-            // Act
+            // Act & Assert
-            var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => page.ExecuteAsync());
-                                () => page.ExecuteAsync());
-
-            // Assert
             Assert.Equal("There is no active writing scope to end.", ex.Message);
         }
 
@@ -159,12 +208,10 @@ namespace Microsoft.AspNet.Mvc.Razor
         {
             // Arrange
             var viewContext = CreateViewContext();
-
-            // Act
             var page = CreatePage(v =>
             {
                 v.HtmlEncoder = new HtmlTestEncoder();
-                v.StartTagHelperWritingScope();
+                v.StartTagHelperWritingScope(encoder: null);
                 v.Write("Hello World!");
                 var returnValue = v.EndTagHelperWritingScope();
 
@@ -172,6 +219,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 var content = Assert.IsType<DefaultTagHelperContent>(returnValue);
                 Assert.Equal("HtmlEncode[[Hello World!]]", content.GetContent());
             });
+
+            // Act & Assert
             await page.ExecuteAsync();
         }
 
@@ -186,11 +235,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 v.DefineSection("qux", _nullRenderAsyncDelegate);
             });
 
-            // Act
+            // Act & Assert
-            var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => page.ExecuteAsync());
-                                () => page.ExecuteAsync());
-
-            // Assert
             Assert.Equal("Section 'qux' is already defined.", ex.Message);
         }
 
@@ -227,10 +273,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 ex = Assert.Throws<InvalidOperationException>(() => v.RenderSection("bar"));
             });
 
-            // Act
+            // Act & Assert
             await page.ExecuteAsync();
-
-            // Assert
             Assert.Equal("RenderSection invocation in '/Views/TestPath/Test.cshtml' is invalid. " +
                 "RenderSection can only be called from a layout page.",
                 ex.Message);
@@ -250,10 +294,8 @@ namespace Microsoft.AspNet.Mvc.Razor
                 { "baz", _nullRenderAsyncDelegate }
             };
 
-            // Act
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => page.ExecuteAsync());
-
-            // Assert
             Assert.Equal("Section 'bar' is not defined in path '/Views/TestPath/Test.cshtml'.", ex.Message);
         }
 
@@ -265,9 +307,9 @@ namespace Microsoft.AspNet.Mvc.Razor
             {
                 v.Path = "/Views/TestPath/Test.cshtml";
             });
-
-            // Act and Assert
             page.ExecuteAsync();
+
+            // Act & Assert
             ExceptionAssert.Throws<InvalidOperationException>(() => page.IsSectionDefined("foo"),
                 "IsSectionDefined invocation in '/Views/TestPath/Test.cshtml' is invalid." +
                 " IsSectionDefined can only be called from a layout page.");
@@ -337,12 +379,12 @@ namespace Microsoft.AspNet.Mvc.Razor
                 { "header", _nullRenderAsyncDelegate }
             };
 
-            // Act
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(page.ExecuteAsync);
-
+            Assert.Equal(
-            // Assert
+                "RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
-            Assert.Equal("RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
+                " The section 'header' has already been rendered.",
-                " The section 'header' has already been rendered.", ex.Message);
+                ex.Message);
         }
 
         [Fact]
@@ -361,12 +403,12 @@ namespace Microsoft.AspNet.Mvc.Razor
                 { "header", _nullRenderAsyncDelegate }
             };
 
-            // Act
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(page.ExecuteAsync);
-
+            Assert.Equal(
-            // Assert
+                "RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
-            Assert.Equal("RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
+                " The section 'header' has already been rendered.",
-                " The section 'header' has already been rendered.", ex.Message);
+                ex.Message);
         }
 
         [Fact]
@@ -385,12 +427,12 @@ namespace Microsoft.AspNet.Mvc.Razor
                 { "header", _nullRenderAsyncDelegate }
             };
 
-            // Act
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(page.ExecuteAsync);
-
+            Assert.Equal(
-            // Assert
+                "RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
-            Assert.Equal("RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid." +
+                " The section 'header' has already been rendered.",
-                " The section 'header' has already been rendered.", ex.Message);
+                ex.Message);
         }
 
         [Fact]
@@ -404,12 +446,12 @@ namespace Microsoft.AspNet.Mvc.Razor
                 await v.RenderSectionAsync("header");
             });
 
-            // Act
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(page.ExecuteAsync);
-
+            Assert.Equal(
-            // Assert
+                "RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid. " +
-            Assert.Equal("RenderSectionAsync invocation in '/Views/TestPath/Test.cshtml' is invalid. " +
+                "RenderSectionAsync can only be called from a layout page.",
-                "RenderSectionAsync can only be called from a layout page.", ex.Message);
+                ex.Message);
         }
 
         [Fact]
@@ -422,12 +464,10 @@ namespace Microsoft.AspNet.Mvc.Razor
             });
             page.Path = path;
             page.BodyContent = new HtmlString("some content");
-
-            // Act
             await page.ExecuteAsync();
-            var ex = Assert.Throws<InvalidOperationException>(() => page.EnsureRenderedBodyOrSections());
 
-            // Assert
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() => page.EnsureRenderedBodyOrSections());
             Assert.Equal($"RenderBody has not been called for the page at '{path}'.", ex.Message);
         }
 
@@ -446,14 +486,14 @@ namespace Microsoft.AspNet.Mvc.Razor
             {
                 { sectionName, _nullRenderAsyncDelegate }
             };
-
-            // Act
             await page.ExecuteAsync();
-            var ex = Assert.Throws<InvalidOperationException>(() => page.EnsureRenderedBodyOrSections());
 
-            // Assert
+            // Act & Assert
-            Assert.Equal("The following sections have been defined but have not been rendered by the page at " +
+            var ex = Assert.Throws<InvalidOperationException>(() => page.EnsureRenderedBodyOrSections());
-                $"'{path}': '{sectionName}'.", ex.Message);
+            Assert.Equal(
+                "The following sections have been defined but have not been rendered by the page at " +
+                $"'{path}': '{sectionName}'.",
+                ex.Message);
         }
 
         [Fact]
@@ -474,7 +514,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 { sectionB, _nullRenderAsyncDelegate },
             };
 
-            // Act and Assert
+            // Act & Assert (does not throw)
             await page.ExecuteAsync();
             page.EnsureRenderedBodyOrSections();
         }
@@ -593,7 +633,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 await p.FlushAsync();
             }, context);
 
-            // Act and Assert
+            // Act & Assert
             var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => page.ExecuteAsync());
             Assert.Equal(expected, ex.Message);
         }
@@ -923,7 +963,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 items: new Dictionary<object, object>(),
                 uniqueId: string.Empty,
                 executeChildContentAsync: () => Task.FromResult(result: true),
-                startTagHelperWritingScope: () => { },
+                startTagHelperWritingScope: _ => { },
                 endTagHelperWritingScope: () => new DefaultTagHelperContent());
 
             // Act
@@ -964,7 +1004,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 items: new Dictionary<object, object>(),
                 uniqueId: string.Empty,
                 executeChildContentAsync: () => Task.FromResult(result: true),
-                startTagHelperWritingScope: () => { },
+                startTagHelperWritingScope: _ => { },
                 endTagHelperWritingScope: () => new DefaultTagHelperContent());
 
             // Act
@@ -992,7 +1032,7 @@ namespace Microsoft.AspNet.Mvc.Razor
                 items: new Dictionary<object, object>(),
                 uniqueId: string.Empty,
                 executeChildContentAsync: () => Task.FromResult(result: true),
-                startTagHelperWritingScope: () => { },
+                startTagHelperWritingScope: _ => { },
                 endTagHelperWritingScope: () => new DefaultTagHelperContent());
 
             // Act

test/Microsoft.AspNet.Mvc.Razor.Test/TagHelpers/UrlResolutionTagHelperTest.cs

@@ -47,7 +47,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", url }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var urlHelperMock = new Mock<IUrlHelper>();
             urlHelperMock
                 .Setup(urlHelper => urlHelper.Content(It.IsAny<string>()))
@@ -103,7 +103,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", url }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var urlHelperMock = new Mock<IUrlHelper>();
             urlHelperMock
                 .Setup(urlHelper => urlHelper.Content(It.IsAny<string>()))
@@ -158,7 +158,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", url }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var urlHelperMock = new Mock<IUrlHelper>();
             urlHelperMock
                 .Setup(urlHelper => urlHelper.Content(It.IsAny<string>()))
@@ -213,7 +213,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", url }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var urlHelperMock = new Mock<IUrlHelper>();
             urlHelperMock
                 .Setup(urlHelper => urlHelper.Content(It.IsAny<string>()))
@@ -251,7 +251,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", true }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var tagHelper = new UrlResolutionTagHelper(urlHelperFactory: null, htmlEncoder: null);
 
             var context = new TagHelperContext(
@@ -288,7 +288,7 @@ namespace Microsoft.AspNet.Mvc.Razor.TagHelpers
                 {
                     { "href", new HtmlString(relativeUrl) }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var urlHelperMock = new Mock<IUrlHelper>();
             urlHelperMock
                 .Setup(urlHelper => urlHelper.Content(It.IsAny<string>()))

test/Microsoft.AspNet.Mvc.TagHelpers.Test/AnchorTagHelperTest.cs

@@ -44,7 +44,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "id", "myanchor" },
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something Else");
@@ -99,7 +99,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "a",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -148,7 +148,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "a",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -209,7 +209,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "href", "http://www.contoso.com" }
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             if (propertyName == "asp-route-")
             {
                 anchorTagHelper.RouteValues.Add("name", "value");
@@ -255,7 +255,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "a",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var expectedErrorMessage = "Cannot determine an 'href' attribute for <a>. An <a> with a specified " +
                 "'asp-route' must not have an 'asp-action' or 'asp-controller' attribute.";
 

test/Microsoft.AspNet.Mvc.TagHelpers.Test/CacheTagHelperTest.cs

@@ -740,7 +740,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 "cache",
                 new TagHelperAttributeList { { "attr", "value" } },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     TagHelperContent tagHelperContent;
                     if (!cache.TryGetValue("key1", out tagHelperContent))
@@ -806,7 +806,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             return new TagHelperOutput(
                 tagName,
                 attributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetHtmlContent(childContent);

test/Microsoft.AspNet.Mvc.TagHelpers.Test/EnvironmentTagHelperTest.cs

@@ -143,7 +143,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers.Test
             return new TagHelperOutput(
                 tagName,
                 attributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent(childContent);

test/Microsoft.AspNet.Mvc.TagHelpers.Test/FormTagHelperTest.cs

@@ -49,7 +49,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "id", "myform" },
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something Else");
@@ -116,7 +116,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -168,7 +168,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -239,7 +239,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -290,7 +290,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -357,7 +357,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "aCTiON", "my-action" },
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -397,7 +397,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "action", "my-action" },
                 },
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             if (propertyName == "asp-route-")
             {
                 formTagHelper.RouteValues.Add("name", "value");
@@ -438,7 +438,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: _ => Task.FromResult<TagHelperContent>(null));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
             var expectedErrorMessage = "Cannot determine an 'action' attribute for <form>. A <form> with a specified " +
                 "'asp-route' must not have an 'asp-action' or 'asp-controller' attribute.";
 

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ImageTagHelperTest.cs

@@ -54,7 +54,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "img",
                 outputAttributes,
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var hostingEnvironment = MakeHostingEnvironment();
             var viewContext = MakeViewContext();
             var urlHelper = new Mock<IUrlHelper>();
@@ -294,7 +295,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             return new TagHelperOutput(
                 "img",
                 attributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent(default(string));

test/Microsoft.AspNet.Mvc.TagHelpers.Test/InputTagHelperTest.cs

@@ -94,7 +94,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 originalTagName,
                 outputAttributes,
-                getChildContentAsync: useCachedResult => Task.FromResult<TagHelperContent>(result: null))
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(result: null))
             {
                 TagMode = TagMode.SelfClosing,
             };
@@ -204,7 +204,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -268,7 +268,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 originalTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -367,7 +367,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -468,7 +468,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -566,7 +566,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -675,7 +675,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -792,7 +792,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()))
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()))
             {
                 TagMode = TagMode.SelfClosing,
             };
@@ -875,7 +876,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()))
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()))
             {
                 TagMode = TagMode.SelfClosing,
             };

test/Microsoft.AspNet.Mvc.TagHelpers.Test/LabelTagHelperTest.cs

@@ -201,7 +201,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 htmlAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.AppendHtml(tagHelperOutputContent.OriginalChildContent);

test/Microsoft.AspNet.Mvc.TagHelpers.Test/LinkTagHelperTest.cs

@@ -844,7 +844,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             return new TagHelperOutput(
                 tagName,
                 attributes,
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
         }
 
         private static IHostingEnvironment MakeHostingEnvironment()

test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs

@@ -408,7 +408,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagHelperOutput.TagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     // GetChildContentAsync should not be invoked since we are setting the content below.
                     Assert.True(false);
@@ -478,7 +478,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 originalTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent(originalContent);
@@ -542,7 +542,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 originalTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent(originalContent);
@@ -574,7 +574,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName,
                 attributes,
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             tagHelperOutput.Content.SetContent(content);
 
             return tagHelperOutput;

test/Microsoft.AspNet.Mvc.TagHelpers.Test/RenderAtEndOfFormTagHelperTest.cs

@@ -51,7 +51,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "form",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (useCachedResult) =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     Assert.True(viewContext.FormContext.CanRenderAtEndOfForm);
                     foreach (var item in tagBuilderList)
@@ -103,7 +103,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
 
                     return Task.FromResult(true);
                 },
-                startTagHelperWritingScope: () => { },
+                startTagHelperWritingScope: _ => { },
                 endTagHelperWritingScope: () => new DefaultTagHelperContent());
 
             // This TagHelper will pre-execute the child content forcing the body to be cached.

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ScriptTagHelperTest.cs

@@ -847,7 +847,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             return new TagHelperOutput(
                 tagName,
                 attributes,
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
         }
 
         private static IHostingEnvironment MakeHostingEnvironment()

test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs

@@ -208,7 +208,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -297,7 +297,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.AppendHtml("Something");
@@ -401,7 +401,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.AppendHtml("Something");
@@ -489,7 +489,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -570,7 +570,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName,
                 originalAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");

test/Microsoft.AspNet.Mvc.TagHelpers.Test/TagHelperOutputExtensionsTest.cs

@@ -336,7 +336,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(outputAttributes),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var context = new TagHelperContext(
                 allAttributes,
                 items: new Dictionary<object, object>(),
@@ -436,7 +437,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var context = new TagHelperContext(
                 allAttributes,
                 items: new Dictionary<object, object>(),
@@ -458,7 +460,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.Append("Something");
@@ -492,7 +494,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { attributeName, "world2" }
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.Append("Something Else");
@@ -523,7 +525,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.Append("Something");
@@ -555,7 +557,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                     { "route-Hello", "World" },
                     { "Route-I", "Am" }
                 },
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedAttribute = new TagHelperAttribute("type", "btn");
             tagHelperOutput.Attributes.Add(expectedAttribute);
 
@@ -582,7 +585,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                     { "route-Hello", "World" },
                     { "Route-I", "Am" }
                 },
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedAttribute = new TagHelperAttribute("type", "btn");
             tagHelperOutput.Attributes.Add(expectedAttribute);
             var attributes = tagHelperOutput.Attributes
@@ -607,7 +611,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                     { "route-Hello", "World" },
                     { "Route-I", "Am" }
                 },
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedAttribute = new TagHelperAttribute("type", "btn");
             tagHelperOutput.Attributes.Add(expectedAttribute);
 
@@ -765,7 +770,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 "p",
                 outputAttributes,
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
 
             var tagBuilder = new TagBuilder("p");
             foreach (var attr in tagBuilderAttributes)
@@ -790,7 +796,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedAttribute = new TagHelperAttribute("type", "btn");
             tagHelperOutput.Attributes.Add(expectedAttribute);
 
@@ -812,7 +819,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             tagHelperOutput.Attributes.Add("class", "Hello");
 
             var tagBuilder = new TagBuilder("p");
@@ -839,7 +847,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             tagHelperOutput.Attributes.Add(originalName, "Hello");
 
             var tagBuilder = new TagBuilder("p");
@@ -860,7 +869,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
 
             var tagBuilder = new TagBuilder("p");
             var expectedAttribute = new TagHelperAttribute("visible", "val < 3");
@@ -881,7 +891,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
 
             var tagBuilder = new TagBuilder("p");
             var expectedAttribute1 = new TagHelperAttribute("class", "btn");
@@ -907,7 +918,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedAttribute = new TagHelperAttribute("class", "btn");
             tagHelperOutput.Attributes.Add(expectedAttribute);
 
@@ -928,7 +940,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var tagHelperOutput = new TagHelperOutput(
                 tagName: "p",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             var expectedOutputAttribute = new TagHelperAttribute("class", "btn");
             tagHelperOutput.Attributes.Add(expectedOutputAttribute);
 

test/Microsoft.AspNet.Mvc.TagHelpers.Test/TextAreaTagHelperTest.cs

@@ -135,7 +135,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 expectedTagName,
                 htmlAttributes,
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ValidationMessageTagHelperTest.cs

@@ -53,7 +53,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "id", "myvalidationmessage" }
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -115,7 +115,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "span",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -168,7 +168,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "span",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.AppendHtml(childContent);
@@ -227,7 +227,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 "span",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent(childContent);
@@ -268,7 +268,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "span",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);

test/Microsoft.AspNet.Mvc.TagHelpers.Test/ValidationSummaryTagHelperTest.cs

@@ -49,7 +49,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 {
                     { "class", "form-control" }
                 },
-                getChildContentAsync: useCachedResult =>
+                getChildContentAsync: (useCachedResult, encoder) =>
                 {
                     var tagHelperContent = new DefaultTagHelperContent();
                     tagHelperContent.SetContent("Something");
@@ -111,7 +111,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "div",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);
@@ -165,7 +166,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "div",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent("Content of validation summary");
@@ -213,7 +215,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "div",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent(expectedPostContent);
@@ -268,7 +271,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var output = new TagHelperOutput(
                 tagName: "div",
                 attributes: new TagHelperAttributeList(),
-                getChildContentAsync: (_) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
             output.PreContent.SetContent(expectedPreContent);
             output.Content.SetContent(expectedContent);
             output.PostContent.SetContent("Content of validation message");

test/WebSites/TagHelpersWebSite/Controllers/EncodersController.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNet.Mvc;
+
+namespace TagHelpersWebSite.Controllers
+{
+    public class EncodersController : Controller
+    {
+        public IActionResult Index()
+        {
+            ViewData["Title"] = "Using the default HTML encoder";
+            return View();
+        }
+
+        public IActionResult CustomEncoder()
+        {
+            ViewData["Title"] = "Using a custom HTML encoder";
+            return View();
+        }
+
+        public IActionResult NullEncoder()
+        {
+            ViewData["Title"] = "Using the null HTML encoder";
+            return View();
+        }
+
+        // We've defined the behavior when multiple tag helpers target the same element. But this is an extreme corner
+        // case since one tag helper even using anything but the default HTML encoder is not going to be common.
+        public IActionResult TwoEncoders()
+        {
+            ViewData["Title"] = "Using two HTML encoders";
+            return View();
+        }
+
+        // We've defined the behavior when multiple tag helpers target the same element. But this is an extreme corner
+        // case since one tag helper even using anything but the default HTML encoder is not going to be common.
+        public IActionResult ThreeEncoders()
+        {
+            ViewData["Title"] = "Using three HTML encoders";
+            return View();
+        }
+    }
+}

test/WebSites/TagHelpersWebSite/TagHelpers/CustomEncoderTagHelper.cs

@@ -0,0 +1,81 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.IO;
+using System.Text.Encodings.Web;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Razor.TagHelpers;
+
+namespace TagHelpersWebSite.TagHelpers
+{
+    [HtmlTargetElement("pre")]
+    public class CustomEncoderTagHelper : TagHelper
+    {
+        public override int Order => 1;
+
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            var encoder = new CustomEncoder();
+            var customContent = await output.GetChildContentAsync(encoder);
+
+            // Note this is very unsafe. Should always post-process content that may not be fully HTML encoded before
+            // writing it into a response. Here for example, could pass SetContent() a string and that would be
+            // HTML encoded later.
+            output.PreContent
+                .SetHtmlContent("Custom encoder: ")
+                .AppendHtml(customContent)
+                .AppendHtml("<br />");
+        }
+
+        // Simple encoder that just wraps "string" as "Custom[[string]]". Note: Lacks all parameter checks.
+        private class CustomEncoder : HtmlEncoder
+        {
+            public CustomEncoder()
+            {
+            }
+
+            public override int MaxOutputCharactersPerInputCharacter => 1;
+
+            public override string Encode(string value) => $"Custom[[{ value }]]";
+
+            public override void Encode(TextWriter output, char[] value, int startIndex, int characterCount)
+            {
+                if (characterCount == 0)
+                {
+                    return;
+                }
+
+                output.Write("Custom[[");
+                output.Write(value, startIndex, characterCount);
+                output.Write("]]");
+            }
+
+            public override void Encode(TextWriter output, string value, int startIndex, int characterCount)
+            {
+                if (characterCount == 0)
+                {
+                    return;
+                }
+
+                output.Write("Custom[[");
+                output.Write(value.Substring(startIndex, characterCount));
+                output.Write("]]");
+            }
+
+            public override unsafe int FindFirstCharacterToEncode(char* text, int textLength) => -1;
+
+            public override unsafe bool TryEncodeUnicodeScalar(
+                int unicodeScalar,
+                char* buffer,
+                int bufferLength,
+                out int numberOfCharactersWritten)
+            {
+                numberOfCharactersWritten = 0;
+
+                return false;
+            }
+
+            public override bool WillEncode(int unicodeScalar) => false;
+        }
+    }
+}

test/WebSites/TagHelpersWebSite/TagHelpers/DefaultEncoderTagHelper.cs

@@ -0,0 +1,26 @@
+// Copyright (c) .NET Foundation. 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;
+using Microsoft.AspNet.Razor.TagHelpers;
+
+namespace TagHelpersWebSite.TagHelpers
+{
+    [HtmlTargetElement("pre")]
+    [HtmlTargetElement("inner")]
+    [OutputElementHint("pre")]
+    public class DefaultEncoderTagHelper : TagHelper
+    {
+        public override int Order => 2;
+
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            var defaultContent = await output.GetChildContentAsync();
+
+            output.Content
+                .SetHtmlContent("Default encoder: ")
+                .AppendHtml(defaultContent);
+            output.TagName = "pre";
+        }
+    }
+}

test/WebSites/TagHelpersWebSite/TagHelpers/NullEncoderTagHelper.cs

@@ -0,0 +1,26 @@
+// Copyright (c) .NET Foundation. 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;
+using Microsoft.AspNet.Razor.TagHelpers;
+
+namespace TagHelpersWebSite.TagHelpers
+{
+    [HtmlTargetElement("pre")]
+    public class NullEncoderTagHelper : TagHelper
+    {
+        public override int Order => 3;
+
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            var nullContent = await output.GetChildContentAsync(NullHtmlEncoder.Default);
+
+            // Note this is very unsafe. Should always post-process content that may not be fully HTML encoded before
+            // writing it into a response. Here for example, could pass SetContent() a string and that would be
+            // HTML encoded later.
+            output.PostContent
+                .SetHtmlContent("<br />Null encoder: ")
+                .AppendHtml(nullContent);
+        }
+    }
+}

test/WebSites/TagHelpersWebSite/Views/Encoders/CustomEncoder.cshtml

@@ -0,0 +1,9 @@
+@addTagHelper TagHelpersWebSite.TagHelpers.CustomEncoderTagHelper, TagHelpersWebSite
+
+@{
+    var count = 0;
+    var innerCount = 0;
+}
+
+<pre>@($"Outer knows <b>{ ++count } < 4</b>")
+<inner>@($"Inner knows <b>{ ++innerCount } < 4</b>")</inner></pre>

test/WebSites/TagHelpersWebSite/Views/Encoders/Index.cshtml

@@ -0,0 +1,9 @@
+@addTagHelper TagHelpersWebSite.TagHelpers.DefaultEncoderTagHelper, TagHelpersWebSite
+
+@{
+    var count = 0;
+    var innerCount = 0;
+}
+
+<pre>@($"Outer knows <b>{ ++count } < 4</b>")
+<inner>@($"Inner knows <b>{ ++innerCount } < 4</b>")</inner></pre>

test/WebSites/TagHelpersWebSite/Views/Encoders/NullEncoder.cshtml

@@ -0,0 +1,9 @@
+@addTagHelper TagHelpersWebSite.TagHelpers.NullEncoderTagHelper, TagHelpersWebSite
+
+@{
+    var count = 0;
+    var innerCount = 0;
+}
+
+<pre>@($"Outer knows <b>{ ++count } < 4</b>")
+<inner>@($"Inner knows <b>{ ++innerCount } < 4</b>")</inner></pre>

test/WebSites/TagHelpersWebSite/Views/Encoders/ThreeEncoders.cshtml

@@ -0,0 +1,11 @@
+@addTagHelper TagHelpersWebSite.TagHelpers.CustomEncoderTagHelper, TagHelpersWebSite
+@addTagHelper TagHelpersWebSite.TagHelpers.DefaultEncoderTagHelper, TagHelpersWebSite
+@addTagHelper TagHelpersWebSite.TagHelpers.NullEncoderTagHelper, TagHelpersWebSite
+
+@{
+    var count = 0;
+    var innerCount = 0;
+}
+
+<pre>@($"Outer knows <b>{ ++count } < 4</b>")
+<inner>@($"Inner knows <b>{ ++innerCount } < 4</b>")</inner></pre>

test/WebSites/TagHelpersWebSite/Views/Encoders/TwoEncoders.cshtml

@@ -0,0 +1,10 @@
+@addTagHelper TagHelpersWebSite.TagHelpers.CustomEncoderTagHelper, TagHelpersWebSite
+@addTagHelper TagHelpersWebSite.TagHelpers.NullEncoderTagHelper, TagHelpersWebSite
+
+@{
+    var count = 0;
+    var innerCount = 0;
+}
+
+<pre>@($"Outer knows <b>{ ++count } < 4</b>")
+<inner>@($"Inner knows <b>{ ++innerCount } < 4</b>")</inner></pre>

test/WebSites/TagHelpersWebSite/Views/Encoders/_Layout.cshtml

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>@ViewData["Title"] - My MVC 6 Application</title>
+    </head>
+    <body>
+        <h1>MVC 6 - @ViewData["Title"]</h1>
+        <div>
+            @RenderBody()
+        </div>
+    </body>
+</html>

test/WebSites/TagHelpersWebSite/Views/Encoders/_ViewImports.cshtml

@@ -0,0 +1 @@
+@removeTagHelper "TagHelpersWebSite.TagHelpers.RootViewStartTagHelper, TagHelpersWebSite"

test/WebSites/TagHelpersWebSite/Views/Encoders/_ViewStart.cshtml

@@ -0,0 +1,3 @@
+@{
+    Layout = "_Layout.cshtml";
+}

test/WebSites/TagHelpersWebSite/project.json

@@ -1,6 +1,8 @@
 {
   "compilationOptions": {
-    "emitEntryPoint": true
+    "allowUnsafe": true,
+    "emitEntryPoint": true,
+    "warningsAsErrors": true
   },
   "commands": {
     "web": "TagHelpersWebSite"

test/WebSites/TagHelpersWebSite/wwwroot/web.config

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <system.webServer>
+    <handlers>
+      <add name="httpPlatformHandler" path="*" verb="*" modules="httpPlatformHandler" resourceType="Unspecified" />
+    </handlers>
+    <httpPlatform processPath="%DNX_PATH%" arguments="%DNX_ARGS%" forwardWindowsAuthToken="false" startupTimeLimit="3600" />
+  </system.webServer>
+</configuration>