Add TagHelperComponentTagHelper

Addresses #5728

src/Microsoft.AspNetCore.Mvc.Razor.Host/MvcRazorTemplateEngine.cs

@@ -52,6 +52,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                 writer.WriteLine("@inject global::Microsoft.AspNetCore.Mvc.IUrlHelper Url");
                 writer.WriteLine("@inject global::Microsoft.AspNetCore.Mvc.ViewFeatures.IModelExpressionProvider ModelExpressionProvider");
                 writer.WriteLine("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResolutionTagHelper, Microsoft.AspNetCore.Mvc.Razor");
+                writer.WriteLine("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor");
+                writer.WriteLine("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor");
                 writer.Flush();
 
                 stream.Position = 0;

src/Microsoft.AspNetCore.Mvc.Razor/Internal/MvcRazorLoggerExtensions.cs

@@ -21,6 +21,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         private static readonly Action<ILogger, string, string, Exception> _viewLookupCacheHit;
         private static readonly Action<ILogger, string, Exception> _precompiledViewFound;
 
+        private static readonly Action<ILogger, string, Exception> _tagHelperComponentInitialized;
+        private static readonly Action<ILogger, string, Exception> _tagHelperComponentProcessed;
+
         static MvcRazorLoggerExtensions()
         {
             _razorFileToCodeCompilationStart = LoggerMessage.Define<string>(
@@ -57,6 +60,16 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
                 LogLevel.Debug,
                 2,
                 "Compilation of the generated code for the Razor file at '{FilePath}' completed in {ElapsedMilliseconds}ms.");
+
+            _tagHelperComponentInitialized = LoggerMessage.Define<string>(
+                LogLevel.Debug,
+                2,
+                "Tag helper component '{ComponentName}' initialized.");
+
+            _tagHelperComponentProcessed = LoggerMessage.Define<string>(
+                LogLevel.Debug,
+                3,
+                "Tag helper component '{ComponentName}' processed.");
         }
 
         public static void RazorFileToCodeCompilationStart(this ILogger logger, string filePath)
@@ -95,6 +108,16 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             _generatedCodeToAssemblyCompilationStart(logger, filePath, null);
         }
 
+        public static void TagHelperComponentInitialized(this ILogger logger, string componentName)
+        {
+            _tagHelperComponentInitialized(logger, componentName, null);
+        }
+
+        public static void TagHelperComponentProcessed(this ILogger logger, string componentName)
+        {
+            _tagHelperComponentProcessed(logger, componentName, null);
+        }
+
         public static void GeneratedCodeToAssemblyCompilationEnd(this ILogger logger, string filePath, long startTimestamp)
         {
             // Don't log if logging wasn't enabled at start of request as time will be wildly wrong.

src/Microsoft.AspNetCore.Mvc.Razor/TagHelpers/BodyTagHelper.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.Collections.Generic;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    /// <summary>
+    /// A <see cref="TagHelperComponentTagHelper"/> targeting the &lt;body&gt; HTML element.
+    /// </summary>
+    [HtmlTargetElement("body")]
+    public class BodyTagHelper : TagHelperComponentTagHelper
+    {
+        /// <summary>
+        /// Creates a new <see cref="BodyTagHelper"/>.
+        /// </summary>
+        /// <param name="components">The list of <see cref="ITagHelperComponent"/>.</param>
+        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
+        public BodyTagHelper(IEnumerable<ITagHelperComponent> components, ILoggerFactory loggerFactory)
+            : base(components, loggerFactory)
+        {
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor/TagHelpers/HeadTagHelper.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.Collections.Generic;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    /// <summary>
+    /// A <see cref="TagHelperComponentTagHelper"/> targeting the &lt;head&gt; HTML element.
+    /// </summary>
+    [HtmlTargetElement("head")]
+    public class HeadTagHelper : TagHelperComponentTagHelper
+    {
+        /// <summary>
+        /// Creates a new <see cref="HeadTagHelper"/>.
+        /// </summary>
+        /// <param name="components">The list of <see cref="ITagHelperComponent"/>.</param>
+        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
+        public HeadTagHelper(IEnumerable<ITagHelperComponent> components, ILoggerFactory loggerFactory)
+            : base(components, loggerFactory)
+        {
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor/TagHelpers/TagHelperComponentTagHelper.cs

@@ -0,0 +1,69 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc.Razor.Internal;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    public abstract class TagHelperComponentTagHelper : TagHelper
+    {
+        private readonly ILogger _logger;
+
+        private IEnumerable<ITagHelperComponent> _components;
+
+        /// <summary>
+        /// Creates a new <see cref="TagHelperComponentTagHelper"/>.
+        /// </summary>
+        /// <param name="components">The list of <see cref="ITagHelperComponent"/>.</param>
+        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
+        public TagHelperComponentTagHelper(IEnumerable<ITagHelperComponent> components,
+            ILoggerFactory loggerFactory)
+        {
+            if (components == null)
+            {
+                throw new ArgumentNullException(nameof(components));
+            }
+
+            if (loggerFactory == null)
+            {
+                throw new ArgumentNullException(nameof(loggerFactory));
+            }
+
+            _components = components;
+            _logger = loggerFactory.CreateLogger(GetType());
+        }
+
+        /// <inheritdoc />
+        public override void Init(TagHelperContext context)
+        {
+            _components = _components.OrderBy(p => p.Order);
+            foreach (var component in _components)
+            {
+                component.Init(context);
+                if (_logger.IsEnabled(LogLevel.Debug))
+                {
+                    _logger.TagHelperComponentInitialized(component.GetType().FullName);
+                }
+            }
+        }
+
+        /// <inheritdoc />
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            foreach (var component in _components)
+            {
+                await component.ProcessAsync(context, output);
+                if (_logger.IsEnabled(LogLevel.Debug))
+                {
+                    _logger.TagHelperComponentProcessed(component.GetType().FullName);
+                }
+            }
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.FunctionalTests/TagHelperComponentTagHelperTest.cs

@@ -0,0 +1,71 @@
+// 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.Net;
+using System.Net.Http;
+using System.Reflection;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests
+{
+    public class TagHelperComponentTagHelperTest : IClassFixture<MvcTestFixture<RazorWebSite.Startup>>
+    {
+        private static readonly Assembly _resourcesAssembly = typeof(TagHelperComponentTagHelperTest).GetTypeInfo().Assembly;
+
+        public TagHelperComponentTagHelperTest(MvcTestFixture<RazorWebSite.Startup> fixture)
+        {
+            Client = fixture.Client;
+        }
+
+        public HttpClient Client { get; }
+
+        [Fact]
+        public async Task InjectsTestHeadTagHelperComponent()
+        {
+            // Arrange
+            var url = "http://localhost/TagHelperComponent/GetHead";
+            var request = new HttpRequestMessage(HttpMethod.Get, url);
+            var outputFile = "compiler/resources/RazorWebSite.TagHelperComponent.Head.html";
+            var expectedContent =
+                await ResourceFile.ReadResourceAsync(_resourcesAssembly, outputFile, sourceFile: false);
+
+            // Act
+            var response = await Client.SendAsync(request);
+            var responseContent = await response.Content.ReadAsStringAsync();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+#if GENERATE_BASELINES
+            ResourceFile.UpdateFile(_resourcesAssembly, outputFile, expectedContent, responseContent);
+#else
+            Assert.Equal(expectedContent, responseContent, ignoreLineEndingDifferences: true);
+#endif
+        }
+
+        [Fact]
+        public async Task InjectsTestBodyTagHelperComponent()
+        {
+            // Arrange
+            var url = "http://localhost/TagHelperComponent/GetBody";
+            var request = new HttpRequestMessage(HttpMethod.Get, url);
+            var outputFile = "compiler/resources/RazorWebSite.TagHelperComponent.Body.html";
+            var expectedContent =
+                await ResourceFile.ReadResourceAsync(_resourcesAssembly, outputFile, sourceFile: false);
+
+            // Act
+            var response = await Client.SendAsync(request);
+            var responseContent = await response.Content.ReadAsStringAsync();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+#if GENERATE_BASELINES
+            ResourceFile.UpdateFile(_resourcesAssembly, outputFile, expectedContent, responseContent);
+#else
+            Assert.Equal(expectedContent, responseContent, ignoreLineEndingDifferences: true);
+#endif
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/RazorWebSite.TagHelperComponent.Body.html

@@ -0,0 +1,3 @@
+<body inject="true">
+Hello from Body Tag Helper Component
+<script>'This was injected!!'</script></body>

test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/RazorWebSite.TagHelperComponent.Head.html

@@ -0,0 +1,3 @@
+<head inject="true">
+Hello from Head Tag Helper Component
+<script>'This was injected!!'</script></head>

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/MvcRazorTemplateEngineTest.cs

@@ -81,9 +81,13 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Host
             var importContent = GetContent(imports)
                 .Split(new[] { Environment.NewLine }, StringSplitOptions.None)
                 .Where(line => line.StartsWith("@addTagHelper"));
-            var addTagHelper = Assert.Single(importContent);
-            Assert.Equal("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResolutionTagHelper, Microsoft.AspNetCore.Mvc.Razor",
-                addTagHelper);
+
+            Assert.Contains("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResolutionTagHelper, Microsoft.AspNetCore.Mvc.Razor",
+                importContent);
+            Assert.Contains("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor",
+                importContent);
+            Assert.Contains("@addTagHelper Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor",
+                importContent);
         }
 
         [Fact]

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Basic.cs

@@ -74,6 +74,14 @@ System.Object ModelExpressionProvider = null;
         ))();
         ((System.Action)(() => {
 System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResolutionTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
         }
         ))();
         }

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Basic.mappings.txt

@@ -1,10 +1,10 @@
 Source Location: (13:0,13 [4] TestFiles/Input/Basic.cshtml)
 |logo|
-Generated Location: (2329:85,13 [4] )
+Generated Location: (2691:93,13 [4] )
 |logo|
 
 Source Location: (43:2,5 [21] TestFiles/Input/Basic.cshtml)
 |Html.Input("SomeKey")|
-Generated Location: (2413:90,6 [21] )
+Generated Location: (2775:98,6 [21] )
 |Html.Input("SomeKey")|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Inject.cs

@@ -82,6 +82,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 MyApp __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Inject.mappings.txt

@@ -1,10 +1,10 @@
 Source Location: (28:1,8 [5] TestFiles/Input/Inject.cshtml)
 |MyApp|
-Generated Location: (2174:84,0 [5] )
+Generated Location: (2536:92,0 [5] )
 |MyApp|
 
 Source Location: (34:1,14 [14] TestFiles/Input/Inject.cshtml)
 |MyPropertyName|
-Generated Location: (2276:88,14 [14] )
+Generated Location: (2638:96,14 [14] )
 |MyPropertyName|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/InjectWithModel.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 MyModel __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/InjectWithModel.mappings.txt

@@ -1,25 +1,25 @@
 Source Location: (7:0,7 [7] TestFiles/Input/InjectWithModel.cshtml)
 |MyModel|
-Generated Location: (2091:79,0 [7] )
+Generated Location: (2453:87,0 [7] )
 |MyModel|
 
 Source Location: (24:1,8 [5] TestFiles/Input/InjectWithModel.cshtml)
 |MyApp|
-Generated Location: (2181:83,0 [5] )
+Generated Location: (2543:91,0 [5] )
 |MyApp|
 
 Source Location: (30:1,14 [14] TestFiles/Input/InjectWithModel.cshtml)
 |MyPropertyName|
-Generated Location: (2283:87,14 [14] )
+Generated Location: (2645:95,14 [14] )
 |MyPropertyName|
 
 Source Location: (54:2,8 [17] TestFiles/Input/InjectWithModel.cshtml)
 |MyService<TModel>|
-Generated Location: (2367:91,0 [17] )
+Generated Location: (2729:99,0 [17] )
 |MyService<TModel>|
 
 Source Location: (72:2,26 [4] TestFiles/Input/InjectWithModel.cshtml)
 |Html|
-Generated Location: (2481:95,14 [4] )
+Generated Location: (2843:103,14 [4] )
 |Html|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/InjectWithSemicolon.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 MyModel __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/InjectWithSemicolon.mappings.txt

@@ -1,45 +1,45 @@
 Source Location: (7:0,7 [7] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyModel|
-Generated Location: (2095:79,0 [7] )
+Generated Location: (2457:87,0 [7] )
 |MyModel|
 
 Source Location: (24:1,8 [5] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyApp|
-Generated Location: (2185:83,0 [5] )
+Generated Location: (2547:91,0 [5] )
 |MyApp|
 
 Source Location: (30:1,14 [14] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyPropertyName|
-Generated Location: (2287:87,14 [14] )
+Generated Location: (2649:95,14 [14] )
 |MyPropertyName|
 
 Source Location: (58:2,8 [17] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyService<TModel>|
-Generated Location: (2371:91,0 [17] )
+Generated Location: (2733:99,0 [17] )
 |MyService<TModel>|
 
 Source Location: (76:2,26 [4] TestFiles/Input/InjectWithSemicolon.cshtml)
 |Html|
-Generated Location: (2485:95,14 [4] )
+Generated Location: (2847:103,14 [4] )
 |Html|
 
 Source Location: (93:3,8 [5] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyApp|
-Generated Location: (2559:99,0 [5] )
+Generated Location: (2921:107,0 [5] )
 |MyApp|
 
 Source Location: (99:3,14 [15] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyPropertyName2|
-Generated Location: (2661:103,14 [15] )
+Generated Location: (3023:111,14 [15] )
 |MyPropertyName2|
 
 Source Location: (129:4,8 [17] TestFiles/Input/InjectWithSemicolon.cshtml)
 |MyService<TModel>|
-Generated Location: (2746:107,0 [17] )
+Generated Location: (3108:115,0 [17] )
 |MyService<TModel>|
 
 Source Location: (147:4,26 [5] TestFiles/Input/InjectWithSemicolon.cshtml)
 |Html2|
-Generated Location: (2860:111,14 [5] )
+Generated Location: (3222:119,14 [5] )
 |Html2|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Model.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 System.Collections.IEnumerable __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/Model.mappings.txt

@@ -1,5 +1,5 @@
 Source Location: (7:0,7 [30] TestFiles/Input/Model.cshtml)
 |System.Collections.IEnumerable|
-Generated Location: (2104:79,0 [30] )
+Generated Location: (2466:87,0 [30] )
 |System.Collections.IEnumerable|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/ModelExpressionTagHelper.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 DateTime __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/ModelExpressionTagHelper.mappings.txt

@@ -1,40 +1,40 @@
 Source Location: (7:0,7 [8] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |DateTime|
-Generated Location: (2101:79,0 [8] )
+Generated Location: (2463:87,0 [8] )
 |DateTime|
 
 Source Location: (33:2,14 [91] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Microsoft.AspNetCore.Mvc.Razor.InputTestTagHelper, Microsoft.AspNetCore.Mvc.Razor.Host.Test|
-Generated Location: (2222:83,30 [91] )
+Generated Location: (2584:91,30 [91] )
 |Microsoft.AspNetCore.Mvc.Razor.InputTestTagHelper, Microsoft.AspNetCore.Mvc.Razor.Host.Test|
 
 Source Location: (140:3,14 [102] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Microsoft.AspNetCore.Mvc.Razor.DictionaryPrefixTestTagHelper, Microsoft.AspNetCore.Mvc.Razor.Host.Test|
-Generated Location: (2407:87,30 [102] )
+Generated Location: (2769:95,30 [102] )
 |Microsoft.AspNetCore.Mvc.Razor.DictionaryPrefixTestTagHelper, Microsoft.AspNetCore.Mvc.Razor.Host.Test|
 
 Source Location: (263:5,17 [3] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Now|
-Generated Location: (3397:100,133 [3] )
+Generated Location: (3759:108,133 [3] )
 |Now|
 
 Source Location: (290:6,18 [5] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Model|
-Generated Location: (3764:106,125 [5] )
+Generated Location: (4126:114,125 [5] )
 |Model|
 
 Source Location: (322:8,19 [5] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Model|
-Generated Location: (4183:112,153 [5] )
+Generated Location: (4545:120,153 [5] )
 |Model|
 
 Source Location: (357:9,19 [4] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Hour|
-Generated Location: (4611:118,161 [4] )
+Generated Location: (4973:126,161 [4] )
 |Hour|
 
 Source Location: (378:9,40 [6] TestFiles/Input/ModelExpressionTagHelper.cshtml)
 |Minute|
-Generated Location: (4873:123,163 [6] )
+Generated Location: (5235:131,163 [6] )
 |Minute|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/MultipleModels.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 ThisShouldBeGenerated __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/MultipleModels.mappings.txt

@@ -1,10 +1,10 @@
 Source Location: (7:0,7 [21] TestFiles/Input/MultipleModels.cshtml)
 |ThisShouldBeGenerated|
-Generated Location: (2113:79,0 [21] )
+Generated Location: (2475:87,0 [21] )
 |ThisShouldBeGenerated|
 
 Source Location: (37:1,7 [30] TestFiles/Input/MultipleModels.cshtml)
 |System.Collections.IEnumerable|
-Generated Location: (2217:83,0 [30] )
+Generated Location: (2579:91,0 [30] )
 |System.Collections.IEnumerable|
 

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/_ViewImports.cs

@@ -77,6 +77,14 @@ System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.UrlResol
         }
         ))();
         ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.HeadTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
+System.Object __typeHelper = "Microsoft.AspNetCore.Mvc.Razor.TagHelpers.BodyTagHelper, Microsoft.AspNetCore.Mvc.Razor";
+        }
+        ))();
+        ((System.Action)(() => {
 IHtmlHelper<TModel> __typeHelper = null;
         }
         ))();

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/DesignTime/_ViewImports.mappings.txt

@@ -1,10 +1,10 @@
 Source Location: (8:0,8 [19] TestFiles/Input/_ViewImports.cshtml)
 |IHtmlHelper<TModel>|
-Generated Location: (2088:79,0 [19] )
+Generated Location: (2450:87,0 [19] )
 |IHtmlHelper<TModel>|
 
 Source Location: (28:0,28 [5] TestFiles/Input/_ViewImports.cshtml)
 |Model|
-Generated Location: (2204:83,14 [5] )
+Generated Location: (2566:91,14 [5] )
 |Model|
 

test/Microsoft.AspNetCore.Mvc.Razor.Test/TagHelpers/TagHelperComponentTagHelperTest.cs

@@ -0,0 +1,292 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Logging.Testing;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    public class TagHelperComponentTagHelperTest
+    {
+        [Fact]
+        public void Init_InvokesComponentsInitInCorrectOrder()
+        {
+            // Arrange            
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var incrementer = 0;
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new CallbackTagHelperComponent(
+                    order: 2,
+                    initCallback: () =>
+                    {
+                        Assert.Equal(1, incrementer);
+                        incrementer++;
+                    },
+                    processAsyncCallback: null),
+                new CallbackTagHelperComponent(
+                    order: 3,
+                    initCallback: () =>
+                    {
+                        Assert.Equal(2, incrementer);
+                        incrementer++;
+                    },
+                    processAsyncCallback: null),
+                new CallbackTagHelperComponent(
+                    order: 1,
+                    initCallback: () =>
+                    {
+                        Assert.Equal(0, incrementer);
+                        incrementer++;
+                    },
+                    processAsyncCallback: null),
+            }, NullLoggerFactory.Instance);
+
+            // Act
+            testTagHelperComponentTagHelper.Init(tagHelperContext);
+
+            // Assert
+            Assert.Equal(3, incrementer);
+        }
+
+        [Fact]
+        public async void ProcessAsync_InvokesComponentsProcessAsyncInCorrectOrder()
+        {
+            // Arrange            
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var output = new TagHelperOutput(
+                "head",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
+
+            var incrementer = 0;
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new CallbackTagHelperComponent(
+                    order: 2,
+                    initCallback: () => { },
+                    processAsyncCallback: () =>
+                    {
+                        Assert.Equal(1, incrementer);
+                        incrementer++;
+                    }),
+                new CallbackTagHelperComponent(
+                    order: 3,
+                    initCallback: () => { },
+                    processAsyncCallback: () =>
+                    {
+                        Assert.Equal(2, incrementer);
+                        incrementer++;
+                    }),
+                new CallbackTagHelperComponent(
+                    order: 1,
+                    initCallback: () => { },
+                    processAsyncCallback: () =>
+                    {
+                        Assert.Equal(0, incrementer);
+                        incrementer++;
+                    }),
+            }, NullLoggerFactory.Instance);
+
+            // Act
+            testTagHelperComponentTagHelper.Init(tagHelperContext);
+            await testTagHelperComponentTagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            Assert.Equal(3, incrementer);
+        }
+
+        [Fact]
+        public void Init_InvokesTagHelperComponentInit()
+        {
+            // Arrange            
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var output = new TagHelperOutput(
+                "head",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
+
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new TestTagHelperComponent()
+            }, NullLoggerFactory.Instance);
+
+            // Act
+            testTagHelperComponentTagHelper.Init(tagHelperContext);
+
+            // Assert
+            Assert.Equal("Value", tagHelperContext.Items["Key"]);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_InvokesTagHelperComponentProcessAsync()
+        {
+            // Arrange
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var output = new TagHelperOutput(
+                "head",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
+
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new TestTagHelperComponent()
+            }, NullLoggerFactory.Instance);
+
+            // Act
+            await testTagHelperComponentTagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert           
+            Assert.Equal("Processed", output.PostContent.GetContent());
+        }
+
+        [Fact]
+        public void Init_LogsTagHelperComponentInitialized()
+        {
+            // Arrange
+            var sink = new TestSink();
+            var loggerFactory = new TestLoggerFactory(sink, enabled: true);
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var output = new TagHelperOutput(
+                "head",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
+
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new TestTagHelperComponent()
+            }, loggerFactory);
+
+            // Act
+            testTagHelperComponentTagHelper.Init(tagHelperContext);
+
+            // Assert
+            Assert.Equal($"Tag helper component '{typeof(TestTagHelperComponent)}' initialized.", sink.Writes[0].State.ToString(), StringComparer.Ordinal);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_LogsTagHelperComponentProcessed()
+        {
+            // Arrange
+            var sink = new TestSink();
+            var loggerFactory = new TestLoggerFactory(sink, enabled: true);
+            var tagHelperContext = new TagHelperContext(
+                "head",
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+
+            var output = new TagHelperOutput(
+                "head",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(
+                    new DefaultTagHelperContent()));
+
+            var testTagHelperComponentTagHelper = new TestTagHelperComponentTagHelper(new []
+            {
+                new TestTagHelperComponent()
+            }, loggerFactory);
+
+            // Act
+            await testTagHelperComponentTagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert           
+            Assert.Equal($"Tag helper component '{typeof(TestTagHelperComponent)}' processed.", sink.Writes[0].State.ToString(), StringComparer.Ordinal);
+        }
+
+        private class TestTagHelperComponentTagHelper : TagHelperComponentTagHelper
+        {
+            public TestTagHelperComponentTagHelper(
+                IEnumerable<ITagHelperComponent> components,
+                ILoggerFactory loggerFactory)
+                : base(components, loggerFactory)
+            {
+            }
+        }
+
+        private class CallbackTagHelperComponent : ITagHelperComponent
+        {
+            private readonly Action _initCallback;
+            private readonly Action _processAsyncCallback;
+            private readonly int _order;
+
+            public CallbackTagHelperComponent(int order, Action initCallback, Action processAsyncCallback)
+            {
+                _initCallback = initCallback;
+                _processAsyncCallback = processAsyncCallback;
+                _order = order;
+            }
+
+            public int Order => _order;
+
+            public void Init(TagHelperContext context)
+            {
+                _initCallback();
+            }
+
+            public Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+            {
+                _processAsyncCallback();
+                return Task.CompletedTask;
+            }
+        }
+
+        private class TestTagHelperComponent : ITagHelperComponent
+        {
+            public int Order => 1;
+
+            public void Init(TagHelperContext context)
+            {
+                context.Items["Key"] = "Value";
+            }
+
+            public Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+            {
+                output.PostContent.AppendHtml("Processed");
+                return Task.CompletedTask;
+            }
+        }
+    }
+}

test/WebSites/RazorWebSite/Controllers/TagHelperComponentController.cs

@@ -0,0 +1,21 @@
+// 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.AspNetCore.Mvc;
+
+namespace RazorWebSite
+{
+    public class TagHelperComponentController : Controller
+    {
+        // GET: /<controller>/
+        public IActionResult GetHead()
+        {
+            return View("Head");
+        }
+
+        public IActionResult GetBody()
+        {
+            return View("Body");
+        }
+    }
+}

test/WebSites/RazorWebSite/Services/TestBodyTagHelperComponent.cs

@@ -0,0 +1,24 @@
+// 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;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace RazorWebSite
+{
+    public class TestBodyTagHelperComponent : TagHelperComponent
+    {
+        public override int Order => 1;
+
+        public override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            if (string.Equals(context.TagName, "body", StringComparison.Ordinal) && output.Attributes.ContainsName("inject"))
+            {
+                output.PostContent.AppendHtml("<script>'This was injected!!'</script>");
+            }
+
+            return Task.FromResult(0);
+        }
+    }
+}

test/WebSites/RazorWebSite/Services/TestHeadTagHelperComponent.cs

@@ -0,0 +1,24 @@
+// 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;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace RazorWebSite
+{
+    public class TestHeadTagHelperComponent : TagHelperComponent
+    {
+        public override int Order => 1;
+
+        public override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            if (string.Equals(context.TagName, "head", StringComparison.Ordinal) && output.Attributes.ContainsName("inject"))
+            {
+                output.PostContent.AppendHtml("<script>'This was injected!!'</script>");
+            }
+
+            return Task.FromResult(0);
+        }
+    }
+}

test/WebSites/RazorWebSite/Startup.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Localization;
 using Microsoft.AspNetCore.Mvc.Razor;
+using Microsoft.AspNetCore.Razor.TagHelpers;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.FileProviders;
 
@@ -20,6 +21,9 @@ namespace RazorWebSite
         {
             var updateableFileProvider = new UpdateableFileProvider();
             services.AddSingleton(updateableFileProvider);
+            services.AddSingleton<ITagHelperComponent, TestHeadTagHelperComponent>();
+            services.AddSingleton<ITagHelperComponent, TestBodyTagHelperComponent>();
+
             services
                 .AddMvc()
                 .AddRazorOptions(options =>

test/WebSites/RazorWebSite/Views/TagHelperComponent/Body.cshtml

@@ -0,0 +1,3 @@
+<body inject="true">
+Hello from Body Tag Helper Component
+</body>

test/WebSites/RazorWebSite/Views/TagHelperComponent/Head.cshtml

@@ -0,0 +1,3 @@
+<head inject="true">
+Hello from Head Tag Helper Component
+</head>