Add ITagHelperComponent

Addresses aspnet/Mvc#5728

src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperRunner.cs

@@ -14,7 +14,7 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
     public class TagHelperRunner
     {
         /// <summary>
-        /// Calls the <see cref="ITagHelper.ProcessAsync"/> method on <see cref="ITagHelper"/>s.
+        /// Calls the <see cref="ITagHelperComponent.ProcessAsync"/> method on <see cref="ITagHelper"/>s.
         /// </summary>
         /// <param name="executionContext">Contains information associated with running <see cref="ITagHelper"/>s.
         /// </param>

src/Microsoft.AspNetCore.Razor.Runtime/TagHelpers/ITagHelper.cs

@@ -1,41 +1,13 @@
 // 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;
-
 namespace Microsoft.AspNetCore.Razor.TagHelpers
 {
     /// <summary>
     /// Contract used to filter matching HTML elements.
+    /// Marker interface for <see cref="TagHelper"/>s.
     /// </summary>
-    public interface ITagHelper
+    public interface ITagHelper : ITagHelperComponent
     {
-        /// <summary>
-        /// When a set of<see cref= "ITagHelper" /> s are executed, their<see cref="Init(TagHelperContext)"/>'s
-        /// are first invoked in the specified <see cref="Order"/>; then their
-        /// <see cref="ProcessAsync(TagHelperContext, TagHelperOutput)"/>'s are invoked in the specified
-        /// <see cref="Order"/>. Lower values are executed first.
-        /// </summary>
-        int Order { get; }
-
-        /// <summary>
-        /// Initializes the <see cref="ITagHelper"/> with the given <paramref name="context"/>. Additions to
-        /// <see cref="TagHelperContext.Items"/> should be done within this method to ensure they're added prior to
-        /// executing the children.
-        /// </summary>
-        /// <param name="context">Contains information associated with the current HTML tag.</param>
-        /// <remarks>When more than one <see cref="ITagHelper"/> runs on the same element,
-        /// <see cref="M:TagHelperOutput.GetChildContentAsync"/> may be invoked prior to <see cref="ProcessAsync"/>.
-        /// </remarks>
-        void Init(TagHelperContext context);
-
-        /// <summary>
-        /// Asynchronously executes the <see cref="ITagHelper"/> with the given <paramref name="context"/> and
-        /// <paramref name="output"/>.
-        /// </summary>
-        /// <param name="context">Contains information associated with the current HTML tag.</param>
-        /// <param name="output">A stateful HTML element used to generate an HTML tag.</param>
-        /// <returns>A <see cref="Task"/> that on completion updates the <paramref name="output"/>.</returns>
-        Task ProcessAsync(TagHelperContext context, TagHelperOutput output);
     }
 }

src/Microsoft.AspNetCore.Razor.Runtime/TagHelpers/ITagHelperComponent.cs

@@ -0,0 +1,41 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Razor.TagHelpers
+{
+    /// <summary>
+    /// Contract used to modify an HTML element. 
+    /// </summary>
+    public interface ITagHelperComponent
+    {
+        /// <summary>
+        /// When a set of <see cref="ITagHelperComponent"/>s are executed, their <see cref="Init(TagHelperContext)"/>'s
+        /// are first invoked in the specified <see cref="Order"/>; then their
+        /// <see cref="ProcessAsync(TagHelperContext, TagHelperOutput)"/>'s are invoked in the specified
+        /// <see cref="Order"/>. Lower values are executed first.
+        /// </summary>
+        int Order { get; }
+
+        /// <summary>
+        /// Initializes the <see cref="ITagHelperComponent"/> with the given <paramref name="context"/>. Additions to
+        /// <see cref="TagHelperContext.Items"/> should be done within this method to ensure they're added prior to
+        /// executing the children.
+        /// </summary>
+        /// <param name="context">Contains information associated with the current HTML tag.</param>
+        /// <remarks>When more than one <see cref="ITagHelperComponent"/> runs on the same element,
+        /// <see cref="M:TagHelperOutput.GetChildContentAsync"/> may be invoked prior to <see cref="ProcessAsync"/>.
+        /// </remarks>
+        void Init(TagHelperContext context);
+
+        /// <summary>
+        /// Asynchronously executes the <see cref="ITagHelperComponent"/> with the given <paramref name="context"/> and
+        /// <paramref name="output"/>.
+        /// </summary>
+        /// <param name="context">Contains information associated with the current HTML tag.</param>
+        /// <param name="output">A stateful HTML element used to generate an HTML tag.</param>
+        /// <returns>A <see cref="Task"/> that on completion updates the <paramref name="output"/>.</returns>
+        Task ProcessAsync(TagHelperContext context, TagHelperOutput output);
+    }
+}

src/Microsoft.AspNetCore.Razor.Runtime/TagHelpers/TagHelper.cs

@@ -7,15 +7,28 @@
 namespace Microsoft.AspNetCore.Razor.TagHelpers
 {
     /// <summary>
-    /// Class used to filter matching HTML elements.
+    /// An abstract base class for <see cref="ITagHelper"/>.
     /// </summary>
     public abstract class TagHelper : ITagHelper
     {
-        /// <inheritdoc />
+        /// <summary>
+        /// When a set of <see cref="ITagHelper"/>s are executed, their <see cref="Init(TagHelperContext)"/>'s
+        /// are first invoked in the specified <see cref="Order"/>; then their
+        /// <see cref="ProcessAsync(TagHelperContext, TagHelperOutput)"/>'s are invoked in the specified
+        /// <see cref="Order"/>. Lower values are executed first.
+        /// </summary>
         /// <remarks>Default order is <c>0</c>.</remarks>
         public virtual int Order { get; } = 0;
 
-        /// <inheritdoc />
+        /// <summary>
+        /// Initializes the <see cref="ITagHelper"/> with the given <paramref name="context"/>. Additions to
+        /// <see cref="TagHelperContext.Items"/> should be done within this method to ensure they're added prior to
+        /// executing the children.
+        /// </summary>
+        /// <param name="context">Contains information associated with the current HTML tag.</param>
+        /// <remarks>When more than one <see cref="ITagHelper"/> runs on the same element,
+        /// <see cref="M:TagHelperOutput.GetChildContentAsync"/> may be invoked prior to <see cref="ProcessAsync"/>.
+        /// </remarks>
         public virtual void Init(TagHelperContext context)
         {
         }

src/Microsoft.AspNetCore.Razor.Runtime/TagHelpers/TagHelperComponent.cs

@@ -0,0 +1,40 @@
+// 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.Extensions.Internal;
+
+namespace Microsoft.AspNetCore.Razor.TagHelpers
+{
+    /// <summary>
+    /// An abstract base class for <see cref="ITagHelperComponent"/>.
+    /// </summary>
+    public abstract class TagHelperComponent : ITagHelperComponent
+    {
+        /// <inheritdoc />
+        /// <remarks>Default order is <c>0</c>.</remarks>
+        public virtual int Order => 0;
+
+        /// <inheritdoc />
+        public virtual void Init(TagHelperContext context)
+        {
+        }
+
+        /// <summary>
+        /// Synchronously executes the <see cref="ITagHelperComponent"/> with the given <paramref name="context"/> and
+        /// <paramref name="output"/>.
+        /// </summary>
+        /// <param name="context">Contains information associated with the current HTML tag.</param>
+        /// <param name="output">A stateful HTML element used to generate an HTML tag.</param>
+        public virtual void Process(TagHelperContext context, TagHelperOutput output)
+        {
+        }
+
+        /// <inheritdoc />
+        public virtual Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            Process(context, output);
+            return TaskCache.CompletedTask;
+        }
+    }
+}