Add Items bag to TagHelperContext.

- Add a an Item properties on TagHelperExecutionContext to propagate to the TagHelperContext.
- Updated TagHelperScopeManager to create CopyOnWriteDictionary item bags for created TagHelperExecutionContexts.

#238

src/Microsoft.AspNet.Razor.Runtime/NotNullArgument.cs

@@ -1,12 +0,0 @@
-// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-
-namespace Microsoft.AspNet.Razor.Runtime
-{
-    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false)]
-    internal sealed class NotNullAttribute : Attribute
-    {
-    }
-}

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/HtmlElementNameAttribute.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperContext.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {
@@ -18,15 +19,19 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// Instantiates a new <see cref="TagHelperContext"/>.
         /// </summary>
         /// <param name="allAttributes">Every attribute associated with the current HTML element.</param>
+        /// <param name="items">Collection of items used to communicate with other <see cref="ITagHelper"/>s.</param>
         /// <param name="uniqueId">The unique identifier for the source element this <see cref="TagHelperContext" /> 
         /// applies to.</param>
         /// <param name="getChildContentAsync">A delegate used to execute and retrieve the rendered child content 
         /// asynchronously.</param>
-        public TagHelperContext([NotNull] IDictionary<string, object> allAttributes,
+        public TagHelperContext(
-                                [NotNull] string uniqueId,
+            [NotNull] IDictionary<string, object> allAttributes,
-                                [NotNull] Func<Task<string>> getChildContentAsync)
+            [NotNull] IDictionary<object, object> items,
+            [NotNull] string uniqueId,
+            [NotNull] Func<Task<string>> getChildContentAsync)
         {
             AllAttributes = allAttributes;
+            Items = items;
             UniqueId = uniqueId;
             _getChildContentAsync = getChildContentAsync;
         }
@@ -36,6 +41,15 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// </summary>
         public IDictionary<string, object> AllAttributes { get; }
 
+        /// <summary>
+        /// Gets the collection of items used to communicate with other <see cref="ITagHelper"/>s.
+        /// </summary>
+        /// <remarks>
+        /// This <see cref="IDictionary{object, object}"/> is copy-on-write in order to ensure items added to this 
+        /// collection are visible only to other <see cref="ITagHelper"/>s targeting child elements.
+        /// </remarks>
+        public IDictionary<object, object> Items { get; }
+
         /// <summary>
         /// An identifier unique to the HTML element this context is for.
         /// </summary>

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperDescriptorResolver.cs

@@ -9,6 +9,7 @@ using System.Text.RegularExpressions;
 using Microsoft.AspNet.Razor.Parser;
 using Microsoft.AspNet.Razor.TagHelpers;
 using Microsoft.AspNet.Razor.Text;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperExecutionContext.cs

@@ -2,9 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {
@@ -25,6 +27,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         internal TagHelperExecutionContext(string tagName, bool selfClosing)
             : this(tagName,
                    selfClosing,
+                   items: new Dictionary<object, object>(),
                    uniqueId: string.Empty,
                    executeChildContentAsync: async () => await Task.FromResult(result: true),
                    startWritingScope: () => { },
@@ -37,18 +40,21 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// </summary>
         /// <param name="tagName">The HTML tag name in the Razor source.</param>
         /// <param name="selfClosing">
-        /// <see cref="bool"/> indicating whether or not the tag in the Razor source was self-closing.
+        /// <see cref="bool"/> indicating whether or not the tag in the Razor source was self-closing.</param>
-        /// </param>
+        /// <param name="items">The collection of items used to communicate with other 
+        /// <see cref="ITagHelper"/>s</param>
         /// <param name="uniqueId">An identifier unique to the HTML element this context is for.</param>
         /// <param name="executeChildContentAsync">A delegate used to execute the child content asynchronously.</param>
         /// <param name="startWritingScope">A delegate used to start a writing scope in a Razor page.</param>
         /// <param name="endWritingScope">A delegate used to end a writing scope in a Razor page.</param>
-        public TagHelperExecutionContext([NotNull] string tagName,
+        public TagHelperExecutionContext(
-                                         bool selfClosing,
+            [NotNull] string tagName,
-                                         [NotNull] string uniqueId,
+            bool selfClosing,
-                                         [NotNull] Func<Task> executeChildContentAsync,
+            [NotNull] IDictionary<object, object> items,
-                                         [NotNull] Action startWritingScope,
+            [NotNull] string uniqueId,
-                                         [NotNull] Func<TextWriter> endWritingScope)
+            [NotNull] Func<Task> executeChildContentAsync,
+            [NotNull] Action startWritingScope,
+            [NotNull] Func<TextWriter> endWritingScope)
         {
             _tagHelpers = new List<ITagHelper>();
             _executeChildContentAsync = executeChildContentAsync;
@@ -59,6 +65,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             AllAttributes = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
             HTMLAttributes = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
             TagName = tagName;
+            Items = items;
             UniqueId = uniqueId;
         }
 
@@ -78,6 +85,11 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             }
         }
 
+        /// <summary>
+        /// Gets the collection of items used to communicate with other <see cref="ITagHelper"/>s.
+        /// </summary>
+        public IDictionary<object, object> Items { get; }
+
         /// <summary>
         /// HTML attributes.
         /// </summary>

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperOutput.cs

@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Net;
 using System.Text;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {

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

@@ -3,6 +3,7 @@
 
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {
@@ -22,6 +23,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         {
             var tagHelperContext = new TagHelperContext(
                 executionContext.AllAttributes,
+                executionContext.Items,
                 executionContext.UniqueId,
                 executionContext.GetChildContentAsync);
             var tagHelperOutput = new TagHelperOutput(executionContext.TagName, executionContext.HTMLAttributes)

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperScopeManager.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {
@@ -35,19 +36,36 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <param name="startWritingScope">A delegate used to start a writing scope in a Razor page.</param>
         /// <param name="endWritingScope">A delegate used to end a writing scope in a Razor page.</param>
         /// <returns>A <see cref="TagHelperExecutionContext"/> to use.</returns>
-        public TagHelperExecutionContext Begin([NotNull] string tagName,
+        public TagHelperExecutionContext Begin(
-                                               bool selfClosing,
+            [NotNull] string tagName,
-                                               [NotNull] string uniqueId,
+            bool selfClosing,
-                                               [NotNull] Func<Task> executeChildContentAsync,
+            [NotNull] string uniqueId,
-                                               [NotNull] Action startWritingScope,
+            [NotNull] Func<Task> executeChildContentAsync,
-                                               [NotNull] Func<TextWriter> endWritingScope)
+            [NotNull] Action startWritingScope,
+            [NotNull] Func<TextWriter> endWritingScope)
         {
-            var executionContext = new TagHelperExecutionContext(tagName,
+            IDictionary<object, object> items;
-                                                                 selfClosing,
+
-                                                                 uniqueId,
+            // If we're not wrapped by another TagHelper, then there will not be a parentExecutionContext.
-                                                                 executeChildContentAsync,
+            if (_executionScopes.Count > 0)
-                                                                 startWritingScope,
+            {
-                                                                 endWritingScope);
+                items = new CopyOnWriteDictionary<object, object>(
+                    _executionScopes.Peek().Items,
+                    comparer: EqualityComparer<object>.Default);
+            }
+            else
+            {
+                items = new Dictionary<object, object>();
+            }
+
+            var executionContext = new TagHelperExecutionContext(
+                tagName,
+                selfClosing,
+                items,
+                uniqueId,
+                executeChildContentAsync,
+                startWritingScope,
+                endWritingScope);
 
             _executionScopes.Push(executionContext);
 

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/TagHelperTypeResolver.cs

@@ -7,6 +7,7 @@ using System.Linq;
 using System.Reflection;
 using Microsoft.AspNet.Razor.Parser;
 using Microsoft.AspNet.Razor.Text;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 {

src/Microsoft.AspNet.Razor.Runtime/project.json

@@ -2,7 +2,9 @@
     "description": "Runtime components for rendering Razor pages.",
     "version": "4.0.0-*",
     "dependencies": {
-        "Microsoft.AspNet.Razor": "4.0.0-*"
+        "Microsoft.AspNet.Razor": "4.0.0-*",
+        "Microsoft.Framework.CopyOnWriteDictionary.Internal": { "type": "build", "version": "1.0.0-*" },
+        "Microsoft.Framework.NotNullAttribute.Internal": { "type": "build", "version": "1.0.0-*" }
     },
     "frameworks": {
         "net45": { },