Add TagName to TagHelperContext

Addresses #1065

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

@@ -74,7 +74,7 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
             _tagHelpers = new List<ITagHelper>();
             _allAttributes = new TagHelperAttributeList();
 
-            Context = new TagHelperContext(_allAttributes, items, uniqueId);
+            Context = new TagHelperContext(tagName, _allAttributes, items, uniqueId);
             Output = new TagHelperOutput(tagName, new TagHelperAttributeList(), GetChildContentAsync)
             {
                 TagMode = tagMode
@@ -242,7 +242,7 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
             _perEncoderChildContent?.Clear();
             _childContent = null;
 
-            Context.Reinitialize(Items, uniqueId);
+            Context.Reinitialize(tagName, Items, uniqueId);
             Output.Reinitialize(tagName, tagMode);
         }
 

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

@@ -13,6 +13,28 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
     {
         private readonly TagHelperAttributeList _allAttributes;
 
+        /// <summary>
+        /// Instantiates a new <see cref="TagHelperContext"/>.
+        /// </summary>
+        /// <param name="tagName">The parsed HTML tag name of the element.</param>
+        /// <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>
+        public TagHelperContext(
+            string tagName,
+            TagHelperAttributeList allAttributes,
+            IDictionary<object, object> items,
+            string uniqueId) : this(allAttributes, items, uniqueId)
+        {
+            if (tagName == null)
+            {
+                throw new ArgumentNullException(nameof(tagName));
+            }
+
+            TagName = tagName;
+        }
+
         /// <summary>
         /// Instantiates a new <see cref="TagHelperContext"/>.
         /// </summary>
@@ -45,6 +67,11 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
             UniqueId = uniqueId;
         }
 
+        /// <summary>
+        /// The parsed HTML tag name of the element.
+        /// </summary>
+        public string TagName { get; private set; }
+
         /// <summary>
         /// Every attribute associated with the current HTML element.
         /// </summary>
@@ -64,6 +91,18 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
         /// </summary>
         public string UniqueId { get; private set; }
 
+        /// <summary>
+        /// Clears the <see cref="TagHelperContext"/> and updates its state with the provided values.
+        /// </summary>
+        /// <param name="tagName">The HTML tag name to use.</param>
+        /// <param name="items">The <see cref="IDictionary{Object, Object}"/> to use.</param>
+        /// <param name="uniqueId">The unique id to use.</param>
+        public void Reinitialize(string tagName, IDictionary<object, object> items, string uniqueId)
+        {
+            TagName = tagName;
+            Reinitialize(items, uniqueId);
+        }
+
         /// <summary>
         /// Clears the <see cref="TagHelperContext"/> and updates its state with the provided values.
         /// </summary>

test/Microsoft.AspNetCore.Razor.Runtime.Test/Runtime/TagHelpers/TagHelperExecutionContextTest.cs

@@ -138,6 +138,7 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
             // Assert
             var context = executionContext.Context;
             var attribute = Assert.Single(context.AllAttributes);
+            Assert.Equal(tagName, context.TagName);
             Assert.Equal(attribute.Name, "Another attribute");
             Assert.Equal(updatedUniqueId, context.UniqueId);
             Assert.Same(updatedItems, context.Items);

test/Microsoft.AspNetCore.Razor.Runtime.Test/TagHelpers/TagHelperContextTest.cs

@@ -13,6 +13,7 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
         public void Reinitialize_AllowsContextToBeReused()
         {
             // Arrange
+            var tagName = "test";
             var initialUniqueId = "123";
             var expectedUniqueId = "456";
             var initialItems = new Dictionary<object, object>
@@ -27,19 +28,49 @@ namespace Microsoft.AspNetCore.Razor.TagHelpers
             {
                 { "name", "value" }
             };
-            var context = new TagHelperContext(initialAttributes, initialItems, initialUniqueId);
+            var context = new TagHelperContext(
+                tagName,
+                initialAttributes, 
+                initialItems, 
+                initialUniqueId);
 
             // Act
-            context.Reinitialize(expectedItems, expectedUniqueId);
+            context.Reinitialize(tagName, expectedItems, expectedUniqueId);
 
             // Assert
+            Assert.Equal(tagName, context.TagName);
             Assert.Same(expectedItems, context.Items);
             Assert.Equal(expectedUniqueId, context.UniqueId);
             Assert.Empty(context.AllAttributes);
         }
 
         [Fact]
-        public void Constructor_SetsProperties_AsExpected()
+        public void Constructor_SetsProperties_AsExpected_WithTagName()
+        {
+            // Arrange
+            var expectedItems = new Dictionary<object, object>
+            {
+                { "test-entry", 1234 }
+            };
+
+            // Act
+            var context = new TagHelperContext(
+                tagName: "test",
+                allAttributes: new TagHelperAttributeList(),
+                items: expectedItems,
+                uniqueId: string.Empty);
+
+            // Assert
+            Assert.Equal("test", context.TagName);
+            Assert.NotNull(context.Items);
+            Assert.Same(expectedItems, context.Items);
+            var item = Assert.Single(context.Items);
+            Assert.Equal("test-entry", (string)item.Key, StringComparer.Ordinal);
+            Assert.Equal(1234, item.Value);
+        }
+
+        [Fact]
+        public void Constructor_SetsProperties_AsExpected_WithoutTagName()
         {
             // Arrange
             var expectedItems = new Dictionary<object, object>