Add methods to TagBuilder (#6287)

Addresses #5689

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Rendering/TagBuilder.cs

@@ -298,37 +298,69 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
                 throw new ArgumentNullException(nameof(encoder));
             }
 
-            switch (TagRenderMode)
+            WriteTo(this, writer, encoder, TagRenderMode);
+        }
+
+        /// <summary>
+        /// Returns an <see cref="IHtmlContent"/> that renders the body.
+        /// </summary>
+        /// <returns>An <see cref="IHtmlContent"/> that renders the body.</returns>
+        public IHtmlContent RenderBody() => _innerHtml;
+
+        /// <summary>
+        /// Returns an <see cref="IHtmlContent"/> that renders the start tag.
+        /// </summary>
+        /// <returns>An <see cref="IHtmlContent"/> that renders the start tag.</returns>
+        public IHtmlContent RenderStartTag() => new RenderTagHtmlContent(this, TagRenderMode.StartTag);
+
+        /// <summary>
+        /// Returns an <see cref="IHtmlContent"/> that renders the end tag.
+        /// </summary>
+        /// <returns>An <see cref="IHtmlContent"/> that renders the end tag.</returns>
+        public IHtmlContent RenderEndTag() => new RenderTagHtmlContent(this, TagRenderMode.EndTag);
+
+        /// <summary>
+        /// Returns an <see cref="IHtmlContent"/> that renders the self-closing tag.
+        /// </summary>
+        /// <returns>An <see cref="IHtmlContent"/> that renders the self-closing tag.</returns>
+        public IHtmlContent RenderSelfClosingTag() => new RenderTagHtmlContent(this, TagRenderMode.SelfClosing);
+
+        private static void WriteTo(
+            TagBuilder tagBuilder,
+            TextWriter writer,
+            HtmlEncoder encoder,
+            TagRenderMode tagRenderMode)
+        {
+            switch (tagRenderMode)
             {
                 case TagRenderMode.StartTag:
                     writer.Write("<");
-                    writer.Write(TagName);
+                    writer.Write(tagBuilder.TagName);
-                    AppendAttributes(writer, encoder);
+                    tagBuilder.AppendAttributes(writer, encoder);
                     writer.Write(">");
                     break;
                 case TagRenderMode.EndTag:
                     writer.Write("</");
-                    writer.Write(TagName);
+                    writer.Write(tagBuilder.TagName);
                     writer.Write(">");
                     break;
                 case TagRenderMode.SelfClosing:
                     writer.Write("<");
-                    writer.Write(TagName);
+                    writer.Write(tagBuilder.TagName);
-                    AppendAttributes(writer, encoder);
+                    tagBuilder.AppendAttributes(writer, encoder);
                     writer.Write(" />");
                     break;
                 default:
                     writer.Write("<");
-                    writer.Write(TagName);
+                    writer.Write(tagBuilder.TagName);
-                    AppendAttributes(writer, encoder);
+                    tagBuilder.AppendAttributes(writer, encoder);
                     writer.Write(">");
-                    if (_innerHtml != null)
+                    if (tagBuilder._innerHtml != null)
                     {
-                        _innerHtml.WriteTo(writer, encoder);
+                        tagBuilder._innerHtml.WriteTo(writer, encoder);
                     }
-
                     writer.Write("</");
-                    writer.Write(TagName);
+                    writer.Write(tagBuilder.TagName);
                     writer.Write(">");
                     break;
             }
@@ -343,6 +375,23 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             }
         }
 
+        private class RenderTagHtmlContent : IHtmlContent
+        {
+            private readonly TagBuilder _tagBuilder;
+            private readonly TagRenderMode _tagRenderMode;
+
+            public RenderTagHtmlContent(TagBuilder tagBuilder, TagRenderMode tagRenderMode)
+            {
+                _tagBuilder = tagBuilder;
+                _tagRenderMode = tagRenderMode;
+            }
+
+            public void WriteTo(TextWriter writer, HtmlEncoder encoder)
+            {
+                TagBuilder.WriteTo(_tagBuilder, writer, encoder, _tagRenderMode);
+            }
+        }
+
         private static class Html401IdUtil
         {
             public static bool IsAsciiLetter(char testChar)

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/TagBuilderTest.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.TestCommon;
 using Microsoft.Extensions.WebEncoders.Testing;
 using Xunit;
 
@@ -169,5 +170,89 @@ namespace Microsoft.AspNetCore.Mvc.Core.Rendering
             Assert.False(tagBuilder.HasInnerHtml);
             Assert.NotNull(innerHtml);
         }
+
+        [Fact]
+        public void RenderStartTag_RendersExpectedStartTag()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+
+            // Act
+            var tag = tagBuilder.RenderStartTag();
+
+            // Assert
+            Assert.Equal("<p>", HtmlContentUtilities.HtmlContentToString(tag));
+        }
+
+        [Fact]
+        public void RenderStartTag_RendersExpectedStartTag_TagBuilderRendersAsExpected()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+            tagBuilder.TagRenderMode = TagRenderMode.EndTag;
+
+            // Act
+            var tag = tagBuilder.RenderStartTag();
+
+            // Assert
+            Assert.Equal("<p>", HtmlContentUtilities.HtmlContentToString(tag));
+            Assert.Equal("</p>", HtmlContentUtilities.HtmlContentToString(tagBuilder));
+        }
+
+        [Fact]
+        public void RenderEndTag_RendersExpectedEndTag()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+
+            // Act
+            var tag = tagBuilder.RenderEndTag();
+
+            // Assert
+            Assert.Equal("</p>", HtmlContentUtilities.HtmlContentToString(tag));
+        }
+
+        [Fact]
+        public void RenderEndTag_RendersExpectedEndTag_TagBuilderRendersAsExpected()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+            tagBuilder.TagRenderMode = TagRenderMode.Normal;
+
+            // Act
+            var tag = tagBuilder.RenderEndTag();
+
+            // Assert
+            Assert.Equal("</p>", HtmlContentUtilities.HtmlContentToString(tag));
+            Assert.Equal("<p></p>", HtmlContentUtilities.HtmlContentToString(tagBuilder));
+        }
+
+        [Fact]
+        public void RenderSelfClosingTag_RendersExpectedSelfClosingTag()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+
+            // Act
+            var tag = tagBuilder.RenderSelfClosingTag();
+
+            // Assert
+            Assert.Equal("<p />", HtmlContentUtilities.HtmlContentToString(tag));
+
+        }
+
+        [Fact]
+        public void RenderBody_RendersExpectedBody()
+        {
+            // Arrange
+            var tagBuilder = new TagBuilder("p");
+            tagBuilder.InnerHtml.AppendHtml("<span>Hello</span>");
+
+            // Act
+            var tag = tagBuilder.RenderBody();
+
+            // Assert
+            Assert.Equal("<span>Hello</span>", HtmlContentUtilities.HtmlContentToString(tag));
+        }
     }
 }