feat: Add feature to reset markdig extension settings that are added by default

docs/reference/docfx-json-reference.md

@@ -199,6 +199,28 @@ Sets the max parallelism. Setting 0 (default) is the same as setting to the coun
 
 Sets the parameters for the markdown engine, value is a JSON object.
 
+For example. It can enable additional markdig extensions with following settings.
+
+```json
+{
+  "build": {
+    "markdownEngineProperties": {
+      "markdigExtensions": [
+        "advanced"
+      ]
+    }
+  }
+}
+```
+
+List of available built-in markdig extensions are available at [this URL](https://github.com/xoofx/markdig/blob/fcb56fb03701cc1a07a52769908579adb8927ee2/src/Markdig/MarkdownExtensions.cs#L537-L650).
+
+It can't remove existing markdig extensions added by docfx.
+But It can reset settings to markdig default when specifing following extension names.
+ - `AutoIdentifiers`
+ - `EmphasisExtras`
+ - `Emojis`
+
 ### `sitemap`
 
 Specifies the options for generating [sitemap.xml](https://www.sitemaps.org/protocol.html) file:

src/Docfx.MarkdigEngine.Extensions/MarkdownExtensions.cs

@@ -4,6 +4,7 @@
 using Markdig;
 using Markdig.Extensions.AutoIdentifiers;
 using Markdig.Extensions.CustomContainers;
+using Markdig.Extensions.Emoji;
 using Markdig.Extensions.EmphasisExtras;
 using Markdig.Parsers;
 
@@ -17,7 +18,7 @@ public static MarkdownPipelineBuilder UseDocfxExtensions(
     {
         return pipeline
             .UseMathematics()
-            .UseEmphasisExtras()
+            .UseEmphasisExtras(EmphasisExtraOptions.Strikethrough)
             .UseAutoIdentifiers(AutoIdentifierOptions.GitHub)
             .UseMediaLinks()
             .UsePipeTables()
@@ -56,9 +57,34 @@ public static MarkdownPipelineBuilder UseOptionalExtensions(
             return pipeline;
         }
 
+        ReplaceExistingExtensions();
+
         pipeline.Configure(string.Join("+", optionalExtensions));
 
         return pipeline;
+
+        // Some markdig extensions are added by UseDocfxExtensions with non-default settings.
+        // This methods replace these extensions with default settings.
+        void ReplaceExistingExtensions()
+        {
+            // AutoIdentifierExtension
+            if (optionalExtensions.Contains("autoidentifiers", StringComparer.OrdinalIgnoreCase))
+            {
+                pipeline.Extensions.Replace<AutoIdentifierExtension>(new AutoIdentifierExtension(AutoIdentifierOptions.Default));
+            }
+
+            // EmphasisExtraExtension
+            if (optionalExtensions.Contains("emphasisextras", StringComparer.OrdinalIgnoreCase))
+            {
+                pipeline.Extensions.Replace<EmphasisExtraExtension>(new EmphasisExtraExtension(EmphasisExtraOptions.Default));
+            }
+
+            // EmojiExtension
+            if (optionalExtensions.Contains("emojis", StringComparer.OrdinalIgnoreCase))
+            {
+                pipeline.Extensions.Replace<EmojiExtension>(new EmojiExtension(EmojiMapping.DefaultEmojisAndSmileysMapping));
+            }
+        }
     }
 
     private static MarkdownPipelineBuilder RemoveUnusedExtensions(this MarkdownPipelineBuilder pipeline)

test/Docfx.MarkdigEngine.Extensions.Tests/EmojiTest.cs

@@ -15,4 +15,20 @@ public void EmojiTestGeneral()
 
         TestUtility.VerifyMarkup(content, expected);
     }
+
+    [Fact]
+    public void EmojiTestWithSmileys()
+    {
+        var content = @":)";
+
+        // By default Docfx use `UseEmojiAndSmiley(enableSmileys:false)` setting.
+        {
+            var expected = @"<p>:)</p>";
+            TestUtility.VerifyMarkup(content, expected);
+        }
+        {
+            var expected = @"<p>😃</p>";
+            TestUtility.VerifyMarkup(content, expected, optionalExtensions: ["Emojis"]);
+        }
+    }
 }

test/Docfx.MarkdigEngine.Extensions.Tests/EmphasisExtraTest.cs

@@ -0,0 +1,69 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Xunit;
+
+namespace Docfx.MarkdigEngine.Tests;
+
+public class EmphasisExtraTest
+{
+    [Fact]
+    public void EmphasisExtraTest_Strikethrough()
+    {
+        var content = @"The following text ~~is deleted~~";
+        var expected = @"<p>The following text <del>is deleted</del></p>";
+
+        // `Strikethrough` is enabled by default.
+        TestUtility.VerifyMarkup(content, expected);
+        TestUtility.VerifyMarkup(content, expected, optionalExtensions: ["EmphasisExtras"]);
+    }
+
+    [Fact]
+    public void EmphasisExtraTest_SuperscriptAndSubscript()
+    {
+        var content = @"H~2~O is a liquid. 2^10^ is 1024";
+
+        // `Superscript` and `Subscript` are disabled by default.
+        {
+            var expected = $"<p>{content}</p>";
+            TestUtility.VerifyMarkup(content, expected);
+        }
+        {
+            var expected = @"<p>H<sub>2</sub>O is a liquid. 2<sup>10</sup> is 1024</p>";
+            TestUtility.VerifyMarkup(content, expected, optionalExtensions: ["EmphasisExtras"]);
+        }
+    }
+
+    [Fact]
+    public void EmphasisExtraTest_Inserted()
+    {
+        var content = @"++Inserted text++";
+
+        // `Inserted` is disabled by default.
+        {
+            var expected = $"<p>{content}</p>";
+            TestUtility.VerifyMarkup(content, expected);
+        }
+        {
+            var expected = @"<p><ins>Inserted text</ins></p>";
+            TestUtility.VerifyMarkup(content, expected, optionalExtensions: ["EmphasisExtras"]);
+        }
+    }
+
+    [Fact]
+    public void EmphasisExtraTest_Marked()
+    {
+        var content = @"==Marked text==";
+
+        // `Marked` is disabled by default.
+        {
+            var expected = $"<p>{content}</p>";
+            TestUtility.VerifyMarkup(content, expected);
+        }
+        {
+            var expected = @"<p><mark>Marked text</mark></p>";
+            TestUtility.VerifyMarkup(content, expected, optionalExtensions: ["EmphasisExtras"]);
+        }
+
+    }
+}