Add support for inline anchors in Markdown parsing (#331)

* Add support for inline anchors in Markdown parsing

Introduced a parser for inline anchors using `$$$` syntax and updated related components to handle and render them as HTML anchor tags. Enhanced heading slug generation to exclude inline anchors, and added comprehensive tests to ensure correct behavior.

* add documentation for inline anchors

* dotnet format

* add inline anchors to additional labels on markdown file so they can be resolved

* added tests linking to inline anchors

* dotnet format

docs/syntax/links.md

@@ -91,4 +91,15 @@ Do note that these inline anchors will be normalized.
 ## This Is A Header [What about this for an anchor!]
 ```
 
-Will result in the anchor `what-about-this-for-an-anchor`.
+Will result in the anchor `what-about-this-for-an-anchor`.
+
+
+## Inline anchors
+
+Docsbuilder temporary supports the abbility to create a linkable anchor anywhere on any document. 
+
+```markdown
+This is text and $$$this-is-an-inline-anchor$$$
+```
+
+This feature exists to aid with migration however is scheduled for removal and new content should **NOT** utilize this feature.

src/Elastic.Markdown/Helpers/SlugExtensions.cs

@@ -0,0 +1,16 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using Slugify;
+
+namespace Elastic.Markdown.Helpers;
+
+public static class SlugExtensions
+{
+	private static readonly SlugHelper _slugHelper = new();
+
+
+	public static string Slugify(this string? text) => _slugHelper.GenerateSlug(text);
+
+}

src/Elastic.Markdown/IO/MarkdownFile.cs

@@ -8,18 +8,17 @@
 using Elastic.Markdown.Myst;
 using Elastic.Markdown.Myst.Directives;
 using Elastic.Markdown.Myst.FrontMatter;
+using Elastic.Markdown.Myst.InlineParsers;
 using Elastic.Markdown.Slices;
 using Markdig;
 using Markdig.Extensions.Yaml;
 using Markdig.Syntax;
-using Slugify;
 
 namespace Elastic.Markdown.IO;
 
 
 public record MarkdownFile : DocumentationFile
 {
-	private readonly SlugHelper _slugHelper = new();
 	private string? _navigationTitle;
 
 	public MarkdownFile(IFileInfo sourceFile, IDirectoryInfo rootPath, MarkdownParser parser, BuildContext context)
@@ -151,16 +150,14 @@ private void ReadDocumentInstructions(MarkdownDocument document)
 			Collector.EmitWarning(FilePath, "Document has no title, using file name as title.");
 		}
 
-
-
 		var contents = document
 			.Where(block => block is HeadingBlock { Level: >= 2 })
 			.Cast<HeadingBlock>()
 			.Select(h => (h.GetData("header") as string, h.GetData("anchor") as string))
 			.Select(h => new PageTocItem
 			{
 				Heading = h.Item1!.Replace("`", "").Replace("*", ""),
-				Slug = _slugHelper.GenerateSlug(h.Item2 ?? h.Item1)
+				Slug = (h.Item2 ?? h.Item1).Slugify()
 			})
 			.ToList();
 		_tableOfContent.Clear();
@@ -170,8 +167,10 @@ private void ReadDocumentInstructions(MarkdownDocument document)
 		var labels = document.Descendants<DirectiveBlock>()
 			.Select(b => b.CrossReferenceName)
 			.Where(l => !string.IsNullOrWhiteSpace(l))
-			.Select(_slugHelper.GenerateSlug)
+			.Select(s => s.Slugify())
+			.Concat(document.Descendants<InlineAnchor>().Select(a => a.Anchor))
 			.ToArray();
+
 		foreach (var label in labels)
 		{
 			if (!string.IsNullOrEmpty(label))

src/Elastic.Markdown/Myst/InlineParsers/HeadingBlockWithSlugParser.cs

@@ -51,6 +51,10 @@ public override bool Close(BlockProcessor processor, Block block)
 
 			var newSlice = new StringSlice(header.ToString());
 			headerBlock.Lines.Lines[0] = new StringLine(ref newSlice);
+
+			if (header.IndexOf('$') >= 0)
+				anchor = HeadingAnchorParser.MatchAnchor().Replace(anchor.ToString(), "");
+
 			headerBlock.SetData("anchor", anchor.ToString());
 			headerBlock.SetData("header", header.ToString());
 			return base.Close(processor, block);
@@ -67,4 +71,7 @@ public static partial class HeadingAnchorParser
 
 	[GeneratedRegex(@"(?:\[[^[]+\])\s*$", RegexOptions.IgnoreCase, "en-US")]
 	public static partial Regex MatchAnchor();
+
+	[GeneratedRegex(@"\$\$\$[^\$]+\$\$\$", RegexOptions.IgnoreCase, "en-US")]
+	public static partial Regex InlineAnchors();
 }

src/Elastic.Markdown/Myst/InlineParsers/InlineAnchorParser.cs

@@ -0,0 +1,81 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using Elastic.Markdown.Helpers;
+using Markdig;
+using Markdig.Extensions.SmartyPants;
+using Markdig.Helpers;
+using Markdig.Parsers;
+using Markdig.Parsers.Inlines;
+using Markdig.Renderers;
+using Markdig.Renderers.Html;
+using Markdig.Renderers.Html.Inlines;
+using Markdig.Syntax.Inlines;
+
+namespace Elastic.Markdown.Myst.InlineParsers;
+
+public static class InlineAnchorBuilderExtensions
+{
+	public static MarkdownPipelineBuilder UseInlineAnchors(this MarkdownPipelineBuilder pipeline)
+	{
+		pipeline.Extensions.AddIfNotAlready<InlineAnchorBuilderExtension>();
+		return pipeline;
+	}
+}
+
+public class InlineAnchorBuilderExtension : IMarkdownExtension
+{
+	public void Setup(MarkdownPipelineBuilder pipeline) =>
+		pipeline.InlineParsers.InsertAfter<EmphasisInlineParser>(new InlineAnchorParser());
+
+	public void Setup(MarkdownPipeline pipeline, IMarkdownRenderer renderer) =>
+		renderer.ObjectRenderers.InsertAfter<EmphasisInlineRenderer>(new InlineAnchorRenderer());
+}
+
+public class InlineAnchorParser : InlineParser
+{
+	public InlineAnchorParser()
+	{
+		OpeningCharacters = ['$'];
+	}
+
+	public override bool Match(InlineProcessor processor, ref StringSlice slice)
+	{
+		var startPosition = processor.GetSourcePosition(slice.Start, out var line, out var column);
+		var c = slice.CurrentChar;
+
+		var span = slice.AsSpan();
+		if (!span.StartsWith("$$$"))
+			return false;
+
+		var closingStart = span[3..].IndexOf('$');
+		if (closingStart <= 0)
+			return false;
+
+		//not ending with three dollar signs
+		if (!span[(closingStart + 3)..].StartsWith("$$$"))
+			return false;
+
+		processor.Inline = new InlineAnchor { Anchor = span[3..(closingStart + 3)].ToString().Slugify() };
+
+		var sliceEnd = slice.Start + closingStart + 6;
+		while (slice.Start != sliceEnd)
+			slice.SkipChar();
+
+		return true;
+	}
+
+
+}
+
+public class InlineAnchor : LeafInline
+{
+	public required string Anchor { get; init; }
+}
+
+public class InlineAnchorRenderer : HtmlObjectRenderer<InlineAnchor>
+{
+	protected override void Write(HtmlRenderer renderer, InlineAnchor obj) =>
+		renderer.Write("<a id=\"").Write(obj.Anchor).Write("\"></a>");
+}

src/Elastic.Markdown/Myst/MarkdownParser.cs

@@ -31,13 +31,15 @@ public class MarkdownParser(
 	public static MarkdownPipeline MinimalPipeline { get; } =
 		new MarkdownPipelineBuilder()
 			.UseYamlFrontMatter()
+			.UseInlineAnchors()
 			.UseHeadingsWithSlugs()
 			.UseDirectives()
 			.Build();
 
 	public static MarkdownPipeline Pipeline { get; } =
 		new MarkdownPipelineBuilder()
 			.EnableTrackTrivia()
+			.UseInlineAnchors()
 			.UsePreciseSourceLocation()
 			.UseDiagnosticLinks()
 			.UseHeadingsWithSlugs()

src/Elastic.Markdown/Myst/SectionedHeadingRenderer.cs

@@ -1,17 +1,16 @@
 // Licensed to Elasticsearch B.V under one or more agreements.
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
+using Elastic.Markdown.Helpers;
+using Elastic.Markdown.Myst.InlineParsers;
 using Markdig.Renderers;
 using Markdig.Renderers.Html;
 using Markdig.Syntax;
-using Markdig.Syntax.Inlines;
-using Slugify;
 
 namespace Elastic.Markdown.Myst;
 
 public class SectionedHeadingRenderer : HtmlObjectRenderer<HeadingBlock>
 {
-	private readonly SlugHelper _slugHelper = new();
 	private static readonly string[] HeadingTexts =
 	[
 		"h1",
@@ -33,7 +32,11 @@ protected override void Write(HtmlRenderer renderer, HeadingBlock obj)
 		var header = obj.GetData("header") as string;
 		var anchor = obj.GetData("anchor") as string;
 
-		var slug = _slugHelper.GenerateSlug(anchor ?? header);
+		var slugTarget = (anchor ?? header) ?? string.Empty;
+		if (slugTarget.IndexOf('$') >= 0)
+			slugTarget = HeadingAnchorParser.InlineAnchors().Replace(slugTarget, "");
+
+		var slug = slugTarget.Slugify();
 
 		renderer.Write(@"<section id=""");
 		renderer.Write(slug);