Add autolinks rendering

docs/syntax/links.md

@@ -104,6 +104,49 @@
 [Elastic Documentation](https://www.elastic.co/guide)
 ```
 
+### Autolinks
+
+Bare `https://` URLs in text are automatically converted to clickable links.
+
+Autolinks:
+
+- Only work with `https://` URLs (not `http://`).
+- Open in a new tab.
+- Display the external link indicator.
+- Are not rendered inside code blocks or inline code.
+
+#### Examples
+
+::::{tab-set}
+
+:::{tab-item} Output
+
+- Documentation: https://example.com/docs/guide
+- Search: https://example.com/search?q=elasticsearch&page=1
+- Section link: https://example.com/page#configuration
+
+:::
+
+:::{tab-item} Markdown
+
+```markdown
+- Documentation: https://example.com/docs/guide
+- Search: https://example.com/search?q=elasticsearch&page=1
+- Section link: https://example.com/page#configuration
+```
+
+:::
+
+::::
+
+#### Hint for elastic.co/docs URLs
+
+Autolinks pointing to `elastic.co/docs` trigger a hint during build, suggesting you replace them with a [cross-repository link](#cross-repository-links) or relative link for better maintainability.
+
+For example, this autolink triggers the hint: https://www.elastic.co/docs
+
+Instead, use a cross-repository link or a relative link.
+
 ## Link formatting
 
 ### Style link text

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

@@ -0,0 +1,145 @@
+// 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.Diagnostics;
+using Markdig;
+using Markdig.Helpers;
+using Markdig.Parsers;
+using Markdig.Parsers.Inlines;
+using Markdig.Syntax;
+using Markdig.Syntax.Inlines;
+
+namespace Elastic.Markdown.Myst.InlineParsers;
+
+public static class AutoLinkBuilderExtensions
+{
+	public static MarkdownPipelineBuilder UseAutoLinks(this MarkdownPipelineBuilder pipeline)
+	{
+		pipeline.Extensions.AddIfNotAlready<AutoLinkBuilderExtension>();
+		return pipeline;
+	}
+}
+
+public class AutoLinkBuilderExtension : IMarkdownExtension
+{
+	public void Setup(MarkdownPipelineBuilder pipeline) =>
+		pipeline.InlineParsers.InsertBefore<LinkInlineParser>(new AutoLinkInlineParser());
+
+	public void Setup(MarkdownPipeline pipeline, Markdig.Renderers.IMarkdownRenderer renderer)
+	{
+		// No custom renderer needed - we create standard LinkInline objects
+		// that are rendered by HtmxLinkInlineRenderer
+	}
+}
+
+/// <summary>
+/// Parses bare https:// URLs and converts them to clickable links.
+/// URLs containing elastic.co/docs emit a hint suggesting crosslinks or relative links.
+/// </summary>
+public class AutoLinkInlineParser : InlineParser
+{
+	public AutoLinkInlineParser() => OpeningCharacters = ['h'];
+
+	public override bool Match(InlineProcessor processor, ref StringSlice slice)
+	{
+		// Must start with https://
+		var span = slice.AsSpan();
+		if (!span.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
+			return false;
+
+		// Find the end of the URL
+		var urlLength = FindUrlEnd(span);
+		if (urlLength <= "https://".Length)
+			return false; // Just "https://" with nothing after is not valid
+
+		var url = span[..urlLength].ToString();
+
+		// Get source position for proper diagnostics
+		var startPosition = slice.Start;
+		var start = processor.GetSourcePosition(startPosition, out var line, out var column);
+		var spanEnd = start + urlLength - 1;
+
+		// Create a LinkInline with the URL as both href and text
+		var linkInline = new LinkInline(url, string.Empty)
+		{
+			IsClosed = true,
+			IsAutoLink = true,
+			Span = new SourceSpan(start, spanEnd),
+			Line = line,
+			Column = column
+		};
+		_ = linkInline.AppendChild(new LiteralInline(url));
+
+		// Store context data for the renderer (same pattern as DiagnosticLinkInlineParser)
+		var context = processor.GetContext();
+		linkInline.SetData(nameof(context.CurrentUrlPath), context.CurrentUrlPath);
+		linkInline.SetData("isCrossLink", false);
+
+		processor.Inline = linkInline;
+
+		// Emit hint for elastic.co/docs URLs (after setting Inline so position is correct)
+		if (url.Contains("elastic.co/docs", StringComparison.OrdinalIgnoreCase))
+			processor.EmitHint(linkInline, "Autolink points to elastic.co/docs. Consider using a crosslink or relative link instead.");
+
+		// Advance the slice past the URL
+		var end = slice.Start + urlLength;
+		while (slice.Start < end)
+			slice.SkipChar();
+
+		return true;
+	}
+
+	/// <summary>
+	/// Finds the end of a URL in the given span, handling trailing punctuation correctly.
+	/// </summary>
+	private static int FindUrlEnd(ReadOnlySpan<char> span)
+	{
+		var length = 0;
+		var parenDepth = 0;
+		var bracketDepth = 0;
+
+		for (var i = 0; i < span.Length; i++)
+		{
+			var c = span[i];
+
+			// URL terminates at whitespace or control characters
+			if (char.IsWhiteSpace(c) || char.IsControl(c))
+				break;
+
+			// Track balanced parentheses (common in Wikipedia URLs)
+			if (c == '(')
+				parenDepth++;
+			else if (c == ')')
+			{
+				if (parenDepth > 0)
+					parenDepth--;
+				else
+					break; // Unbalanced closing paren - not part of URL
+			}
+
+			// Track balanced brackets
+			if (c == '[')
+				bracketDepth++;
+			else if (c == ']')
+			{
+				if (bracketDepth > 0)
+					bracketDepth--;
+				else
+					break; // Unbalanced closing bracket - not part of URL
+			}
+
+			// These characters end the URL (Markdown syntax)
+			if (c is '<' or '>')
+				break;
+
+			length = i + 1;
+		}
+
+		// Remove trailing punctuation that's likely sentence punctuation, not part of URL
+		while (length > 0 && span[length - 1] is '.' or ',' or ';' or ':' or '!' or '?' or '\'' or '"')
+			length--;
+
+		return length;
+	}
+}

src/Elastic.Markdown/Myst/MarkdownParser.cs

@@ -157,6 +157,7 @@ public static MarkdownPipeline Pipeline
 				.UsePreciseSourceLocation()
 				.UseFootnotes() // Must be before UseDiagnosticLinks to ensure FootnoteLinkParser is inserted correctly
 				.UseDiagnosticLinks()
+				.UseAutoLinks()
 				.UseHeadingsWithSlugs()
 				.UseEmphasisExtras(EmphasisExtraOptions.Default)
 				.UseSubstitutionInlineCode()

tests/Elastic.Markdown.Tests/Directives/AdmonitionTests.cs

@@ -186,7 +186,8 @@ public void ContainsContentWithColons()
 	{
 		var html = Html;
 		html.Should().Contain("Time: 10:30 AM");
-		html.Should().Contain("URL: https://example.com:8080/path");
+		// URL is now autolinked
+		html.Should().Contain("""URL: <a href="https://example.com:8080/path" target="_blank" rel="noopener noreferrer">https://example.com:8080/path</a>""");
 		html.Should().Contain("Configuration: key:value pairs");
 		html.Should().Contain("function test() { return &quot;hello:world&quot;; }");
 	}