Don't autolink URLs used as markdown link text (#3319)

* stop autolinking links that are markdown link titles

* move nested-link guard to the renderer

The parser-level check only caught the case where the autolink URL
appeared immediately after `[`. Once any literal text intervened, the
LinkDelimiterInline walk-back missed it. Detecting nested links in the
renderer instead works for every parse shape.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Strengthen nested-anchor regression tests for #3317

Replace fragile exact-string NotContain with NotMatchRegex to catch
nested <a> regardless of attribute ordering. Add ImageInsideLinkTests
to confirm the IsImage branch is unaffected by the IsNestedInsideLink
guard.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Fabrizio Ferri Benedetti <fabri.ferribenedetti@elastic.co>
Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: 4 people

src/Elastic.Markdown/Myst/Renderers/HtmxLinkInlineRenderer.cs

@@ -18,6 +18,13 @@ protected override void Write(HtmlRenderer renderer, LinkInline link)
 	{
 		if (renderer.EnableHtmlForInline && !link.IsImage)
 		{
+			// Avoid nested <a> tags when a URL inside link text was autolinked (elastic/docs-builder#3317).
+			if (IsNestedInsideLink(link))
+			{
+				renderer.WriteChildren(link);
+				return;
+			}
+
 			if (link.GetData(nameof(ParserContext.CurrentUrlPath)) is not string)
 			{
 				base.Write(renderer, link);
@@ -107,6 +114,18 @@ private static void WriteImage(HtmlRenderer renderer, LinkInline link)
 
 	private static IHtmxAttributeProvider? GetHtmxProvider(LinkInline link) =>
 		link.GetData(nameof(IHtmxAttributeProvider)) as IHtmxAttributeProvider;
+
+	private static bool IsNestedInsideLink(LinkInline link)
+	{
+		var parent = link.Parent;
+		while (parent != null)
+		{
+			if (parent is LinkInline)
+				return true;
+			parent = parent.Parent;
+		}
+		return false;
+	}
 }
 
 public static class CustomLinkInlineRendererExtensions

tests/Elastic.Markdown.Tests/Inline/AutoLinkTests.cs

@@ -245,6 +245,58 @@ public void BothLinksWork() =>
 	public void HasNoErrors() => Collector.Diagnostics.Should().HaveCount(0);
 }
 
+// Regression test for elastic/docs-builder#3317: no nested <a> when a URL is the link text.
+public class AutoLinkInsideLinkTextTests(ITestOutputHelper output) : AutoLinkTestBase(output,
+"""
+Upload to a service like [https://gist.github.com](https://gist.github.com).
+"""
+)
+{
+	[Fact]
+	public void DoesNotCreateNestedAnchor() =>
+		Html.Should().Contain(
+			"""<a href="https://gist.github.com" target="_blank" rel="noopener noreferrer">https://gist.github.com</a>"""
+		).And.NotMatchRegex(@"<a\b[^>]*><a\b");
+
+	[Fact]
+	public void HasNoErrors() => Collector.Diagnostics.Should().HaveCount(0);
+}
+
+public class AutoLinkInsideLinkTextWithSurroundingTextTests(ITestOutputHelper output) : AutoLinkTestBase(output,
+"""
+See [the page at https://example.test.io for details](https://docs.test.io).
+"""
+)
+{
+	[Fact]
+	public void DoesNotAutolinkUrlInsideLinkText() =>
+		Html.Should().Contain(
+			"""<a href="https://docs.test.io" target="_blank" rel="noopener noreferrer">the page at https://example.test.io for details</a>"""
+		);
+
+	[Fact]
+	public void HasNoErrors() => Collector.Diagnostics.Should().HaveCount(0);
+}
+
+// Verify that image-inside-link is unaffected by the IsNestedInsideLink guard (images bypass it via the IsImage branch).
+public class ImageInsideLinkTests(ITestOutputHelper output) : InlineTest<LinkInline>(output,
+"""
+[![alt text](https://example.com/image.png)](https://example.com)
+"""
+)
+{
+	[Fact]
+	public void RendersOuterAnchor() =>
+		Html.Should().Contain("""<a href="https://example.com" target="_blank" rel="noopener noreferrer">""");
+
+	[Fact]
+	public void RendersImage() =>
+		Html.Should().Contain("<img src=\"https://example.com/image.png\"");
+
+	[Fact]
+	public void HasNoErrors() => Collector.Diagnostics.Should().HaveCount(0);
+}
+
 public class MultipleAutoLinksTests(ITestOutputHelper output) : AutoLinkTestBase(output,
 """
 First https://first.com then https://second.com and finally https://third.com are all linked.