Add crosslinks to toc: in docset.yml

docs/_docset.yml

@@ -129,6 +129,9 @@ toc:
       - file: req.md
       - folder: nested
       - file: cross-links.md
+        children:
+          - title: "Getting Started Guide"
+            crosslink: docs-content://get-started/introduction.md
       - file: custom-highlighters.md
       - hidden: archive.md
       - hidden: landing-page.md
@@ -153,4 +156,4 @@ toc:
           - file: bar.md
           - folder: baz
             children:
-              - file: qux.md
+              - file: qux.md

docs/configure/content-set/navigation.md

@@ -72,12 +72,38 @@ cross_links:
   - docs-content
 ```
 
+#### Adding cross-links in Markdown content
+
 To link to a document in the `docs-content` repository, you would write the link as follows:
 
-```
+```markdown
 [Link to docs-content doc](docs-content://directory/another-directory/file.md)
 ```
 
+You can also link to specific anchors within the document:
+
+```markdown
+[Link to specific section](docs-content://directory/file.md#section-id)
+```
+
+#### Adding cross-links in navigation
+
+Cross-links can also be included in navigation structures. When creating a `toc.yml` file or defining navigation in `docset.yml`, you can add cross-links as follows:
+
+```yaml
+toc:
+  - file: index.md
+  - title: External Documentation
+    crosslink: docs-content://directory/file.md
+  - folder: local-section
+    children:
+      - file: index.md
+      - title: API Reference
+        crosslink: elasticsearch://api/index.html
+```
+
+Cross-links in navigation will be automatically resolved during the build process, maintaining consistent linking between related documentation across repositories.
+
 ### `exclude`
 
 Files to exclude from the TOC. Supports glob patterns.

src/Elastic.ApiExplorer/Landing/LandingNavigationItem.cs

@@ -33,6 +33,7 @@ public class LandingNavigationItem : IApiGroupingNavigationItem<ApiLanding, INav
 	public IReadOnlyCollection<INavigationItem> NavigationItems { get; set; } = [];
 	public INodeNavigationItem<INavigationModel, INavigationItem>? Parent { get; set; }
 	public int NavigationIndex { get; set; }
+	public bool IsCrossLink => false; // API landing items are never cross-links
 	public string Url { get; }
 	public bool Hidden => false;
 
@@ -83,6 +84,7 @@ public abstract class ApiGroupingNavigationItem<TGroupingModel, TNavigationItem>
 	public bool Hidden => false;
 	/// <inheritdoc />
 	public int NavigationIndex { get; set; }
+	public bool IsCrossLink => false; // API grouping items are never cross-links
 
 	/// <inheritdoc />
 	public int Depth => 0;
@@ -141,6 +143,7 @@ public class EndpointNavigationItem(ApiEndpoint endpoint, IRootNavigationItem<IA
 
 	/// <inheritdoc />
 	public int NavigationIndex { get; set; }
+	public bool IsCrossLink => false; // API endpoint items are never cross-links
 
 	/// <inheritdoc />
 	public int Depth => 0;

src/Elastic.ApiExplorer/Operations/OperationNavigationItem.cs

@@ -70,5 +70,6 @@ IApiGroupingNavigationItem<IApiGroupingModel, INavigationItem> parent
 	public INodeNavigationItem<INavigationModel, INavigationItem>? Parent { get; set; }
 
 	public int NavigationIndex { get; set; }
+	public bool IsCrossLink => false; // API operations are never cross-links
 
 }

src/Elastic.Documentation.Configuration/Assembler/AssemblyConfiguration.cs

@@ -31,9 +31,9 @@ public static AssemblyConfiguration Deserialize(string yaml, bool skipPrivateRep
 				config.ReferenceRepositories[name] = repository;
 			}
 
-			// if we are not running in CI, and we are skipping private repositories, and we can locate the solution directory. build the local docs-content repository
-			if (string.IsNullOrWhiteSpace(Environment.GetEnvironmentVariable("CI"))
-				&& skipPrivateRepositories
+			// If we are skipping private repositories, and we can locate the solution directory. include the local docs-content repository
+			// this allows us to test new docset features as part of the assembler build
+			if (skipPrivateRepositories
 				&& config.ReferenceRepositories.TryGetValue("docs-builder", out var docsContentRepository)
 				&& Paths.GetSolutionDirectory() is { } solutionDir
 			)

src/Elastic.Documentation.Configuration/Builder/TableOfContentsConfiguration.cs

@@ -6,6 +6,7 @@
 using System.Runtime.InteropServices;
 using Elastic.Documentation.Configuration.Plugins.DetectionRules.TableOfContents;
 using Elastic.Documentation.Configuration.TableOfContents;
+using Elastic.Documentation.Links;
 using Elastic.Documentation.Navigation;
 using YamlDotNet.RepresentationModel;
 
@@ -129,6 +130,8 @@ private IReadOnlyCollection<ITocItem> ReadChildren(YamlStreamReader reader, KeyV
 	private IEnumerable<ITocItem>? ReadChild(YamlStreamReader reader, YamlMappingNode tocEntry, string parentPath)
 	{
 		string? file = null;
+		string? crossLink = null;
+		string? title = null;
 		string? folder = null;
 		string[]? detectionRules = null;
 		TableOfContentsConfiguration? toc = null;
@@ -148,6 +151,19 @@ private IReadOnlyCollection<ITocItem> ReadChildren(YamlStreamReader reader, KeyV
 					hiddenFile = key == "hidden";
 					file = ReadFile(reader, entry, parentPath);
 					break;
+				case "title":
+					title = reader.ReadString(entry);
+					break;
+				case "crosslink":
+					hiddenFile = false;
+					crossLink = reader.ReadString(entry);
+					// Validate crosslink URI early
+					if (!CrossLinkValidator.IsValidCrossLink(crossLink, out var errorMessage))
+					{
+						reader.EmitError(errorMessage!, tocEntry);
+						crossLink = null; // Reset to prevent further processing
+					}
+					break;
 				case "folder":
 					folder = ReadFolder(reader, entry, parentPath);
 					parentPath += $"{Path.DirectorySeparatorChar}{folder}";
@@ -165,6 +181,22 @@ private IReadOnlyCollection<ITocItem> ReadChildren(YamlStreamReader reader, KeyV
 			}
 		}
 
+		// Validate that crosslink entries have titles
+		if (crossLink is not null && string.IsNullOrWhiteSpace(title))
+		{
+			reader.EmitError($"Cross-link entries must have a 'title' specified. Cross-link: {crossLink}", tocEntry);
+			return null;
+		}
+
+		// Validate that standalone titles (without content) are not allowed
+		if (!string.IsNullOrWhiteSpace(title) &&
+			file is null && crossLink is null && folder is null && toc is null &&
+			(detectionRules is null || detectionRules.Length == 0))
+		{
+			reader.EmitError($"Table of contents entries with only a 'title' are not allowed. Entry must specify content (file, crosslink, folder, or toc). Title: '{title}'", tocEntry);
+			return null;
+		}
+
 		if (toc is not null)
 		{
 			foreach (var f in toc.Files)
@@ -199,6 +231,11 @@ private IReadOnlyCollection<ITocItem> ReadChildren(YamlStreamReader reader, KeyV
 			return [new FileReference(this, path, hiddenFile, children ?? [])];
 		}
 
+		if (crossLink is not null)
+		{
+			return [new CrossLinkReference(this, crossLink, title, hiddenFile, children ?? [])];
+		}
+
 		if (folder is not null)
 		{
 			if (children is null)

src/Elastic.Documentation.Configuration/TableOfContents/ITocItem.cs

@@ -14,6 +14,9 @@ public interface ITocItem
 public record FileReference(ITableOfContentsScope TableOfContentsScope, string RelativePath, bool Hidden, IReadOnlyCollection<ITocItem> Children)
 	: ITocItem;
 
+public record CrossLinkReference(ITableOfContentsScope TableOfContentsScope, string CrossLinkUri, string? Title, bool Hidden, IReadOnlyCollection<ITocItem> Children)
+	: ITocItem;
+
 public record FolderReference(ITableOfContentsScope TableOfContentsScope, string RelativePath, IReadOnlyCollection<ITocItem> Children)
 	: ITocItem;
 

src/Elastic.Documentation.Site/Navigation/INavigationItem.cs

@@ -34,6 +34,9 @@ public interface INavigationItem
 	bool Hidden { get; }
 
 	int NavigationIndex { get; set; }
+
+	/// Gets whether this navigation item is a cross-link to another repository.
+	bool IsCrossLink { get; }
 }
 
 /// Represents a leaf node in the navigation tree with associated model data.

src/Elastic.Documentation.Site/Navigation/_TocTreeNav.cshtml

@@ -79,10 +79,11 @@
 	}
 	else if (item is ILeafNavigationItem<INavigationModel> leaf)
 	{
+		var hasSameTopLevelGroup = !leaf.IsCrossLink && (Model.IsPrimaryNavEnabled && leaf.NavigationRoot.Id == Model.RootNavigationId || true);
 		<li class="flex group/li pr-8 @(isTopLevel ? "font-semibold mt-6" : "mt-4")">
 			<a
 				href="@leaf.Url"
-				@Htmx.GetNavHxAttributes(Model.IsPrimaryNavEnabled && leaf.NavigationRoot.Id == Model.RootNavigationId || true)
+				@Htmx.GetNavHxAttributes(hasSameTopLevelGroup)
 				class="sidebar-link grow group-[.current]/li:text-blue-elastic!"
 			>
 				@leaf.NavigationTitle

src/Elastic.Documentation/Links/CrossLinkValidator.cs

@@ -0,0 +1,69 @@
+// 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 System.Collections.Immutable;
+
+namespace Elastic.Documentation.Links;
+
+/// <summary>
+/// Utility class for validating and identifying cross-repository links
+/// </summary>
+public static class CrossLinkValidator
+{
+	/// <summary>
+	/// URI schemes that are excluded from being treated as cross-repository links.
+	/// These are standard web/protocol schemes that should not be processed as crosslinks.
+	/// </summary>
+	private static readonly ImmutableHashSet<string> ExcludedSchemes =
+		ImmutableHashSet.Create(StringComparer.OrdinalIgnoreCase,
+			"http", "https", "ftp", "file", "tel", "jdbc", "mailto");
+
+	/// <summary>
+	/// Validates that a URI string is a valid cross-repository link.
+	/// </summary>
+	/// <param name="uriString">The URI string to validate</param>
+	/// <param name="errorMessage">Error message if validation fails</param>
+	/// <returns>True if valid crosslink, false otherwise</returns>
+	public static bool IsValidCrossLink(string? uriString, out string? errorMessage)
+	{
+		errorMessage = null;
+
+		if (string.IsNullOrWhiteSpace(uriString))
+		{
+			errorMessage = "Cross-link entries must specify a non-empty URI";
+			return false;
+		}
+
+		if (!Uri.TryCreate(uriString, UriKind.Absolute, out var uri))
+		{
+			errorMessage = $"Cross-link URI '{uriString}' is not a valid absolute URI format";
+			return false;
+		}
+
+		if (ExcludedSchemes.Contains(uri.Scheme))
+		{
+			errorMessage = $"Cross-link URI '{uriString}' cannot use standard web/protocol schemes ({string.Join(", ", ExcludedSchemes)}). Use cross-repository schemes like 'docs-content://', 'kibana://', etc.";
+			return false;
+		}
+
+		return true;
+	}
+
+	/// <summary>
+	/// Determines if a URI is a cross-repository link (for identification purposes).
+	/// This is more permissive than validation and is used by the Markdown parser.
+	/// </summary>
+	/// <param name="uri">The URI to check</param>
+	/// <returns>True if this should be treated as a crosslink</returns>
+	public static bool IsCrossLink(Uri? uri) =>
+		uri != null
+		&& !ExcludedSchemes.Contains(uri.Scheme)
+		&& !uri.IsFile
+		&& !string.IsNullOrEmpty(uri.Scheme);
+
+	/// <summary>
+	/// Gets the list of excluded URI schemes for reference
+	/// </summary>
+	public static IReadOnlySet<string> GetExcludedSchemes() => ExcludedSchemes;
+}

src/Elastic.Markdown/DocumentationGenerator.cs

@@ -97,7 +97,7 @@ public DocumentationGenerator(
 	public async Task ResolveDirectoryTree(Cancel ctx)
 	{
 		_logger.LogInformation("Resolving tree");
-		await DocumentationSet.Tree.Resolve(ctx);
+		await DocumentationSet.ResolveDirectoryTree(ctx);
 		_logger.LogInformation("Resolved tree");
 	}
 

src/Elastic.Markdown/IO/DocumentationSet.cs

@@ -222,6 +222,10 @@ private void UpdateNavigationIndex(IReadOnlyCollection<INavigationItem> navigati
 					var fileIndex = Interlocked.Increment(ref navigationIndex);
 					fileNavigationItem.NavigationIndex = fileIndex;
 					break;
+				case CrossLinkNavigationItem crossLinkNavigationItem:
+					var crossLinkIndex = Interlocked.Increment(ref navigationIndex);
+					crossLinkNavigationItem.NavigationIndex = crossLinkIndex;
+					break;
 				case DocumentationGroup documentationGroup:
 					var groupIndex = Interlocked.Increment(ref navigationIndex);
 					documentationGroup.NavigationIndex = groupIndex;
@@ -241,6 +245,9 @@ private static IReadOnlyCollection<INavigationItem> CreateNavigationLookup(INavi
 		if (item is ILeafNavigationItem<INavigationModel> leaf)
 			return [leaf];
 
+		if (item is CrossLinkNavigationItem crossLink)
+			return [crossLink];
+
 		if (item is INodeNavigationItem<INavigationModel, INavigationItem> node)
 		{
 			var items = node.NavigationItems.SelectMany(CreateNavigationLookup);
@@ -254,6 +261,8 @@ public static (string, INavigationItem)[] Pairs(INavigationItem item)
 	{
 		if (item is FileNavigationItem f)
 			return [(f.Model.CrossLink, item)];
+		if (item is CrossLinkNavigationItem cl)
+			return [(cl.Url, item)]; // Use the URL as the key for cross-links
 		if (item is DocumentationGroup g)
 		{
 			var index = new List<(string, INavigationItem)>
@@ -365,9 +374,27 @@ void ValidateExists(string from, string to, IReadOnlyDictionary<string, string?>
 		return FlatMappedFiles.GetValueOrDefault(relativePath);
 	}
 
-	public async Task ResolveDirectoryTree(Cancel ctx) =>
+	public async Task ResolveDirectoryTree(Cancel ctx)
+	{
 		await Tree.Resolve(ctx);
 
+		// Validate cross-repo links in navigation
+		try
+		{
+			await NavigationCrossLinkValidator.ValidateNavigationCrossLinksAsync(
+				Tree,
+				LinkResolver,
+				(msg) => Context.EmitError(Context.ConfigurationPath, msg),
+				ctx
+			);
+		}
+		catch (Exception e)
+		{
+			// Log the error but don't fail the build
+			Context.EmitError(Context.ConfigurationPath, $"Error validating cross-links in navigation: {e.Message}");
+		}
+	}
+
 	private DocumentationFile CreateMarkDownFile(IFileInfo file, BuildContext context)
 	{
 		var relativePath = Path.GetRelativePath(SourceDirectory.FullName, file.FullName);

src/Elastic.Markdown/IO/Navigation/CrossLinkNavigationItem.cs

@@ -0,0 +1,39 @@
+// 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 System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using Elastic.Documentation.Site.Navigation;
+
+namespace Elastic.Markdown.IO.Navigation;
+
+[DebuggerDisplay("CrossLink: {Url}")]
+public record CrossLinkNavigationItem : ILeafNavigationItem<INavigationModel>
+{
+	// Override Url accessor to use ResolvedUrl if available
+	string INavigationItem.Url => ResolvedUrl ?? Url;
+	public CrossLinkNavigationItem(string url, string title, DocumentationGroup group, bool hidden = false)
+	{
+		_url = url;
+		NavigationTitle = title;
+		Parent = group;
+		NavigationRoot = group.NavigationRoot;
+		Hidden = hidden;
+	}
+
+	public INodeNavigationItem<INavigationModel, INavigationItem>? Parent { get; set; }
+	public IRootNavigationItem<INavigationModel, INavigationItem> NavigationRoot { get; }
+	// Original URL from the cross-link
+	private readonly string _url;
+
+	// Store resolved URL for rendering
+	public string? ResolvedUrl { get; set; }
+
+	// Implement the INavigationItem.Url property to use ResolvedUrl if available
+	public string Url => ResolvedUrl ?? _url; public string NavigationTitle { get; }
+	public int NavigationIndex { get; set; }
+	public bool Hidden { get; }
+	public bool IsCrossLink => true; // This is always a cross-link
+	public INavigationModel Model => null!; // Cross-link has no local model
+}