Also write the used link-index to the filesystem and add it as part of the new CheckoutResult record

src/Elastic.Documentation/Links/LinkRegistry.cs

@@ -2,6 +2,7 @@
 // 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.CodeAnalysis;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using Elastic.Documentation.Serialization;

src/tooling/docs-assembler/Cli/RepositoryCommands.cs

@@ -18,6 +18,7 @@
 using Documentation.Assembler.Navigation;
 using Documentation.Assembler.Sourcing;
 using Elastic.Documentation.Configuration.Assembler;
+using Elastic.Documentation.Links;
 using Elastic.Documentation.Tooling.Diagnostics.Console;
 using Elastic.Markdown;
 using Elastic.Markdown.Exporters;
@@ -104,9 +105,10 @@ public async Task<int> BuildAll(
 			await assembleContext.Collector.StopAsync(ctx);
 			return 1;
 		}
-
 		var cloner = new AssemblerRepositorySourcer(logger, assembleContext);
-		var checkouts = cloner.GetAll().ToArray();
+		var checkoutResult = cloner.GetAll();
+		var checkouts = checkoutResult.Checkouts.ToArray();
+
 		if (checkouts.Length == 0)
 			throw new Exception("No checkouts found");
 
@@ -123,6 +125,8 @@ public async Task<int> BuildAll(
 		var builder = new AssemblerBuilder(logger, assembleContext, navigation, htmlWriter, pathProvider, historyMapper);
 		await builder.BuildAllAsync(assembleSources.AssembleSets, ctx);
 
+		await cloner.WriteLinkRegistrySnapshot(checkoutResult.LinkRegistrySnapshot, ctx);
+
 		var sitemapBuilder = new SitemapBuilder(navigation.NavigationItems, assembleContext.WriteFileSystem, assembleContext.OutputDirectory);
 		sitemapBuilder.Generate();
 

src/tooling/docs-assembler/Sourcing/GitFacade.cs

@@ -0,0 +1,96 @@
+// 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.IO.Abstractions;
+using Elastic.Documentation.Diagnostics;
+using ProcNet;
+
+namespace Documentation.Assembler.Sourcing;
+
+
+public interface IGitRepository
+{
+	void Init();
+	string GetCurrentCommit();
+	void GitAddOrigin(string origin);
+	bool IsInitialized();
+	void Pull(string branch);
+	void Fetch(string reference);
+	void EnableSparseCheckout(string folder);
+	void DisableSparseCheckout();
+	void Checkout(string reference);
+}
+
+// This git repository implementation is optimized for pull and fetching single commits.
+// It uses `git pull --depth 1` and `git fetch --depth 1` to minimize the amount of data transferred.
+public class SingleCommitOptimizedGitRepository(DiagnosticsCollector collector, IDirectoryInfo workingDirectory) : IGitRepository
+{
+	public string GetCurrentCommit() => Capture("git", "rev-parse", "HEAD");
+
+	public void Init() => ExecIn("git", "init");
+	public bool IsInitialized() => Directory.Exists(Path.Combine(workingDirectory.FullName, ".git"));
+	public void Pull(string branch) => ExecIn("git", "pull", "--depth", "1", "--allow-unrelated-histories", "--no-ff", "origin", branch);
+	public void Fetch(string reference) => ExecIn("git", "fetch", "--no-tags", "--prune", "--no-recurse-submodules", "--depth", "1", "origin", reference);
+	public void EnableSparseCheckout(string folder) => ExecIn("git", "sparse-checkout", "set", folder);
+	public void DisableSparseCheckout() => ExecIn("git", "sparse-checkout", "disable");
+	public void Checkout(string reference) => ExecIn("git", "checkout", "--force", reference);
+
+	public void GitAddOrigin(string origin) => ExecIn("git", "remote", "add", "origin", origin);
+
+	private void ExecIn(string binary, params string[] args)
+	{
+		var arguments = new ExecArguments(binary, args)
+		{
+			WorkingDirectory = workingDirectory.FullName,
+			Environment = new Dictionary<string, string>
+			{
+				// Disable git editor prompts:
+				// There are cases where `git pull` would prompt for an editor to write a commit message.
+				// This env variable prevents that.
+				{ "GIT_EDITOR", "true" }
+			},
+		};
+		var result = Proc.Exec(arguments);
+		if (result != 0)
+			collector.EmitError("", $"Exit code: {result} while executing {binary} {string.Join(" ", args)} in {workingDirectory}");
+	}
+	private string Capture(string binary, params string[] args)
+	{
+		// Try 10 times to capture the output of the command, if it fails, we'll throw an exception on the last try
+		Exception? e = null;
+		for (var i = 0; i <= 9; i++)
+		{
+			try
+			{
+				return CaptureOutput();
+			}
+			catch (Exception ex)
+			{
+				if (ex is not null)
+					e = ex;
+			}
+		}
+
+		if (e is not null)
+			collector.EmitError("", "failure capturing stdout", e);
+
+		return string.Empty;
+
+		string CaptureOutput()
+		{
+			var arguments = new StartArguments(binary, args)
+			{
+				WorkingDirectory = workingDirectory.FullName,
+				Timeout = TimeSpan.FromSeconds(3),
+				WaitForExit = TimeSpan.FromSeconds(3),
+				ConsoleOutWriter = NoopConsoleWriter.Instance
+			};
+			var result = Proc.Start(arguments);
+			var line = result.ExitCode != 0
+				? throw new Exception($"Exit code is not 0. Received {result.ExitCode} from {binary}: {workingDirectory}")
+				: result.ConsoleOut.FirstOrDefault()?.Line ?? throw new Exception($"No output captured for {binary}: {workingDirectory}");
+			return line;
+		}
+	}
+}

src/tooling/docs-assembler/Sourcing/RepositorySourcesFetcher.cs

@@ -3,13 +3,11 @@
 // See the LICENSE file in the project root for more information
 
 using System.Collections.Concurrent;
-using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.IO.Abstractions;
 using Elastic.Documentation.Configuration.Assembler;
 using Elastic.Documentation.Diagnostics;
 using Elastic.Documentation.LinkIndex;
-using Elastic.Markdown.IO;
+using Elastic.Documentation.Links;
 using Microsoft.Extensions.Logging;
 using ProcNet;
 using ProcNet.Std;
@@ -25,29 +23,42 @@ public class AssemblerRepositorySourcer(ILoggerFactory logger, AssembleContext c
 
 	private RepositorySourcer RepositorySourcer => new(logger, context.CheckoutDirectory, context.ReadFileSystem, context.Collector);
 
-	public IReadOnlyCollection<Checkout> GetAll()
+	public CheckoutResult GetAll()
 	{
 		var fs = context.ReadFileSystem;
 		var repositories = Configuration.ReferenceRepositories.Values.Concat<Repository>([Configuration.Narrative]);
 		var checkouts = new List<Checkout>();
+		var linkRegistrySnapshotPath = Path.Combine(context.CheckoutDirectory.FullName, CheckoutResult.LinkRegistrySnapshotFileName);
+		if (!fs.File.Exists(linkRegistrySnapshotPath))
+			throw new FileNotFoundException("Link-index snapshot not found. Run the clone-all command first.", linkRegistrySnapshotPath);
+		var linkRegistrySnapshotStr = File.ReadAllText(linkRegistrySnapshotPath);
+		var linkRegistry = LinkRegistry.Deserialize(linkRegistrySnapshotStr);
 		foreach (var repo in repositories)
 		{
 			var checkoutFolder = fs.DirectoryInfo.New(Path.Combine(context.CheckoutDirectory.FullName, repo.Name));
+			IGitRepository gitFacade = new SingleCommitOptimizedGitRepository(context.Collector, checkoutFolder);
+			if (!checkoutFolder.Exists)
+			{
+				context.Collector.EmitError(checkoutFolder.FullName, $"'{repo.Name}' does not exist in link index checkout directory");
+				continue;
+			}
+			var head = gitFacade.GetCurrentCommit();
 			var checkout = new Checkout
 			{
 				Repository = repo,
 				Directory = checkoutFolder,
-				//TODO read from links.json and ensure we check out exactly that git reference
-				//+ validate that git reference belongs to the appropriate branch
-				HeadReference = Guid.NewGuid().ToString("N")
+				HeadReference = head
 			};
 			checkouts.Add(checkout);
 		}
-
-		return checkouts;
+		return new CheckoutResult
+		{
+			Checkouts = checkouts,
+			LinkRegistrySnapshot = linkRegistry
+		};
 	}
 
-	public async Task<IReadOnlyCollection<Checkout>> CloneAll(bool fetchLatest, Cancel ctx = default)
+	public async Task<CheckoutResult> CloneAll(bool fetchLatest, Cancel ctx = default)
 	{
 		_logger.LogInformation("Cloning all repositories for environment {EnvironmentName} using '{ContentSourceStrategy}' content sourcing strategy",
 			PublishEnvironment.Name,
@@ -91,8 +102,23 @@ await Task.Run(() =>
 					checkouts.Add(RepositorySourcer.CloneRef(repo.Value, gitRef, fetchLatest));
 				}, c);
 			}).ConfigureAwait(false);
-		return checkouts;
+		await File.WriteAllTextAsync(
+			Path.Combine(context.CheckoutDirectory.FullName, CheckoutResult.LinkRegistrySnapshotFileName),
+			LinkRegistry.Serialize(linkRegistry),
+			ctx
+		);
+		return new CheckoutResult
+		{
+			Checkouts = checkouts,
+			LinkRegistrySnapshot = linkRegistry
+		};
 	}
+
+	public async Task WriteLinkRegistrySnapshot(LinkRegistry linkRegistrySnapshot, Cancel ctx = default) => await File.WriteAllTextAsync(
+			Path.Combine(context.OutputDirectory.FullName, "docs", CheckoutResult.LinkRegistrySnapshotFileName),
+			LinkRegistry.Serialize(linkRegistrySnapshot),
+			ctx
+		);
 }
 
 
@@ -108,6 +134,7 @@ public class RepositorySourcer(ILoggerFactory logger, IDirectoryInfo checkoutDir
 	public Checkout CloneRef(Repository repository, string gitRef, bool pull = false, int attempt = 1)
 	{
 		var checkoutFolder = readFileSystem.DirectoryInfo.New(Path.Combine(checkoutDirectory.FullName, repository.Name));
+		IGitRepository git = new SingleCommitOptimizedGitRepository(collector, checkoutFolder);
 		if (attempt > 3)
 		{
 			collector.EmitError("", $"Failed to clone repository {repository.Name}@{gitRef} after 3 attempts");
@@ -125,13 +152,13 @@ public Checkout CloneRef(Repository repository, string gitRef, bool pull = false
 			checkoutFolder.Create();
 			checkoutFolder.Refresh();
 		}
-		var isGitInitialized = GitInit(repository, checkoutFolder);
+		var isGitInitialized = GitInit(git, repository);
 		string? head = null;
 		if (isGitInitialized)
 		{
 			try
 			{
-				head = Capture(checkoutFolder, "git", "rev-parse", "HEAD");
+				head = git.GetCurrentCommit();
 			}
 			catch (Exception e)
 			{
@@ -147,7 +174,7 @@ public Checkout CloneRef(Repository repository, string gitRef, bool pull = false
 			_logger.LogInformation("{RepositoryName}: HEAD already at {GitRef}", repository.Name, gitRef);
 		else
 		{
-			FetchAndCheckout(repository, gitRef, checkoutFolder);
+			FetchAndCheckout(git, repository, gitRef);
 			if (!pull)
 			{
 				return new Checkout
@@ -159,11 +186,11 @@ public Checkout CloneRef(Repository repository, string gitRef, bool pull = false
 			}
 			try
 			{
-				ExecIn(checkoutFolder, "git", "pull", "--depth", "1", "--allow-unrelated-histories", "--no-ff", "origin", gitRef);
+				git.Pull(gitRef);
 			}
 			catch (Exception e)
 			{
-				_logger.LogError(e, "{RepositoryName}: Failed to update {GitRef} from {RelativePath}, falling back to recreating from scratch",
+				_logger.LogError(e, "{RepositoryName}: Failed to update {GitRef} from {Path}, falling back to recreating from scratch",
 					repository.Name, gitRef, checkoutFolder.FullName);
 				checkoutFolder.Delete(true);
 				checkoutFolder.Refresh();
@@ -183,84 +210,31 @@ public Checkout CloneRef(Repository repository, string gitRef, bool pull = false
 	/// Initializes the git repository if it is not already initialized.
 	/// Returns true if the repository was already initialized.
 	/// </summary>
-	private bool GitInit(Repository repository, IDirectoryInfo checkoutFolder)
+	private static bool GitInit(IGitRepository git, Repository repository)
 	{
-		var isGitAlreadyInitialized = Directory.Exists(Path.Combine(checkoutFolder.FullName, ".git"));
+		var isGitAlreadyInitialized = git.IsInitialized();
 		if (isGitAlreadyInitialized)
 			return true;
-		ExecIn(checkoutFolder, "git", "init");
-		ExecIn(checkoutFolder, "git", "remote", "add", "origin", repository.Origin);
+		git.Init();
+		git.GitAddOrigin(repository.Origin);
 		return false;
 	}
 
-	private void FetchAndCheckout(Repository repository, string gitRef, IDirectoryInfo checkoutFolder)
+	private static void FetchAndCheckout(IGitRepository git, Repository repository, string gitRef)
 	{
-		ExecIn(checkoutFolder, "git", "fetch", "--no-tags", "--prune", "--no-recurse-submodules", "--depth", "1", "origin", gitRef);
+		git.Fetch(gitRef);
 		switch (repository.CheckoutStrategy)
 		{
 			case CheckoutStrategy.Full:
-				ExecIn(checkoutFolder, "git", "sparse-checkout", "disable");
+				git.DisableSparseCheckout();
 				break;
 			case CheckoutStrategy.Partial:
-				ExecIn(checkoutFolder, "git", "sparse-checkout", "set", "docs");
+				git.EnableSparseCheckout("docs");
 				break;
 			default:
 				throw new ArgumentOutOfRangeException(nameof(repository), repository.CheckoutStrategy, null);
 		}
-		ExecIn(checkoutFolder, "git", "checkout", "--force", gitRef);
-	}
-
-	private void ExecIn(IDirectoryInfo? workingDirectory, string binary, params string[] args)
-	{
-		var arguments = new ExecArguments(binary, args)
-		{
-			WorkingDirectory = workingDirectory?.FullName
-		};
-		var result = Proc.Exec(arguments);
-		if (result != 0)
-			collector.EmitError("", $"Exit code: {result} while executing {binary} {string.Join(" ", args)} in {workingDirectory}");
-	}
-
-	// ReSharper disable once UnusedMember.Local
-	private string Capture(IDirectoryInfo? workingDirectory, string binary, params string[] args)
-	{
-		// Try 10 times to capture the output of the command, if it fails, we'll throw an exception on the last try
-		Exception? e = null;
-		for (var i = 0; i <= 9; i++)
-		{
-			try
-			{
-				return CaptureOutput();
-			}
-			catch (Exception ex)
-			{
-				if (ex is not null)
-					e = ex;
-			}
-		}
-
-		if (e is not null)
-			collector.EmitError("", "failure capturing stdout", e);
-
-
-		return string.Empty;
-
-		string CaptureOutput()
-		{
-			var arguments = new StartArguments(binary, args)
-			{
-				WorkingDirectory = workingDirectory?.FullName,
-				//WaitForStreamReadersTimeout = TimeSpan.FromSeconds(3),
-				Timeout = TimeSpan.FromSeconds(3),
-				WaitForExit = TimeSpan.FromSeconds(3),
-				ConsoleOutWriter = NoopConsoleWriter.Instance
-			};
-			var result = Proc.Start(arguments);
-			var line = result.ExitCode != 0
-				? throw new Exception($"Exit code is not 0. Received {result.ExitCode} from {binary}: {workingDirectory}")
-				: result.ConsoleOut.FirstOrDefault()?.Line ?? throw new Exception($"No output captured for {binary}: {workingDirectory}");
-			return line;
-		}
+		git.Checkout(gitRef);
 	}
 }
 
@@ -272,3 +246,10 @@ public void Write(Exception e) { }
 
 	public void Write(ConsoleOut consoleOut) { }
 }
+
+public record CheckoutResult
+{
+	public static string LinkRegistrySnapshotFileName => "link-index.snapshot.json";
+	public required LinkRegistry LinkRegistrySnapshot { get; init; }
+	public required IReadOnlyCollection<Checkout> Checkouts { get; init; }
+}