Implement support for relativeworktrees extension

Author: tmat

src/Microsoft.Build.Tasks.Git.UnitTests/GitRepositoryTests.cs

@@ -65,21 +65,27 @@ public void TryFindRepository_Worktree_Realistic()
         {
             using var temp = new TempRoot();
 
-            var mainWorkingDir = temp.CreateDirectory();
+            var repoDir = temp.CreateDirectory();
+
+            var mainWorkingDir = repoDir.CreateDirectory("main");
             var mainWorkingSubDir = mainWorkingDir.CreateDirectory("A");
             var mainGitDir = mainWorkingDir.CreateDirectory(".git");
             mainGitDir.CreateFile("HEAD");
 
             var worktreesDir = mainGitDir.CreateDirectory("worktrees");
             var worktreeGitDir = worktreesDir.CreateDirectory("myworktree");
             var worktreeGitSubDir = worktreeGitDir.CreateDirectory("B");
-            var worktreeDir = temp.CreateDirectory();
+            var worktreeDir = repoDir.CreateDirectory("worktree");
             var worktreeSubDir = worktreeDir.CreateDirectory("C");
-            var worktreeGitFile = worktreeDir.CreateFile(".git").WriteAllText("gitdir: " + worktreeGitDir + " \r\n\t\v");
+
+            // test relative path to work tree dir:
+            var worktreeGitFile = worktreeDir.CreateFile(".git").WriteAllText("gitdir: ../main/.git/worktrees/myworktree \r\n\t\v");
 
             worktreeGitDir.CreateFile("HEAD");
             worktreeGitDir.CreateFile("commondir").WriteAllText("../..\n");
-            worktreeGitDir.CreateFile("gitdir").WriteAllText(worktreeGitFile.Path + " \r\n\t\v");
+
+            // test relative path to work tree .git file:
+            worktreeGitDir.CreateFile("gitdir").WriteAllText("../../../../worktree/.git \r\n\t\v");
 
             // start under main repository directory:
             Assert.True(GitRepository.TryFindRepository(mainWorkingSubDir.Path, out var location));
@@ -226,6 +232,7 @@ public void OpenRepository_Version1_Extensions()
     preciousObjects = true
     partialClone = promisor_remote
     worktreeConfig = true
+    relativeWorktrees = true
     objectformat = sha256
 ");
 
@@ -338,7 +345,7 @@ public void OpenRepository_Worktree_GitdirFileMissing()
             Assert.Equal(worktreeGitDir.Path, location.GitDirectory);
             Assert.Equal(mainGitDir.Path, location.CommonDirectory);
             Assert.Equal(worktreeDir.Path, location.WorkingDirectory);
-            
+
             var repository = GitRepository.OpenRepository(location, GitEnvironment.Empty);
             Assert.Equal(repository.GitDirectory, location.GitDirectory);
             Assert.Equal(repository.CommonDirectory, location.CommonDirectory);
@@ -377,7 +384,7 @@ public void OpenRepository_Worktree_GitdirFileDifferentPath()
             var repository = GitRepository.OpenRepository(location, GitEnvironment.Empty);
             Assert.Equal(repository.GitDirectory, location.GitDirectory);
             Assert.Equal(repository.CommonDirectory, location.CommonDirectory);
-            
+
             // actual working dir is not affected:
             Assert.Equal(worktreeDir.Path, location.WorkingDirectory);
         }

src/Microsoft.Build.Tasks.Git/GitDataReader/GitConfig.cs

@@ -21,10 +21,11 @@ internal sealed partial class GitConfig
 
         private const string RefStorageExtensionName = "refstorage";
         private const string ObjectFormatExtensionName = "objectFormat";
+        private const string RelativeWorktreesExtensionName = "relativeWorktrees";
         private const string RepositoryFormatVersionVariableName = "repositoryformatversion";
 
         private static readonly ImmutableArray<string> s_knownExtensions =
-            ["noop", "preciousObjects", "partialclone", "worktreeConfig", RefStorageExtensionName, ObjectFormatExtensionName];
+            ["noop", "preciousObjects", "partialclone", "worktreeConfig", RefStorageExtensionName, ObjectFormatExtensionName, RelativeWorktreesExtensionName];
 
         public readonly ImmutableDictionary<GitVariableName, ImmutableArray<string>> Variables;
         public readonly ReferenceStorageFormat ReferenceStorageFormat;