worktree: conditionally allow worktree on VFS-enabled repos

builtin/worktree.c

@@ -838,6 +838,14 @@ static int add(int ac, const char **av, const char *prefix,
 	if (ac < 1 || ac > 2)
 		usage_with_options(git_worktree_add_usage, options);
 
+	/*
+	 * When the virtual file system is active, skip checkout during
+	 * worktree creation. The VFS layer will handle the checkout
+	 * after the worktree structure is set up.
+	 */
+	if (gvfs_config_is_set(the_repository, GVFS_USE_VIRTUAL_FILESYSTEM))
+		opts.checkout = 0;
+
 	path = prefix_filename(prefix, av[0]);
 	branch = ac < 2 ? "HEAD" : av[1];
 	used_new_branch_options = new_branch || new_branch_force;
@@ -1358,6 +1366,21 @@ static int delete_git_work_tree(struct worktree *wt)
 	return ret;
 }
 
+/*
+ * Check if a pre-command hook has already verified worktree cleanliness
+ * and written a marker file to skip git's own check. VFSForGit uses this
+ * to unmount ProjFS after its own status check; without it, git's status
+ * call would fail because the virtual filesystem is no longer available.
+ */
+static int should_skip_clean_check(struct worktree *wt)
+{
+	char *path = repo_common_path(the_repository,
+		"worktrees/%s/skip-clean-check", wt->id);
+	int skip = file_exists(path);
+	free(path);
+	return skip;
+}
+
 static int remove_worktree(int ac, const char **av, const char *prefix,
 			   struct repository *repo UNUSED)
 {
@@ -1397,7 +1420,7 @@ static int remove_worktree(int ac, const char **av, const char *prefix,
 	strbuf_release(&errmsg);
 
 	if (file_exists(wt->path)) {
-		if (!force)
+		if (!force && !should_skip_clean_check(wt))
 			check_clean_worktree(wt, av[0]);
 
 		ret |= delete_git_work_tree(wt);

git.c

@@ -574,7 +574,8 @@ static int run_builtin(struct cmd_struct *p, int argc, const char **argv, struct
 		die("'git %s' is not supported on a GVFS repo", p->cmd);
 
 	if (!help && p->option & BLOCK_ON_VFS_ENABLED && gvfs_config_is_set(repo, GVFS_USE_VIRTUAL_FILESYSTEM))
-		die("'git %s' is not supported when using the virtual file system", p->cmd);
+		if (strcmp(p->cmd, "worktree") != 0 || !gvfs_config_is_set(repo, GVFS_SUPPORTS_WORKTREES))
+			die("'git %s' is not supported when using the virtual file system", p->cmd);
 
 	if (run_pre_command_hook(the_repository, argv))
 		die("pre-command hook aborted command");

gvfs.h

@@ -30,6 +30,13 @@ struct repository;
 #define GVFS_BLOCK_FILTERS_AND_EOL_CONVERSIONS      (1 << 6)
 #define GVFS_PREFETCH_DURING_FETCH		    (1 << 7)
 
+/*
+ * When set, this flag indicates that the VFS layer supports
+ * git worktrees. This allows `git worktree add/remove` to
+ * operate on VFS-enabled repositories.
+ */
+#define GVFS_SUPPORTS_WORKTREES                     (1 << 8)
+
 #define GVFS_ANY_MASK                               0xFFFFFFFF
 
 int gvfs_config_is_set(struct repository *r, int mask);

t/t0402-block-command-on-gvfs.sh

@@ -27,7 +27,55 @@ not_with_gvfs update-index --index-version 2
 not_with_gvfs update-index --skip-worktree
 not_with_gvfs update-index --no-skip-worktree
 not_with_gvfs update-index --split-index
-not_with_gvfs worktree list
+
+# worktree is conditionally allowed: blocked when VFS enabled without
+# GVFS_SUPPORTS_WORKTREES, but core.gvfs=true sets all bits including
+# SUPPORTS_WORKTREES, so we test the blocked case with a specific bitmask.
+test_expect_success 'worktree blocked with VFS but without SUPPORTS_WORKTREES' '
+	test_config core.gvfs 95 &&
+	test_must_fail git worktree list 2>err &&
+	test_grep "not supported when using the virtual file system" err
+'
+
+# core.gvfs bitmask values:
+#   GVFS_USE_VIRTUAL_FILESYSTEM = (1 << 3) = 8
+#   GVFS_SUPPORTS_WORKTREES     = (1 << 8) = 256
+# A typical VFS-enabled repo has core.gvfs=95 (bits 0-4,6).
+# Adding SUPPORTS_WORKTREES: 95 + 256 = 351.
+
+test_expect_success 'setup for worktree tests' '
+	test_commit initial
+'
+
+test_expect_success 'worktree allowed when SUPPORTS_WORKTREES bit is set' '
+	test_when_finished "git worktree remove --force ../allowed-wt 2>/dev/null; true" &&
+	test_config core.gvfs 351 &&
+	git worktree add ../allowed-wt &&
+	test_path_exists ../allowed-wt/.git
+'
+
+test_expect_success 'worktree add forces --no-checkout when VFS active' '
+	test_when_finished "git worktree remove --force ../nocheckout-wt 2>/dev/null; true" &&
+	test_config core.gvfs 351 &&
+	git worktree add ../nocheckout-wt &&
+	test_path_exists ../nocheckout-wt/.git &&
+	! test_path_exists ../nocheckout-wt/initial.t
+'
+
+test_expect_success 'worktree list works with SUPPORTS_WORKTREES' '
+	test_when_finished "git worktree remove --force ../list-wt 2>/dev/null; true" &&
+	test_config core.gvfs 351 &&
+	git worktree add ../list-wt &&
+	git worktree list >out &&
+	grep "list-wt" out
+'
+
+test_expect_success 'worktree remove works with SUPPORTS_WORKTREES' '
+	test_config core.gvfs 351 &&
+	git worktree add ../remove-wt &&
+	git worktree remove --force ../remove-wt &&
+	! test_path_exists ../remove-wt
+'
 
 test_expect_success 'test gc --auto succeeds when disabled via config' '
 	test_config core.gvfs true &&