v3, 5 partsOptionally link worktrees with relative paths

diff --git a/worktree.c b/worktree.c
index ec95ea2986107b3bc12d38b0825d7c6e87402bc6..ad60ba0b5843f1676e89b05eca3c82aace5fb49b 100644
--- a/worktree.c
+++ b/worktree.c
@@ -641,13 +641,15 @@ static int is_main_worktree_path(const char *path)
  * won't know which <repo>/worktrees/<id>/gitdir to repair. However, we may
  * be able to infer the gitdir by manually reading /path/to/worktree/.git,
  * extracting the <id>, and checking if <repo>/worktrees/<id> exists.
+ *
+ * Returns -1 on failure and strbuf.len on success.
  */
-static char *infer_backlink(const char *gitfile)
+static int infer_backlink(const char *gitfile, struct strbuf *inferred)
 {
 	struct strbuf actual = STRBUF_INIT;
-	struct strbuf inferred = STRBUF_INIT;
 	const char *id;
 
+	strbuf_reset(inferred);
 	if (strbuf_read_file(&actual, gitfile, 0) < 0)
 		goto error;
 	if (!starts_with(actual.buf, "gitdir:"))
@@ -658,17 +660,16 @@ static char *infer_backlink(const char *gitfile)
 	id++; /* advance past '/' to point at <id> */
 	if (!*id)
 		goto error;
-	strbuf_git_common_path(&inferred, the_repository, "worktrees/%s", id);
-	if (!is_directory(inferred.buf))
+	strbuf_git_common_path(inferred, the_repository, "worktrees/%s", id);
+	if (!is_directory(inferred->buf))
 		goto error;
 
 	strbuf_release(&actual);
-	return strbuf_detach(&inferred, NULL);
-
+	return inferred->len;
 error:
 	strbuf_release(&actual);
-	strbuf_release(&inferred);
-	return NULL;
+	strbuf_reset(inferred); /* clear invalid path */
+	return -1;
 }
 
 /*
@@ -680,10 +681,11 @@ void repair_worktree_at_path(const char *path,
 {
 	struct strbuf dotgit = STRBUF_INIT;
 	struct strbuf realdotgit = STRBUF_INIT;
+	struct strbuf backlink = STRBUF_INIT;
+	struct strbuf inferred_backlink = STRBUF_INIT;
 	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf olddotgit = STRBUF_INIT;
-	char *backlink = NULL;
-	char *inferred_backlink = NULL;
+	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
 
@@ -699,23 +701,23 @@ void repair_worktree_at_path(const char *path,
 		goto done;
 	}
 
-	inferred_backlink = infer_backlink(realdotgit.buf);
-	backlink = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
-	if (err == READ_GITFILE_ERR_NOT_A_FILE) {
+	infer_backlink(realdotgit.buf, &inferred_backlink);
+	dotgit_contents = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
+	if (dotgit_contents) {
+		strbuf_addstr(&backlink, dotgit_contents);
+	} else if (err == READ_GITFILE_ERR_NOT_A_FILE) {
 		fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
 		goto done;
 	} else if (err == READ_GITFILE_ERR_NOT_A_REPO) {
-		if (inferred_backlink) {
+		if (inferred_backlink.len) {
 			/*
 			 * Worktree's .git file does not point at a repository
 			 * but we found a .git/worktrees/<id> in this
 			 * repository with the same <id> as recorded in the
 			 * worktree's .git file so make the worktree point at
-			 * the discovered .git/worktrees/<id>. (Note: backlink
-			 * is already NULL, so no need to free it first.)
+			 * the discovered .git/worktrees/<id>.
 			 */
-			backlink = inferred_backlink;
-			inferred_backlink = NULL;
+			strbuf_swap(&backlink, &inferred_backlink);
 		} else {
 			fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
 			goto done;
@@ -743,13 +745,10 @@ void repair_worktree_at_path(const char *path,
 	 * in the "copy" repository. In this case, point the "copy" worktree's
 	 * .git file at the "copy" repository.
 	 */
-	if (inferred_backlink && fspathcmp(backlink, inferred_backlink)) {
-		free(backlink);
-		backlink = inferred_backlink;
-		inferred_backlink = NULL;
-	}
+	if (inferred_backlink.len && fspathcmp(backlink.buf, inferred_backlink.buf))
+		strbuf_swap(&backlink, &inferred_backlink);
 
-	strbuf_addf(&gitdir, "%s/gitdir", backlink);
+	strbuf_addf(&gitdir, "%s/gitdir", backlink.buf);
 	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
 		repair = _("gitdir unreadable");
 	else {
@@ -763,9 +762,10 @@ void repair_worktree_at_path(const char *path,
 		write_file(gitdir.buf, "%s", realdotgit.buf);
 	}
 done:
-	free(backlink);
-	free(inferred_backlink);
+	free(dotgit_contents);
 	strbuf_release(&olddotgit);
+	strbuf_release(&backlink);
+	strbuf_release(&inferred_backlink);
 	strbuf_release(&gitdir);
 	strbuf_release(&realdotgit);
 	strbuf_release(&dotgit);

diff --git a/worktree.c b/worktree.c
index ad60ba0b5843f1676e89b05eca3c82aace5fb49b..cf578c447589425d642fc8aa7a7fa07600e60a70 100644
--- a/worktree.c
+++ b/worktree.c
@@ -110,6 +110,12 @@ struct worktree *get_linked_worktree(const char *id,
 	strbuf_rtrim(&worktree_path);
 	strbuf_strip_suffix(&worktree_path, "/.git");
 
+	if (!is_absolute_path(worktree_path.buf)) {
+		strbuf_strip_suffix(&path, "gitdir");
+		strbuf_addbuf(&path, &worktree_path);
+		strbuf_realpath_forgiving(&worktree_path, path.buf, 0);
+	}
+
 	CALLOC_ARRAY(worktree, 1);
 	worktree->repo = the_repository;
 	worktree->path = strbuf_detach(&worktree_path, NULL);
@@ -564,28 +570,38 @@ static void repair_gitfile(struct worktree *wt,
 {
 	struct strbuf dotgit = STRBUF_INIT;
 	struct strbuf repo = STRBUF_INIT;
-	char *backlink;
+	struct strbuf backlink = STRBUF_INIT;
+	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
 
 	/* missing worktree can't be repaired */
 	if (!file_exists(wt->path))
-		return;
+		goto done;
 
 	if (!is_directory(wt->path)) {
 		fn(1, wt->path, _("not a directory"), cb_data);
-		return;
+		goto done;
 	}
 
 	strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
 	strbuf_addf(&dotgit, "%s/.git", wt->path);
-	backlink = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
+	dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
+
+	if (dotgit_contents) {
+		if (is_absolute_path(dotgit_contents)) {
+			strbuf_addstr(&backlink, dotgit_contents);
+		} else {
+			strbuf_addf(&backlink, "%s/%s", wt->path, dotgit_contents);
+			strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
+		}
+	}
 
 	if (err == READ_GITFILE_ERR_NOT_A_FILE)
 		fn(1, wt->path, _(".git is not a file"), cb_data);
 	else if (err)
 		repair = _(".git file broken");
-	else if (fspathcmp(backlink, repo.buf))
+	else if (fspathcmp(backlink.buf, repo.buf))
 		repair = _(".git file incorrect");
 
 	if (repair) {
@@ -593,9 +609,11 @@ static void repair_gitfile(struct worktree *wt,
 		write_file(dotgit.buf, "gitdir: %s", repo.buf);
 	}
 
-	free(backlink);
+done:
+	free(dotgit_contents);
 	strbuf_release(&repo);
 	strbuf_release(&dotgit);
+	strbuf_release(&backlink);
 }
 
 static void repair_noop(int iserr UNUSED,
@@ -685,6 +703,7 @@ void repair_worktree_at_path(const char *path,
 	struct strbuf inferred_backlink = STRBUF_INIT;
 	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf olddotgit = STRBUF_INIT;
+	struct strbuf realolddotgit = STRBUF_INIT;
 	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
@@ -702,9 +721,17 @@ void repair_worktree_at_path(const char *path,
 	}
 
 	infer_backlink(realdotgit.buf, &inferred_backlink);
+	strbuf_realpath_forgiving(&inferred_backlink, inferred_backlink.buf, 0);
 	dotgit_contents = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
 	if (dotgit_contents) {
-		strbuf_addstr(&backlink, dotgit_contents);
+		if (is_absolute_path(dotgit_contents)) {
+			strbuf_addstr(&backlink, dotgit_contents);
+		} else {
+			strbuf_addbuf(&backlink, &realdotgit);
+			strbuf_strip_suffix(&backlink, ".git");
+			strbuf_addstr(&backlink, dotgit_contents);
+			strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
+		}
 	} else if (err == READ_GITFILE_ERR_NOT_A_FILE) {
 		fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
 		goto done;
@@ -722,7 +749,7 @@ void repair_worktree_at_path(const char *path,
 			fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
 			goto done;
 		}
-	} else if (err) {
+	} else {
 		fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
 		goto done;
 	}
@@ -753,7 +780,13 @@ void repair_worktree_at_path(const char *path,
 		repair = _("gitdir unreadable");
 	else {
 		strbuf_rtrim(&olddotgit);
-		if (fspathcmp(olddotgit.buf, realdotgit.buf))
+		if (is_absolute_path(olddotgit.buf)) {
+			strbuf_addbuf(&realolddotgit, &olddotgit);
+		} else {
+			strbuf_addf(&realolddotgit, "%s/%s", backlink.buf, olddotgit.buf);
+			strbuf_realpath_forgiving(&realolddotgit, realolddotgit.buf, 0);
+		}
+		if (fspathcmp(realolddotgit.buf, realdotgit.buf))
 			repair = _("gitdir incorrect");
 	}
 
@@ -764,6 +797,7 @@ void repair_worktree_at_path(const char *path,
 done:
 	free(dotgit_contents);
 	strbuf_release(&olddotgit);
+	strbuf_release(&realolddotgit);
 	strbuf_release(&backlink);
 	strbuf_release(&inferred_backlink);
 	strbuf_release(&gitdir);
@@ -774,69 +808,88 @@ void repair_worktree_at_path(const char *path,
 int should_prune_worktree(const char *id, struct strbuf *reason, char **wtpath, timestamp_t expire)
 {
 	struct stat st;
-	char *path;
+	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
+	struct strbuf repo = STRBUF_INIT;
+	struct strbuf file = STRBUF_INIT;
+	char *path = NULL;
+	int rc = 0;
 	int fd;
 	size_t len;
 	ssize_t read_result;
 
 	*wtpath = NULL;
-	if (!is_directory(git_path("worktrees/%s", id))) {
+	strbuf_realpath(&repo, git_common_path("worktrees/%s", id), 1);
+	strbuf_addf(&gitdir, "%s/gitdir", repo.buf);
+	if (!is_directory(repo.buf)) {
 		strbuf_addstr(reason, _("not a valid directory"));
-		return 1;
+		rc = 1;
+		goto done;
 	}
-	if (file_exists(git_path("worktrees/%s/locked", id)))
-		return 0;
-	if (stat(git_path("worktrees/%s/gitdir", id), &st)) {
+	strbuf_addf(&file, "%s/locked", repo.buf);
+	if (file_exists(file.buf)) {
+		goto done;
+	}
+	if (stat(gitdir.buf, &st)) {
 		strbuf_addstr(reason, _("gitdir file does not exist"));
-		return 1;
+		rc = 1;
+		goto done;
 	}
-	fd = open(git_path("worktrees/%s/gitdir", id), O_RDONLY);
+	fd = open(gitdir.buf, O_RDONLY);
 	if (fd < 0) {
 		strbuf_addf(reason, _("unable to read gitdir file (%s)"),
 			    strerror(errno));
-		return 1;
+		rc = 1;
+		goto done;
 	}
 	len = xsize_t(st.st_size);
 	path = xmallocz(len);
 
 	read_result = read_in_full(fd, path, len);
+	close(fd);
 	if (read_result < 0) {
 		strbuf_addf(reason, _("unable to read gitdir file (%s)"),
 			    strerror(errno));
-		close(fd);
-		free(path);
-		return 1;
-	}
-	close(fd);
-
-	if (read_result != len) {
+		rc = 1;
+		goto done;
+	} else if (read_result != len) {
 		strbuf_addf(reason,
 			    _("short read (expected %"PRIuMAX" bytes, read %"PRIuMAX")"),
 			    (uintmax_t)len, (uintmax_t)read_result);
-		free(path);
-		return 1;
+		rc = 1;
+		goto done;
 	}
 	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
 		len--;
 	if (!len) {
 		strbuf_addstr(reason, _("invalid gitdir file"));
-		free(path);
-		return 1;
+		rc = 1;
+		goto done;
 	}
 	path[len] = '\0';
-	if (!file_exists(path)) {
-		if (stat(git_path("worktrees/%s/index", id), &st) ||
-		    st.st_mtime <= expire) {
+	if (is_absolute_path(path)) {
+		strbuf_addstr(&dotgit, path);
+	} else {
+		strbuf_addf(&dotgit, "%s/%s", repo.buf, path);
+		strbuf_realpath_forgiving(&dotgit, dotgit.buf, 0);
+	}
+	if (!file_exists(dotgit.buf)) {
+		strbuf_reset(&file);
+		strbuf_addf(&file, "%s/index", repo.buf);
+		if (stat(file.buf, &st) || st.st_mtime <= expire) {
 			strbuf_addstr(reason, _("gitdir file points to non-existent location"));
-			free(path);
-			return 1;
-		} else {
-			*wtpath = path;
-			return 0;
+			rc = 1;
+			goto done;
 		}
 	}
-	*wtpath = path;
-	return 0;
+	*wtpath = strbuf_detach(&dotgit, NULL);
+done:
+	free(path);
+	strbuf_release(&dotgit);
+	strbuf_release(&gitdir);
+	strbuf_release(&repo);
+	strbuf_release(&file);
+	return rc;
 }
 
 static int move_config_setting(const char *key, const char *value,

diff --git a/t/t2401-worktree-prune.sh b/t/t2401-worktree-prune.sh
index 71aa9bcd620f8a504fe628a2d7332d8b47fd4701..5eb52b9abbf29514dc082c260ebb7a5e8e63aae0 100755
--- a/t/t2401-worktree-prune.sh
+++ b/t/t2401-worktree-prune.sh
@@ -120,4 +120,24 @@ test_expect_success 'prune duplicate (main/linked)' '
 	! test -d .git/worktrees/wt
 '
 
+test_expect_success 'not prune proper worktrees inside linked worktree with relative paths' '
+	test_when_finished rm -rf repo wt_ext &&
+	git init repo &&
+	(
+	    cd repo &&
+	    git config worktree.useRelativePaths true &&
+	    echo content >file &&
+	    git add file &&
+	    git commit -m msg &&
+	    git worktree add ../wt_ext &&
+	    git worktree add wt_int &&
+	    cd wt_int &&
+	    git worktree prune -v >out &&
+	    test_must_be_empty out &&
+	    cd ../../wt_ext &&
+	    git worktree prune -v >out &&
+	    test_must_be_empty out
+	)
+'
+
 test_done

Documentation/config/worktree.txt, Documentation/git-worktree.txt, builtin/worktree.c, setup.c, t/t0001-init.sh, t/t2400-worktree-add.sh, t/t2402-worktree-list.sh, t/t2403-worktree-move.sh, t/t2406-worktree-repair.sh, worktree.c, worktree.h

diff --git a/Documentation/config/worktree.txt b/Documentation/config/worktree.txt
index 048e349482df6c892055720eb53cdcd6c327b6ed..d0589c21d034f07f70ca172947520d7d78720cca 100644
--- a/Documentation/config/worktree.txt
+++ b/Documentation/config/worktree.txt
@@ -7,3 +7,8 @@ worktree.guessRemote::
 	such a branch exists, it is checked out and set as "upstream"
 	for the new branch.  If no such match can be found, it falls
 	back to creating a new branch from the current HEAD.
+worktree.useRelativePaths::
+	If set to `true`, the worktree paths will be stored relative to the
+	repository’s top-level directory, rather than using absolute paths.
+	This is particularly useful for setups where the repository may be moved
+	between different locations or environments.
diff --git a/Documentation/git-worktree.txt b/Documentation/git-worktree.txt
index 70437c815f13852bd2eb862176b8b933e6de0acf..4a6ad481ee1d44b43683bd67881a2771e2b090c7 100644
--- a/Documentation/git-worktree.txt
+++ b/Documentation/git-worktree.txt
@@ -216,6 +216,15 @@ To remove a locked worktree, specify `--force` twice.
 This can also be set up as the default behaviour by using the
 `worktree.guessRemote` config option.
 
+--[no-]relative-paths::
+	The worktree paths will be stored relative to the repository’s
+	top-level directory, rather than using absolute paths.
+	This is particularly useful for setups where the repository may be moved
+	between different locations or environments.
++
+This can also be set up as the default behaviour by using the
+`worktree.useRelativePaths` config option.
+
 --[no-]track::
 	When creating a new branch, if `<commit-ish>` is a branch,
 	mark it as "upstream" from the new branch.  This is the
diff --git a/builtin/worktree.c b/builtin/worktree.c
index fc31d072a620d7b455d7f150bd3a9e773ee9d4ed..bb06830d6fe82aa97833c6e87f034115dfaa23bd 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -134,6 +134,9 @@ static int git_worktree_config(const char *var, const char *value,
 	if (!strcmp(var, "worktree.guessremote")) {
 		guess_remote = git_config_bool(var, value);
 		return 0;
+	} else if (!strcmp(var, "worktree.userelativepaths")) {
+		use_relative_paths = git_config_bool(var, value);
+		return 0;
 	}
 
 	return git_default_config(var, value, ctx, cb);
@@ -414,7 +417,7 @@ static int add_worktree(const char *path, const char *refname,
 			const struct add_opts *opts)
 {
 	struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
-	struct strbuf sb = STRBUF_INIT, realpath = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
 	const char *name;
 	struct strvec child_env = STRVEC_INIT;
 	unsigned int counter = 0;
@@ -490,11 +493,7 @@ static int add_worktree(const char *path, const char *refname,
 
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
-	strbuf_realpath(&realpath, sb_git.buf, 1);
-	write_file(sb.buf, "%s", realpath.buf);
-	strbuf_realpath(&realpath, repo_get_common_dir(the_repository), 1);
-	write_file(sb_git.buf, "gitdir: %s/worktrees/%s",
-		   realpath.buf, name);
+	write_worktree_linking_files(sb_git, sb);
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
 	write_file(sb.buf, "../..");
@@ -582,7 +581,6 @@ static int add_worktree(const char *path, const char *refname,
 	strbuf_release(&sb_repo);
 	strbuf_release(&sb_git);
 	strbuf_release(&sb_name);
-	strbuf_release(&realpath);
 	free_worktree(wt);
 	return ret;
 }
@@ -794,6 +792,8 @@ static int add(int ac, const char **av, const char *prefix)
 			     PARSE_OPT_NOARG | PARSE_OPT_OPTARG),
 		OPT_BOOL(0, "guess-remote", &guess_remote,
 			 N_("try to match the new branch name with a remote-tracking branch")),
+		OPT_BOOL(0, "relative-paths", &use_relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	int ret;
@@ -1187,6 +1187,8 @@ static int move_worktree(int ac, const char **av, const char *prefix)
 		OPT__FORCE(&force,
 			 N_("force move even if worktree is dirty or locked"),
 			 PARSE_OPT_NOCOMPLETE),
+		OPT_BOOL(0, "relative-paths", &use_relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	struct worktree **worktrees, *wt;
@@ -1380,6 +1382,8 @@ static int repair(int ac, const char **av, const char *prefix)
 	const char **p;
 	const char *self[] = { ".", NULL };
 	struct option options[] = {
+		OPT_BOOL(0, "relative-paths", &use_relative_paths,
+			 N_("use relative paths for worktrees")),
 		OPT_END()
 	};
 	int rc = 0;
diff --git a/setup.c b/setup.c
index 94e79b2e487f3faa537547e190acf9b7ea0be3b5..7b648de0279116b381eea46800ad130606926103 100644
--- a/setup.c
+++ b/setup.c
@@ -2420,7 +2420,7 @@ static void separate_git_dir(const char *git_dir, const char *git_link)
 
 		if (rename(src, git_dir))
 			die_errno(_("unable to move %s to %s"), src, git_dir);
-		repair_worktrees(NULL, NULL);
+		repair_worktrees_after_gitdir_move(src);
 	}
 
 	write_file(git_link, "gitdir: %s", git_dir);
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 0178aa62a41f1606f2382a4a10ab593ccf11e0e8..03ac9624cb418d05adb8dfb786c31b809c73efec 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -435,19 +435,27 @@ sep_git_dir_worktree ()  {
 	test_when_finished "rm -rf mainwt linkwt seprepo" &&
 	git init mainwt &&
 	test_commit -C mainwt gumby &&
-	git -C mainwt worktree add --detach ../linkwt &&
-	git -C "$1" init --separate-git-dir ../seprepo &&
+	git -C mainwt worktree add $1 --detach ../linkwt &&
+	git -C "$2" init --separate-git-dir ../seprepo &&
 	git -C mainwt rev-parse --git-common-dir >expect &&
 	git -C linkwt rev-parse --git-common-dir >actual &&
 	test_cmp expect actual
 }
 
-test_expect_success 're-init to move gitdir with linked worktrees' '
-	sep_git_dir_worktree mainwt
+test_expect_success 're-init to move gitdir with linked worktrees (absolute)' '
+	sep_git_dir_worktree --no-relative-paths mainwt
 '
 
-test_expect_success 're-init to move gitdir within linked worktree' '
-	sep_git_dir_worktree linkwt
+test_expect_success 're-init to move gitdir within linked worktree (absolute)' '
+	sep_git_dir_worktree --no-relative-paths linkwt
+'
+
+test_expect_success 're-init to move gitdir with linked worktrees (relative)' '
+	sep_git_dir_worktree --relative-paths mainwt
+'
+
+test_expect_success 're-init to move gitdir within linked worktree (relative)' '
+	sep_git_dir_worktree --relative-paths linkwt
 '
 
 test_expect_success MINGW '.git hidden' '
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index cfc4aeb1798c6d023909cec771e5b74e983af5ea..630c13230b3cc762ce8d943e22be8891aa2b1871 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -1207,4 +1207,45 @@ test_expect_success '"add" with initialized submodule, with submodule.recurse se
 	git -C project-clone -c submodule.recurse worktree add ../project-5
 '
 
+test_expect_success 'can create worktrees with relative paths' '
+	test_when_finished "git worktree remove relative" &&
+	git config worktree.useRelativePaths false &&
+	git worktree add --relative-paths ./relative &&
+	cat relative/.git >actual &&
+	echo "gitdir: ../.git/worktrees/relative" >expect &&
+	test_cmp expect actual &&
+	cat .git/worktrees/relative/gitdir >actual &&
+	echo "../../../relative/.git" >expect &&
+	test_cmp expect actual
+
+'
+
+test_expect_success 'can create worktrees with absolute paths' '
+	git config worktree.useRelativePaths true &&
+	git worktree add ./relative &&
+	cat relative/.git >actual &&
+	echo "gitdir: ../.git/worktrees/relative" >expect &&
+	test_cmp expect actual &&
+	git worktree add --no-relative-paths ./absolute &&
+	cat absolute/.git >actual &&
+	echo "gitdir: $(pwd)/.git/worktrees/absolute" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'move repo without breaking relative internal links' '
+	test_when_finished rm -rf repo moved &&
+	git init repo &&
+	(
+		cd repo &&
+		git config worktree.useRelativePaths true &&
+		test_commit initial &&
+		git worktree add wt1 &&
+		cd .. &&
+		mv repo moved &&
+		cd moved/wt1 &&
+		git status >out 2>err &&
+		test_must_be_empty err
+	)
+'
+
 test_done
diff --git a/t/t2402-worktree-list.sh b/t/t2402-worktree-list.sh
index 33ea9cb21ba07c9563530b54da06753eaa993fe2..780daa6cd6351f8fa9434619cc212aade8f01420 100755
--- a/t/t2402-worktree-list.sh
+++ b/t/t2402-worktree-list.sh
@@ -261,6 +261,7 @@ test_expect_success 'broken main worktree still at the top' '
 '
 
 test_expect_success 'linked worktrees are sorted' '
+	test_when_finished "rm -rf sorted" &&
 	mkdir sorted &&
 	git init sorted/main &&
 	(
@@ -280,6 +281,27 @@ test_expect_success 'linked worktrees are sorted' '
 	test_cmp expected sorted/main/actual
 '
 
+test_expect_success 'linked worktrees with relative paths are shown with absolute paths' '
+	test_when_finished "rm -rf sorted" &&
+	mkdir sorted &&
+	git init sorted/main &&
+	(
+		cd sorted/main &&
+		test_tick &&
+		test_commit new &&
+		git worktree add --relative-paths ../first &&
+		git worktree add ../second &&
+		git worktree list --porcelain >out &&
+		grep ^worktree out >actual
+	) &&
+	cat >expected <<-EOF &&
+	worktree $(pwd)/sorted/main
+	worktree $(pwd)/sorted/first
+	worktree $(pwd)/sorted/second
+	EOF
+	test_cmp expected sorted/main/actual
+'
+
 test_expect_success 'worktree path when called in .git directory' '
 	git worktree list >list1 &&
 	git -C .git worktree list >list2 &&
diff --git a/t/t2403-worktree-move.sh b/t/t2403-worktree-move.sh
index 901342ea09b51a8e832f1109fbb737df84283aa2..6ce9ed3f1e6b3f73d2a290e770233eec30221fe5 100755
--- a/t/t2403-worktree-move.sh
+++ b/t/t2403-worktree-move.sh
@@ -247,4 +247,26 @@ test_expect_success 'not remove a repo with initialized submodule' '
 	)
 '
 
+test_expect_success 'move worktree with absolute path to relative path' '
+	git config worktree.useRelativePaths false &&
+	git worktree add ./absolute &&
+	git worktree move --relative-paths absolute relative &&
+	cat relative/.git >actual &&
+	echo "gitdir: ../.git/worktrees/absolute" >expect &&
+	test_cmp expect actual &&
+	git config worktree.useRelativePaths true &&
+	git worktree move relative relative2 &&
+	cat relative2/.git >actual &&
+	echo "gitdir: ../.git/worktrees/absolute" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'move worktree with relative path to absolute path' '
+	git config worktree.useRelativePaths true &&
+	git worktree move --no-relative-paths relative2 absolute &&
+	cat absolute/.git >actual &&
+	echo "gitdir: $(pwd)/.git/worktrees/absolute" >expect &&
+	test_cmp expect actual
+'
+
 test_done
diff --git a/t/t2406-worktree-repair.sh b/t/t2406-worktree-repair.sh
index 7686e60f6ad186519b275f11a5e14064c905b207..84451e903b2ef3c645c0311faf055c846588baf6 100755
--- a/t/t2406-worktree-repair.sh
+++ b/t/t2406-worktree-repair.sh
@@ -216,4 +216,30 @@ test_expect_success 'repair copied main and linked worktrees' '
 	test_cmp dup/linked.expect dup/linked/.git
 '
 
+test_expect_success 'repair absolute worktree to use relative paths' '
+	test_when_finished "rm -rf main side sidemoved" &&
+	test_create_repo main &&
+	test_commit -C main init &&
+	git -C main worktree add --detach ../side &&
+	echo "../../../../sidemoved/.git" >expect-gitdir &&
+	echo "gitdir: ../main/.git/worktrees/side" >expect-gitfile &&
+	mv side sidemoved &&
+	git -C main worktree repair --relative-paths ../sidemoved &&
+	test_cmp expect-gitdir main/.git/worktrees/side/gitdir &&
+	test_cmp expect-gitfile sidemoved/.git
+'
+
+test_expect_success 'repair relative worktree to use absolute paths' '
+	test_when_finished "rm -rf main side sidemoved" &&
+	test_create_repo main &&
+	test_commit -C main init &&
+	git -C main worktree add --relative-paths --detach ../side &&
+	echo "$(pwd)/sidemoved/.git" >expect-gitdir &&
+	echo "gitdir: $(pwd)/main/.git/worktrees/side" >expect-gitfile &&
+	mv side sidemoved &&
+	git -C main worktree repair ../sidemoved &&
+	test_cmp expect-gitdir main/.git/worktrees/side/gitdir &&
+	test_cmp expect-gitfile sidemoved/.git
+'
+
 test_done
diff --git a/worktree.c b/worktree.c
index cf578c447589425d642fc8aa7a7fa07600e60a70..0d1685b892fcddf74a91304424a94e5ee847388b 100644
--- a/worktree.c
+++ b/worktree.c
@@ -14,6 +14,8 @@
 #include "wt-status.h"
 #include "config.h"
 
+int use_relative_paths = 0;
+
 void free_worktree(struct worktree *worktree)
 {
 	if (!worktree)
@@ -379,18 +381,24 @@ int validate_worktree(const struct worktree *wt, struct strbuf *errmsg,
 void update_worktree_location(struct worktree *wt, const char *path_)
 {
 	struct strbuf path = STRBUF_INIT;
+	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
 
 	if (is_main_worktree(wt))
 		BUG("can't relocate main worktree");
 
+	strbuf_realpath(&gitdir, git_common_path("worktrees/%s/gitdir", wt->id), 1);
 	strbuf_realpath(&path, path_, 1);
+	strbuf_addf(&dotgit, "%s/.git", path.buf);
 	if (fspathcmp(wt->path, path.buf)) {
-		write_file(git_common_path("worktrees/%s/gitdir", wt->id),
-			   "%s/.git", path.buf);
+		write_worktree_linking_files(dotgit, gitdir);
+
 		free(wt->path);
 		wt->path = strbuf_detach(&path, NULL);
 	}
 	strbuf_release(&path);
+	strbuf_release(&dotgit);
+	strbuf_release(&gitdir);
 }
 
 int is_worktree_being_rebased(const struct worktree *wt,
@@ -569,6 +577,7 @@ static void repair_gitfile(struct worktree *wt,
 			   worktree_repair_fn fn, void *cb_data)
 {
 	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf repo = STRBUF_INIT;
 	struct strbuf backlink = STRBUF_INIT;
 	char *dotgit_contents = NULL;
@@ -586,6 +595,7 @@ static void repair_gitfile(struct worktree *wt,
 
 	strbuf_realpath(&repo, git_common_path("worktrees/%s", wt->id), 1);
 	strbuf_addf(&dotgit, "%s/.git", wt->path);
+	strbuf_addf(&gitdir, "%s/gitdir", repo.buf);
 	dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
 
 	if (dotgit_contents) {
@@ -603,16 +613,19 @@ static void repair_gitfile(struct worktree *wt,
 		repair = _(".git file broken");
 	else if (fspathcmp(backlink.buf, repo.buf))
 		repair = _(".git file incorrect");
+	else if (use_relative_paths == is_absolute_path(dotgit_contents))
+		repair = _(".git file absolute/relative path mismatch");
 
 	if (repair) {
 		fn(0, wt->path, repair, cb_data);
-		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+		write_worktree_linking_files(dotgit, gitdir);
 	}
 
 done:
 	free(dotgit_contents);
 	strbuf_release(&repo);
 	strbuf_release(&dotgit);
+	strbuf_release(&gitdir);
 	strbuf_release(&backlink);
 }
 
@@ -636,6 +649,45 @@ void repair_worktrees(worktree_repair_fn fn, void *cb_data)
 	free_worktrees(worktrees);
 }
 
+void repair_worktree_after_gitdir_move(struct worktree *wt,
+				       const char *old_path)
+{
+	struct strbuf gitdir = STRBUF_INIT;
+	struct strbuf dotgit = STRBUF_INIT;
+
+	if (is_main_worktree(wt))
+		goto done;
+
+	strbuf_realpath(&gitdir, git_common_path("worktrees/%s/gitdir", wt->id), 1);
+
+	if (strbuf_read_file(&dotgit, gitdir.buf, 0) < 0)
+		goto done;
+
+	strbuf_rtrim(&dotgit);
+	if (!is_absolute_path(dotgit.buf)) {
+		strbuf_insertf(&dotgit, 0, "%s/worktrees/%s/", old_path, wt->id);
+		strbuf_realpath_forgiving(&dotgit, dotgit.buf, 0);
+	}
+
+	if (!file_exists(dotgit.buf))
+		goto done;
+
+	write_worktree_linking_files(dotgit, gitdir);
+done:
+	strbuf_release(&gitdir);
+	strbuf_release(&dotgit);
+}
+
+void repair_worktrees_after_gitdir_move(const char *old_path)
+{
+	struct worktree **worktrees = get_worktrees_internal(1);
+	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
+
+	for (; *wt; wt++)
+		repair_worktree_after_gitdir_move(*wt, old_path);
+	free_worktrees(worktrees);
+}
+
 static int is_main_worktree_path(const char *path)
 {
 	struct strbuf target = STRBUF_INIT;
@@ -698,12 +750,10 @@ void repair_worktree_at_path(const char *path,
 			     worktree_repair_fn fn, void *cb_data)
 {
 	struct strbuf dotgit = STRBUF_INIT;
-	struct strbuf realdotgit = STRBUF_INIT;
 	struct strbuf backlink = STRBUF_INIT;
 	struct strbuf inferred_backlink = STRBUF_INIT;
 	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf olddotgit = STRBUF_INIT;
-	struct strbuf realolddotgit = STRBUF_INIT;
 	char *dotgit_contents = NULL;
 	const char *repair = NULL;
 	int err;
@@ -715,25 +765,25 @@ void repair_worktree_at_path(const char *path,
 		goto done;
 
 	strbuf_addf(&dotgit, "%s/.git", path);
-	if (!strbuf_realpath(&realdotgit, dotgit.buf, 0)) {
+	if (!strbuf_realpath(&dotgit, dotgit.buf, 0)) {
 		fn(1, path, _("not a valid path"), cb_data);
 		goto done;
 	}
 
-	infer_backlink(realdotgit.buf, &inferred_backlink);
+	infer_backlink(dotgit.buf, &inferred_backlink);
 	strbuf_realpath_forgiving(&inferred_backlink, inferred_backlink.buf, 0);
-	dotgit_contents = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
+	dotgit_contents = xstrdup_or_null(read_gitfile_gently(dotgit.buf, &err));
 	if (dotgit_contents) {
 		if (is_absolute_path(dotgit_contents)) {
 			strbuf_addstr(&backlink, dotgit_contents);
 		} else {
-			strbuf_addbuf(&backlink, &realdotgit);
+			strbuf_addbuf(&backlink, &dotgit);
 			strbuf_strip_suffix(&backlink, ".git");
 			strbuf_addstr(&backlink, dotgit_contents);
 			strbuf_realpath_forgiving(&backlink, backlink.buf, 0);
 		}
 	} else if (err == READ_GITFILE_ERR_NOT_A_FILE) {
-		fn(1, realdotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
+		fn(1, dotgit.buf, _("unable to locate repository; .git is not a file"), cb_data);
 		goto done;
 	} else if (err == READ_GITFILE_ERR_NOT_A_REPO) {
 		if (inferred_backlink.len) {
@@ -746,11 +796,11 @@ void repair_worktree_at_path(const char *path,
 			 */
 			strbuf_swap(&backlink, &inferred_backlink);
 		} else {
-			fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
+			fn(1, dotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
 			goto done;
 		}
 	} else {
-		fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
+		fn(1, dotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
 		goto done;
 	}
 
@@ -778,30 +828,28 @@ void repair_worktree_at_path(const char *path,
 	strbuf_addf(&gitdir, "%s/gitdir", backlink.buf);
 	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
 		repair = _("gitdir unreadable");
+	else if (use_relative_paths == is_absolute_path(olddotgit.buf))
+		repair = _("gitdir absolute/relative path mismatch");
 	else {
 		strbuf_rtrim(&olddotgit);
-		if (is_absolute_path(olddotgit.buf)) {
-			strbuf_addbuf(&realolddotgit, &olddotgit);
-		} else {
-			strbuf_addf(&realolddotgit, "%s/%s", backlink.buf, olddotgit.buf);
-			strbuf_realpath_forgiving(&realolddotgit, realolddotgit.buf, 0);
+		if (!is_absolute_path(olddotgit.buf)) {
+			strbuf_insertf(&olddotgit, 0, "%s/", backlink.buf);
+			strbuf_realpath_forgiving(&olddotgit, olddotgit.buf, 0);
 		}
-		if (fspathcmp(realolddotgit.buf, realdotgit.buf))
+		if (fspathcmp(olddotgit.buf, dotgit.buf))
 			repair = _("gitdir incorrect");
 	}
 
 	if (repair) {
 		fn(0, gitdir.buf, repair, cb_data);
-		write_file(gitdir.buf, "%s", realdotgit.buf);
+		write_worktree_linking_files(dotgit, gitdir);
 	}
 done:
 	free(dotgit_contents);
 	strbuf_release(&olddotgit);
-	strbuf_release(&realolddotgit);
 	strbuf_release(&backlink);
 	strbuf_release(&inferred_backlink);
 	strbuf_release(&gitdir);
-	strbuf_release(&realdotgit);
 	strbuf_release(&dotgit);
 }
 
@@ -963,3 +1011,29 @@ int init_worktree_config(struct repository *r)
 	free(main_worktree_file);
 	return res;
 }
+
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir)
+{
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf repo = STRBUF_INIT;
+	struct strbuf tmp = STRBUF_INIT;
+
+	strbuf_addbuf(&path, &dotgit);
+	strbuf_strip_suffix(&path, "/.git");
+	strbuf_realpath(&path, path.buf, 1);
+	strbuf_addbuf(&repo, &gitdir);
+	strbuf_strip_suffix(&repo, "/gitdir");
+	strbuf_realpath(&repo, repo.buf, 1);
+
+	if (use_relative_paths) {
+		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
+		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));
+	} else {
+		write_file(gitdir.buf, "%s/.git", path.buf);
+		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+	}
+
+	strbuf_release(&path);
+	strbuf_release(&repo);
+	strbuf_release(&tmp);
+}
diff --git a/worktree.h b/worktree.h
index 11279d0c8fe249bb30642563bf221a8de7f3b0a3..5929089891c97318a8f5329f7938264c717050d5 100644
--- a/worktree.h
+++ b/worktree.h
@@ -5,6 +5,8 @@
 
 struct strbuf;
 
+extern int use_relative_paths;
+
 struct worktree {
 	/* The repository this worktree belongs to. */
 	struct repository *repo;
@@ -131,6 +133,16 @@ typedef void (* worktree_repair_fn)(int iserr, const char *path,
  */
 void repair_worktrees(worktree_repair_fn, void *cb_data);
 
+/*
+ * Repair the linked worktrees after the gitdir has been moved.
+ */
+void repair_worktrees_after_gitdir_move(const char *old_path);
+
+/*
+ * Repair the linked worktree after the gitdir has been moved.
+ */
+void repair_worktree_after_gitdir_move(struct worktree *wt, const char *old_path);
+
 /*
  * Repair administrative files corresponding to the worktree at the given path.
  * The worktree's .git file pointing at the repository must be intact for the
@@ -205,4 +217,16 @@ void strbuf_worktree_ref(const struct worktree *wt,
  */
 int init_worktree_config(struct repository *r);
 
+/**
+ * Write the .git file and gitdir file that links the worktree to the repository.
+ *
+ * The `dotgit` parameter is the path to the worktree's .git file, and `gitdir`
+ * is the path to the repository's `gitdir` file.
+ *
+ * Example
+ *  dotgit: "/path/to/foo/.git"
+ *  gitdir: "/path/to/repo/worktrees/foo/gitdir"
+ */
+void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir);
+
 #endif

Documentation/config/extensions.txt, repository.c, repository.h, setup.c, setup.h, t/t2400-worktree-add.sh, worktree.c

diff --git a/Documentation/config/extensions.txt b/Documentation/config/extensions.txt
index 5dc569d1c9c77c15e32441493289f9c9dd5e7f0b..5cb4721a0e0ae1ed64f90492c0dc18b96473cb33 100644
--- a/Documentation/config/extensions.txt
+++ b/Documentation/config/extensions.txt
@@ -63,6 +63,12 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1]. Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
+relativeWorktrees::
+	If enabled, indicates at least one worktree has been linked with
+	relative paths. Automatically set if a worktree has been created or
+	repaired with either the `--relative-paths` option or with the
+	`worktree.useRelativePaths` config set to `true`.
+
 worktreeConfig::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
diff --git a/repository.c b/repository.c
index f988b8ae68a6a29792e7f2c980a02bd0e388a3b9..1a6a62bbd03a5dc4fdade3eb45ea2696968abc23 100644
--- a/repository.c
+++ b/repository.c
@@ -283,6 +283,7 @@ int repo_init(struct repository *repo,
 	repo_set_compat_hash_algo(repo, format.compat_hash_algo);
 	repo_set_ref_storage_format(repo, format.ref_storage_format);
 	repo->repository_format_worktree_config = format.worktree_config;
+	repo->repository_format_relative_worktrees = format.relative_worktrees;
 
 	/* take ownership of format.partial_clone */
 	repo->repository_format_partial_clone = format.partial_clone;
diff --git a/repository.h b/repository.h
index 24a66a496a6ff516ce06d47b7329b3d36eb701ca..c4c92b2ab9c9e3b425dc2974636e33d1f4089c69 100644
--- a/repository.h
+++ b/repository.h
@@ -150,6 +150,7 @@ struct repository {
 
 	/* Configurations */
 	int repository_format_worktree_config;
+	int repository_format_relative_worktrees;
 
 	/* Indicate if a repository has a different 'commondir' from 'gitdir' */
 	unsigned different_commondir:1;
diff --git a/setup.c b/setup.c
index 7b648de0279116b381eea46800ad130606926103..6bf56cf72c4b46a95f46f9b3901f7e77d702cec7 100644
--- a/setup.c
+++ b/setup.c
@@ -683,6 +683,9 @@ static enum extension_result handle_extension(const char *var,
 				     "extensions.refstorage", value);
 		data->ref_storage_format = format;
 		return EXTENSION_OK;
+	} else if (!strcmp(ext, "relativeworktrees")) {
+		data->relative_worktrees = git_config_bool(var, value);
+		return EXTENSION_OK;
 	}
 	return EXTENSION_UNKNOWN;
 }
@@ -1854,6 +1857,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 						    repo_fmt.ref_storage_format);
 			the_repository->repository_format_worktree_config =
 				repo_fmt.worktree_config;
+			the_repository->repository_format_relative_worktrees =
+				repo_fmt.relative_worktrees;
 			/* take ownership of repo_fmt.partial_clone */
 			the_repository->repository_format_partial_clone =
 				repo_fmt.partial_clone;
@@ -1950,6 +1955,8 @@ void check_repository_format(struct repository_format *fmt)
 				    fmt->ref_storage_format);
 	the_repository->repository_format_worktree_config =
 		fmt->worktree_config;
+	the_repository->repository_format_relative_worktrees =
+		fmt->relative_worktrees;
 	the_repository->repository_format_partial_clone =
 		xstrdup_or_null(fmt->partial_clone);
 	clear_repository_format(&repo_fmt);
diff --git a/setup.h b/setup.h
index e496ab3e4de580c2d9f95a7ea0eaf90e0d41b070..18dc3b73686ce28fac2fe04282ce95f8bf3e6b74 100644
--- a/setup.h
+++ b/setup.h
@@ -129,6 +129,7 @@ struct repository_format {
 	int precious_objects;
 	char *partial_clone; /* value of extensions.partialclone */
 	int worktree_config;
+	int relative_worktrees;
 	int is_bare;
 	int hash_algo;
 	int compat_hash_algo;
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 630c13230b3cc762ce8d943e22be8891aa2b1871..d36d8a4db0e924877787697579544f10f92dc0cf 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -1248,4 +1248,17 @@ test_expect_success 'move repo without breaking relative internal links' '
 	)
 '
 
+test_expect_success 'relative worktree sets extension config' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	git -C repo commit --allow-empty -m base &&
+	git -C repo worktree add --relative-paths ./foo &&
+	git -C repo config get core.repositoryformatversion >actual &&
+	echo 1 >expected &&
+	test_cmp expected actual &&
+	git -C repo config get extensions.relativeworktrees >actual &&
+	echo true >expected &&
+	test_cmp expected actual
+'
+
 test_done
diff --git a/worktree.c b/worktree.c
index 0d1685b892fcddf74a91304424a94e5ee847388b..41ebddb495d146e302fedefdb03e0d2637fb2831 100644
--- a/worktree.c
+++ b/worktree.c
@@ -1025,6 +1025,14 @@ void write_worktree_linking_files(struct strbuf dotgit, struct strbuf gitdir)
 	strbuf_strip_suffix(&repo, "/gitdir");
 	strbuf_realpath(&repo, repo.buf, 1);
 
+	if (use_relative_paths && !the_repository->repository_format_relative_worktrees) {
+		if (upgrade_repository_format(1) < 0)
+			die(_("unable to upgrade repository format to support relative worktrees"));
+		if (git_config_set_gently("extensions.relativeWorktrees", "true"))
+			die(_("unable to set extensions.relativeWorktrees setting"));
+		the_repository->repository_format_relative_worktrees = 1;
+	}
+
 	if (use_relative_paths) {
 		write_file(gitdir.buf, "%s/.git", relative_path(path.buf, repo.buf, &tmp));
 		write_file(dotgit.buf, "gitdir: %s", relative_path(repo.buf, path.buf, &tmp));