Adding upstream version 1:2.39.2.upstream/1%2.39.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 851 insertions, 0 deletions

diff --git a/worktree.c b/worktree.c
new file mode 100644
index 0000000..aa43c64
--- /dev/null
+++ b/worktree.c
@@ -0,0 +1,851 @@
+#include "cache.h"
+#include "repository.h"
+#include "refs.h"
+#include "strbuf.h"
+#include "worktree.h"
+#include "dir.h"
+#include "wt-status.h"
+#include "config.h"
+
+void free_worktrees(struct worktree **worktrees)
+{
+	int i = 0;
+
+	for (i = 0; worktrees[i]; i++) {
+		free(worktrees[i]->path);
+		free(worktrees[i]->id);
+		free(worktrees[i]->head_ref);
+		free(worktrees[i]->lock_reason);
+		free(worktrees[i]->prune_reason);
+		free(worktrees[i]);
+	}
+	free (worktrees);
+}
+
+/**
+ * Update head_oid, head_ref and is_detached of the given worktree
+ */
+static void add_head_info(struct worktree *wt)
+{
+	int flags;
+	const char *target;
+
+	target = refs_resolve_ref_unsafe(get_worktree_ref_store(wt),
+					 "HEAD",
+					 0,
+					 &wt->head_oid, &flags);
+	if (!target)
+		return;
+
+	if (flags & REF_ISSYMREF)
+		wt->head_ref = xstrdup(target);
+	else
+		wt->is_detached = 1;
+}
+
+/**
+ * get the main worktree
+ */
+static struct worktree *get_main_worktree(void)
+{
+	struct worktree *worktree = NULL;
+	struct strbuf worktree_path = STRBUF_INIT;
+
+	strbuf_add_real_path(&worktree_path, get_git_common_dir());
+	strbuf_strip_suffix(&worktree_path, "/.git");
+
+	CALLOC_ARRAY(worktree, 1);
+	worktree->path = strbuf_detach(&worktree_path, NULL);
+	/*
+	 * NEEDSWORK: If this function is called from a secondary worktree and
+	 * config.worktree is present, is_bare_repository_cfg will reflect the
+	 * contents of config.worktree, not the contents of the main worktree.
+	 * This means that worktree->is_bare may be set to 0 even if the main
+	 * worktree is configured to be bare.
+	 */
+	worktree->is_bare = (is_bare_repository_cfg == 1) ||
+		is_bare_repository();
+	add_head_info(worktree);
+	return worktree;
+}
+
+static struct worktree *get_linked_worktree(const char *id)
+{
+	struct worktree *worktree = NULL;
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf worktree_path = STRBUF_INIT;
+
+	if (!id)
+		die("Missing linked worktree name");
+
+	strbuf_git_common_path(&path, the_repository, "worktrees/%s/gitdir", id);
+	if (strbuf_read_file(&worktree_path, path.buf, 0) <= 0)
+		/* invalid gitdir file */
+		goto done;
+	strbuf_rtrim(&worktree_path);
+	strbuf_strip_suffix(&worktree_path, "/.git");
+
+	CALLOC_ARRAY(worktree, 1);
+	worktree->path = strbuf_detach(&worktree_path, NULL);
+	worktree->id = xstrdup(id);
+	add_head_info(worktree);
+
+done:
+	strbuf_release(&path);
+	strbuf_release(&worktree_path);
+	return worktree;
+}
+
+static void mark_current_worktree(struct worktree **worktrees)
+{
+	char *git_dir = absolute_pathdup(get_git_dir());
+	int i;
+
+	for (i = 0; worktrees[i]; i++) {
+		struct worktree *wt = worktrees[i];
+		const char *wt_git_dir = get_worktree_git_dir(wt);
+
+		if (!fspathcmp(git_dir, absolute_path(wt_git_dir))) {
+			wt->is_current = 1;
+			break;
+		}
+	}
+	free(git_dir);
+}
+
+struct worktree **get_worktrees(void)
+{
+	struct worktree **list = NULL;
+	struct strbuf path = STRBUF_INIT;
+	DIR *dir;
+	struct dirent *d;
+	int counter = 0, alloc = 2;
+
+	ALLOC_ARRAY(list, alloc);
+
+	list[counter++] = get_main_worktree();
+
+	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
+	dir = opendir(path.buf);
+	strbuf_release(&path);
+	if (dir) {
+		while ((d = readdir_skip_dot_and_dotdot(dir)) != NULL) {
+			struct worktree *linked = NULL;
+
+			if ((linked = get_linked_worktree(d->d_name))) {
+				ALLOC_GROW(list, counter + 1, alloc);
+				list[counter++] = linked;
+			}
+		}
+		closedir(dir);
+	}
+	ALLOC_GROW(list, counter + 1, alloc);
+	list[counter] = NULL;
+
+	mark_current_worktree(list);
+	return list;
+}
+
+const char *get_worktree_git_dir(const struct worktree *wt)
+{
+	if (!wt)
+		return get_git_dir();
+	else if (!wt->id)
+		return get_git_common_dir();
+	else
+		return git_common_path("worktrees/%s", wt->id);
+}
+
+static struct worktree *find_worktree_by_suffix(struct worktree **list,
+						const char *suffix)
+{
+	struct worktree *found = NULL;
+	int nr_found = 0, suffixlen;
+
+	suffixlen = strlen(suffix);
+	if (!suffixlen)
+		return NULL;
+
+	for (; *list && nr_found < 2; list++) {
+		const char	*path	 = (*list)->path;
+		int		 pathlen = strlen(path);
+		int		 start	 = pathlen - suffixlen;
+
+		/* suffix must start at directory boundary */
+		if ((!start || (start > 0 && is_dir_sep(path[start - 1]))) &&
+		    !fspathcmp(suffix, path + start)) {
+			found = *list;
+			nr_found++;
+		}
+	}
+	return nr_found == 1 ? found : NULL;
+}
+
+struct worktree *find_worktree(struct worktree **list,
+			       const char *prefix,
+			       const char *arg)
+{
+	struct worktree *wt;
+	char *to_free = NULL;
+
+	if ((wt = find_worktree_by_suffix(list, arg)))
+		return wt;
+
+	if (prefix)
+		arg = to_free = prefix_filename(prefix, arg);
+	wt = find_worktree_by_path(list, arg);
+	free(to_free);
+	return wt;
+}
+
+struct worktree *find_worktree_by_path(struct worktree **list, const char *p)
+{
+	struct strbuf wt_path = STRBUF_INIT;
+	char *path = real_pathdup(p, 0);
+
+	if (!path)
+		return NULL;
+	for (; *list; list++) {
+		if (!strbuf_realpath(&wt_path, (*list)->path, 0))
+			continue;
+
+		if (!fspathcmp(path, wt_path.buf))
+			break;
+	}
+	free(path);
+	strbuf_release(&wt_path);
+	return *list;
+}
+
+int is_main_worktree(const struct worktree *wt)
+{
+	return !wt->id;
+}
+
+const char *worktree_lock_reason(struct worktree *wt)
+{
+	if (is_main_worktree(wt))
+		return NULL;
+
+	if (!wt->lock_reason_valid) {
+		struct strbuf path = STRBUF_INIT;
+
+		strbuf_addstr(&path, worktree_git_path(wt, "locked"));
+		if (file_exists(path.buf)) {
+			struct strbuf lock_reason = STRBUF_INIT;
+			if (strbuf_read_file(&lock_reason, path.buf, 0) < 0)
+				die_errno(_("failed to read '%s'"), path.buf);
+			strbuf_trim(&lock_reason);
+			wt->lock_reason = strbuf_detach(&lock_reason, NULL);
+		} else
+			wt->lock_reason = NULL;
+		wt->lock_reason_valid = 1;
+		strbuf_release(&path);
+	}
+
+	return wt->lock_reason;
+}
+
+const char *worktree_prune_reason(struct worktree *wt, timestamp_t expire)
+{
+	struct strbuf reason = STRBUF_INIT;
+	char *path = NULL;
+
+	if (is_main_worktree(wt))
+		return NULL;
+	if (wt->prune_reason_valid)
+		return wt->prune_reason;
+
+	if (should_prune_worktree(wt->id, &reason, &path, expire))
+		wt->prune_reason = strbuf_detach(&reason, NULL);
+	wt->prune_reason_valid = 1;
+
+	strbuf_release(&reason);
+	free(path);
+	return wt->prune_reason;
+}
+
+/* convenient wrapper to deal with NULL strbuf */
+__attribute__((format (printf, 2, 3)))
+static void strbuf_addf_gently(struct strbuf *buf, const char *fmt, ...)
+{
+	va_list params;
+
+	if (!buf)
+		return;
+
+	va_start(params, fmt);
+	strbuf_vaddf(buf, fmt, params);
+	va_end(params);
+}
+
+int validate_worktree(const struct worktree *wt, struct strbuf *errmsg,
+		      unsigned flags)
+{
+	struct strbuf wt_path = STRBUF_INIT;
+	struct strbuf realpath = STRBUF_INIT;
+	char *path = NULL;
+	int err, ret = -1;
+
+	strbuf_addf(&wt_path, "%s/.git", wt->path);
+
+	if (is_main_worktree(wt)) {
+		if (is_directory(wt_path.buf)) {
+			ret = 0;
+			goto done;
+		}
+		/*
+		 * Main worktree using .git file to point to the
+		 * repository would make it impossible to know where
+		 * the actual worktree is if this function is executed
+		 * from another worktree. No .git file support for now.
+		 */
+		strbuf_addf_gently(errmsg,
+				   _("'%s' at main working tree is not the repository directory"),
+				   wt_path.buf);
+		goto done;
+	}
+
+	/*
+	 * Make sure "gitdir" file points to a real .git file and that
+	 * file points back here.
+	 */
+	if (!is_absolute_path(wt->path)) {
+		strbuf_addf_gently(errmsg,
+				   _("'%s' file does not contain absolute path to the working tree location"),
+				   git_common_path("worktrees/%s/gitdir", wt->id));
+		goto done;
+	}
+
+	if (flags & WT_VALIDATE_WORKTREE_MISSING_OK &&
+	    !file_exists(wt->path)) {
+		ret = 0;
+		goto done;
+	}
+
+	if (!file_exists(wt_path.buf)) {
+		strbuf_addf_gently(errmsg, _("'%s' does not exist"), wt_path.buf);
+		goto done;
+	}
+
+	path = xstrdup_or_null(read_gitfile_gently(wt_path.buf, &err));
+	if (!path) {
+		strbuf_addf_gently(errmsg, _("'%s' is not a .git file, error code %d"),
+				   wt_path.buf, err);
+		goto done;
+	}
+
+	strbuf_realpath(&realpath, git_common_path("worktrees/%s", wt->id), 1);
+	ret = fspathcmp(path, realpath.buf);
+
+	if (ret)
+		strbuf_addf_gently(errmsg, _("'%s' does not point back to '%s'"),
+				   wt->path, git_common_path("worktrees/%s", wt->id));
+done:
+	free(path);
+	strbuf_release(&wt_path);
+	strbuf_release(&realpath);
+	return ret;
+}
+
+void update_worktree_location(struct worktree *wt, const char *path_)
+{
+	struct strbuf path = STRBUF_INIT;
+
+	if (is_main_worktree(wt))
+		BUG("can't relocate main worktree");
+
+	strbuf_realpath(&path, path_, 1);
+	if (fspathcmp(wt->path, path.buf)) {
+		write_file(git_common_path("worktrees/%s/gitdir", wt->id),
+			   "%s/.git", path.buf);
+		free(wt->path);
+		wt->path = strbuf_detach(&path, NULL);
+	}
+	strbuf_release(&path);
+}
+
+int is_worktree_being_rebased(const struct worktree *wt,
+			      const char *target)
+{
+	struct wt_status_state state;
+	int found_rebase;
+
+	memset(&state, 0, sizeof(state));
+	found_rebase = wt_status_check_rebase(wt, &state) &&
+		       (state.rebase_in_progress ||
+			state.rebase_interactive_in_progress) &&
+		       state.branch &&
+		       skip_prefix(target, "refs/heads/", &target) &&
+		       !strcmp(state.branch, target);
+	wt_status_state_free_buffers(&state);
+	return found_rebase;
+}
+
+int is_worktree_being_bisected(const struct worktree *wt,
+			       const char *target)
+{
+	struct wt_status_state state;
+	int found_bisect;
+
+	memset(&state, 0, sizeof(state));
+	found_bisect = wt_status_check_bisect(wt, &state) &&
+		       state.branch &&
+		       skip_prefix(target, "refs/heads/", &target) &&
+		       !strcmp(state.branch, target);
+	wt_status_state_free_buffers(&state);
+	return found_bisect;
+}
+
+/*
+ * note: this function should be able to detect shared symref even if
+ * HEAD is temporarily detached (e.g. in the middle of rebase or
+ * bisect). New commands that do similar things should update this
+ * function as well.
+ */
+const struct worktree *find_shared_symref(struct worktree **worktrees,
+					  const char *symref,
+					  const char *target)
+{
+	const struct worktree *existing = NULL;
+	int i = 0;
+
+	for (i = 0; worktrees[i]; i++) {
+		struct worktree *wt = worktrees[i];
+		const char *symref_target;
+		struct ref_store *refs;
+		int flags;
+
+		if (wt->is_bare)
+			continue;
+
+		if (wt->is_detached && !strcmp(symref, "HEAD")) {
+			if (is_worktree_being_rebased(wt, target)) {
+				existing = wt;
+				break;
+			}
+			if (is_worktree_being_bisected(wt, target)) {
+				existing = wt;
+				break;
+			}
+		}
+
+		refs = get_worktree_ref_store(wt);
+		symref_target = refs_resolve_ref_unsafe(refs, symref, 0,
+							NULL, &flags);
+		if ((flags & REF_ISSYMREF) &&
+		    symref_target && !strcmp(symref_target, target)) {
+			existing = wt;
+			break;
+		}
+	}
+
+	return existing;
+}
+
+int submodule_uses_worktrees(const char *path)
+{
+	char *submodule_gitdir;
+	struct strbuf sb = STRBUF_INIT, err = STRBUF_INIT;
+	DIR *dir;
+	struct dirent *d;
+	int ret = 0;
+	struct repository_format format = REPOSITORY_FORMAT_INIT;
+
+	submodule_gitdir = git_pathdup_submodule(path, "%s", "");
+	if (!submodule_gitdir)
+		return 0;
+
+	/* The env would be set for the superproject. */
+	get_common_dir_noenv(&sb, submodule_gitdir);
+	free(submodule_gitdir);
+
+	strbuf_addstr(&sb, "/config");
+	read_repository_format(&format, sb.buf);
+	if (verify_repository_format(&format, &err)) {
+		strbuf_release(&err);
+		strbuf_release(&sb);
+		clear_repository_format(&format);
+		return 1;
+	}
+	clear_repository_format(&format);
+	strbuf_release(&err);
+
+	/* Replace config by worktrees. */
+	strbuf_setlen(&sb, sb.len - strlen("config"));
+	strbuf_addstr(&sb, "worktrees");
+
+	/* See if there is any file inside the worktrees directory. */
+	dir = opendir(sb.buf);
+	strbuf_release(&sb);
+
+	if (!dir)
+		return 0;
+
+	d = readdir_skip_dot_and_dotdot(dir);
+	if (d)
+		ret = 1;
+	closedir(dir);
+	return ret;
+}
+
+void strbuf_worktree_ref(const struct worktree *wt,
+			 struct strbuf *sb,
+			 const char *refname)
+{
+	if (parse_worktree_ref(refname, NULL, NULL, NULL) ==
+		    REF_WORKTREE_CURRENT &&
+	    wt && !wt->is_current) {
+		if (is_main_worktree(wt))
+			strbuf_addstr(sb, "main-worktree/");
+		else
+			strbuf_addf(sb, "worktrees/%s/", wt->id);
+	}
+	strbuf_addstr(sb, refname);
+}
+
+int other_head_refs(each_ref_fn fn, void *cb_data)
+{
+	struct worktree **worktrees, **p;
+	struct strbuf refname = STRBUF_INIT;
+	int ret = 0;
+
+	worktrees = get_worktrees();
+	for (p = worktrees; *p; p++) {
+		struct worktree *wt = *p;
+		struct object_id oid;
+		int flag;
+
+		if (wt->is_current)
+			continue;
+
+		strbuf_reset(&refname);
+		strbuf_worktree_ref(wt, &refname, "HEAD");
+		if (refs_resolve_ref_unsafe(get_main_ref_store(the_repository),
+					    refname.buf,
+					    RESOLVE_REF_READING,
+					    &oid, &flag))
+			ret = fn(refname.buf, &oid, flag, cb_data);
+		if (ret)
+			break;
+	}
+	free_worktrees(worktrees);
+	strbuf_release(&refname);
+	return ret;
+}
+
+/*
+ * Repair worktree's /path/to/worktree/.git file if missing, corrupt, or not
+ * pointing at <repo>/worktrees/<id>.
+ */
+static void repair_gitfile(struct worktree *wt,
+			   worktree_repair_fn fn, void *cb_data)
+{
+	struct strbuf dotgit = STRBUF_INIT;
+	struct strbuf repo = STRBUF_INIT;
+	char *backlink;
+	const char *repair = NULL;
+	int err;
+
+	/* missing worktree can't be repaired */
+	if (!file_exists(wt->path))
+		return;
+
+	if (!is_directory(wt->path)) {
+		fn(1, wt->path, _("not a directory"), cb_data);
+		return;
+	}
+
+	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));
+
+	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))
+		repair = _(".git file incorrect");
+
+	if (repair) {
+		fn(0, wt->path, repair, cb_data);
+		write_file(dotgit.buf, "gitdir: %s", repo.buf);
+	}
+
+	free(backlink);
+	strbuf_release(&repo);
+	strbuf_release(&dotgit);
+}
+
+static void repair_noop(int iserr, const char *path, const char *msg,
+			void *cb_data)
+{
+	/* nothing */
+}
+
+void repair_worktrees(worktree_repair_fn fn, void *cb_data)
+{
+	struct worktree **worktrees = get_worktrees();
+	struct worktree **wt = worktrees + 1; /* +1 skips main worktree */
+
+	if (!fn)
+		fn = repair_noop;
+	for (; *wt; wt++)
+		repair_gitfile(*wt, fn, cb_data);
+	free_worktrees(worktrees);
+}
+
+static int is_main_worktree_path(const char *path)
+{
+	struct strbuf target = STRBUF_INIT;
+	struct strbuf maindir = STRBUF_INIT;
+	int cmp;
+
+	strbuf_add_real_path(&target, path);
+	strbuf_strip_suffix(&target, "/.git");
+	strbuf_add_real_path(&maindir, get_git_common_dir());
+	strbuf_strip_suffix(&maindir, "/.git");
+	cmp = fspathcmp(maindir.buf, target.buf);
+
+	strbuf_release(&maindir);
+	strbuf_release(&target);
+	return !cmp;
+}
+
+/*
+ * If both the main worktree and linked worktree have been moved, then the
+ * gitfile /path/to/worktree/.git won't point into the repository, thus we
+ * 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.
+ */
+static char *infer_backlink(const char *gitfile)
+{
+	struct strbuf actual = STRBUF_INIT;
+	struct strbuf inferred = STRBUF_INIT;
+	const char *id;
+
+	if (strbuf_read_file(&actual, gitfile, 0) < 0)
+		goto error;
+	if (!starts_with(actual.buf, "gitdir:"))
+		goto error;
+	if (!(id = find_last_dir_sep(actual.buf)))
+		goto error;
+	strbuf_trim(&actual);
+	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))
+		goto error;
+
+	strbuf_release(&actual);
+	return strbuf_detach(&inferred, NULL);
+
+error:
+	strbuf_release(&actual);
+	strbuf_release(&inferred);
+	return NULL;
+}
+
+/*
+ * Repair <repo>/worktrees/<id>/gitdir if missing, corrupt, or not pointing at
+ * the worktree's path.
+ */
+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 gitdir = STRBUF_INIT;
+	struct strbuf olddotgit = STRBUF_INIT;
+	char *backlink = NULL;
+	const char *repair = NULL;
+	int err;
+
+	if (!fn)
+		fn = repair_noop;
+
+	if (is_main_worktree_path(path))
+		goto done;
+
+	strbuf_addf(&dotgit, "%s/.git", path);
+	if (!strbuf_realpath(&realdotgit, dotgit.buf, 0)) {
+		fn(1, path, _("not a valid path"), cb_data);
+		goto done;
+	}
+
+	backlink = xstrdup_or_null(read_gitfile_gently(realdotgit.buf, &err));
+	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 (!(backlink = infer_backlink(realdotgit.buf))) {
+			fn(1, realdotgit.buf, _("unable to locate repository; .git file does not reference a repository"), cb_data);
+			goto done;
+		}
+	} else if (err) {
+		fn(1, realdotgit.buf, _("unable to locate repository; .git file broken"), cb_data);
+		goto done;
+	}
+
+	strbuf_addf(&gitdir, "%s/gitdir", backlink);
+	if (strbuf_read_file(&olddotgit, gitdir.buf, 0) < 0)
+		repair = _("gitdir unreadable");
+	else {
+		strbuf_rtrim(&olddotgit);
+		if (fspathcmp(olddotgit.buf, realdotgit.buf))
+			repair = _("gitdir incorrect");
+	}
+
+	if (repair) {
+		fn(0, gitdir.buf, repair, cb_data);
+		write_file(gitdir.buf, "%s", realdotgit.buf);
+	}
+done:
+	free(backlink);
+	strbuf_release(&olddotgit);
+	strbuf_release(&gitdir);
+	strbuf_release(&realdotgit);
+	strbuf_release(&dotgit);
+}
+
+int should_prune_worktree(const char *id, struct strbuf *reason, char **wtpath, timestamp_t expire)
+{
+	struct stat st;
+	char *path;
+	int fd;
+	size_t len;
+	ssize_t read_result;
+
+	*wtpath = NULL;
+	if (!is_directory(git_path("worktrees/%s", id))) {
+		strbuf_addstr(reason, _("not a valid directory"));
+		return 1;
+	}
+	if (file_exists(git_path("worktrees/%s/locked", id)))
+		return 0;
+	if (stat(git_path("worktrees/%s/gitdir", id), &st)) {
+		strbuf_addstr(reason, _("gitdir file does not exist"));
+		return 1;
+	}
+	fd = open(git_path("worktrees/%s/gitdir", id), O_RDONLY);
+	if (fd < 0) {
+		strbuf_addf(reason, _("unable to read gitdir file (%s)"),
+			    strerror(errno));
+		return 1;
+	}
+	len = xsize_t(st.st_size);
+	path = xmallocz(len);
+
+	read_result = read_in_full(fd, path, len);
+	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) {
+		strbuf_addf(reason,
+			    _("short read (expected %"PRIuMAX" bytes, read %"PRIuMAX")"),
+			    (uintmax_t)len, (uintmax_t)read_result);
+		free(path);
+		return 1;
+	}
+	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
+		len--;
+	if (!len) {
+		strbuf_addstr(reason, _("invalid gitdir file"));
+		free(path);
+		return 1;
+	}
+	path[len] = '\0';
+	if (!file_exists(path)) {
+		if (stat(git_path("worktrees/%s/index", id), &st) ||
+		    st.st_mtime <= expire) {
+			strbuf_addstr(reason, _("gitdir file points to non-existent location"));
+			free(path);
+			return 1;
+		} else {
+			*wtpath = path;
+			return 0;
+		}
+	}
+	*wtpath = path;
+	return 0;
+}
+
+static int move_config_setting(const char *key, const char *value,
+			       const char *from_file, const char *to_file)
+{
+	if (git_config_set_in_file_gently(to_file, key, value))
+		return error(_("unable to set %s in '%s'"), key, to_file);
+	if (git_config_set_in_file_gently(from_file, key, NULL))
+		return error(_("unable to unset %s in '%s'"), key, from_file);
+	return 0;
+}
+
+int init_worktree_config(struct repository *r)
+{
+	int res = 0;
+	int bare = 0;
+	struct config_set cs = { { 0 } };
+	const char *core_worktree;
+	char *common_config_file;
+	char *main_worktree_file;
+
+	/*
+	 * If the extension is already enabled, then we can skip the
+	 * upgrade process.
+	 */
+	if (repository_format_worktree_config)
+		return 0;
+	if ((res = git_config_set_gently("extensions.worktreeConfig", "true")))
+		return error(_("failed to set extensions.worktreeConfig setting"));
+
+	common_config_file = xstrfmt("%s/config", r->commondir);
+	main_worktree_file = xstrfmt("%s/config.worktree", r->commondir);
+
+	git_configset_init(&cs);
+	git_configset_add_file(&cs, common_config_file);
+
+	/*
+	 * If core.bare is true in the common config file, then we need to
+	 * move it to the main worktree's config file or it will break all
+	 * worktrees. If it is false, then leave it in place because it
+	 * _could_ be negating a global core.bare=true.
+	 */
+	if (!git_configset_get_bool(&cs, "core.bare", &bare) && bare) {
+		if ((res = move_config_setting("core.bare", "true",
+					       common_config_file,
+					       main_worktree_file)))
+			goto cleanup;
+	}
+	/*
+	 * If core.worktree is set, then the main worktree is located
+	 * somewhere different than the parent of the common Git dir.
+	 * Relocate that value to avoid breaking all worktrees with this
+	 * upgrade to worktree config.
+	 */
+	if (!git_configset_get_value(&cs, "core.worktree", &core_worktree)) {
+		if ((res = move_config_setting("core.worktree", core_worktree,
+					       common_config_file,
+					       main_worktree_file)))
+			goto cleanup;
+	}
+
+	/*
+	 * Ensure that we use worktree config for the remaining lifetime
+	 * of the current process.
+	 */
+	repository_format_worktree_config = 1;
+
+cleanup:
+	git_configset_clear(&cs);
+	free(common_config_file);
+	free(main_worktree_file);
+	return res;
+}