Merge branch 'nd/worktree-various-heads'

The experimental "multiple worktree" feature gains more safety to
forbid operations on a branch that is checked out or being actively
worked on elsewhere, by noticing that e.g. it is being rebased.

* nd/worktree-various-heads:
  branch: do not rename a branch under bisect or rebase
  worktree.c: check whether branch is bisected in another worktree
  wt-status.c: split bisect detection out of wt_status_get_state()
  worktree.c: check whether branch is rebased in another worktree
  worktree.c: avoid referencing to worktrees[i] multiple times
  wt-status.c: make wt_status_check_rebase() work on any worktree
  wt-status.c: split rebase detection out of wt_status_get_state()
  path.c: refactor and add worktree_git_path()
  worktree.c: mark current worktree
  worktree.c: make find_shared_symref() return struct worktree *
  worktree.c: store "id" instead of "git_dir"
  path.c: add git_common_path() and strbuf_git_common_path()
  dir.c: rename str(n)cmp_icase to fspath(n)cmp

branch.c

@@ -334,15 +334,16 @@ void remove_branch_state(void)
 	unlink(git_path_squash_msg());
 }
 
-void die_if_checked_out(const char *branch)
+void die_if_checked_out(const char *branch, int ignore_current_worktree)
 {
-	char *existing;
+	const struct worktree *wt;
 
-	existing = find_shared_symref("HEAD", branch);
-	if (existing) {
-		skip_prefix(branch, "refs/heads/", &branch);
-		die(_("'%s' is already checked out at '%s'"), branch, existing);
-	}
+	wt = find_shared_symref("HEAD", branch);
+	if (!wt || (ignore_current_worktree && wt->is_current))
+		return;
+	skip_prefix(branch, "refs/heads/", &branch);
+	die(_("'%s' is already checked out at '%s'"),
+	    branch, wt->path);
 }
 
 int replace_each_worktree_head_symref(const char *oldref, const char *newref)
@@ -357,7 +358,8 @@ int replace_each_worktree_head_symref(const char *oldref, const char *newref)
 		if (strcmp(oldref, worktrees[i]->head_ref))
 			continue;
 
-		if (set_worktree_head_symref(worktrees[i]->git_dir, newref)) {
+		if (set_worktree_head_symref(get_worktree_git_dir(worktrees[i]),
+					     newref)) {
 			ret = -1;
 			error(_("HEAD of working tree %s is not updated"),
 			      worktrees[i]->path);

branch.h

@@ -58,7 +58,7 @@ extern int read_branch_desc(struct strbuf *, const char *branch_name);
  * worktree and die (with a message describing its checkout location) if
  * it is.
  */
-extern void die_if_checked_out(const char *branch);
+extern void die_if_checked_out(const char *branch, int ignore_current_worktree);
 
 /*
  * Update all per-worktree HEADs pointing at the old ref to point the new ref.

builtin/branch.c

@@ -220,12 +220,12 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 		name = mkpathdup(fmt, bname.buf);
 
 		if (kinds == FILTER_REFS_BRANCHES) {
-			char *worktree = find_shared_symref("HEAD", name);
-			if (worktree) {
+			const struct worktree *wt =
+				find_shared_symref("HEAD", name);
+			if (wt) {
 				error(_("Cannot delete branch '%s' "
 					"checked out at '%s'"),
-				      bname.buf, worktree);
-				free(worktree);
+				      bname.buf, wt->path);
 				ret = 1;
 				continue;
 			}
@@ -526,6 +526,29 @@ static void print_ref_list(struct ref_filter *filter, struct ref_sorting *sortin
 	ref_array_clear(&array);
 }
 
+static void reject_rebase_or_bisect_branch(const char *target)
+{
+	struct worktree **worktrees = get_worktrees();
+	int i;
+
+	for (i = 0; worktrees[i]; i++) {
+		struct worktree *wt = worktrees[i];
+
+		if (!wt->is_detached)
+			continue;
+
+		if (is_worktree_being_rebased(wt, target))
+			die(_("Branch %s is being rebased at %s"),
+			    target, wt->path);
+
+		if (is_worktree_being_bisected(wt, target))
+			die(_("Branch %s is being bisected at %s"),
+			    target, wt->path);
+	}
+
+	free_worktrees(worktrees);
+}
+
 static void rename_branch(const char *oldname, const char *newname, int force)
 {
 	struct strbuf oldref = STRBUF_INIT, newref = STRBUF_INIT, logmsg = STRBUF_INIT;
@@ -555,6 +578,8 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 
 	validate_new_branchname(newname, &newref, force, clobber_head_ok);
 
+	reject_rebase_or_bisect_branch(oldref.buf);
+
 	strbuf_addf(&logmsg, "Branch: renamed %s to %s",
 		 oldref.buf, newref.buf);
 

builtin/checkout.c

@@ -1110,7 +1110,7 @@ static int checkout_branch(struct checkout_opts *opts,
 		char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
 		if (head_ref &&
 		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
-			die_if_checked_out(new->path);
+			die_if_checked_out(new->path, 1);
 		free(head_ref);
 	}
 

builtin/notes.c

@@ -847,15 +847,15 @@ static int merge(int argc, const char **argv, const char *prefix)
 		update_ref(msg.buf, default_notes_ref(), result_sha1, NULL,
 			   0, UPDATE_REFS_DIE_ON_ERR);
 	else { /* Merge has unresolved conflicts */
-		char *existing;
+		const struct worktree *wt;
 		/* Update .git/NOTES_MERGE_PARTIAL with partial merge result */
 		update_ref(msg.buf, "NOTES_MERGE_PARTIAL", result_sha1, NULL,
 			   0, UPDATE_REFS_DIE_ON_ERR);
 		/* Store ref-to-be-updated into .git/NOTES_MERGE_REF */
-		existing = find_shared_symref("NOTES_MERGE_REF", default_notes_ref());
-		if (existing)
+		wt = find_shared_symref("NOTES_MERGE_REF", default_notes_ref());
+		if (wt)
 			die(_("A notes merge into %s is already in-progress at %s"),
-			    default_notes_ref(), existing);
+			    default_notes_ref(), wt->path);
 		if (create_symref("NOTES_MERGE_REF", default_notes_ref(), NULL))
 			die("Failed to store link to current notes ref (%s)",
 			    default_notes_ref());

builtin/worktree.c

@@ -205,7 +205,7 @@ static int add_worktree(const char *path, const char *refname,
 	if (!opts->detach && !strbuf_check_branch_ref(&symref, refname) &&
 		 ref_exists(symref.buf)) { /* it's a branch */
 		if (!opts->force)
-			die_if_checked_out(symref.buf);
+			die_if_checked_out(symref.buf, 0);
 	} else { /* must be a commit */
 		commit = lookup_commit_reference_by_name(refname);
 		if (!commit)
@@ -349,7 +349,7 @@ static int add(int ac, const char **av, const char *prefix)
 		if (!opts.force &&
 		    !strbuf_check_branch_ref(&symref, opts.new_branch) &&
 		    ref_exists(symref.buf))
-			die_if_checked_out(symref.buf);
+			die_if_checked_out(symref.buf, 0);
 		strbuf_release(&symref);
 	}
 

cache.h

@@ -808,11 +808,14 @@ extern void check_repository_format(void);
  */
 extern const char *mkpath(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
 extern const char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
+extern const char *git_common_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
 
 extern char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 	__attribute__((format (printf, 3, 4)));
 extern void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
+extern void strbuf_git_common_path(struct strbuf *sb, const char *fmt, ...)
+	__attribute__((format (printf, 2, 3)));
 extern char *git_path_buf(struct strbuf *buf, const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
 extern void strbuf_git_path_submodule(struct strbuf *sb, const char *path,

dir.c

@@ -53,13 +53,12 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
 	int check_only, const struct path_simplify *simplify);
 static int get_dtype(struct dirent *de, const char *path, int len);
 
-/* helper string functions with support for the ignore_case flag */
-int strcmp_icase(const char *a, const char *b)
+int fspathcmp(const char *a, const char *b)
 {
 	return ignore_case ? strcasecmp(a, b) : strcmp(a, b);
 }
 
-int strncmp_icase(const char *a, const char *b, size_t count)
+int fspathncmp(const char *a, const char *b, size_t count)
 {
 	return ignore_case ? strncasecmp(a, b, count) : strncmp(a, b, count);
 }
@@ -795,12 +794,12 @@ int match_basename(const char *basename, int basenamelen,
 {
 	if (prefix == patternlen) {
 		if (patternlen == basenamelen &&
-		    !strncmp_icase(pattern, basename, basenamelen))
+		    !fspathncmp(pattern, basename, basenamelen))
 			return 1;
 	} else if (flags & EXC_FLAG_ENDSWITH) {
 		/* "*literal" matching against "fooliteral" */
 		if (patternlen - 1 <= basenamelen &&
-		    !strncmp_icase(pattern + 1,
+		    !fspathncmp(pattern + 1,
 				   basename + basenamelen - (patternlen - 1),
 				   patternlen - 1))
 			return 1;
@@ -837,7 +836,7 @@ int match_pathname(const char *pathname, int pathlen,
 	 */
 	if (pathlen < baselen + 1 ||
 	    (baselen && pathname[baselen] != '/') ||
-	    strncmp_icase(pathname, base, baselen))
+	    fspathncmp(pathname, base, baselen))
 		return 0;
 
 	namelen = baselen ? pathlen - baselen - 1 : pathlen;
@@ -851,7 +850,7 @@ int match_pathname(const char *pathname, int pathlen,
 		if (prefix > namelen)
 			return 0;
 
-		if (strncmp_icase(pattern, name, prefix))
+		if (fspathncmp(pattern, name, prefix))
 			return 0;
 		pattern += prefix;
 		patternlen -= prefix;

dir.h

@@ -270,8 +270,8 @@ extern int remove_dir_recursively(struct strbuf *path, int flag);
 /* tries to remove the path with empty directories along it, ignores ENOENT */
 extern int remove_path(const char *path);
 
-extern int strcmp_icase(const char *a, const char *b);
-extern int strncmp_icase(const char *a, const char *b, size_t count);
+extern int fspathcmp(const char *a, const char *b);
+extern int fspathncmp(const char *a, const char *b, size_t count);
 
 /*
  * The prefix part of pattern must not contains wildcards.

fast-import.c

@@ -1512,7 +1512,7 @@ static int tree_content_set(
 	t = root->tree;
 	for (i = 0; i < t->entry_count; i++) {
 		e = t->entries[i];
-		if (e->name->str_len == n && !strncmp_icase(p, e->name->str_dat, n)) {
+		if (e->name->str_len == n && !fspathncmp(p, e->name->str_dat, n)) {
 			if (!*slash1) {
 				if (!S_ISDIR(mode)
 						&& e->versions[1].mode == mode
@@ -1602,7 +1602,7 @@ static int tree_content_remove(
 	t = root->tree;
 	for (i = 0; i < t->entry_count; i++) {
 		e = t->entries[i];
-		if (e->name->str_len == n && !strncmp_icase(p, e->name->str_dat, n)) {
+		if (e->name->str_len == n && !fspathncmp(p, e->name->str_dat, n)) {
 			if (*slash1 && !S_ISDIR(e->versions[1].mode))
 				/*
 				 * If p names a file in some subdirectory, and a
@@ -1669,7 +1669,7 @@ static int tree_content_get(
 	t = root->tree;
 	for (i = 0; i < t->entry_count; i++) {
 		e = t->entries[i];
-		if (e->name->str_len == n && !strncmp_icase(p, e->name->str_dat, n)) {
+		if (e->name->str_len == n && !fspathncmp(p, e->name->str_dat, n)) {
 			if (!*slash1)
 				goto found_entry;
 			if (!S_ISDIR(e->versions[1].mode))

path.c

@@ -5,6 +5,7 @@
 #include "strbuf.h"
 #include "string-list.h"
 #include "dir.h"
+#include "worktree.h"
 
 static int get_st_mode_bits(const char *path, int *mode)
 {
@@ -383,10 +384,11 @@ static void adjust_git_path(struct strbuf *buf, int git_dir_len)
 		update_common_dir(buf, git_dir_len, NULL);
 }
 
-static void do_git_path(struct strbuf *buf, const char *fmt, va_list args)
+static void do_git_path(const struct worktree *wt, struct strbuf *buf,
+			const char *fmt, va_list args)
 {
 	int gitdir_len;
-	strbuf_addstr(buf, get_git_dir());
+	strbuf_addstr(buf, get_worktree_git_dir(wt));
 	if (buf->len && !is_dir_sep(buf->buf[buf->len - 1]))
 		strbuf_addch(buf, '/');
 	gitdir_len = buf->len;
@@ -400,7 +402,7 @@ char *git_path_buf(struct strbuf *buf, const char *fmt, ...)
 	va_list args;
 	strbuf_reset(buf);
 	va_start(args, fmt);
-	do_git_path(buf, fmt, args);
+	do_git_path(NULL, buf, fmt, args);
 	va_end(args);
 	return buf->buf;
 }
@@ -409,7 +411,7 @@ void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
 {
 	va_list args;
 	va_start(args, fmt);
-	do_git_path(sb, fmt, args);
+	do_git_path(NULL, sb, fmt, args);
 	va_end(args);
 }
 
@@ -418,7 +420,7 @@ const char *git_path(const char *fmt, ...)
 	struct strbuf *pathname = get_pathname();
 	va_list args;
 	va_start(args, fmt);
-	do_git_path(pathname, fmt, args);
+	do_git_path(NULL, pathname, fmt, args);
 	va_end(args);
 	return pathname->buf;
 }
@@ -428,7 +430,7 @@ char *git_pathdup(const char *fmt, ...)
 	struct strbuf path = STRBUF_INIT;
 	va_list args;
 	va_start(args, fmt);
-	do_git_path(&path, fmt, args);
+	do_git_path(NULL, &path, fmt, args);
 	va_end(args);
 	return strbuf_detach(&path, NULL);
 }
@@ -454,6 +456,16 @@ const char *mkpath(const char *fmt, ...)
 	return cleanup_path(pathname->buf);
 }
 
+const char *worktree_git_path(const struct worktree *wt, const char *fmt, ...)
+{
+	struct strbuf *pathname = get_pathname();
+	va_list args;
+	va_start(args, fmt);
+	do_git_path(wt, pathname, fmt, args);
+	va_end(args);
+	return pathname->buf;
+}
+
 static void do_submodule_path(struct strbuf *buf, const char *path,
 			      const char *fmt, va_list args)
 {
@@ -503,6 +515,35 @@ void strbuf_git_path_submodule(struct strbuf *buf, const char *path,
 	va_end(args);
 }
 
+static void do_git_common_path(struct strbuf *buf,
+			       const char *fmt,
+			       va_list args)
+{
+	strbuf_addstr(buf, get_git_common_dir());
+	if (buf->len && !is_dir_sep(buf->buf[buf->len - 1]))
+		strbuf_addch(buf, '/');
+	strbuf_vaddf(buf, fmt, args);
+	strbuf_cleanup_path(buf);
+}
+
+const char *git_common_path(const char *fmt, ...)
+{
+	struct strbuf *pathname = get_pathname();
+	va_list args;
+	va_start(args, fmt);
+	do_git_common_path(pathname, fmt, args);
+	va_end(args);
+	return pathname->buf;
+}
+
+void strbuf_git_common_path(struct strbuf *sb, const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	do_git_common_path(sb, fmt, args);
+	va_end(args);
+}
+
 int validate_headref(const char *path)
 {
 	struct stat st;

sha1_file.c

@@ -301,7 +301,7 @@ static int link_alt_odb_entry(const char *entry, const char *relative_base,
 			return -1;
 		}
 	}
-	if (!strcmp_icase(ent->base, normalized_objdir)) {
+	if (!fspathcmp(ent->base, normalized_objdir)) {
 		free(ent);
 		return -1;
 	}

t/t2025-worktree-add.sh

@@ -4,6 +4,8 @@ test_description='test git worktree add'
 
 . ./test-lib.sh
 
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
 test_expect_success 'setup' '
 	test_commit init
 '
@@ -225,4 +227,61 @@ test_expect_success '"add" worktree with --checkout' '
 	test_cmp init.t swamp2/init.t
 '
 
+test_expect_success 'put a worktree under rebase' '
+	git worktree add under-rebase &&
+	(
+		cd under-rebase &&
+		set_fake_editor &&
+		FAKE_LINES="edit 1" git rebase -i HEAD^ &&
+		git worktree list | grep "under-rebase.*detached HEAD"
+	)
+'
+
+test_expect_success 'add a worktree, checking out a rebased branch' '
+	test_must_fail git worktree add new-rebase under-rebase &&
+	! test -d new-rebase
+'
+
+test_expect_success 'checking out a rebased branch from another worktree' '
+	git worktree add new-place &&
+	test_must_fail git -C new-place checkout under-rebase
+'
+
+test_expect_success 'not allow to delete a branch under rebase' '
+	(
+		cd under-rebase &&
+		test_must_fail git branch -D under-rebase
+	)
+'
+
+test_expect_success 'rename a branch under rebase not allowed' '
+	test_must_fail git branch -M under-rebase rebase-with-new-name
+'
+
+test_expect_success 'check out from current worktree branch ok' '
+	(
+		cd under-rebase &&
+		git checkout under-rebase &&
+		git checkout - &&
+		git rebase --abort
+	)
+'
+
+test_expect_success 'checkout a branch under bisect' '
+	git worktree add under-bisect &&
+	(
+		cd under-bisect &&
+		git bisect start &&
+		git bisect bad &&
+		git bisect good HEAD~2 &&
+		git worktree list | grep "under-bisect.*detached HEAD" &&
+		test_must_fail git worktree add new-bisect under-bisect &&
+		! test -d new-bisect
+	)
+'
+
+test_expect_success 'rename a branch under bisect not allowed' '
+	test_must_fail git branch -M under-bisect bisect-with-new-name
+'
+
 test_done

worktree.c

@@ -2,6 +2,8 @@
 #include "refs.h"
 #include "strbuf.h"
 #include "worktree.h"
+#include "dir.h"
+#include "wt-status.h"
 
 void free_worktrees(struct worktree **worktrees)
 {
@@ -9,7 +11,7 @@ void free_worktrees(struct worktree **worktrees)
 
 	for (i = 0; worktrees[i]; i++) {
 		free(worktrees[i]->path);
-		free(worktrees[i]->git_dir);
+		free(worktrees[i]->id);
 		free(worktrees[i]->head_ref);
 		free(worktrees[i]);
 	}
@@ -74,13 +76,11 @@ static struct worktree *get_main_worktree(void)
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;
 	struct strbuf worktree_path = STRBUF_INIT;
-	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf head_ref = STRBUF_INIT;
 	int is_bare = 0;
 	int is_detached = 0;
 
-	strbuf_addf(&gitdir, "%s", absolute_path(get_git_common_dir()));
-	strbuf_addbuf(&worktree_path, &gitdir);
+	strbuf_addstr(&worktree_path, absolute_path(get_git_common_dir()));
 	is_bare = !strbuf_strip_suffix(&worktree_path, "/.git");
 	if (is_bare)
 		strbuf_strip_suffix(&worktree_path, "/.");
@@ -92,15 +92,15 @@ static struct worktree *get_main_worktree(void)
 
 	worktree = xmalloc(sizeof(struct worktree));
 	worktree->path = strbuf_detach(&worktree_path, NULL);
-	worktree->git_dir = strbuf_detach(&gitdir, NULL);
+	worktree->id = NULL;
 	worktree->is_bare = is_bare;
 	worktree->head_ref = NULL;
 	worktree->is_detached = is_detached;
+	worktree->is_current = 0;
 	add_head_info(&head_ref, worktree);
 
 done:
 	strbuf_release(&path);
-	strbuf_release(&gitdir);
 	strbuf_release(&worktree_path);
 	strbuf_release(&head_ref);
 	return worktree;
@@ -111,16 +111,13 @@ static struct worktree *get_linked_worktree(const char *id)
 	struct worktree *worktree = NULL;
 	struct strbuf path = STRBUF_INIT;
 	struct strbuf worktree_path = STRBUF_INIT;
-	struct strbuf gitdir = STRBUF_INIT;
 	struct strbuf head_ref = STRBUF_INIT;
 	int is_detached = 0;
 
 	if (!id)
 		die("Missing linked worktree name");
 
-	strbuf_addf(&gitdir, "%s/worktrees/%s",
-			absolute_path(get_git_common_dir()), id);
-	strbuf_addf(&path, "%s/gitdir", gitdir.buf);
+	strbuf_git_common_path(&path, "worktrees/%s/gitdir", id);
 	if (strbuf_read_file(&worktree_path, path.buf, 0) <= 0)
 		/* invalid gitdir file */
 		goto done;
@@ -140,20 +137,39 @@ static struct worktree *get_linked_worktree(const char *id)
 
 	worktree = xmalloc(sizeof(struct worktree));
 	worktree->path = strbuf_detach(&worktree_path, NULL);
-	worktree->git_dir = strbuf_detach(&gitdir, NULL);
+	worktree->id = xstrdup(id);
 	worktree->is_bare = 0;
 	worktree->head_ref = NULL;
 	worktree->is_detached = is_detached;
+	worktree->is_current = 0;
 	add_head_info(&head_ref, worktree);
 
 done:
 	strbuf_release(&path);
-	strbuf_release(&gitdir);
 	strbuf_release(&worktree_path);
 	strbuf_release(&head_ref);
 	return worktree;
 }
 
+static void mark_current_worktree(struct worktree **worktrees)
+{
+	struct strbuf git_dir = STRBUF_INIT;
+	struct strbuf path = STRBUF_INIT;
+	int i;
+
+	strbuf_addstr(&git_dir, absolute_path(get_git_dir()));
+	for (i = 0; worktrees[i]; i++) {
+		struct worktree *wt = worktrees[i];
+		strbuf_addstr(&path, absolute_path(get_worktree_git_dir(wt)));
+		wt->is_current = !fspathcmp(git_dir.buf, path.buf);
+		strbuf_reset(&path);
+		if (wt->is_current)
+			break;
+	}
+	strbuf_release(&git_dir);
+	strbuf_release(&path);
+}
+
 struct worktree **get_worktrees(void)
 {
 	struct worktree **list = NULL;
@@ -185,35 +201,105 @@ struct worktree **get_worktrees(void)
 	}
 	ALLOC_GROW(list, counter + 1, alloc);
 	list[counter] = NULL;
+
+	mark_current_worktree(list);
 	return list;
 }
 
-char *find_shared_symref(const char *symref, const char *target)
+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);
+}
+
+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 &&
+		 starts_with(target, "refs/heads/") &&
+		 !strcmp(state.branch, target + strlen("refs/heads/")));
+	free(state.branch);
+	free(state.onto);
+	return found_rebase;
+}
+
+int is_worktree_being_bisected(const struct worktree *wt,
+			       const char *target)
 {
-	char *existing = NULL;
+	struct wt_status_state state;
+	int found_rebase;
+
+	memset(&state, 0, sizeof(state));
+	found_rebase = wt_status_check_bisect(wt, &state) &&
+		state.branch &&
+		starts_with(target, "refs/heads/") &&
+		!strcmp(state.branch, target + strlen("refs/heads/"));
+	free(state.branch);
+	return found_rebase;
+}
+
+/*
+ * 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(const char *symref,
+					  const char *target)
+{
+	const struct worktree *existing = NULL;
 	struct strbuf path = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
-	struct worktree **worktrees = get_worktrees();
+	static struct worktree **worktrees;
 	int i = 0;
 
+	if (worktrees)
+		free_worktrees(worktrees);
+	worktrees = get_worktrees();
+
 	for (i = 0; worktrees[i]; i++) {
+		struct worktree *wt = worktrees[i];
+
+		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;
+			}
+		}
+
 		strbuf_reset(&path);
 		strbuf_reset(&sb);
-		strbuf_addf(&path, "%s/%s", worktrees[i]->git_dir, symref);
+		strbuf_addf(&path, "%s/%s",
+			    get_worktree_git_dir(wt),
+			    symref);
 
 		if (parse_ref(path.buf, &sb, NULL)) {
 			continue;
 		}
 
 		if (!strcmp(sb.buf, target)) {
-			existing = xstrdup(worktrees[i]->path);
+			existing = wt;
 			break;
 		}
 	}
 
 	strbuf_release(&path);
 	strbuf_release(&sb);
-	free_worktrees(worktrees);
 
 	return existing;
 }

worktree.h

@@ -3,11 +3,12 @@
 
 struct worktree {
 	char *path;
-	char *git_dir;
+	char *id;
 	char *head_ref;
 	unsigned char head_sha1[20];
 	int is_detached;
 	int is_bare;
+	int is_current;
 };
 
 /* Functions for acting on the information about worktrees. */
@@ -22,6 +23,12 @@ struct worktree {
  */
 extern struct worktree **get_worktrees(void);
 
+/*
+ * Return git dir of the worktree. Note that the path may be relative.
+ * If wt is NULL, git dir of current worktree is returned.
+ */
+extern const char *get_worktree_git_dir(const struct worktree *wt);
+
 /*
  * Free up the memory for worktree(s)
  */
@@ -29,10 +36,21 @@ extern void free_worktrees(struct worktree **);
 
 /*
  * Check if a per-worktree symref points to a ref in the main worktree
- * or any linked worktree, and return the path to the exising worktree
- * if it is.  Returns NULL if there is no existing ref.  The caller is
- * responsible for freeing the returned path.
+ * or any linked worktree, and return the worktree that holds the ref,
+ * or NULL otherwise. The result may be destroyed by the next call.
+ */
+extern const struct worktree *find_shared_symref(const char *symref,
+						 const char *target);
+
+int is_worktree_being_rebased(const struct worktree *wt, const char *target);
+int is_worktree_being_bisected(const struct worktree *wt, const char *target);
+
+/*
+ * Similar to git_path() but can produce paths for a specified
+ * worktree instead of current one
  */
-extern char *find_shared_symref(const char *symref, const char *target);
+extern const char *worktree_git_path(const struct worktree *wt,
+				     const char *fmt, ...)
+	__attribute__((format (printf, 2, 3)));
 
 #endif

wt-status.c

@@ -15,6 +15,7 @@
 #include "column.h"
 #include "strbuf.h"
 #include "utf8.h"
+#include "worktree.h"
 
 static const char cut_line[] =
 "------------------------ >8 ------------------------\n";
@@ -1263,13 +1264,13 @@ static void show_bisect_in_progress(struct wt_status *s,
 /*
  * Extract branch information from rebase/bisect
  */
-static char *read_and_strip_branch(const char *path)
+static char *get_branch(const struct worktree *wt, const char *path)
 {
 	struct strbuf sb = STRBUF_INIT;
 	unsigned char sha1[20];
 	const char *branch_name;
 
-	if (strbuf_read_file(&sb, git_path("%s", path), 0) <= 0)
+	if (strbuf_read_file(&sb, worktree_git_path(wt, "%s", path), 0) <= 0)
 		goto got_nothing;
 
 	while (sb.len && sb.buf[sb.len - 1] == '\n')
@@ -1361,40 +1362,62 @@ static void wt_status_get_detached_from(struct wt_status_state *state)
 	strbuf_release(&cb.buf);
 }
 
-void wt_status_get_state(struct wt_status_state *state,
-			 int get_detached_from)
+int wt_status_check_rebase(const struct worktree *wt,
+			   struct wt_status_state *state)
 {
 	struct stat st;
-	unsigned char sha1[20];
 
-	if (!stat(git_path_merge_head(), &st)) {
-		state->merge_in_progress = 1;
-	} else if (!stat(git_path("rebase-apply"), &st)) {
-		if (!stat(git_path("rebase-apply/applying"), &st)) {
+	if (!stat(worktree_git_path(wt, "rebase-apply"), &st)) {
+		if (!stat(worktree_git_path(wt, "rebase-apply/applying"), &st)) {
 			state->am_in_progress = 1;
-			if (!stat(git_path("rebase-apply/patch"), &st) && !st.st_size)
+			if (!stat(worktree_git_path(wt, "rebase-apply/patch"), &st) && !st.st_size)
 				state->am_empty_patch = 1;
 		} else {
 			state->rebase_in_progress = 1;
-			state->branch = read_and_strip_branch("rebase-apply/head-name");
-			state->onto = read_and_strip_branch("rebase-apply/onto");
+			state->branch = get_branch(wt, "rebase-apply/head-name");
+			state->onto = get_branch(wt, "rebase-apply/onto");
 		}
-	} else if (!stat(git_path("rebase-merge"), &st)) {
-		if (!stat(git_path("rebase-merge/interactive"), &st))
+	} else if (!stat(worktree_git_path(wt, "rebase-merge"), &st)) {
+		if (!stat(worktree_git_path(wt, "rebase-merge/interactive"), &st))
 			state->rebase_interactive_in_progress = 1;
 		else
 			state->rebase_in_progress = 1;
-		state->branch = read_and_strip_branch("rebase-merge/head-name");
-		state->onto = read_and_strip_branch("rebase-merge/onto");
+		state->branch = get_branch(wt, "rebase-merge/head-name");
+		state->onto = get_branch(wt, "rebase-merge/onto");
+	} else
+		return 0;
+	return 1;
+}
+
+int wt_status_check_bisect(const struct worktree *wt,
+			   struct wt_status_state *state)
+{
+	struct stat st;
+
+	if (!stat(worktree_git_path(wt, "BISECT_LOG"), &st)) {
+		state->bisect_in_progress = 1;
+		state->branch = get_branch(wt, "BISECT_START");
+		return 1;
+	}
+	return 0;
+}
+
+void wt_status_get_state(struct wt_status_state *state,
+			 int get_detached_from)
+{
+	struct stat st;
+	unsigned char sha1[20];
+
+	if (!stat(git_path_merge_head(), &st)) {
+		state->merge_in_progress = 1;
+	} else if (wt_status_check_rebase(NULL, state)) {
+		;		/* all set */
 	} else if (!stat(git_path_cherry_pick_head(), &st) &&
 			!get_sha1("CHERRY_PICK_HEAD", sha1)) {
 		state->cherry_pick_in_progress = 1;
 		hashcpy(state->cherry_pick_head_sha1, sha1);
 	}
-	if (!stat(git_path("BISECT_LOG"), &st)) {
-		state->bisect_in_progress = 1;
-		state->branch = read_and_strip_branch("BISECT_START");
-	}
+	wt_status_check_bisect(NULL, state);
 	if (!stat(git_path_revert_head(), &st) &&
 	    !get_sha1("REVERT_HEAD", sha1)) {
 		state->revert_in_progress = 1;

wt-status.h

@@ -6,6 +6,8 @@
 #include "color.h"
 #include "pathspec.h"
 
+struct worktree;
+
 enum color_wt_status {
 	WT_STATUS_HEADER = 0,
 	WT_STATUS_UPDATED,
@@ -100,6 +102,10 @@ void wt_status_prepare(struct wt_status *s);
 void wt_status_print(struct wt_status *s);
 void wt_status_collect(struct wt_status *s);
 void wt_status_get_state(struct wt_status_state *state, int get_detached_from);
+int wt_status_check_rebase(const struct worktree *wt,
+			   struct wt_status_state *state);
+int wt_status_check_bisect(const struct worktree *wt,
+			   struct wt_status_state *state);
 
 void wt_shortstatus_print(struct wt_status *s);
 void wt_porcelain_print(struct wt_status *s);