Merge branch 'ky/branch-m-worktree'

When "git worktree" feature is in use, "git branch -m" renamed a
branch that is checked out in another worktree without adjusting
the HEAD symbolic ref for the worktree.

* ky/branch-m-worktree:
  set_worktree_head_symref(): fix error message
  branch -m: update all per-worktree HEADs
  refs: add a new function set_worktree_head_symref

branch.c

@@ -344,3 +344,26 @@ void die_if_checked_out(const char *branch)
 		die(_("'%s' is already checked out at '%s'"), branch, existing);
 	}
 }
+
+int replace_each_worktree_head_symref(const char *oldref, const char *newref)
+{
+	int ret = 0;
+	struct worktree **worktrees = get_worktrees();
+	int i;
+
+	for (i = 0; worktrees[i]; i++) {
+		if (worktrees[i]->is_detached)
+			continue;
+		if (strcmp(oldref, worktrees[i]->head_ref))
+			continue;
+
+		if (set_worktree_head_symref(worktrees[i]->git_dir, newref)) {
+			ret = -1;
+			error(_("HEAD of working tree %s is not updated"),
+			      worktrees[i]->path);
+		}
+	}
+
+	free_worktrees(worktrees);
+	return ret;
+}

branch.h

@@ -60,4 +60,11 @@ extern int read_branch_desc(struct strbuf *, const char *branch_name);
  */
 extern void die_if_checked_out(const char *branch);
 
+/*
+ * Update all per-worktree HEADs pointing at the old ref to point the new ref.
+ * This will be used when renaming a branch. Returns 0 if successful, non-zero
+ * otherwise.
+ */
+extern int replace_each_worktree_head_symref(const char *oldref, const char *newref);
+
 #endif

builtin/branch.c

@@ -558,8 +558,7 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 	if (recovery)
 		warning(_("Renamed a misnamed branch '%s' away"), oldref.buf + 11);
 
-	/* no need to pass logmsg here as HEAD didn't really move */
-	if (!strcmp(oldname, head) && create_symref("HEAD", newref.buf, NULL))
+	if (replace_each_worktree_head_symref(oldref.buf, newref.buf))
 		die(_("Branch renamed to %s, but HEAD is not updated!"), newname);
 
 	strbuf_addf(&oldsection, "branch.%s", oldref.buf + 11);

refs.h

@@ -306,6 +306,15 @@ extern int rename_ref(const char *oldref, const char *newref, const char *logmsg
 
 extern int create_symref(const char *refname, const char *target, const char *logmsg);
 
+/*
+ * Update HEAD of the specified gitdir.
+ * Similar to create_symref("relative-git-dir/HEAD", target, NULL), but
+ * this can update the main working tree's HEAD regardless of where
+ * $GIT_DIR points to.
+ * Return 0 if successful, non-zero otherwise.
+ * */
+extern int set_worktree_head_symref(const char *gitdir, const char *target);
+
 enum action_on_err {
 	UPDATE_REFS_MSG_ON_ERR,
 	UPDATE_REFS_DIE_ON_ERR,

refs/files-backend.c

@@ -2894,6 +2894,42 @@ int create_symref(const char *refname, const char *target, const char *logmsg)
 	return ret;
 }
 
+int set_worktree_head_symref(const char *gitdir, const char *target)
+{
+	static struct lock_file head_lock;
+	struct ref_lock *lock;
+	struct strbuf head_path = STRBUF_INIT;
+	const char *head_rel;
+	int ret;
+
+	strbuf_addf(&head_path, "%s/HEAD", absolute_path(gitdir));
+	if (hold_lock_file_for_update(&head_lock, head_path.buf,
+				      LOCK_NO_DEREF) < 0) {
+		struct strbuf err = STRBUF_INIT;
+		unable_to_lock_message(head_path.buf, errno, &err);
+		error("%s", err.buf);
+		strbuf_release(&err);
+		strbuf_release(&head_path);
+		return -1;
+	}
+
+	/* head_rel will be "HEAD" for the main tree, "worktrees/wt/HEAD" for
+	   linked trees */
+	head_rel = remove_leading_path(head_path.buf,
+				       absolute_path(get_git_common_dir()));
+	/* to make use of create_symref_locked(), initialize ref_lock */
+	lock = xcalloc(1, sizeof(struct ref_lock));
+	lock->lk = &head_lock;
+	lock->ref_name = xstrdup(head_rel);
+	lock->orig_ref_name = xstrdup(head_rel);
+
+	ret = create_symref_locked(lock, head_rel, target, NULL);
+
+	unlock_ref(lock); /* will free lock */
+	strbuf_release(&head_path);
+	return ret;
+}
+
 int reflog_exists(const char *refname)
 {
 	struct stat st;

t/t3200-branch.sh

@@ -126,7 +126,28 @@ test_expect_success 'git branch -M foo bar should fail when bar is checked out'
 test_expect_success 'git branch -M baz bam should succeed when baz is checked out' '
 	git checkout -b baz &&
 	git branch bam &&
-	git branch -M baz bam
+	git branch -M baz bam &&
+	test $(git rev-parse --abbrev-ref HEAD) = bam
+'
+
+test_expect_success 'git branch -M baz bam should succeed when baz is checked out as linked working tree' '
+	git checkout master &&
+	git worktree add -b baz bazdir &&
+	git worktree add -f bazdir2 baz &&
+	git branch -M baz bam &&
+	test $(git -C bazdir rev-parse --abbrev-ref HEAD) = bam &&
+	test $(git -C bazdir2 rev-parse --abbrev-ref HEAD) = bam
+'
+
+test_expect_success 'git branch -M baz bam should succeed within a worktree in which baz is checked out' '
+	git checkout -b baz &&
+	git worktree add -f bazdir3 baz &&
+	(
+		cd bazdir3 &&
+		git branch -M baz bam &&
+		test $(git rev-parse --abbrev-ref HEAD) = bam
+	) &&
+	test $(git rev-parse --abbrev-ref HEAD) = bam
 '
 
 test_expect_success 'git branch -M master should work when master is checked out' '