[PATCH v3 3/3] branch: rename orphan branches in any worktree

["Rubén Justo" <rjusto@gmail.com>]

In cfaff3aac (branch -m: allow renaming a yet-unborn branch, 2020-12-13)
we added support for renaming an orphan branch, skipping rename_ref() if
the branch being renamed is an orphan branch; checking the current HEAD.

But the orphan branch to be renamed can be an orphan branch in a
different worktree than the current one, i.e. not the current HEAD.

Let's make "die_if_branch_is_being_rebased_or_bisected()" return if the
specified branch is HEAD and orphan, and use it to extend what we did in
cfaff3aac, to check all HEADs in the repository.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
---
 builtin/branch.c  | 16 +++++++++-------
 t/t3200-branch.sh | 14 ++++++++++++++
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index 28cec344ad..7efda62224 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -488,7 +488,8 @@ static void print_current_branch_name(void)
 
 /*
  * Dies if the specified branch is being rebased or bisected.  Otherwise returns
- * 0 or, if the branch is HEAD in any worktree, returns 1.
+ * 0 or, if the branch is HEAD in any worktree, returns 1. If the branch is HEAD
+ * and also orphan, returns 2.
  */
 static int die_if_branch_is_being_rebased_or_bisected(const char *target)
 {
@@ -499,7 +500,7 @@ static int die_if_branch_is_being_rebased_or_bisected(const char *target)
 		struct worktree *wt = worktrees[i];
 
 		if (wt->head_ref && !strcmp(target, wt->head_ref))
-			ret = 1;
+			ret = is_null_oid(&wt->head_oid) ? 2 : 1;
 
 		if (!wt->is_detached)
 			continue;
@@ -523,7 +524,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	struct strbuf oldsection = STRBUF_INIT, newsection = STRBUF_INIT;
 	const char *interpreted_oldname = NULL;
 	const char *interpreted_newname = NULL;
-	int recovery = 0, oldref_is_head;
+	int recovery = 0, oldref_is_head, oldref_is_orphan;
 
 	if (strbuf_check_branch_ref(&oldref, oldname)) {
 		/*
@@ -537,9 +538,11 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	}
 
 	oldref_is_head = die_if_branch_is_being_rebased_or_bisected(oldref.buf);
+	oldref_is_orphan = (oldref_is_head > 1);
 
-	if ((copy || !oldref_is_head) && !ref_exists(oldref.buf))
-		die(oldref_is_head
+	if ((copy || !oldref_is_head) &&
+	    (oldref_is_orphan || !ref_exists(oldref.buf)))
+		die(oldref_is_orphan
 		    ? _("No commit on branch '%s' yet.")
 		    : _("No branch named '%s'."), oldname);
 
@@ -564,8 +567,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 		strbuf_addf(&logmsg, "Branch: renamed %s to %s",
 			    oldref.buf, newref.buf);
 
-	if (!copy &&
-	    (!head || strcmp(oldname, head) || !is_null_oid(&head_oid)) &&
+	if (!copy && !oldref_is_orphan &&
 	    rename_ref(oldref.buf, newref.buf, logmsg.buf))
 		die(_("Branch rename failed"));
 	if (copy && copy_existing_ref(oldref.buf, newref.buf, logmsg.buf))
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index 5a169b68d6..5aef00efde 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -279,6 +279,20 @@ test_expect_success 'git branch -M and -C fail on detached HEAD' '
 	test_cmp expect err
 '
 
+test_expect_success 'git branch -m should work with orphan branches' '
+	test_when_finished git checkout - &&
+	test_when_finished git worktree remove -f wt &&
+	git worktree add wt --detach &&
+	# rename orphan in another worktreee
+	git -C wt checkout --orphan orphan-foo-wt &&
+	git branch -m orphan-foo-wt orphan-bar-wt &&
+	test orphan-bar-wt=$(git -C orphan-worktree branch --show-current) &&
+	# rename orphan in the current worktree
+	git checkout --orphan orphan-foo &&
+	git branch -m orphan-foo orphan-bar &&
+	test orphan-bar=$(git branch --show-current)
+'
+
 test_expect_success 'git branch -d on orphan HEAD (merged)' '
 	test_when_finished git checkout main &&
 	git checkout --orphan orphan &&
-- 
2.39.0