[PATCH v4 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.

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

In "copy_or_rename_branch()" we are traversing the worktrees checking if
the branch to be renamed is HEAD in any worktree.  Let's include also a
check for HEAD being NULL, which is the indication of an orphan branch,
and use it to extend what we did in cfaff3aac, to 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, 24 insertions(+), 6 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index aecf009993..24cd66bae7 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -489,6 +489,7 @@ static void print_current_branch_name(void)
 #define IS_BISECTED 1
 #define IS_REBASED 2
 #define IS_HEAD 4
+#define IS_ORPHAN 8
 
 static void copy_or_rename_branch(const char *oldname, const char *newname, int copy, int force)
 {
@@ -514,8 +515,11 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 	for (int i = 0; worktrees[i]; i++) {
 		struct worktree *wt = worktrees[i];
 
-		if (wt->head_ref && !strcmp(oldref.buf, wt->head_ref))
+		if (wt->head_ref && !strcmp(oldref.buf, wt->head_ref)) {
 			oldref_usage |= IS_HEAD;
+			if (is_null_oid(&wt->head_oid))
+				oldref_usage |= IS_ORPHAN;
+		}
 
 		if (!wt->is_detached)
 			continue;
@@ -531,8 +535,9 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 		}
 	}
 
-	if ((copy || !(oldref_usage & IS_HEAD)) && !ref_exists(oldref.buf)) {
-		if (oldref_usage & IS_HEAD)
+	if ((copy || !(oldref_usage & IS_HEAD)) &&
+	    ((oldref_usage & IS_ORPHAN) || !ref_exists(oldref.buf))) {
+		if (oldref_usage & IS_ORPHAN)
 			die(_("No commit on branch '%s' yet."), oldname);
 		else
 			die(_("No branch named '%s'."), oldname);
@@ -567,8 +572,7 @@ 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_usage & 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))
@@ -583,7 +587,7 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 				interpreted_oldname);
 	}
 
-	if (!copy) {
+	if (!copy && (oldref_usage & IS_HEAD)) {
 		/*
 		 * Update all per-worktree HEADs pointing at the old ref to
 		 * point the new ref.
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 &&
-- 
2.34.1