branch: description for orphan branch errors

In bcfc82bd48 (branch: description for non-existent branch errors,
2022-10-08) we checked the HEAD in the current worktree to detect if the
branch to operate with is an orphan branch, so as to avoid the confusing
error: "No branch named...".

If we are asked to operate with an orphan branch in a different working
tree than the current one, we need to check the HEAD in that different
working tree.

Let's extend the check we did in bcfc82bd48, to check the HEADs in all
worktrees linked to the current repository, using the helper introduced
in 31ad6b61bd (branch: add branch_checked_out() helper, 2022-06-15).

The helper, branch_checked_out(), does its work obtaining internally a
list of worktrees linked to the current repository.  Obtaining that list
is not a lightweight work because it implies disk access.

In copy_or_rename_branch() we already have a list of worktrees.  Let's
use that already obtained list, and avoid using here the helper.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/branch.c

@@ -538,13 +538,15 @@ static int replace_each_worktree_head_symref(struct worktree **worktrees,
 	return ret;
 }
 
+#define IS_HEAD 1
+
 static void copy_or_rename_branch(const char *oldname, const char *newname, int copy, int force)
 {
 	struct strbuf oldref = STRBUF_INIT, newref = STRBUF_INIT, logmsg = STRBUF_INIT;
 	struct strbuf oldsection = STRBUF_INIT, newsection = STRBUF_INIT;
 	const char *interpreted_oldname = NULL;
 	const char *interpreted_newname = NULL;
-	int recovery = 0;
+	int recovery = 0, oldref_usage = 0;
 	struct worktree **worktrees = get_worktrees();
 
 	if (strbuf_check_branch_ref(&oldref, oldname)) {
@@ -558,8 +560,17 @@ static void copy_or_rename_branch(const char *oldname, const char *newname, int
 			die(_("Invalid branch name: '%s'"), oldname);
 	}
 
-	if ((copy || strcmp(head, oldname)) && !ref_exists(oldref.buf)) {
+	for (int i = 0; worktrees[i]; i++) {
-		if (copy && !strcmp(head, oldname))
+		struct worktree *wt = worktrees[i];
+
+		if (wt->head_ref && !strcmp(oldref.buf, wt->head_ref)) {
+			oldref_usage |= IS_HEAD;
+			break;
+		}
+	}
+
+	if ((copy || !(oldref_usage & IS_HEAD)) && !ref_exists(oldref.buf)) {
+		if (oldref_usage & IS_HEAD)
 			die(_("No commit on branch '%s' yet."), oldname);
 		else
 			die(_("No branch named '%s'."), oldname);
@@ -838,7 +849,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 
 		strbuf_addf(&branch_ref, "refs/heads/%s", branch_name);
 		if (!ref_exists(branch_ref.buf))
-			error((!argc || !strcmp(head, branch_name))
+			error((!argc || branch_checked_out(branch_ref.buf))
 			      ? _("No commit on branch '%s' yet.")
 			      : _("No branch named '%s'."),
 			      branch_name);
@@ -883,7 +894,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 		}
 
 		if (!ref_exists(branch->refname)) {
-			if (!argc || !strcmp(head, branch->name))
+			if (!argc || branch_checked_out(branch->refname))
 				die(_("No commit on branch '%s' yet."), branch->name);
 			die(_("branch '%s' does not exist"), branch->name);
 		}

t/t3202-show-branch.sh

@@ -221,4 +221,22 @@ test_expect_success 'fatal descriptions on non-existent branch' '
 	test_cmp expect actual
 '
 
+test_expect_success 'error descriptions on orphan branch' '
+	test_when_finished git worktree remove -f wt &&
+	git worktree add wt --detach &&
+	git -C wt checkout --orphan orphan-branch &&
+	test_branch_op_in_wt() {
+		test_orphan_error() {
+			test_must_fail git $* 2>actual &&
+			test_i18ngrep "No commit on branch .orphan-branch. yet.$" actual
+		} &&
+		test_orphan_error -C wt branch $1 $2 &&                # implicit branch
+		test_orphan_error -C wt branch $1 orphan-branch $2 &&  # explicit branch
+		test_orphan_error branch $1 orphan-branch $2           # different worktree
+	} &&
+	test_branch_op_in_wt --edit-description &&
+	test_branch_op_in_wt --set-upstream-to=ne &&
+	test_branch_op_in_wt -c new-branch
+'
+
 test_done