[PATCH v3] sequencer: rectify empty hint in call of require_clean_work_tree()

[Oswald Buddenhagen <oswald.buddenhagen@gmx.de>]

The canonical way to represent "no error hint" is making it NULL, which
shortcuts the error() call altogether. This fixes the output by removing
the line which said just "error:", which would appear when starting a
rebase whose initial checkout worked fine despite a dirty worktree. This
was introduced by 97e1873 (rebase -i: rewrite complete_action() in C,
2018-08-28), which did a somewhat inaccurate conversion from shell.

To avoid that such bugs re-appear, test for the condition in
require_clean_work_tree().

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
---
v3:
- added BUG()
- rewrote commit message again
v2:
- expanded commit message

Cc: Junio C Hamano <gitster@pobox.com>
---
 sequencer.c | 2 +-
 wt-status.c | 6 +++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index cc9821ece2..d15a7409d8 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -6182,7 +6182,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 	if (checkout_onto(r, opts, onto_name, &oid, orig_head))
 		goto cleanup;
 
-	if (require_clean_work_tree(r, "rebase", "", 1, 1))
+	if (require_clean_work_tree(r, "rebase", NULL, 1, 1))
 		goto cleanup;
 
 	todo_list_write_total_nr(&new_todo);
diff --git a/wt-status.c b/wt-status.c
index 8a1a4fb1f0..c8c1780566 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -2654,8 +2654,12 @@ int require_clean_work_tree(struct repository *r,
 	}
 
 	if (err) {
-		if (hint)
+		if (hint) {
+			if (!*hint)
+				BUG("empty hint passed to require_clean_work_tree();"
+				    " use NULL instead");
 			error("%s", hint);
+		}
 		if (!gently)
 			exit(128);
 	}
-- 
2.40.0.152.g15d061e6df