[PATCH] rebase -i: permit 'drop' of a merge commit

[Johannes Sixt <j6t@kdbg.org>]

4c063c82e9 (rebase -i: improve error message when picking merge,
2024-05-30) added advice texts for cases when a merge commit is
passed as argument of sequencer command that cannot operate with
a merge commit. However, it forgot about the 'drop' command, so
that in this case the BUG() in the default branch is reached.

Handle 'drop' like 'merge', i.e., permit it without a message.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
---
 sequencer.c                   | 1 +
 t/t3404-rebase-interactive.sh | 1 +
 2 files changed, 2 insertions(+)

diff --git a/sequencer.c b/sequencer.c
index aaf2e4df64..9ae40a91b2 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2720,8 +2720,9 @@ static int check_merge_commit_insn(enum todo_command command)
 	case TODO_SQUASH:
 		return error(_("cannot squash merge commit into another commit"));
 
 	case TODO_MERGE:
+	case TODO_DROP:
 		return 0;
 
 	default:
 		BUG("unexpected todo_command");
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 6bac217ed3..34d6ad0770 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -2262,8 +2262,9 @@ rebase_setup_and_clean () {
 	reword $oid
 	edit $oid
 	fixup $oid
 	squash $oid
+	drop $oid # acceptable, no advice
 	EOF
 	(
 		set_replace_editor todo &&
 		test_must_fail git rebase -i HEAD 2>actual
-- 
2.50.1.837.g8c5950ae16