rebase -i: demonstrate a bug with --autosquash

When rearranging the edit script, we happily mistake the comment
character for a command, and the command for a SHA-1. As a consequence,
when we move fixup! and squash! commits, our logic to skip lines with
already handled SHA-1s mistakenly skips anything but the first
commented-out pick line, too.

The upcoming rebase--helper patches will address this bug, therefore we
do not need to make the current autosquash code even more complex than
it already is, just to fix this bug.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3415-rebase-autosquash.sh

@@ -271,4 +271,28 @@ test_expect_success 'autosquash with custom inst format' '
 	test 2 = $(git cat-file commit HEAD^ | grep squash | wc -l)
 '
 
+set_backup_editor () {
+	write_script backup-editor.sh <<-\EOF
+	cp "$1" .git/backup-"$(basename "$1")"
+	EOF
+	test_set_editor "$PWD/backup-editor.sh"
+}
+
+test_expect_failure 'autosquash with multiple empty patches' '
+	test_tick &&
+	git commit --allow-empty -m "empty" &&
+	test_tick &&
+	git commit --allow-empty -m "empty2" &&
+	test_tick &&
+	>fixup &&
+	git add fixup &&
+	git commit --fixup HEAD^^ &&
+	(
+		set_backup_editor &&
+		GIT_USE_REBASE_HELPER=false \
+		git rebase -i --force-rebase --autosquash HEAD~4 &&
+		grep empty2 .git/backup-git-rebase-todo
+	)
+'
+
 test_done