rebase -i: recognize short commands without arguments

The sequencer instruction 'b', short for 'break', is rejected:

  error: invalid line 2: b

The reason is that the parser expects all short commands to have
an argument. Permit short commands without arguments.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -1954,7 +1954,8 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 		if (skip_prefix(bol, todo_command_info[i].str, &bol)) {
 			item->command = i;
 			break;
-		} else if (bol[1] == ' ' && *bol == todo_command_info[i].c) {
+		} else if ((bol + 1 == eol || bol[1] == ' ') &&
+			   *bol == todo_command_info[i].c) {
 			bol++;
 			item->command = i;
 			break;

t/lib-rebase.sh

@@ -49,7 +49,7 @@ set_fake_editor () {
 		case $line in
 		squash|fixup|edit|reword|drop)
 			action="$line";;
-		exec*|break)
+		exec*|break|b)
 			echo "$line" | sed 's/_/ /g' >> "$1";;
 		"#")
 			echo '# comment' >> "$1";;

t/t3418-rebase-continue.sh

@@ -243,7 +243,9 @@ unset GIT_SEQUENCE_EDITOR
 
 test_expect_success 'the todo command "break" works' '
 	rm -f execed &&
-	FAKE_LINES="break exec_>execed" git rebase -i HEAD &&
+	FAKE_LINES="break b exec_>execed" git rebase -i HEAD &&
+	test_path_is_missing execed &&
+	git rebase --continue &&
 	test_path_is_missing execed &&
 	git rebase --continue &&
 	test_path_is_file execed