Re: [PATCH v2 06/16] sequencer: refactor sequencer_add_exec_commands() to work on a todo_list

On 27/10/2018 22:29, Alban Gruin wrote:

This refactors sequencer_add_exec_commands() to work on a todo_list to
avoid redundant reads and writes to the disk.

An obvious way to do this would be to insert the `exec' command between
the other commands, and reparse it once this is done.  This is not what
is done here.  Instead, the command is appended to the buffer once, and
a new list of items is created.  Items from the old list are copied to
it, and new `exec' items are appended when necessary.  This eliminates
the need to reparse the todo list, but this also means its buffer cannot
be directly written to the disk, hence todo_list_write_to_disk().

I'd reword this slightly, maybe

Instead of just inserting the `exec' command between the other commands, 
and re-parsing the buffer at the end the exec command is appended to the 
buffer once, and a new list of items is created.  Items from the old 
list are copied across and new `exec' items are appended when necessary. 
  This eliminates the need to reparse the buffer, but this also means we 
have to use todo_list_write_to_disk() to write the file.

sequencer_add_exec_commands() still reads the todo list from the disk,
as it is needed by rebase -p.  todo_list_add_exec_commands() works on a
todo_list structure, and reparses it at the end.

I think the saying 'reparses' is confusing as that is what we're trying 
to avoid.

Minor nit pick, I think it is clearer if first is initialized just 
before the loop as it is in the deleted code below.

+	struct todo_item *items = NULL,
+		base_item = {TODO_EXEC, NULL, 0, 0, commands_len, 0};
+
+	strbuf_addstr(buf, commands);
+	base_item.offset_in_buf = buf->len - commands_len - 1;
+	base_item.arg = buf->buf + base_item.offset_in_buf;

I think if the user gives --exec more than once on the command line then 
commands will contain more than one exec command so this needs to parse 
commands and create one todo_item for each command.

+
+	/*
+	 * Insert <commands> after every pick. Here, fixup/squash chains
+	 * are considered part of the pick, so we insert the commands *after*
+	 * those chains if there are any.
+	 */
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
+		if (todo_list->items[i].arg)
+			todo_list->items[i].arg = todo_list->items[i].arg - old_buf + buf->buf;
+
+		if (command == TODO_PICK && !first) {
+			ALLOC_GROW(items, nr + 1, alloc);
+			memcpy(items + nr++, &base_item, sizeof(struct todo_item));

I think it would be clearer to say
	items[nr++] = base_item;
rather than using memcpy. This applies below and to some of the other 
patches as well. Also this needs to loop over all the base_items if the 
user gave --exec more than once on the command line.

Best Wishes

Phillip