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

[Phillip Wood <phillip.wood@talktalk.net>]

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.

> complete_action() still uses sequencer_add_exec_commands() for now.
> This will be changed in a future commit.
> 
> Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
> ---
>   sequencer.c | 69 +++++++++++++++++++++++++++++++++++++----------------
>   1 file changed, 49 insertions(+), 20 deletions(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index e12860c047..12a3efeca8 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -4216,6 +4216,50 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
>   	return 0;
>   }
>   
> +static void todo_list_add_exec_commands(struct todo_list *todo_list,
> +					const char *commands)
> +{
> +	struct strbuf *buf = &todo_list->buf;
> +	const char *old_buf = buf->buf;
> +	size_t commands_len = strlen(commands + strlen("exec ")) - 1;
> +	int i, first = 1, nr = 0, alloc = 0;

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

> +		}
> +
> +		ALLOC_GROW(items, nr + 1, alloc);
> +		memcpy(items + nr++, todo_list->items + i, sizeof(struct todo_item));
> +		first = 0;
> +	}
> +
> +	/* insert or append final <commands> */
> +	ALLOC_GROW(items, nr + 1, alloc);
> +	memcpy(items + nr++, &base_item, sizeof(struct todo_item));
> +
> +	FREE_AND_NULL(todo_list->items);
> +	todo_list->items = items;
> +	todo_list->nr = nr;
> +	todo_list->alloc = alloc;
> +}
> +
>   /*
>    * Add commands after pick and (series of) squash/fixup commands
>    * in the todo list.
> @@ -4224,10 +4268,7 @@ int sequencer_add_exec_commands(const char *commands)
>   {
>   	const char *todo_file = rebase_path_todo();
>   	struct todo_list todo_list = TODO_LIST_INIT;
> -	struct todo_item *item;
> -	struct strbuf *buf = &todo_list.buf;
> -	size_t offset = 0, commands_len = strlen(commands);
> -	int i, first;
> +	int res;
>   
>   	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
>   		return error(_("could not read '%s'."), todo_file);
> @@ -4237,23 +4278,11 @@ int sequencer_add_exec_commands(const char *commands)
>   		return error(_("unusable todo list: '%s'"), todo_file);
>   	}
>   
> -	first = 1;
> -	/* insert <commands> before every pick except the first one */
> -	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
> -		if (item->command == TODO_PICK && !first) {
> -			strbuf_insert(buf, item->offset_in_buf + offset,
> -				      commands, commands_len);
> -			offset += commands_len;
> -		}
> -		first = 0;
> -	}
> -
> -	/* append final <commands> */
> -	strbuf_add(buf, commands, commands_len);
> -
> -	i = write_message(buf->buf, buf->len, todo_file, 0);
> +	todo_list_add_exec_commands(&todo_list, commands);
> +	res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1, 0);
>   	todo_list_release(&todo_list);
> -	return i;
> +
> +	return res;
>   }
>   
>   static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,
>