Re: [PATCH v2 2/2] rebase --exec: make it work with --rebase-merges

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

On 09/08/18 10:22, Johannes Schindelin wrote:
> Hi Phillip,
> 
> On Mon, 6 Aug 2018, Phillip Wood wrote:
> 
>> On 06/08/18 10:52, Johannes Schindelin via GitGitGadget wrote:
>>>
>>> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>>>
>>> The idea of `--exec` is to append an `exec` call after each `pick`.
>>>
>>> Since the introduction of fixup!/squash! commits, this idea was extended
>>> to apply to "pick, possibly followed by a fixup/squash chain", i.e. an
>>> exec would not be inserted between a `pick` and any of its corresponding
>>> `fixup` or `squash` lines.
>>>
>>> The current implementation uses a dirty trick to achieve that: it
>>> assumes that there are only pick/fixup/squash commands, and then
>>> *inserts* the `exec` lines before any `pick` but the first, and appends
>>> a final one.
>>>
>>> With the todo lists generated by `git rebase --rebase-merges`, this
>>> simple implementation shows its problems: it produces the exact wrong
>>> thing when there are `label`, `reset` and `merge` commands.
>>>
>>> Let's change the implementation to do exactly what we want: look for
>>> `pick` lines, skip any fixup/squash chains, and then insert the `exec`
>>> line. Lather, rinse, repeat.
>>>
>>> While at it, also add `exec` lines after `merge` commands, because they
>>> are similar in spirit to `pick` commands: they add new commits.
>>>
>>> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
>>> ---
>>>   sequencer.c              | 37 +++++++++++++++++++++++++++----------
>>>   t/t3430-rebase-merges.sh |  2 +-
>>>   2 files changed, 28 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/sequencer.c b/sequencer.c
>>> index 31038472f..ed2e694ff 100644
>>> --- a/sequencer.c
>>> +++ b/sequencer.c
>>> @@ -4244,10 +4244,9 @@ 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 i, insert;
>>>   
>>>    if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
>>>   		return error(_("could not read '%s'."), todo_file);
>>> @@ -4257,19 +4256,37 @@ 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);
>>> +	/*
>>> +	 * 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.
>>> +	 */
>>> +	insert = -1;
>>> +	for (i = 0; i < todo_list.nr; i++) {
>>> +		enum todo_command command = todo_list.items[i].command;
>>> +
>>> +		if (insert >= 0) {
>>> +			/* skip fixup/squash chains */
>>> +			if (command == TODO_COMMENT)
>>> +				continue;
>>
>> insert is not updated so if the next command is not a fixup the exec
>> line will be inserted before the comment.
> 
> Yes, this is very much on purpose. Take this todo list, for example:
> 
> 	pick 123456 this patch
> 	# pick 987654 this was an empty commit
> 
> You definitely do not want the `exec` to appear after that commented-out
> empty commit.

Yes, I like it, I was just thinking out loud.

>>> +			else if (is_fixup(command)) {
>>> +				insert = i + 1;
>>> +				continue;
>>> +			}
>>> +			strbuf_insert(buf,
>>> +				      todo_list.items[insert].offset_in_buf +
>>> +				      offset, commands, commands_len);
>>>   			offset += commands_len;
>>> +			insert = -1;
>>>   		}
>>> -		first = 0;
>>> +
>>> +		if (command == TODO_PICK || command == TODO_MERGE)
>>> +			insert = i + 1;
>>>    }
>>>   
>>>   	/* append final <commands> */
>>> -	strbuf_add(buf, commands, commands_len);
>>> +	if (insert >= 0 || !offset)
>>> +		strbuf_add(buf, commands, commands_len);
>>
>> Having read your other message about this patch I think if you wanted to fix
>> the position of the final exec in the case where the todo list ends with a
>> comment you could do something like
>>
>> 	if (insert >= 0)
>> 		strbuf_insert(buf,
>> 			      todo_list.items[insert].offset_in_buf +
>> 			      offset, commands, commands_len);
>> 	else
>> 		strbuf_add(buf, commands, commands_len);
> 
> That does not really work, as `insert` can point *after* the last line, in
> which case `todo_list.items[insert]` is undefined (and in the worst case,
> causes a segmentation fault).

Ah, I'd missed that, does changing the conditions to
if (insert >= 0 && insert < todo.list_nr) and
else if (insert >=0 || !offset) work?

>> I'm not sure it matters that much though
> 
> Well, it does matter to me. After having this in the back of my head, and
> after your comment, I think it *is* worth the additional complexity after
> all.

It would definitely be nice to have.

Best Wishes

Phillip

> Will come up with a new iteration.
> 
> Ciao,
> Dscho
>