Re: [PATCH] rebase -i: do not update "done" when rescheduling command

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Junio

Thanks for your comments

On 20/03/2023 17:46, Junio C Hamano wrote:
> "Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>
>> As the sequencer executes todo commands it appends them to
>> .git/rebase-merge/done. This file is used by "git status" to show the
>> recently executed commands. Unfortunately when a command is rescheduled
>> the command preceding it is erroneously appended to the "done" file.
>> This means that when rebase stops after rescheduling "pick B" the "done"
>> file contains
>>
>> 	pick A
>> 	pick B
>> 	pick A
>>
>> instead of
>>
>> 	pick A
>> 	pick B
> 
> Here it may not be clear what you meant with the verb "reschedule"
> to those who weren't closely following the previous discussion that
> led to this fix.
> 
> Is it the same as "the command attempted to execute a step, couldn't
> complete it (e.g. due to conflicts), and gave control to the end
> user until they say 'git rebase --continue'"?  What cases, other
> than interrupted step due to conflicts, involve "rescheduling"?

I'll expand the commit message to explain that if we cannot pick a 
commit because it would overwrite untracked files then we add the 
command back into the todo list and give control to the user until they 
say 'git rebase --continue'. Hopefully they'll have removed the 
problematic files and we try to pick the commit again it will succeed. 
We do the same if an exec command fails and --reschedule-failed-exec was 
given. For conflicts we don't add the command back into the todo list 
because the cherry-pick has happened the user "just" needs to fix the 
conflicts before continuing to the next command.

>> Note that the rescheduled command will still be appended to the "done"
>> file again when it is successfully executed. Arguably it would be better
>> not to do that but fixing it would be more involved.
> 
> And without quite understanding what "reschedule" refers to, it is
> unclear why it is even arguable---it is perfectly sensible that a
> command that is rescheduled (hence not yet done) would not be sent
> to 'done'.  If a command that was once rescheduled (hence it wasn't
> finished initially) gets finished now, shouldn't it be sent to
> 'done'?  It is unclear why is it better not to.

The command is only successfully executed once but may end up in 'done' 
multiple times. While that means we can see which commands ended up 
being rescheduled I'm not sure it is very useful and think really we're 
just cluttering the 'done' file with failed attempts.

>> -static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
>> +static int save_todo(struct todo_list *todo_list, struct replay_opts *opts,
>> +		     int reschedule)
>>   {
> 
> OK, all callers to save_todo() are in pick_commits() that knows what
> the value of "reschedule" is, and it is passed down to this helper ...
> 
>> @@ -3389,7 +3390,7 @@ static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
>>   	 * rebase -i writes "git-rebase-todo" without the currently executing
>>   	 * command, appending it to "done" instead.
>>   	 */
>> -	if (is_rebase_i(opts))
>> +	if (is_rebase_i(opts) && !reschedule)
>>   		next++;
>>   
>>   	fd = hold_lock_file_for_update(&todo_lock, todo_path, 0);
>> @@ -3402,7 +3403,7 @@ static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
>>   	if (commit_lock_file(&todo_lock) < 0)
>>   		return error(_("failed to finalize '%s'"), todo_path);
>>   
>> -	if (is_rebase_i(opts) && next > 0) {
>> +	if (is_rebase_i(opts) && !reschedule && next > 0) {
>>   		const char *done = rebase_path_done();
>>   		int fd = open(done, O_CREAT | O_WRONLY | O_APPEND, 0666);
>>   		int ret = 0;
> 
> ... and the change here is quite straight-forward.  With reschedule,
> we do not advance because by definition we haven't finished the
> step yet.  OK.
> 
>> @@ -4648,7 +4649,7 @@ static int pick_commits(struct repository *r,
>>   		const char *arg = todo_item_get_arg(todo_list, item);
>>   		int check_todo = 0;
>>   
>> -		if (save_todo(todo_list, opts))
>> +		if (save_todo(todo_list, opts, 0))
>>   			return -1;
> 
> I wonder why we pass a hardcoded 0 here---shouldn't the value match
> the local variable 'reschedule'? here?
> 
> The same question for the other two callers, but I admit that when
> the second one is called, the local variable "reschedule" is not
> set...

The rescheduling code is a bit of a mess as rescheduling commands that 
pick a commit does not use the "reschedule" variable and is handled 
separately to other commands like "reset", "merge" and "exec" which do 
use the "reschedule" varibale. I did try and add a preparatory step to 
fix that but failed to find a good way of doing so. The reason I went 
with hardcoded parameters is that for each call the purpose is fixed and 
as you noticed the "reschedule" variable is only used for rescheduling 
"reset", "merge" and "exec". I could expand the commit message or do you 
think a couple of code comments be more helpful?

Best Wishes

Phillip

>>   		if (is_rebase_i(opts)) {
>>   			if (item->command != TODO_COMMENT) {
>> @@ -4695,8 +4696,7 @@ static int pick_commits(struct repository *r,
>>   							    todo_list->current),
>>   				       get_item_line(todo_list,
>>   						     todo_list->current));
>> -				todo_list->current--;
>> -				if (save_todo(todo_list, opts))
>> +				if (save_todo(todo_list, opts, 1))
>>   					return -1;
> 
> ... yet we call the helper with reschedule set to 1.  Puzzled.
> 
>> @@ -4788,8 +4788,7 @@ static int pick_commits(struct repository *r,
>>   			       get_item_line_length(todo_list,
>>   						    todo_list->current),
>>   			       get_item_line(todo_list, todo_list->current));
>> -			todo_list->current--;
>> -			if (save_todo(todo_list, opts))
>> +			if (save_todo(todo_list, opts, 1))
>>   				return -1;
> 
> At this point, reschedule is set and passing it instead of 1 would
> be OK.
> 
> Thanks.