bug#70456: Status of ‘core-updates’

[Maxim Cournoyer]

Hi Christopher,

Christopher Baines <mail@cbaines.net> writes:

> Ludovic Courtès <ludo@gnu.org> writes:
>
>> What’s the status of ‘core-updates’?  What are the areas where help is
>> needed?
>>
>> I know a lot has happened since the last update¹, which is roughly when
>> I dropped the ball due to other commitments, but I’m not sure where we
>> are now.
>
> I haven't really been following core-updates, but I have had a look
> since there's a request to merge it now [1].
>
> I'm really concerned by the commits on the branch though, assuming I'm
> using Git right, there are 6351 commits on the branch:
>
>   git log --pretty=oneline core-updates ^master | wc -l
>
> Somehow, I think there's been a couple of pushes of commits to
> core-updates that have partially duplicated lots of commits from master,
> I put some more details in:
>
>   https://issues.guix.gnu.org/70456#3
>
> I think keeping the Git commit history clean and representative is
> really important, so to me at least this means core-updates can't be
> merged to master in it's current form, even if the changes overall from
> these 6351 commits are reasonable.
>
> I'm really not sure how to move forward though, I had a go at trying to
> rebuild the branch without introducing the thousands of duplicate
> commits and that produced a branch with 765 commits over master, which
> still seems a lot, but a big improvement over 6351:
>
>   https://git.cbaines.net/guix/log/?h=chris-core-updates-no-duplicates-attempt
>
> That was really hard going though, as there's plenty of merge conflicts
> along the way, and I'm pretty sure I solved some of them
> incorrectly. The resulting branch also differs from core-updates.

I also think Git commit history is important, but in this case I weigh
the value of removing ~5000 duplicated rust commits against the risks of
resolving merge conflicts wrong or forgetting commits upon attempting to
recreate the branch from scratch lower than the benefit.

> Maybe someone with more time, care and attention could do a better job,
> but it might be more worthwhile just starting fresh and rather than
> trying to produce a like for like branch just without the thousands of
> duplicate commits, effectively manually rebase the branch (without the
> duplicate commits) on master and try to get the commits in to a usable
> state.

Given the little attention core-updates is currently receiving, I doubt
someone is willing to put the effort to recreate the branch from scratch
to clean its git history; at least speaking for myself I'd rather spend
the little hack time I have to work on it toward getting it finalized.

I believe how these duplicates came to exist was probably two separate
master -> core-updates merge commits, with one of them ending up being
rebased on top of the other, probably so that it could be pushed.
Perhaps we could capture in our contribution guidelines that rebasing a
merge commit should never be done to keep the history clean, and that in
a situation where:

1. a merge has been prepared locally (with conflicts resolved and all)
2. a new commit has appeared on the remote branch

the solution should be to merge the remote branch into the local one
instead of rebasing the local one on the remote one (as is usually
done).  Disclaimer: I haven't actually tried this suggested approach,
which should be done before documenting it, if there's a consensus to do
so.

In other words, I suggest we document what *not* to do to avoid
repeating the same mistake in the future, and move on.

-- 
Thanks,
Maxim