Re: Unreliable 'git rebase --onto'

From: Eugeniu Rosca <erosca@de.adit-jv.com>
Date: Jan 9, 2020, 10:53 UTC
Message-ID: <20200109105307.GA1349@lxhi-065.adit-jv.com>
In-Reply-To: <CABPp-BHsyMOz+hi7EYoAnAWfzms7FRfwqCoarnu8H+vyDoN6SQ@mail.gmail.com>

Hi Elijah, hi Szeder,

On Wed, Jan 08, 2020 at 02:06:22PM -0800, Elijah Newren wrote:

Show 9 quoted lines

> This looks like a known bug in rebase, in particular in the am-backend that
> rebase uses by default.  If I'm correct that it's just a context region
> issue, then this is the same bug that was recently discussed at
> https://lore.kernel.org/git/CAN_72e2h2avv-U9BVBYqXVKiC+5kHy-pjejyMSD3X22uRXE39g@mail.gmail.com/.
> The current plan is to switch the default over to the merge backend (the
> same machinery that cherry-pick uses), which doesn't suffer from the same
> shortcomings (you can see the current work being done in this area at
> https://lore.kernel.org/git/pull.679.v3.git.git.1577217299.gitgitgadget@gmail.com/
> ).

Thank you for your feedback and references, here and in [*].

Once hit by this or similar issues, I think there is high chance for people to go through the same feelings as described by Pavel in [**]:

  ---
  That's so scary that I'm going to stop using "git rebase" for now.
  ---

Some years ago I was hit by 'git merge' producing slightly different results compared to 'git rebase --onto' and 'git cherry-pick A..B' (maybe I can come up with a reproduction scenario for that too).

Since then, I usually contrast the outcomes of merging, cherry-picking and rebasing, to make sure they match, but that's painful and time-consuming.

> In the mean time, you can pass the -m flag to rebase to avoid these types
> of problems.  In fact, if you could retry with -m you may be able to
> confirm whether it's the same issue.

Indeed, neither `git rebase -m` nor `git rebase -i` exhibit the problem.

[*] https://lore.kernel.org/git/CABPp-BHsy75UGm4wTOP2_AYik_dZi-_BxtAn-hyi-ZrNRRWGuw@mail.gmail.com/T/#m1cbf80ef56c260a626146d61291d7fbabd108f1b [**] https://lore.kernel.org/git/CAN_72e2h2avv-U9BVBYqXVKiC+5kHy-pjejyMSD3X22uRXE39g@mail.gmail.com/

Thanks again.

-- 
Best Regards,
Eugeniu