Re: minor interactive rebase regression: HEAD points to wrong commit while rewording

> On 12/08/2019 18:50, SZEDER Gábor wrote:
> >
> > When running interactive rebase to reword a commit message, I would
> > expect that the commit whose message I'm rewording is checked out.
> > This is not quite the case when rewording multiple subsequent commit
> > messages.
> >
> > Let's start with four commits, and start an interactive rebase from
> > the first commit:
> >
> >    $ git log --oneline
> >    5835aa1 (HEAD -> master) fourth
> >    64ecc64 third
> >    d5fad83 second
> >    384b86f first
> >    $ git rebase -i 384b86f
> >
> > Update the instruction sheet to edit the log messages of two
> > subsequent commits:
> >
> >    r d5fad83 second
> >    r 64ecc64 third
> >    pick 5835aa1 fourth
> >
> > Now, after the editor opens up the second commit's log message, start
> > a new terminal and check where HEAD is pointing to:
> >
> >    ~/tmp/reword (master|REBASE-i 1/3)$ head -n1 .git/COMMIT_EDITMSG
> >    second
> >    ~/tmp/reword (master|REBASE-i 1/3)$ git log --oneline -1
> >    d5fad83 (HEAD) second
> >
> > So far so good.
>
> Because the sequencer can fast-forwarded to second from first it does that and
> then run 'commit --amend' to do the reword.
>
> > Save the updated commit message, and after the editor opens up the
> > third commit's log message, check again where HEAD is pointing to now:
> >
> >    ~/tmp/reword (master +|REBASE-i 2/3)$ head -n1 .git/COMMIT_EDITMSG
> >    third
> >    ~/tmp/reword (master +|REBASE-i 2/3)$ git log --oneline -1
> >    c3db735 (HEAD) second - updated
>
> As second has been updated the sequencer cannot fast-forward to third so it
> cherry-picks third and then passes --edit when it runs 'git commit' to commit
> the cherry-pick. HEAD is updated once the reworded commit has been created.
>
> I think the scripted rebase always ran cherry-pick and then ran 'commit
> --amend' afterwards if the commit was being reworded. The C implementation is
> more efficient as it avoids creating an redundant commit but has the side
> effect that HEAD is not updated before the reword which was surprising here.

> I don't think I've ever looked at HEAD while rewording, my shell prompt gets
> the current pick from .git/rebase-merge/done so does not look at HEAD. While
> it might seem odd if the user looks at HEAD it's quite nice not to create a
> new commit only to amend it straight away when it's reworded. We have
> REBASE_HEAD which always points to the current pick - HEAD is also an
> unreliable indicator of the current pick if there are conflicts.