Re: [PATCH] rebase: use reflog to find common base with upstream

[John Keeping <john@keeping.me.uk>]

On Mon, Oct 21, 2013 at 10:40:22PM -0700, Martin von Zweigbergk wrote:
> On Wed, Oct 16, 2013 at 11:53 AM, John Keeping <john@keeping.me.uk> wrote:
> > Commit 15a147e (rebase: use @{upstream} if no upstream specified,
> > 2011-02-09) says:
> >
> >         Make it default to 'git rebase @{upstream}'. That is also what
> >         'git pull [--rebase]' defaults to, so it only makes sense that
> >         'git rebase' defaults to the same thing.
> >
> > but that isn't actually the case.  Since commit d44e712 (pull: support
> > rebased upstream + fetch + pull --rebase, 2009-07-19), pull has actually
> > chosen the most recent reflog entry which is an ancestor of the current
> > branch if it can find one.
> >
> > Change rebase so that it uses the same logic.
> >
> > Signed-off-by: John Keeping <john@keeping.me.uk>
> > ---
> >  git-rebase.sh     | 8 ++++++++
> >  t/t3400-rebase.sh | 6 ++++--
> >  2 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/git-rebase.sh b/git-rebase.sh
> > index 226752f..fd36cf7 100755
> > --- a/git-rebase.sh
> > +++ b/git-rebase.sh
> > @@ -437,6 +437,14 @@ then
> >                         error_on_missing_default_upstream "rebase" "rebase" \
> >                                 "against" "git rebase <branch>"
> >                 fi
> > +               for reflog in $(git rev-list -g "$upstream_name" 2>/dev/null)
> > +               do
> > +                       if test "$reflog" = "$(git merge-base "$reflog" HEAD)"
> > +                       then
> > +                               upstream_name=$reflog
> > +                               break
> > +                       fi
> > +               done
> >                 ;;
> >         *)      upstream_name="$1"
> >                 shift
> 
> A little later, "onto_name" gets assigned like so:
> 
>   onto_name=${onto-"$upstream_name"}
> 
> So if upstream_name was set above, then onto would get the same value,
> which is not what we want, right? It seems like this block of code
> should come a bit later.
> 
> I also think it not be run only when rebase was run without a given
> upstream. If the configured upstream is "origin/master", it seems like
> it would be surprising to get different behavior from "git rebase" and
> "git rebase origin/master".

Hmm... I think you're right.  I originally didn't want to change the
behaviour when the user specifies a branch, but in this case we want to
look for a common ancestor in the reflog of the upstream regardless of
where the ref came from.