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

[Martin von Zweigbergk <martinvonz@gmail.com>]

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".