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

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

On Wed, Oct 16, 2013 at 12:24:13PM -0700, Jonathan Nieder wrote:
> John Keeping wrote:
> 
> >                                    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.
> 
> Nice idea.
> 
> Could pull be made to rely on rebase for this as a follow-up?

It's not an obvious change to do that (at least to me) - pull does the
different steps of figuring out the base and then rebasing at different
points in the script.

> [...]
> > --- 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)"
> 
> "git merge-base --is-ancestor" is faster.

We should probably change git-pull to use that as well.

> What should happen if HEAD is not a valid commit?  (Tested with:
> 
> 	$ git checkout --orphan foo
> 	$ cat >>.git/config <<EOF
> 	[branch "foo"]
> 		remote = origin
> 		merge = refs/heads/master
> 	EOF
> 	$ bin-wrappers/git rebase 2>&1 | wc -l
> 	83
> 
> ).

Adding "2>/dev/null" to the merge-base line silences most of that, all
we're left with is "fatal: Needed a single revision" which is the same
as I get from master's git-rebase.  I think silencing stderr is the
right thing to do here - in the worst case we just use the merge-base of
the two branches instead of the appropriate reflog entry.

> diff --git i/git-rebase.sh w/git-rebase.sh
> index fd36cf7..d2e2c2e 100755
> --- i/git-rebase.sh
> +++ w/git-rebase.sh
> @@ -439,7 +439,7 @@ then
>  		fi
>  		for reflog in $(git rev-list -g "$upstream_name" 2>/dev/null)
>  		do
> -			if test "$reflog" = "$(git merge-base "$reflog" HEAD)"
> +			if git merge-base --is-ancestor "$reflog" HEAD
>  			then
>  				upstream_name=$reflog
>  				break