bot_update: allow rebasing the patch onto an older revision.
When applying a rebase, we normally go from an older base commit to a newer one.
A ---- B ---- C ---- D -origin/master
\
E -branch
In this case, `git rebase D` would certainly work as expected. However,
writing `git rebase B` would NOT get us to the following state:
A ---- B ---- C ---- D -origin/master
\
E' -branch
In fact, it would have no effect.
This article http://matthew-brett.github.io/pydagogue/rebase_without_tears.html
explains the general invocation as
> `git rebase --onto <graft-point> <exclude-from> <include-from>`
> If you don’t specify --onto, <graft-point> defaults to <exclude-from>
So what's happening is, by writing `git rebase B` we're rebasing onto B,
excluding commits that are in B. Commit C is not "in" B so it is kept and we're
back to the starting point.
So I suggest to change the invocation to `git rebase --onto B origin/master`,
which rebases onto B, excluding commits that are in origin/master. This works
more generally and allows rebasing "backwards".
Bug: None
Change-Id: I68e4d805811530b585550bc75099354fef4e9c15
Reviewed-on: https://chromium-review.googlesource.com/904004
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Oleh Prypin <oprypin@chromium.org>
Oleh Prypin