Bug#905975: Issues with using git debrebase for linux

[Ian Jackson <ijackson@chiark.greenend.org.uk>]

Package: git-debrebase
Version: 6.6
Severity: important

Ben Hutchings writes ("Issues with using git debrebase for linux"):
> 1. Safe rebasing
> 
> linux is team-maintained, and it's normal for multiple developers to
> push changes multiple times between releases.  It's therefore not
> acceptable to update branches in a non-fast-forward way.  I believe
> that git debrebase is supposed to avoid doing that, but it seems quite
> easy to defeat the check:
> 
> $ git checkout -b use-dgit-test
> Switched to a new branch 'use-dgit-test'
> $ git branch --set-upstream-to=benh/use-dgit-test
> Branch 'use-dgit-test' set up to track remote branch 'use-dgit-test' from 'benh'.
> $ git debrebase -i 
> OK, you are ahead of refs/remotes/benh/use-dgit-test
> Waiting for Emacs...
> Successfully rebased and updated refs/heads/use-dgit-test.
> $ git rev-list ..benh/use-dgit-test | wc -l
> 109
> $ git debrebase conclude
> 
> git-debrebase: error: No ongoing git-debrebase session.
> $ git-debrebase status
> current branch contents, in git-debrebase terms:
>   branch is laundered
> key git-debrebase commits:
>   anchor
>     470915f1011c git-debrebase import: declare upstream
>   breakwater
>     470915f1011c git-debrebase import: declare upstream
> branch and ref status, in git-debrebase terms:
>   stitched? (no record of git-debrebase work)
> 
> Why was there no pseudo-merge?  Shouldn't the remote tracking branch
> have been recorded as ffq-prev?

To reproduce: clone the linux repo.  Check out use-dgit-test,
   c6eb63c6ed0694b0d22fbe5aaff953d209a3fc4e
It is a laundered-and-stitched branch.

Run git-debrebase -i, and drop these two commits (near the end):
   Revert "aufs4.x-rcN base patch"
   aufs4.x-rcN base patch
The rebase will complete successfully.

Observe that there is no ffq-prev and git-debrebase conclude does not
work, even though the branch is no longer ff from
origin/use-dgit-test.

Ian.