git rebase: retain original head?

[Markus Wiederkehr <markus.wiederkehr@gmail.com>]

Hello,

I frequently run an interactive rebase to change the order of recent
commits, apply fixups, etc. When merge conflicts occur I often want to
compare the result with the original head prior to starting the
rebase.

In the past I used "git diff ORIG_HEAD". This used to work as long as
I did not manually invoke "git reset" during the operation.

Since git version 2.20.1 (not sure, maybe 2.20.0?) this no longer
works because ORIG_HEAD seems to get modified by fixup commits during
rebase. Now I have to search through reflog to find the commit I want
to compare the current head to.

During the rebase operation the original head seems to get stored in
'rebase-merge/orig-head'. Unfortunately this references gets removed
after the rebase operation completes.

Would it be possible to retain this information? Could you set
ORIG_HEAD back to rebase-merge/orig-head after rebase completes?
Alternatively, could something like REBASE_HEAD be added for this
purpose?

Undoing a rebase would be related to this and is a very popular
question on SO [1]. Users recommend using "git reset --hard ORIG_HEAD"
which now no longer works.

Regards,
Markus

[1] https://stackoverflow.com/questions/134882