Re: "git rebase" behavior change in 2.26.0

[Jeff King <peff@peff.net>]

On Tue, Mar 24, 2020 at 08:38:04PM -0700, Norbert Kiesel wrote:

> I track an upstream repo with "pull.rebase = true" where I do a `git
> pull` followed by a `git log -p ORIG_HEAD..` for a branch to see
> changes since the last "pull".  I normally do not commit to this
> branch and thus this normally is a "fast-forward" merge.
> 
> Starting with 2.26 this no longer works because ORIG_HEAD is always
> set to HEAD after my `git pull`.
> 
> I track other prances from the same repo where I do local changes and
> then want the `git pull --rebase` and I thus do not want to
> give up on the `pull.rebase = true` configuration.

I can imagine this is related to the switch to the "merge" backend for
git-pull, which may be more eager to overwrite ORIG_HEAD. Perhaps try:

  git -c rebase.backend=apply pull

and see if that behaves differently.

I tried to reproduce what you're seeing, but my recipe doesn't seem to
show any difference between the two versions:

-- >8 --
#!/bin/sh

rm -rf repo

git init -q repo
cd repo
echo content >base && git add base && git commit -q -m base
git clone -q . dst
echo content >new && git add new && git commit -q -m new

cd dst
git rev-parse HEAD >.git/ORIG_HEAD
echo before: $(git log -1 --oneline ORIG_HEAD)
git -c pull.rebase=true pull -q ..
echo after: $(git log -1 --oneline ORIG_HEAD)
-- 8< --

We don't seem to touch ORIG_HEAD in either case. But maybe a more
complex set of pulled commits would trigger it?

-Peff