Bug with git merge-base and a packed ref

Hello,

first, I observed a bug with git pull --rebase: if the remote branch got rebased and the loval branch was updated, pull tried to rebase the whole branch, not the local increment.

A reproducer would look like that

# in repo1: git checkout tmp cd .. git clone repo1 repo2 cd repo1 git rebase elsewhere tmp cd ../repo2 # edit git commit -a -m 'Another commit' git pull -r

The last command performs something like
   git rebase new-origin/tmp
instead of
   git rebase --onto new-origin/tmp old-origin/tmp

I'm using git version 2.10.1.windows.1

I tried to debug the issue: I found that the bug happens only at the very first pull after clone. I was able to reproduce it with git-pull.sh

The problem seems to be that command
  git merge-base --fork-point refs/remotes/origin/tmp refs/heads/tmp
returns nothing, because the refs are packed.

Could you please fix merge-base so that it understands packed refs?

Thanks,
  Stepan