I should publish it at some point (it's just a simple bash script), but I made a convenient alias `git bisect-rebase` which helps catch up very old branches.

It isn't particularly fast, but it uses bisect to find the first commit on the target branch that conflicts with your branch, then let's you rebase to that commit. You then repeat the process until you are caught up.

The idea is that solving one conflict many times is usually quite easy, especially if you know the conflicting commit messages, but solving many conflicts in one go is not so easy. This was inspired by me rebasing a 6 month old branch which refactored a file that happened to have many edits in between.