Interdiffs! How to make them, and why they are your friends
(If you don't see the slideshow below, you can view it on Google docs.)
An interdiff-friendly workflow for revising core patches
Always pull the latest changes.
git checkout 8.x
git pull origin 8.x
Create a local branch for the previous patch.
git checkout -b old_patch
Apply and commit that patch.
git apply --index old.patch
git commit -m "Old patch."
Create a new local branch and make your changes.
git checkout -b new_patch
git add changed_file
git commit -m "New patch."
Create your new patch with a diff against the main branch.
git diff 8.x > new.patch
Create your interdiff with a diff against the branch for the other patch.
git diff old_patch > interdiff.txt
Tip: You can just use
git add . instead of staging files individually if you configure your .gitignore to ignore patch files.