When you work with many branches in Git, it can be hard to see exactly what changed on one of them. This matters most during code reviews: you want to see all the changes made since the branch was created from main (or any other branch). git diff main does not help here, because it also shows the changes that landed on main after you created the branch.
What you need is the last commit your branch has in common with main, called the merge base. git merge-base HEAD main finds it, and you can pass it to git diff:
git diff $(git merge-base HEAD main)Git also has a shortcut that does the same thing, using three dots:
git diff main...HEADThis works even if you merged main into your branch along the way. After a merge, the merge base moves forward, so the diff still shows only the changes made on the branch.
You can add it as an alias to your .gitconfig file:
[alias]
changes = diff main...HEAD