Rebasing branch on top of branch that is ahead

Question

I am trying to understand what happens in the following situation:

1. Branch out into FB from branch X
2. Branch X gets new commits
3. While being on FB, and without having made any changes on FB I now run git rebase origin/X
4. The result is clear: FB now looks identical to X again.

But I don't really understand what happens here, does git simply replay the commits from X onto FB? Or is the reference to the base-commit simply changed?

I know that if I had made changes on FB, these commits would have been 'moved' to a new base-commit, but what happens exactly in the case where I don't make any changes on my FB?

Answer 1

does git simply replay the commits from X onto FB?

Yes.

If you compare this history of FB before and after the rebase you'll see the commit ids have all changed because the commits have been re-created.

The free Pro Git includes diagrams which makes this easier to follow.