Have I lost my changes after rebasing?

I recently rebased a branch that I was working on. The history of the tree looked something like this:

1 = 2 = 3 = 4
     \
      5 = 6 = 7
           \
            8

I wanted to rebase my changes (number 8 in the diagram) to be on the master branch (up to commit 4 on the diagram now). So I did the following:

git checkout my_branch
git rebase master

< lots of git mergetool/git rebase --skip to resolve conflicts >

Only now when I run:

git checkout my_branch
git diff master

I get zero differences. I haven't lost my branch (I can still recreate my changes from a patch that I saved) but I can't find the merge/rebase that I did. What did I do wrong? Is the rebase still there somewhere with my changes merged with the master or do I have to do it again?

If you're not seeing any difference, I suspect you lost your changes. You can likely use git reflog to identify the branch that existed before the rebase, and use git reset --hard <my-branch-tip-before-rebase> to get back the original branch. And yes, you'll have to run through the process again. :-(

I'm not quite sure how you ended up with them looking the same though. I would have expected to see the following with the command you gave:

1 = 2 = 3 = 4              (master)
     \       \
      \       5' = 6' = 8' (my_branch)
       \
        5 = 6 = 7

In this case, you probably should've used rebase --onto:

git rebase --onto master <commit id for 6> my_branch

That would have left you with a graph that looked like this:

1 = 2 = 3 = 4              (master)
     \       \
      \       8'           (my_branch)
       \
        5 = 6 = 7

As far as losing your changes, it does take a bit of practice dealing with merge conflicts, especially when you have a couple of big blocks that look nearly identical. I always resort to looking at the actual diff introduced by a commit, and the attempting to tease out that change and merge it with what is already on the branch in an appropriate way. I can easily see how your change may have gotten lost in there.

One thing to remember. If you don't expect a bunch of merge conflicts--because you don't feel the sources diverged enough, the seeing one is a warning flag of doing something wrong. It's good to back up, by doing a git rebase --abort, investigating the branches and checking again if you expect a conflict. Make sure to take note of where the conflict happened (there's usually a "Applying ..." just before rebase kicks you to the command line). That's usually a great place to start.

At times, conflicts are unavoidable, and are tedious to work through. But I suspect with practice, you'll run into this problem less.

For more information on transplanting changes between branches, look at the git rebase man page. Search for "rebase --onto". The first hit should land you in a section talking about transplanting changes to another branch.