How to update topic branch with upstream changes on master?

Question

I start some work on a topic branch

    •-•-• < topic
   /
•-•       < master

I push the topic branch

$ git push origin topic

Someone else pushes changes to master

    •-•-• < origin/topic
   /
•-•-•—•   < origin/master

How do I update my local master and rebase my topic?

History should look like this

        •-•-• < topic
       /
•-•-•—•       < master

What I am trying

; update master
$ git checkout master
$ git fetch origin
$ git merge --ff-only origin/master

; rebase topic
$ git checkout topic
$ git rebase master

The problem

All of my commits on topic are seen as uncommitted. So when I try git push origin topic, I get

 ! [rejected]        topic -> topic (non-fast-forward)
error: failed to push some refs to '/path/to/repo.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Merge the remote changes (e.g. 'git pull')
hint: before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

The solution?

Please note, I do not want to merge my topic branch with master. I'd simply like to get my local repo updated without having to merge branches unnecessarily.

Answer 1

Let me rework your example for clarity.

    C-D-E < topic, origin/topic
   /
A-B < master, origin/master

Then someone does work.

    C-D-E < topic, origin/topic
   /
A-B-F-G < origin/master
  ^
master

You fetched F & G from origin, and then rebased topic onto master. So now your repository looks like this.

    C-D-E < origin/topic
   /
A-B-F-G < master, origin/master
       \
        C'-D'-E' < topic

And this is the problem. origin/topic at E can not be fast-forwarded to topic at E'. Rebase is really only meant for commits that have not been pushed to origin. Since you pushed C, D, and E to origin/topic already, you would have to rewrite history on the remote repository. Hence the error. So you really have three options:

1. Stop pushing a topical branch. If it's only you who is working on topic, there's no need to push it. Just keep rebasing topic on top of master, and when done, fast-forward merge master to topic & push master. Delete local topic branch. Voila!

2. Merge topic & master. If you need to collaborate on a topical branch, you should probably suck it up and merge.

3. Force the remote rebase:

   git push origin topic -f

   This will force origin/topic to E'. Except by re-writing history in the remote repository, you'll have fire and brimstone, human sacrifice, dogs and cats living together, mass hysteria... and your fellow developers not liking you very much. Not recommended at all.

Answer 2

; update master
git checkout master
git pull --rebase origin master  

; rebase topic
git rebase master topic

; push topic (force)
git push -f origin topic

Answer 3

There are some problems with your question.

1. You will not get merge conflicts when you push. This can only happen when you merge, rebase, cherry-pick or stash pop/apply.
2. You cannot avoid conflicts if someone else is changing the same content as you are at the same time (even though it may be just you working on another copy of the repo).
3. "All of my commits on topic are seen as uncommitted" doesn't make sense. You probably mean that "all of the changes that my topic branch commits introduce" are not committed yet due to a conflict when I try to rebase.

Your steps are correct, except that you are ignoring that your rebase has stopped on a conflict and you are simply ignoring it. You must resolve your conflicts and then:

git add confilctedfile1.txt conflictedfile2.txt
git rebase --continue

You may need to do this for all of your commits in your topic branch. Only when the rebase is complete should you push.

Another note: For this reason, rebase is not the preferred workflow for day-to-day work. Merge is much easier and more accurate in what is happening with the code base. There are many reasons to favour merge over rebase.