如何在git上同步提交

Question

I have a branch A on which I make a commit C1. I fork another branch from A; call it B; and make an commit C2 (changes independent of C1). Now later I go back to A and make some changes to C1. I need to update B now with the latest changes so I do a "git rebase A" on B. This gives me conflicts. Is there an easy way to sync with A. I just want to overwrite C1 on branch B (actually B.C1 should be a mirror of A.C1). Or when rebasing, can I specify something like: "auto resolve conflicts by taking all changes from branch A"

I can always do the following. Create a new branch D from updated A and cherry-pick C2 on top. When I do this and try to push my changes to gerrit (after updating D.C2) I get the error:

To ssh://xxxx@gerrit.xxxx:29418/xxxxx
 ! [remote rejected] HEAD -> refs/for/master (no changes made)
error: failed to push some refs to 'ssh://xxxx@gerrit.xxxx:29418/xxxxx'

I am trying to understand why.

Thanks in advance.

Answer 1

When you are rebasing commits, you rewrite them completely. So you end up with completely new commit objects that are incompatible with the ones you had before. This is not a problem if you do it locally, but it becomes one when you have already pushed the old commits before (as in your case). Because now, you have the old commits on your remote repository, and rewritten commits in your local repository. That's why you should never rebase commits once you have published them anyway. The same thing happens with cherry-picking btw.: the commit you are cherry-picking gets rewritten completely and applied on top of your branch.

Instead, just merge the branches using git merge A . That way, you end up with commits that are compatible to whatever you might have published before.

Now in your case, to repair the situation, do git push --force . This will overwrite whatever is on the remote repository's branch. So be careful with this and definitly don't use it when others are accessing the repository too (since their commits will then break too). But I guess for gerrit it's okay, as it will update the change request.