Rebasing a Git merge commit

Question

Take the following case  I have some work in a topic branch and now I m ready to merge back to master    eb3b733 3      master   origin master      b62cae6 2    topic         38abeae 1  I perform the merge from master  resolve the conflicts and now I have      8101fe3 Merge branch  topic    master           b62cae6 2                      topic      eb3b733 3                      origin master         38abeae 1  Now  the merge took me some time  so I do another fetch and notice that the remote master branch has new changes      8101fe3 Merge branch  topic    master           b62cae6 2                      topic        e7affba 4                    origin master                    eb3b733 3        38abeae 1  If I try git rebase origin master from master  I m forced to resolve all conflicts again  and I also lose the merge commit    d4de423 2        master    e7affba 4        origin master    eb3b733 3     b62cae6 2      topic         38abeae 1  Is there a clean way to rebase the merge commit so I end up with a history like the one I show below      51984c7 Merge branch  topic    master           b62cae6 2                      topic      e7affba 4                      origin master      eb3b733 3        38abeae 1

User · Answer

Ok  that s an old question and it already have accepted answer by  siride  but that answer wasn t enough in my case  as --preserve-merges forces you to resolve all conflicts second time  My solution based on the idea by  Tobi B but with exact step-by-step commands  So we ll start on such state based on example in the question       8101fe3 Merge branch  topic    HEAD - gt  master           b62cae6 2                      topic            f5a7ca8 5                    origin master        e7affba 4                   eb3b733 3        38abeae 1   Note that we have 2 commits ahead master  so cherry-pick wouldn t work    First of all  let s create correct history that we want   git checkout -b correct-history   create new branch to save master for future git rebase --strategy ours --preserve-merges origin master   We use --preserve-merges to save our merge commit in history  We use --strategy ours to ignore all merge conflicts as we don t care about what contents will be in that merge commit  we only need nice history now   History will looks like that  ignoring master        51984c7 Merge branch  topic    HEAD - gt  correct-history           b62cae6 2                      topic      f5a7ca8 5                      origin master      e7affba 4     eb3b733 3        38abeae 1  Let s get correct index now   git checkout master   return to our master branch git merge origin master   merge origin master on top of our master   We may get some additional merge conflicts here  but that s would only be conflicts from files changed between 8101fe3 and f5a7ca8  but not includes already resolved conflicts from topic  History will looks like this  ignoring correct-history        94f1484 Merge branch  origin master    HEAD - gt  master           f5a7ca8 5                    origin master      e7affba 4       8101fe3 Merge branch  topic               b62cae6 2                      topic           eb3b733 3        38abeae 1  The last stage is to combine our branch with correct history and branch with correct index  git reset --soft correct-history git commit --amend   We use reset --soft to reset our branch  and history  to correct-history  but leave index and working tree as is  Then we use commit --amend to rewrite our merge commit  that used to have incorrect index  with our good index from master    In the end we will have such state  note another id of top commit        13e6d03 Merge branch  topic    HEAD - gt  master           b62cae6 2                      topic      f5a7ca8 5                      origin master      e7affba 4     eb3b733 3        38abeae 1

User · Answer

Given that I just lost a day trying to figure this out and actually found a solution with the help of a coworker  I thought I should chime in   We have a large code base and we have to deal with 2 branch heavily being modified at the same time  There is a main branch and a secondary branch if you which   While I merge the secondary branch into the main branch  work continues in the main branch and by the time i m done  I can t push my changes because they are incompatible   I therefore need to  rebase  my  merge    This is how we finally did it     1  make note of the SHA  ex   c4a924d458ea0629c0d694f1b9e9576a3ecf506b  git log -1   2  Create the proper history but this will break the merge   git rebase -s ours --preserve-merges origin master   3  make note of the SHA  ex   29dd8101d78  git log -1   4  Now reset to where you were before  git reset c4a924d458ea0629c0d694f1b9e9576a3ecf506b --hard   5  Now merge the current master into your working branch  git merge origin master git mergetool git commit -m correct files   6  Now that you have the right files  but the wrong history  get the right  history on top of your change with    git reset 29dd8101d78 --soft   7  And then --amend the results in your original merge commit  git commit --amend   Voila

User · Answer

There are two options here  One is to do an interactive rebase and edit the merge commit  redo the merge manually and continue the rebase  Another is to use the --rebase-merges option on git rebase  which is described as follows from the manual   By default  a rebase will simply drop merge commits from the todo list  and put the rebased commits into a single  linear branch  With --rebase-merges  the rebase will instead try to preserve the branching structure within the commits that are to be rebased  by recreating the merge commits  Any resolved merge conflicts or manual amendments in these merge commits will have to be resolved re-applied manually  quot

User · Answer

It looks like what you want to do is remove your first merge  You could follow the following procedure   git checkout master        Let s make sure we are on master branch git reset --hard master    Let s get back to master before the merge git pull                   or git merge remote master git merge topic   That would give you what you want

User · Answer

From your merge commit Cherry-pick the new change which should be easy copy your stuff redo the merge and resolve the conflicts by just copying the files from your local copy

[git] Rebasing a Git merge commit

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