Git merge master into feature branch

theomega Source

Lets say we have the following situation in git:

  1. A created repository:

    mkdir GitTest2
    cd GitTest2
    git init
    
  2. Some modifications in the master take place and get committed.

    echo "On Master" > file
    git commit -a -m "Initial commit"
    
  3. Feature1 branched off master and some work is done:

    git branch feature1
    git checkout feature1
    echo "Feature1" > featureFile
    git commit -a -m "Commit for feature1"
    
  4. Meanwhile, a bug is discovered in the master-code and a hotfix-branch is established

    git checkout master
    git branch hotfix1
    git checkout hotfix1
    
  5. The bug is fixed in the hotfix branch and merged back into the master (perhaps after a pull request/code review):

    echo "Bugfix" > bugfixFile
    git commit -a -m "Bugfix Commit"
    git checkout master
    git merge --no-ff hotfix1
    
  6. Development on feature1 continues:

    git checkout feature1
    

Now my question: Say I need the hotfix in my feature branch, maybe because the bug also occurs there. How can I achieve this without duplicating the commits into my feature branch? I want to prevent to get two new commits on my feature branch which have no relation to the feature implementation. This especially seems important for me if I use Pull Requests: All these commits will also be included in the Pull Request and have to be reviewed although this has already been done (as the hotfix is already in the master).

I can not do a git merge master --ff-only: "fatal: Not possible to fast-forward, aborting.", but I am not sure if this helped me.

git

Answers

answered 5 years ago David Sulc #1

You should be able to rebase your branch on master:

git checkout feature1
git rebase master

Manage all conflicts that arise. When you get to the commits with the bugfixes (already in master), git will say that there were no changes and that maybe they were already applied. You then continue the rebase (while skipping the commits already in master) with

git rebase --skip

If you perform a git log on your feature branch, you'll see the bugfix commit appear only once, and in the master portion.

For a more detailed discussion, take a look at the Git book docs on git rebase (https://git-scm.com/docs/git-rebase) which cover this exact use case.

answered 5 years ago Sven #2

How to merge the master branch into the feature branch? Easy:

git checkout feature1
git merge master

There is no point in forcing a fast forward merge here, as it cannot be done. You committed both into the feature branch and the master branch. Fast forward is impossible now.

Have a look at gitflow. It is a branching model for git that can be followed, and you unconsciously already did. It also is an extension to git which adds some commands for the new workflow steps that do things automatically which you would otherwise need to do manually.

So what did you do right in your workflow? You have two branches to work with, your feature1 branch is basically the "develop" branch in the gitflow model.

You created a hotfix branch from master and merged it back. And now you are stuck.

The gitflow model asks you to merge the hotfix also to the devel branch, which is "feature1" in your case.

So the real answer would be:

git checkout feature1
git merge --no-ff hotfix1

This adds all the changes that were made inside the hotfix to the feature branch, but ONLY those changes. They might conflict with other development changes in the branch, but they will not conflict with the master branch should you merge the feature branch back to master eventually.

Be very careful with rebasing. Only rebase if the changes you did stayed local to your repository, e.g. you did not push any branches to some other repository. Rebasing is a great tool for you to arrange your local commits into a useful order before pushing it out into the world, but rebasing afterwards will mess up things for the git beginners like you.

answered 5 years ago Bob Gilmore #3

You might be able to do a "cherry-pick" to pull the exact commit(s) that you need in to your feature branch.

Do a git checkout hotfix1 to get on the hotfix1 branch. Then do a git log to get the SHA1 hash (big sequence of random letters and numbers that uniquely identifies a commit) of the commit in question. Copy that (or the first 10 or so characters).

Then, git checkout feature1 to get back onto your feature branch.

Then, git cherry-pick <the SHA1 hash that you just copied>

That will pull that commit, and only that commit, into your feature branch. That change will be in the branch - you just "cherry-picked" it in. Then, resume work, edit, commit, push, etc. to your heart's content.

When, eventually, you perform another merge from one branch into your feature branch (or vice-versa), git will recognize that you've already merged in that particular commit, know that it doesn't have to make it again, and just "skip over" it.

answered 4 years ago zimi #4

Basing on this article you should:

  • create new branch which is based upon new version of master
  • merge your old feature branch into new one
  • resolve conflict on new feature branch

This way your history stays clear because you don't need back merges. And you don't need to be so super cautious since you don't need git rebase

answered 2 years ago jkdev #5

Zimi's answer describes this process generally. Here are the specifics:

1) Create and switch to a new branch. Make sure the new branch is based on master so it will include the recent hotfixes.

git checkout master
git branch feature1_new
git checkout feature1_new

# Or, combined into one command:
git checkout -b feature1_new master

2) After switching to the new branch, merge the changes from your existing feature branch. This will add your commits without duplicating the hotfix commits.

git merge feature1

3) On the new branch, resolve any conflicts between your feature and the master branch.

Done! Now use the new branch to continue to develop your feature.

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