Merging branches
We have developed our Facebook and Twitter login features on two separate sub-feature branches; how can we get these changes back onto the master branch? Following the Driessen Model, we must merge the two sub-feature branches onto the main feature branch, then merge the feature branch into the dev branch, and then create a release branch off dev and merge that release branch into master.
To get started, let's merge the social-login/facebook branch into the social-login/main branch using git merge:
$ git checkout social-login/main
$ git merge social-login/facebook
Updating 8d9f102..09bc8ac
Fast-forward
social-login.txt | 1 +
1 file changed, 1 insertion(+)
Git will attempt to automatically merge the changes from the social-login/facebook branch into the social-login/main branch. Now, our branch structure looks like this:
$ git log --graph --oneline --decorate --all
* 9204a6b (social-login/twitter) Implement Twitter login
| * 09bc8ac (HEAD -> social-login/main, social-login/facebook) Implement Facebook login
|/
* 8d9f102 Add a blank social-login file
* cf3221a (master, dev) Add main script and documentation
* 85434b6 Update README.md
* 6883f4e Initial commit
Next, we need to do the same for our Twitter login sub-feature. However, when we attempt the merge, it fails due to a merge conflict:
$ git checkout social-login/main
$ git merge social-login/twitter
Auto-merging social-login.txt
CONFLICT (content): Merge conflict in social-login.txt
Automatic merge failed; fix conflicts and then commit the result.
A merge conflict occurs when the changes from the two branches being merged overlap each other; Git doesn't know which version is the most appropriate version to move forward with, and so it does not automatically merge them. Instead, it adds special Git markup into the file where the merge conflict occurs and expects you to manually resolve them:
<<<<<<< HEAD
=======
>>>>>>> social-login/twitter
The part between <<<<<<< HEAD and ======= is the version on our current branch, which is social-login/main; the part between ======= and >>>>>>> social-login/twitter is the version on the social-login/twitter branch.
We must resolve this merge conflict before the merge is complete. To do that, we simply need to edit the file to the version we want, and remove the Git-specific sequences. In our example, we want to add the text for twitter after facebook, so we would edit the file to become the following:
Now the conflict is resolved, we need to complete the merge by adding social-login.txt to the staging area and committing it:
$ git status
On branch social-login/main
You have unmerged paths.
Unmerged paths:
both modified: social-login.txt
$ git add -A && git commit -m "Resolve merge conflict"
[social-login/main 8a635ca] Resolve merge conflict
Now, if we look again at our Git history, we can see that we've implemented the Facebook and Twitter login features on two separate branches, and then merged them together in a separate commit (the one with the hash 37eb1b9):
$ git log --graph --oneline --decorate --all
* 37eb1b9 (HEAD -> social-login/main) Resolve merge conflict
|\
| * 9204a6b (social-login/twitter) Implement Twitter login
* | 09bc8ac (social-login/facebook) Implement Facebook login
|/
* 8d9f102 Add a blank social-login file
* cf3221a (master, dev) Add main script and documentation
* 85434b6 Update README.md
* 6883f4e Initial commit