debian-mirror-gitlab/doc/university/training/topics/merge_conflicts.md

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# Merge conflicts

- Happen often
- Learning to fix conflicts is hard
- Practice makes perfect
- Force push after fixing conflicts. Be careful!

## Merge conflicts sample workflow

1. Checkout a new branch and edit `conflicts.rb`. Add 'Line4' and 'Line5'.
1. Commit and push.
1. Checkout master and edit `conflicts.rb`. Add 'Line6' and 'Line7' below 'Line3'.
1. Commit and push to master.
1. Create a merge request and watch it fail.
1. Rebase our new branch with master.
1. Fix conflicts on the `conflicts.rb` file.
1. Stage the file and continue rebasing.
1. Force push the changes.
1. Finally continue with the Merge Request.

```shell
git checkout -b conflicts_branch

# vi conflicts.rb
# Add 'Line4' and 'Line5'

git commit -am "add line4 and line5"
git push origin conflicts_branch

git checkout master

# vi conflicts.rb
# Add 'Line6' and 'Line7'
git commit -am "add line6 and line7"
git push origin master
```

Create a merge request on the GitLab web UI. You'll see a conflict warning.

```shell
git checkout conflicts_branch
git fetch
git rebase master

# Fix conflicts by editing the files.

git add conflicts.rb
# No need to commit this file

git rebase --continue

# Remember that we have rewritten our commit history so we
# need to force push so that our remote branch is restructured
git push origin conflicts_branch -f
```

## Note

- When to use `git merge` and when to use `git rebase`
- Rebase when updating your branch with master
- Merge when bringing changes from feature to master
- Reference: <https://www.atlassian.com/git/tutorials/merging-vs-rebasing>