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Working together & merge conflicts

Do this lesson in pairs. One person is the owner, the other the collaborator.

1. Share a repo

Owner: on your my-robot repo on GitHub, go to Settings → Collaborators → Add people, and add your partner's GitHub username.

Collaborator: accept the invite (check your email or https://github.com/notifications), then clone the owner's repo:

cd ~
git clone https://github.com/<owner-username>/my-robot.git partner-robot
cd partner-robot

2. Take turns

Each of you, one at a time:

  1. git pull
  2. Make a branch, change a file, commit and push.
  3. Open a PR. The other person reviews and merges it.

Changes to different files, or different parts of a file, merge without any trouble.

3. Make a conflict on purpose

A merge conflict happens when two people change the same line differently. Git can't guess which version is right, so it asks you.

  1. Both of you: git switch main && git pull.

  2. Both of you: edit the first line of README.md to say something different, then commit.

    nano README.md
git commit -am "Change title"

  3. Owner: git push. It works.

  4. Collaborator: git push. It's rejected:

    ! [rejected]        main -> main (fetch first)
hint: Updates were rejected because the remote contains work that you do not have locally.

    GitHub has a commit you don't have yet. Pull it:

    git pull

    CONFLICT (content): Merge conflict in README.md
Automatic merge failed; fix conflicts and then commit the result.

4. Resolve the conflict

Open the file:

nano README.md

Git has marked the conflict:

<<<<<<< HEAD
# Collaborator's Robot
=======
# Owner's Robot
>>>>>>> 4c1d2e9...
  • Between <<<<<<< HEAD and ======= is your version.
  • Between ======= and >>>>>>> is the version from GitHub.

Edit the file so it says what it should say: one version, the other, or a mix. Delete all three marker lines. For example:

# Our Robot

Then tell Git it's resolved, and finish the merge:

git add README.md
git commit -m "Merge title changes"
git push

Owner: git pull to get the result.

Avoiding conflicts

  • git pull before you start, and push often.
  • Keep branches small and short-lived.
  • Talk to each other: "I'm editing the motor code" saves a lot of trouble.
  • Conflicts are normal and not a sign anyone did something wrong.

5. Swap roles

Swap owner and collaborator and do the conflict again, so you've both resolved one.