Merge Conflicts in Git and GitHub

Why they occur, what to do when they occur, and how to avoid them

Jonathan Peake

What is a merge conflict?

• Git normally can resolve differences between branches automatically

• Changes on different branches that compete with each other are more difficult to resolve

• Requires manually choosing which changes to keep

When do merge conflicts occur?

1. Changes to the same line of the same file on different branches
2. Deletion of a file edited in another branch
3. Deletion of a line edited in another branch

(more advanced scenarios)

4. Cherry-picking commits
5. Rebasing a branch

What does a merge conflict look like?

• Merge conflicts are denoted by conflict markers: <<<<<<<, =======, >>>>>>>

• Anything between <<<<<<< and ======= is from the base branch

• Anything between ======= and >>>>>>> is from the compare branch

• The name of the base and compare branches are denoted in line with <<<<<<< and >>>>>>>

What does a merge conflict look like?

In this example, we have  
<<<<<<< HEAD 
a change made in the base branch.
======= 
a change made to the same line of the compare branch.
>>>>>>> branch-a

Resolving a merge conflict

1. Open the file where the conflict occurred
2. Find any instances of <<<<<<<
3. Decide what to keep and what to replace
4. Delete the lines containing <<<<<<<, =======, and >>>>>>>
5. Commit your changes and complete the merge

Resolving a merge conflict

In this example, we have:  
<<<<<<< HEAD 
- a change made in the base branch.
======= 
- a change made to the same line of the compare branch.
>>>>>>> branch-a

Resolving a merge conflict

In this example, we have:
- a change made to the same line of the compare branch.

How to avoid merge conflicts

• Communicate

• Make small, frequent commits and pull requests

• Review others’ pull requests