Resolving Conflicts

Git Merge Conflicts

1. What is a Merge Conflict?

A merge conflict is an event that occurs when Git cannot automatically reconcile the changes from two different branches. It is not an error or a failure of Git; it is a logical inevitability when concurrent, incompatible changes are made to the same parts of a file.

Git's automatic merging is excellent for combining changes that don't touch the same lines (e.g., you change function A and I change function B). A conflict arises when this is not the case.

2. When Do Conflicts Happen?

Conflicts occur during operations that combine history:

git merge
git rebase
git cherry-pick
git pull (which is essentially fetch + merge)

3. The Root Cause: Divergent Changes

A conflict requires two conditions to be true simultaneously:

The same file was changed in both branches.
The same part(s) of that file were changed in different ways.

Example Scenario:

Branch main has a line: favorite_ice_cream = "vanilla"
You branch off to feature/cake and change it to: favorite_dessert = "chocolate cake"
Someone else on main changes it to: favorite_ice_cream = "pistachio"
Attempting to merge feature/cake into main will cause a conflict. Git doesn't know which variable name (favorite_ice_cream vs. favorite_dessert) or which value ("pistachio" vs. "chocolate cake") to choose. This requires human judgment.

4. Anatomy of a Conflict Marker

When a conflict occurs, Git modifies the file in your working directory to show you the conflicting sections. It uses a specific syntax:

<<<<<<< HEAD
This is the change that is currently on your branch (the one you are on).
=======
This is the change that is coming from the branch you are merging in.
>>>>>>> branch-being-merged

<<<<<<< HEAD: Marks the start of the conflicting changes from your current branch.
=======: The divider between the two conflicting sets of changes.
>>>>>>> branch-name: Marks the end of the conflicting changes from the incoming branch.

What Happens?

Git can't automatically combine changes from two branches because they edited the same part of the same file. It asks you to decide what the final code should be.

What You'll See in the File

Git adds markers to show the conflict:

<<<<<<< HEAD
Your changes (from your current branch)
=======
Incoming changes (from the branch you're merging)
>>>>>>> branch-name

<<<<<<< HEAD to ======= is your code.
======= to >>>>>>> branch-name is their code.

How to Fix It: 4 Steps

Find the conflicts:
```
git status
```
Look for "Unmerged paths".
Open the file and find the <<<<<<< markers.
Edit the file to choose the correct code. You can:
- Keep only your code
- Keep only their code
- Mix them together
- Write something new
- Delete all the conflict markers (<<<<<<<, =======, >>>>>>>)

Finish up:

git add <file>  # Mark this file as fixed
git commit      # Finalize the merge

Commit the changes