Lesson 9: Resolving Conflicts

What You'll Learn

In this lesson, you'll learn how to resolve merge conflicts - one of the most important skills when working with Git. Conflicts happen when Git can't automatically merge changes, and you need to manually decide what to keep.

What is a Merge Conflict?

A merge conflict occurs when:

• Two branches modify the same lines in a file
• Git can't decide which version to keep
• You must manually resolve the conflict

Part 1: Creating a Conflict (for Practice)

Let's create a conflict on purpose to practice resolving it:

Step 1: Create Two Conflicting Branches

# On main branch
git switch main
echo "<h1>Welcome to My Site</h1>" > index.html
git add index.html
git commit -m "Add heading to main"

# Create and switch to feature branch
git switch -c feature/different-heading

# Make conflicting change
echo "<h1>Hello World</h1>" > index.html
git add index.html
git commit -m "Add different heading"

# Try to merge - this will create a conflict!
git switch main
git merge feature/different-heading

Result: Git can't merge automatically!

Part 2: Understanding Conflict Markers

When a conflict occurs, Git adds special markers to the file:

<<<<<<< HEAD
<h1>Welcome to My Site</h1>
=======
<h1>Hello World</h1>
>>>>>>> feature/different-heading

Part 3: Resolving Conflicts

Step 1: Check Status

git status

You'll see:

both modified:   index.html

Unmerged paths:
  (use "git add <file>..." to mark resolution)

Step 2: Open the Conflicted File

Open index.html in your editor and you'll see the conflict markers.

Step 3: Decide What to Keep

You have three options:

• Keep your version (delete everything else)
• Keep their version (delete your changes)
• Keep both (combine the changes)
• Write something new (start fresh)

Step 4: Edit the File

Remove the markers and keep what you want:

<!-- Option 1: Keep first version -->
<h1>Welcome to My Site</h1>

<!-- Option 2: Keep second version -->
<h1>Hello World</h1>

<!-- Option 3: Combine both -->
<h1>Welcome to My Site - Hello World</h1>

<!-- Option 4: Write something new -->
<h1>My Awesome Website</h1>

Step 5: Stage the Resolved File

git add index.html

Step 6: Complete the Merge

git commit -m "Resolve heading conflict"

Done! The conflict is resolved and the merge is complete.

Part 4: Using VS Code to Resolve Conflicts

VS Code makes conflict resolution easier with visual tools:

1. Open the conflicted file in VS Code
2. You'll see buttons above the conflict:
   • Accept Current Change (your version)
   • Accept Incoming Change (their version)
   • Accept Both Changes
   • Compare Changes
3. Click the option you want
4. Save the file
5. Stage and commit

Part 5: Aborting a Merge

If you want to cancel the merge and start over:

git merge --abort

This returns everything to how it was before the merge attempt.

Part 6: Preventing Conflicts

Part 7: Multiple File Conflicts

If multiple files have conflicts:

# Check which files have conflicts
git status

# Resolve each file one by one
# 1. Edit the file
# 2. Remove conflict markers
# 3. Stage the file
git add file1.html
git add file2.css

# When all files are resolved, commit
git commit -m "Resolve merge conflicts"

Practice Exercise

Practice resolving a conflict:

1. Create a file with some content
2. Commit it to main
3. Create a branch and modify the same line
4. Switch back to main and modify that line differently
5. Try to merge - you'll get a conflict!
6. Resolve the conflict
7. Complete the merge

# Create initial file
echo "Hello" > greeting.txt
git add greeting.txt
git commit -m "Add greeting"

# Create branch and change it
git switch -c branch-a
echo "Hello World" > greeting.txt
git commit -am "Change to Hello World"

# Change it differently on main
git switch main
echo "Hello There" > greeting.txt
git commit -am "Change to Hello There"

# Create conflict
git merge branch-a

# Now resolve it! Edit greeting.txt
# Remove markers, choose what to keep
# Then:
git add greeting.txt
git commit -m "Resolve greeting conflict"

Summary

Remember: Conflicts are normal! Don't panic - just take it step by step.

What's Next?

In the next lesson, you'll learn about Pull Requests - GitHub's way of reviewing code before merging. This is how teams collaborate on professional projects!