Conflict Resolution

Quick Summary

A merge conflict occurs when Git can't automatically combine changes because two branches modified the same lines of the same file. Conflicts aren't errors — they're Git asking you to make a decision. Understanding the process makes them routine instead of scary.

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Why Conflicts Happen

flowchart TD
    A["main: line 10 = 'Hello World'"] --> B["Branch A changes line 10 to 'Hello Git'"]
    A --> C["Branch B changes line 10 to 'Hello GitHub'"]
    B --> D["Merge: CONFLICT!<br/>Which version should line 10 use?"]
    C --> D

Scenario	Conflict?
Two branches edit different files	❌ No — auto-merged
Two branches edit different lines of the same file	❌ No — auto-merged
Two branches edit the same line of the same file	✅ Yes — conflict
One branch deletes a file, the other modifies it	✅ Yes — conflict
Both branches add a file with the same name	✅ Yes — conflict

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Reading Conflict Markers

When a conflict occurs, Git marks the affected sections in the file:

<<<<<<< HEAD
const greeting = "Hello Git";
=======
const greeting = "Hello GitHub";
>>>>>>> feature/github

Marker	Meaning
<<<<<<< HEAD	Start of your changes (current branch)
=======	Divider between the two versions
>>>>>>> feature/github	End of their changes (incoming branch)

Three-Way Conflict (with diff3)

Enable the diff3 style for even clearer conflict markers:

git config --global merge.conflictstyle diff3

<<<<<<< HEAD
const greeting = "Hello Git";
||||||| common ancestor
const greeting = "Hello World";
=======
const greeting = "Hello GitHub";
>>>>>>> feature/github

Now you see the original version too, making the intent of each change much clearer.

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Step-by-Step Resolution

1. Identify Conflicted Files

git status

On branch main
You have unmerged paths.

Unmerged paths:
  (use "git add <file>..." to mark resolution)
        both modified:   src/app.js
        both modified:   src/config.js

2. Open and Resolve Each File

Manual (text editor)

Open the file, find the conflict markers, and edit to the desired result:

// Before: conflict markers
<<<<<<< HEAD
const greeting = "Hello Git";
=======
const greeting = "Hello GitHub";
>>>>>>> feature/github

// After: your resolution (remove ALL markers)
const greeting = "Hello Git and GitHub";

Keep ours

# Keep the current branch's version entirely
git checkout --ours src/app.js

Keep theirs

# Keep the incoming branch's version entirely
git checkout --theirs src/app.js

VS Code

VS Code shows an interactive UI with buttons:

Button	Action
Accept Current Change	Keep HEAD version
Accept Incoming Change	Keep the branch version
Accept Both Changes	Concatenate both
Compare Changes	Side-by-side diff

3. Mark as Resolved

git add src/app.js
git add src/config.js

4. Complete the Merge

git commit
# Git auto-generates a merge commit message

Or if you want a custom message:

git commit -m "Merge feature/github: resolve greeting conflict"

Abort the Merge

# Cancel the entire merge and go back to before
git merge --abort

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Conflict Resolution Strategies

Strategy	When to Use
Keep ours (--ours)	Your version is correct, theirs is outdated
Keep theirs (--theirs)	Their version is correct, yours is outdated
Manual edit	Both changes are partially correct — combine them
Accept both	Both changes are independent additions
Rewrite entirely	Neither version is optimal — write something new

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Common Conflict Scenarios

Scenario 1: Both Edit the Same Function

<<<<<<< HEAD
function calculateTotal(items) {
    return items.reduce((sum, item) => sum + item.price * item.qty, 0);
}
=======
function calculateTotal(items) {
    const subtotal = items.reduce((sum, item) => sum + item.price * item.quantity, 0);
    return subtotal * 1.1; // Add 10% tax
}
>>>>>>> feature/tax

Resolution: Combine both changes:

function calculateTotal(items) {
    const subtotal = items.reduce((sum, item) => sum + item.price * item.qty, 0);
    return subtotal * 1.1; // Add 10% tax
}

Scenario 2: Delete vs Modify Conflict

CONFLICT (modify/delete): src/legacy.js deleted in feature/cleanup
and modified in HEAD. Version HEAD of src/legacy.js left in tree.

Resolution: Decide whether the file should exist. Then:

# Keep the file
git add src/legacy.js

# Or delete it
git rm src/legacy.js

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Preventing Conflicts

Practice	How It Helps
Pull frequently	Stay up-to-date with main, reducing divergence
Small, focused branches	Less code changed = fewer potential conflicts
Communicate with team	Avoid working on the same files simultaneously
Use feature flags	Changes can coexist without modifying the same lines
Rebase before merge	Resolves conflicts earlier, one commit at a time

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Troubleshooting

Problem	Cause	Fix
Can't find conflict markers	Editor hid them or wrong file	Search for <<<<<<< in the file
Merge commit has wrong resolution	Resolved incorrectly	git revert <merge-commit>, then re-merge
Conflicts in binary files	Git can't diff binaries	Choose one version: git checkout --ours/--theirs <file>
Too many conflicts to resolve	Massive branch divergence	Consider rebasing commit-by-commit

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Best Practices

• Enable diff3 conflict style — seeing the common ancestor makes resolution much easier
• Use a visual merge tool — VS Code, IntelliJ, or git mergetool
• Pull/rebase regularly — smaller, more frequent syncs = smaller conflicts
• Don't panic — conflicts are normal; git merge --abort is always available
• Test after resolving — run your tests before committing the resolution

What's Next

1. Remotes, Push, Pull & Fetch — Work with remote repositories
2. Undoing Changes — Undo commits, staged changes, and merges