Timeline Convergence

Combining Parallel Universes

You've developed a feature in a branch. Now it's time to integrate it back into the main timeline with git merge.

Basic Merge

To merge a feature branch into main:

# Switch to the branch you want to merge INTO
git switch main

# Merge the feature branch
git merge feature-branch

Types of Merges

Fast-Forward Merge

When no commits were made to main while you worked on your feature, Git simply moves the pointer forward:

Updating a1b2c3d..e4f5g6h
Fast-forward
 navigation.js | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

No merge commit is created—just a clean, linear history.

Three-Way Merge

When both branches have new commits, Git creates a merge commit:

Merge made by the 'recursive' strategy.
 sensors.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

This merge commit has two parents—one from each branch.

Merge Conflicts

When both branches modified the same lines:

Auto-merging navigation.js
CONFLICT (content): Merge conflict in navigation.js
Automatic merge failed; fix conflicts and then commit the result.

Resolving Conflicts

Open the conflicted file:

function calculateSpeed() {
<<<<<<< HEAD
    return distance / 1500;  // main branch version
=======
    return distance / 2000;  // feature branch version
>>>>>>> feature-propulsion
}

Edit to resolve:

function calculateSpeed() {
    return distance / 2000;  // Use feature branch speed
}

Then complete the merge:

git add navigation.js
git commit

Aborting a Merge

If a merge goes wrong:

git merge --abort

Returns to pre-merge state.

Merge Strategies

No Fast-Forward

Always create a merge commit:

git merge --no-ff feature-branch

Preserves branch history in the graph.

Squash Merge

Combine all feature commits into one:

git merge --squash feature-branch
git commit -m "Add complete sensor system"

Creates cleaner history but loses individual commit details.

Viewing Merge Status

See what's merged:

git branch --merged        # Branches merged into current
git branch --no-merged     # Branches not yet merged

Conflict Resolution Tools

Use a visual merge tool:

git mergetool

Opens configured merge tool (VS Code, Meld, KDiff3, etc.).

Best Practices

• Merge frequently to avoid large conflicts
• Pull main into your feature branch regularly
• Test after merging before pushing
• Use meaningful merge commit messages
• Consider squash merging for messy feature branches

# Finish feature work
git switch feature-sensors
git add .
git commit -m "Complete sensor calibration"

# Update feature branch with latest main
git switch main
git pull
git switch feature-sensors
git merge main  # Resolve any conflicts

# Merge feature into main
git switch main
git merge feature-sensors

# Push updated main
git push

# Clean up
git branch -d feature-sensors
git push origin --delete feature-sensors

Merge vs Rebase

Two ways to integrate changes:

• Merge: Preserves complete history, creates merge commits
• Rebase: Creates linear history, rewrites commits (covered in Phase 29)

Both have their place. Merge is safer for beginners.

Next: Mission Corrections

You can now merge timelines. Next, learn to undo mistakes—because everyone makes them!