git-workshop/module-04-merging/README.md

Module 04: Merging

Learning Objectives

In this module, you will:

• Understand what merging means in Git
• Perform a fast-forward merge
• Perform a three-way merge
• Understand when merge commits are created
• Use git merge to combine branches

Challenge

Setup

Run the setup script to create your challenge environment:

.\setup.ps1

This will create a challenge/ directory with a Git repository that has a main branch and a feature branch ready to merge.

Your Task

This challenge has two parts that teach you about the two types of merges in Git:

Part 1: Fast-Forward Merge

1. Merge the existing feature-api branch into main
2. Observe that this is a "fast-forward" merge (no merge commit created)

Part 2: Three-Way Merge 3. Create a new branch called feature-ui 4. Make commits on the feature-ui branch 5. Switch back to main and make a commit there too (creates divergence) 6. Merge feature-ui into main 7. Observe that this creates a merge commit (three-way merge)

Suggested Approach:

1. Navigate to the challenge directory: cd challenge
2. Check current branch: git branch (should be on main)
3. View existing branches: git branch -a
4. Merge feature-api: git merge feature-api
5. View the log: git log --oneline --graph
6. Create feature-ui branch: git switch -c feature-ui
7. Create a new file ui.py and commit it
8. Make another commit on feature-ui (modify ui.py)
9. Switch back to main: git switch main
10. Make a change on main (modify api.py) and commit it
11. Merge feature-ui: git merge feature-ui
12. View the merge history: git log --oneline --graph --all

Important Notes:

• A fast-forward merge happens when main hasn't changed since the feature branch was created
• A three-way merge creates a merge commit when both branches have diverged
• You can see merge commits with git log --merges
• The --graph option helps visualize the branch history
• After merging, the feature branch still exists but you can delete it with git branch -d

Key Concepts

• Merge: Combining changes from different branches into one branch.
• Fast-Forward Merge: When the target branch hasn't changed, Git simply moves the branch pointer forward. No merge commit is created.
• Three-Way Merge: When both branches have new commits, Git creates a merge commit that has two parent commits.
• Merge Commit: A special commit with two (or more) parent commits, representing the point where branches were merged.
• Divergent Branches: Branches that have different commits since they split from a common ancestor.

Useful Commands

git merge <branch>           # Merge branch into current branch
git log --oneline --graph    # View merge history visually
git log --graph --all        # View all branches and merges
git log --merges             # Show only merge commits
git branch -d <branch>       # Delete a merged branch (optional)

Verification

Once you've completed both merges, verify your solution:

.\verify.ps1

The verification script will check that you've successfully merged both feature branches and understand the different merge types.

Need to Start Over?

If you want to reset the challenge and start fresh:

.\reset.ps1

This will remove the challenge directory and run the setup script again, giving you a clean slate.