# Module 05: Merge Conflicts

## Learning Objectives

In this module, you will:
- Understand what merge conflicts are and why they occur
- Recognize conflict markers in files
- Manually resolve merge conflicts
- Complete a merge after resolving conflicts
- Use `git status` to identify conflicted files

## Challenge

### Setup

Run the setup script to create your challenge environment:

```powershell
.\setup.ps1
```

This will create a `challenge/` directory with a Git repository that has conflicting changes on two branches.

### Your Task

You will intentionally create and resolve a merge conflict - a crucial skill for collaborative development!

**The Scenario:**
- The `main` branch and `feature-updates` branch both modified the same lines in `app.py`
- When you try to merge them, Git can't automatically resolve the differences
- You must manually resolve the conflict

**Steps:**

1. Navigate to the challenge directory: `cd challenge`
2. Verify you're on main: `git branch`
3. Attempt to merge feature-updates: `git merge feature-updates`
4. Git will report a conflict! Don't panic - this is expected
5. Check status: `git status` (shows conflicted files)
6. Open `app.py` in a text editor
7. Look for conflict markers:
   ```
   <<<<<<< HEAD
   (your current branch's version)
   =======
   (the other branch's version)
   >>>>>>> feature-updates
   ```
8. Manually resolve by editing the file:
   - Remove the conflict markers (`<<<<<<<`, `=======`, `>>>>>>>`)
   - Keep the version you want, or combine both changes
9. Save the file
10. Mark as resolved: `git add app.py`
11. Complete the merge: `git commit`
12. View the result: `git log --oneline --graph`

> **Important Notes:**
> - Conflicts occur when the **same lines** are changed differently in both branches
> - Conflict markers show both versions - you choose what to keep
> - You can keep one version, the other, or combine them creatively
> - After editing, you MUST `git add` to mark the conflict as resolved
> - Then `git commit` to complete the merge
> - Use `git merge --abort` if you want to cancel and start over

## Key Concepts

- **Merge Conflict**: Occurs when the same lines in a file are changed differently in both branches being merged.
- **Conflict Markers**: Special markers Git inserts to show the conflicting versions:
  - `<<<<<<< HEAD`: Marks the start of your current branch's changes
  - `=======`: Separates the two conflicting versions
  - `>>>>>>> branch-name`: Marks the end of the other branch's changes
- **Conflict Resolution**: The process of manually editing the file to resolve the differences and remove conflict markers.
- **Staging Resolution**: Using `git add` to tell Git you've resolved the conflict.

## Useful Commands

```bash
git merge <branch>           # Attempt merge (may cause conflict)
git status                   # See which files have conflicts
git diff                     # View conflicts in detail
cat <file>                   # View file with conflict markers
git add <file>               # Mark conflict as resolved
git commit                   # Complete the merge
git commit -m "message"      # Complete merge with message
git merge --abort            # Cancel merge and go back
```

## Verification

Once you've resolved the conflict and completed the merge, verify your solution:

```powershell
.\verify.ps1
```

The verification script will check that you've successfully resolved the conflict and completed the merge.

## Need to Start Over?

If you want to reset the challenge and start fresh:

```powershell
.\reset.ps1
```

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