Lesson 2: The Peacekeeper (Rebase)

Merging creates a merge commit that can clutter the history. Rebase is an alternative that rewrites history to create a clean, linear timeline. It's controversial — but powerful.

Merge vs. Rebase

Merge: Preserves History (Messy but Honest)

main:     A ── B ── C ────── F (merge commit)
                \          /
feature:         D ── E ──┘

Rebase: Rewrites History (Clean but Altered)

Before rebase:
main:     A ── B ── C
feature:  A ── B ── D ── E

After rebase:
main:     A ── B ── C
feature:  A ── B ── C ── D' ── E'

Rebase moves your branch's commits to start from the tip of main, as if you created the branch just now.

How Rebase Works

git checkout feature/login
git rebase main

Git takes each commit on feature/login and replays it on top of main. The commits get new hashes (they're technically new commits).

Interactive Rebase: git rebase -i

The most powerful feature. It lets you edit, combine, reorder, or delete commits:

git rebase -i HEAD~3    # Interactively edit the last 3 commits

This opens an editor:

pick a1b2c3d Add login form
pick e4f5g6h Fix typo in login
pick i7j8k9l Add password validation

You can change pick to:

| Command | Effect | |---------|--------| | pick | Keep the commit as-is | | squash | Combine with the previous commit | | reword | Change the commit message | | edit | Pause to modify the commit | | drop | Delete the commit entirely |

The Golden Rule of Rebase

⚠️ NEVER rebase commits that have been pushed to a shared branch.

Rebasing rewrites history. If others have based work on those commits, you'll create chaos. Only rebase your own local commits.

When to Use What?

| Scenario | Use | |----------|-----| | Feature branch → main | Rebase then merge (clean history) | | Shared/public branch | Merge only (preserve history) | | Cleaning up messy local commits | Interactive rebase | | Hotfix to production | Merge (clear audit trail) |

Mission Objective

Experience the clean side of Git:

1. Rebase: Run git rebase main to replay your commits on top of main.
2. Admire: Run git log --oneline --graph to see the clean linear history.
3. Go interactive: Try git rebase -i HEAD~3 to see the edit interface.

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