Exercises — Stage 6: Merge the Branch

Exercise 1: Delete the merged branch

Goal: Clean up branches that have been merged.

Steps:

1. Run git branch. You still see dark-theme.
2. Run git branch -d dark-theme.
3. Run git branch. dark-theme is gone.

What happened: Once a branch is merged into main, the branch label has served its purpose. git branch -d refuses to delete unmerged branches — that is a safety net. The capital -D force-deletes, which you should only use when you know what you are doing.

Exercise 2: Inspect the merge with --graph

Goal: See the merge visually.

Steps:

1. Run git log --oneline --graph --all.

What happened: You see all four commits on a single straight line. The fast-forward merge left no fork in the history — it is as if the dark theme commit was always on main.

Exercise 3: Force a merge commit

Goal: See the other kind of merge.

Steps:

1. Recreate the branch: git checkout -b dark-theme.
2. Switch back to main: git checkout main.
3. Make a new tiny commit on main so the two branches actually diverge:

   echo "<!-- Box Runner -->" >> index.html
   git add index.html
   git commit -m "Added a comment to index.html"

4. Now merge: git merge dark-theme --no-ff.
5. Run git log --oneline --graph --all.
6. When you are done experimenting, undo: git reset --hard HEAD~2 and optionally re-merge cleanly.

What happened: --no-ff forces Git to create a merge commit even when a fast-forward would be possible, so the history shows a visible fork and join. Many teams prefer this because it preserves the fact that a branch existed.

Exercise 4: Count commits on each branch

Goal: Confirm the merge's effect.

Steps:

1. Run git rev-list --count main.
2. Run git rev-list --count dark-theme (if you still have the branch).

What happened: Both counts are 4. Both branches point at the same commit now, so they have the same number of commits reachable from them.