World 3: Parallel Universes

Fast-forward merge

You will learn: how a finished branch joins main when main has nothing new.

The problem

~/diary $ git log --oneline --graph --all* 203a91f (about) Say what I like* a20da6c Add about page* 270a76e (HEAD -> main) Add style* a8feb63 Add day 1 page* 6d3a9b1 Add README

Your about page is finished on its branch. But main doesn’t have it yet. How do they join?

Watch

On main, git merge about brings the about work in. main has nothing new, so Git just slides the note forward. That’s a .

Watch

~/diary $ git merge aboutUpdating 270a76e..203a91fFast-forward about.html | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 about.html

Look for the word Fast-forward. Git made no new commit. One note just moved.

Try it

You are on main. about into it.

Hint

Type git merge about, then press Enter.

Predict

After a fast-forward, how many new commits did Git make?

Check

Where is main now?

Tap the commit main points at now.

You did it!

You can now merge with a fast-forward.

Go deeper (optional)

git merge --ff-only about merges only if it can fast-forward. If not, it stops safely. git merge --no-ff about always makes a merge commit. Some teams like that, so the branch shows up in history.

~/diary $ git merge --no-ff aboutMerge made by the 'ort' strategy. about.html | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 about.html~/diary $ git log --oneline --graph*   e8fa618 (HEAD -> main) Merge branch 'about'|\  | * 203a91f (about) Say what I like| * a20da6c Add about page|/  * 270a76e Add style* a8feb63 Add day 1 page* 6d3a9b1 Add README