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3.2.2 Git for the impatient

Ok, so you’ve been using lily-git.tcl for a while, but it’s time to take the next step. Since our review process delays patches by 60-120 hours, and you want to be able to work on other stuff while your previous work is getting reviewed, you’re going to use branches.

You can think of a branch as being a separate copy of the source code. But don’t worry about it.

Start work: make a new branch

Let’s pretend you want to add a section to the Contributor’s Guide about using branches.

Start by updating the repository, then making a new branch. Call the branch anything you want as long as the name starts with dev/. Branch names that don’t begin with dev/ are reserved for special things in lilypond.

git checkout master
git pull -r origin master
git branch dev/cg

Switch to that branch

Nothing has happened to the files yet. Let’s change into the new branch. You can think of this as “loading a file”, although in this case it’s really “loading a directory and subdirectories full of files”.

git checkout dev/cg

Your prompt now shows you that you’re on the other branch:

gperciva@LilyDev:~/lilypond-git (dev/cg)$

To be able to manage multiple lilypond issues at once, you’ll need to switch branches. You should have each lilypond issue on a separate branch. Switching branches is easy:

git checkout master
git checkout origin/staging
git checkout origin/release/unstable
git checkout dev/cg

Branches that begin with origin/ are part of the remote repository, rather than your local repository, so when you check them out you get a temporary local branch. You should never make changes directly on a branch beginning with origin/. You get changes into the remote repository by making them in local branches, and then pushing them to origin/staging as described below.

Make your changes

Edit files, then commit them.

git commit -a

Remember how I said that switching to a branch was like “loading a directory”? Well, you’ve just “saved a directory”, so that you can “load” it later.

When you create a new file, you need to add it to git, then commit it:

git add input/regression/avoid-crash-on-condition.ly
git commit -a

Edit more files. Commit them again. Edit yet more files, commit them again. Go eat dinner. Switch to master so you can play with the latest changes from other developers. Switch back to your branch and edit some more. Commit those changes.

At this stage, don’t worry about how many commits you have.

Save commits to external files

Branches are nerve-wracking until you get used to them. You can save your hard work as individual ‘.patch’ files. Be sure to commit your changes first.

git commit -a
git format-patch master

I personally have between 4 and 20 of those files saved in a special folder at any point in time. Git experts might laugh as that behavior, but I feel a lot better knowing that I’ve got those backups.

Prepare your branch for review

After committing, you can update your branch with the latest master:

git commit -a
git checkout master
git pull -r origin master
git checkout dev/cg
git rebase master

Due to the speed of lilypond development, sometimes master has changed so much that your branch can no longer be applied to it. In that happens, you will have a merge conflict. Stop for a moment to either cry or have a stiff drink, then proceed to Merge conflicts.

Upload your branch

Finally, you’re finished your changes. Time to upload for review. Make sure that you’re on your branch, then upload:

git checkout dev/cg
git-cl upload master

Wait for reviews

While you’re waiting for a countdown and reviews, go back to master, make a dev/doc-beams branch, and start adding doc suggestions from issue 12345 from the tracker. Or make a dev/page-breaks and fix bug in page breaking. Or whatever. Don’t worry, your dev/cg is safe.

Combining commits (optional unless you have broken commits)

Does the history of your branch look good?

gitk

If you have a lot of commits on your branch, you might want to combine some of them. Alternately, you may like your commits, but want to edit the commit messages.

git rebase -i master

Follow instructions on the screen.

Push to staging

When you’ve got the coveted Patch-push status, time to prepare your upload:

git fetch
git rebase origin/staging dev/cg~0
gitk HEAD 

If everything looks good, push it:

git push origin HEAD:staging

Then change back to your working branch:

git checkout dev/cg

Delete your branch (safe)

After a few hours, if there’s nothing wrong with your branch, it should be automatically moved to origin/master. Update, then try removing your branch:

git checkout master
git pull -r origin master
git branch -d dev/cg

The last command will fail if the contents of dev/cg are not present in origin/master.

Delete your branch (UNSAFE)

Sometimes everything goes wrong. If you want to remove a branch even though it will cause your work to be lost (that is, if the contents of dev/cg are not present in master), follow the instructions in “Delete your branch (safe)”, but replace the -d on the final line with a -D.

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LilyPond — Contributor’s Guide v2.18.2 (stable-branch).