gauteh edited this page Sep 29, 2014 · 9 revisions
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Contributing to Sup

Sup is versioned with Git. This makes it very easy to contribute code changes and bug fixes. The typical lifecycle of a contributed change looks something like this:

  1. You fork the repository on github
  2. You clone your fork
  3. You develop locally on a feature branch
  4. You push your feature branch to your fork on github
  5. You start a pull request from your feature branch to the develop branch on the upstream repo
  6. You endure public commentary
  7. You revise and go to #5, if necessary
  8. A maintainer merges the pull request into the develop branch
  9. Users tracking 'develop' try out your changes and report problems
  10. You submit bugfix patches and go to #5, if necessary

Then every now and then:

  1. Maintainer merges cumulative changes into 'master' branch
  2. Maintainer cuts a release from master, including your changes

Git has several tools that make this workflow easy. The following is a brief intro on how to use Git when developing Sup. It is meant as a quick-start and is by no means a complete guide to Git. If you're going to be doing significant development, you will definitely need to learn more about Git than is presented here.


In the git world, branches are ubiquitous. They come in two flavors: remote branches, which you can pull changes from (or push to), and local branches, which you can edit. To use a remote branch, you have to make a local branch that mirrors it.

From this lifecycle above, you can see that the Sup repository has two remote branches: master and develop. Master is as stable as possible. develop is where the latest and greatest features go. Users are encouraged to track both.

Once changes mature, they're pulled from develop to master, and releases are cut from master. Simple and obvious bug-fix patches can also be applied directly to master, in which case master is merged into develop to propagate those changes.

If you're interested in trying out the new fancy features, you will want to track develop.

If you're interested in the most stable version possible, you will want to track master.

If you're interested in developing, you will typically develop against develop.

Setting up

First you need to fork the sup repository. Log in to and go to and click on the "Fork" button.

Now, you need to clone your fork of the sup repository.

  git clone<username>/sup.git

This will create a "sup" directory, which contains everything you need to get started. (In fact, it contains a complete copy of the entire development history!)

By default you're on the master branch.

Running from the "develop" branch

To get the latest and greatest features, you need to switch to the develop branch. The Git way to do this is like so:

  git branch --track develop origin/develop
  git checkout develop

The first command creates a local branch called develop, which tracks the remote branch, origin/develop. Tracking means that we can use commands like git pull to keep this branch up to date with the remote repository.

The second command switches you over to that branch. You can switch back to the master branch with a git checkout master at any point.

Keeping up to date

In order to pull in the latest changes from upstream you will need to set up a git remote that points to the upstream repo:

git remote add upstream git://

At any point, you can receive the most recent version of the current branch with a git pull:

git pull upstream

If you've made uncommitted changes locally directly on this branch, this command will probably fail. If you've made changes locally directly on this branch, and committed them, this command will do a merge. In both cases, that probably isn't what you want. Follow the instructions in the next section instead.


To develop a particular feature, Git works best with the "topic branch" methodology --- each feature gets its own branch and is developed independently of everything else. At the end of the day, these branches are merged in to the mainline branches.

New features should be developed off develop. Here's how to get started developing a feature:

 git checkout develop      # switch to develop barnch
 git branch <topic name>   # create a new branch off of here
 git checkout <topic name> # switch to the new branch

These commands can be combined into one: git checkout -b <topic name\> develop

To do the first push to your fork, and to set up your local copy to track the branch on your fork, do:

git push -u origin <topic name>

Now you're on the topic branch, and you can tweak and commit to your heart's content. Committing code is a two-stage process. First, you use git add to select the changes you want to commit. (Hint: git add -p will walk you through on a hunk-by-hunk basis, which is very nice). This is called staging the changes, and you can see what's been staged with git diff --cached

Then, use git commit to commit all staged changes. (Hint: git commit -v will display the diff in the commit message file.)

Important: lots of Git tools rely on a particular format of the commit message, but this isn't really explicitly stated anywhere. The format is:

  <one line lowercased summary of the commit, probably less than 72 chars>
  <blank line>
  <more descriptive stuff>

Get in the habit of writing your commit messages like this. It will make your life easier later down the road. (And when you submit patches to the mailing list, the patches will include the commit messages, and they will be rejected unless they conform to this format.)

Other useful commands for developing locally: git log (try -p) and git stash

Commit early and often. It's all done locally. Before submitting our code to the outside world, we'll have a chance to clean it up by splitting, merging, dropping commits, and editing commit messages.

Bugfix changes against develop

For maximum likelihood of patch acceptance, find the commit that created the bug, create a branch right there with git branch <branchname\> <commit id\>, and do your bugfix commits on that branch. That way, the patches don't have false dependencies on later features of develop.

Keeping up to date while developing

If changes have been made to develop since you started working, instead of merging, we will rebase. Rebasing essentially moves the branch point to the new head of develop, as if you've been developing there all along, by rewinding and replaying them from the new head. (Conflict resolution works the same as with merging.) This keeps your development history clean and simple.

To rebase your topic branch:

 git checkout develop      # switch to develop
 git pull upstream develop # sync develop branch with remote repository
 git checkout <topic name> # switch back
 git rebase develop        # move entire branch up

Preparing to submit changes

Once you've developed and tested locally on your topic branch, you're almost ready to submit your patches to the mailing list. First you should spend some time reviewing your commits, e.g. with git log -p, making sure:

  • They're grouped into logical units
  • They don't introduce extraneous whitespace (use git diff --check, or git log -p with color turned on)
  • The commit messages are formatted properly (see above)

Your biggest tool at this stage is git rebase --interactive, which will help you edit and reorder your commits until they're ready for public exposure. You will definitely need to read the man page, but typical usage will be something like:

 git rebase --interactive develop # edit all commits since branching from develop

Submitting pull requests for review

We prefer to get contributions via pull requests on github. To do this you'll need to push your topic branch to your fork:

git checkout <topic name>
git push

Then you can login to github and go to your fork page at<username>/sup and github will notice that you recently pushed a branch and offer to start a pull request. Click on that button, enter any text you need to explain what your pull request is about and click the Submit button.

There are some good tips for how to submit beautiful patches on the Git project's Contributing pages. In particular, if you want to add explanatory/"cover letter" text, you can place it after the --- but before the diffstat in the email.

Other useful commands

Other useful commands include gitk --all for visualizing the entire development history, git reflog for getting yourself out of a mess you made with git reset or git merge, and git rebase --onto for serious graph editing.

The end

Good luck, and happy patching!