Distributed Development

Git is a tool to exchange commits (organized into branches) with other developers. As a distributed revision control system, it does not have the notion of a central server. The Sage trac server is just one of many possible remote repositories from your point of view. This lets you use and experiment with different ways to interact with other developers. In this chapter, we describe some common ways to develop for Sage.

For simplicity, let us assume two developers (Alice and Bob) are collaborating on a ticket. The first step of opening the ticket is always the same, and could be performed by either Alice or Bob or a third person.

Simple Workflow

_images/flowchart.svg

  1. Alice creates a new local branch and commits changes to the Sage sources.

  2. Alice uploads her branch to the trac server. This fills in the “Branch:” field with her remote branch name u/alice/description.

  3. Bob downloads Alice’s branch, looks through the source, and leaves a comment on the ticket about a mistake in Alice’s code.

  4. Alice fixes the bug on top of her current branch, and uploads the updated branch.

  5. Bob retrieves Alice’s updates and reviews the changes.

  6. Once Bob is satisfied, he sets the ticket to positive review. The “Author:” field is set to Alice’s full name, and the “Reviewer:” field is set to Bob’s full name.

Alternatively, Bob might want to make some changes himself. Then, instead, we would have

  1. Bob downloads Alice’s branch, makes changes, and commits them to his local branch.

  2. Bob uploads his branch to the trac server. This fills in the “Branch:” field with his remote branch name u/bob/description.

  3. Alice downloads Bob’s branch and reviews his changes.

  4. Once Alice is satisfied, she sets the ticket to positive review. If both contributions are of comparable size, then the “Author:” and “Reviewer:” fields are set to both Alice’s and Bob’s full name.

Public Repository

In addition to the user branches (u/<user>/<description> on the Sage trac server with <user> replaced by your trac user name) that only you can write to, you can also create a public branch that everybody with a trac account can write to. These start with public/ plus some description. To avoid branch name collisions it is a good idea to include your trac user name in the branch name, so it is recommended that you use public/<user>/<description> as the branch name. Now all ticket authors push to the same remote branch.

  1. Alice creates a new local branch and commits some changes to the Sage library.

  2. Alice uploads her branch as a public branch to the trac server. This fills in the “Branch:” field with her remote branch name public/alice/description.

  3. Bob downloads Alice’s branch and makes changes to his local copy.

  4. Bob commits changes to his local branch of the Sage sources.

  5. Bob uploads his changes to the joint remote repository:

    [bob@localhost sage]$ git push trac local_branch:public/alice/description

  6. Alice retrieves Bob’s updates, makes more changes, commits, and pushes them to trac.

  7. Charly reviews the final version, and then sets the ticket to positive review. The “Author:” field is set to Alice’s and Bob’s full name, and the “Reviewer:” field is set to Charly’s full name.

GitHub

Yet another possible workflow is to use GitHub (or any other third-party git repository) to collaboratively edit your new branch, and only push the result to trac once you and your ticket co-authors are satisfied.

Fork

The first step is to create your own fork of the Sage repository; simply click “Fork” on the Sage GitHub repository. Then add it as one of the remotes to your local Sage repository. In the following, we will use the label “github” for this remote repository, though you are of course free to use a different one:

$ git remote add github [email protected]:github_user_name/sage.git
$ git remote -v
github      [email protected]:github_user_name/sage.git (fetch)
github      [email protected]:github_user_name/sage.git (push)
trac        [email protected]:sage.git (fetch)
trac        [email protected]:sage.git (push)
$ git fetch github
remote: Counting objects: 107, done.
remote: Compressing objects: 100% (63/63), done.
remote: Total 74 (delta 41), reused 40 (delta 10)
Unpacking objects: 100% (74/74), done.
From github.com:github_user_name/sage
* [new branch]      master     -> github/master

Develop

You now use the github repository to develop your ticket branch; First create a new branch:

$ git checkout -b my_branch --track github/master
Branch my_branch set up to track remote branch master from github.
Switched to a new branch 'my_branch'
$ git push github my_branch
Total 0 (delta 0), reused 0 (delta 0)
To [email protected]:github_user_name/sage.git
 * [new branch]      my_branch -> my_branch

Because of the --track option, the git pull command will default to downloading your coauthor’s changes from your github branch. Alternatively, you can create a new branch on your fork’s GitHub webpage.

At this point you can use the GitHub workflow that you prefer. In particular, your choices are

  • Give your coauthors write permissions to your github fork. Every author edits/commits to their own local copy and they jointly push to your github branch.

  • Have every coauthor create their own fork and send you (the lead author) pull requests to your GitHub fork.

  • Use the GitHub web page editing & committing feature, that way you can make changes without ever using your local machine.

Push to Trac

When you are satisfied with your branch, you push it to the Sage trac server:

$ git push trac HEAD:u/user/description

and then fill in the “Branch” field in the trac ticket description as explained in Pushing Your Changes to a Ticket.