The problem: You want to be an effective contributor to a public project that’s using Git.
The solution: Follow conventions and keep clean branches to make them easier to merge.
For your own projects, it doesn’t really matter what you do to publish and maintain your code, at least until other people start forking and attempting to hack on your stuff. In any case, you should keep things simple. Use topic branches for particular features or refactoring if you want, but no big deal.
GitHub’s search attempts to surface active projects by displaying the number of forks, number of watchers, and recent activity, but it doesn’t tell the full story. The “root” of the fork tree (which isn’t really a tree, but is kinda useful to think of that way) isn’t necessarily the current focus of activity. Someone may have published a project and lost interest, but a community may have formed around one of the forks.
Alternately, a project may have been imported from Subversion by a wannabe contributor prior to the original author joining GitHub and applying community-created patches to his or her own fork (which, at this point, isn’t the root of the fork tree).
If there are a relatively low number of forks (say, one or two), you can (mostly) assume that the fork with the most activity is authoritative. Other contributors, with forks that come and go or that are generally out of date, can be considered “outsiders.”
For projects with a larger number of forks, there may be multiple authorities (and potentially even multiple development directions), with many outsiders periodically contributing patches.
All of this means that you, as a potential contributor, need to do some additional research to determine which fork (or forks) is “active” and/or “authoritative”. They may not be one and the same; the “authoritative” fork may focus on stability; you may need bleeding edge features developed by an “authoritative” member of the community instead.
GitHub’s Network Graph is a great tool for this purpose. From the interface, you can see which forks have been the most active (hint: more •’s), most recently active (•’s further right), or have had the most merges (more ⤴’s). Those don’t tell the full story, so you’ll want to mouse-over individual •’s to see who wrote the patch (and who committed it). That will help distinguish between the forks where the patches originated and where they’ve merely been pulled in. You’ll also get a sense of the number and names of people working on a project.
When hacking on other peoples’ stuff, your eventual goal is (probably) to get those changes applied. Here are a few tips to make life easier for everyone involved.
First rule of thumb: merge from authoritative contributors, cherry pick from outsiders.
By merging (e.g.
git merge user/master) from authoritative contributors, it becomes easier for them to apply your changes if and when they deem them fit. Merging from outsiders may force the authorities into accepting patches (or series) that they may not be ready for (as those branches may include changes unrelated to what you were working on).
GitHub’s Fork Queue cherry picks (e.g.
git cherry-pick 469df8) commits by default, so that’s a good way to get your tree in order before adding your own changes. If there are changes to your fork’s parent, you can fast forward your fork before starting work.
Second rule of thumb: keep your changes easily apply-able to the authoritative repository.
For a single line of development, this is easy: rebase against the authoritative master branch whenever possible. Feel free to rewrite history (i.e.
git push -f) as long as you’re confident no one is treating you as authoritative.
If others are treating you as an authoritative source, create a separate branch that gets periodically rebased and make it clear that it’s not suitable for tracking. Others’ changes will eventually need to be rebased against those changes, but probably not until your changes have been applied by a real authoritative contributor.
For changes that do many things, this means keeping multiple branches active. I usually use a branch per feature, plus a separate branch for general bugfixes and documentation. For minor changes, all branches can diverge from a common commit (usually the tip of the authoritative repository’s master branch).
For more drastic changes, you’ll need to decide which is either the most important feature or the least controversial change. Use that as the first patch series and rebase it against the authoritative repository’s HEAD. Rebase subsequent patch series against the next most important (or least controversial).
Write down the order in which your branches should be merged. You can use your project wiki or put it at the top of the
README in your master branch. (See my fork of xmpp4r to see how I’ve done it.) At this point, your master branch is just the default view of your fork and shouldn’t be considerably different from the branch of the authoritative copy you’re tracking (see the exception below).
In some cases, you’ll have branches that aren’t quite ready for prime-time. Treat them the same as branches that are, but don’t make apply-able branches dependent on them (i.e. they should always be the last changes to be applied). Include them in the summary in your
README, but make it clear that they’re not ready yet.
Third rule of thumb: reset your history to match an authoritative repository’s history if their content is the same (or essentially the same).
If your history frequently diverges from an authoritative repository’s history, you’re going to have more trouble applying others’ changes and synchronizing with authoritative repositories.
The simplest way is to delete your repository and re-fork. If you have minor changes, generate a diff to apply once you’ve re-forked.
Because GitHub will only build gems for changes on the master branch, if you have changes that you want to publish (prepared neatly in topic branches, as above), you’ll need to break the rules somewhat.
To handle this scenario, start with your master branch matching the authoritative branch you’re tracking, then merge branches like the owner of the authoritative branch would (this has the helpful side-effect of discovering whether your changes will apply cleanly).
The tip of your master should always contain the most up-to-date gemspec (in order to trigger GitHub’s building and publishing of your fork) as well as a
README that contains information on the state of your repository (including branches, as above, but also information about how you’re treating the master branch).
Over the last couple months, I’ve become one of the authoritative forks for the OAuth gem, indirectly resulting in this document. I’ve attempted to be consistent in the management of my fork, including publishing periodic releases for others to test functionality, but it became clear that my methods weren’t as transparent as they ought to be.
As a maintainer (or authoritative fork), you frequently find the need to merge in work from other developers. GitHub’s Fork Queue is excellent for this, but it’s not the last word.
The Fork Queue is perfect for merging individual commits, but when someone submits a patch series, it’s time to make a decision: you can cherry-pick (e.g.
git cherry-pick 469df8) all of their commits (which is what the Fork Queue does behind the scenes)–retaining authorship but setting the committer field to yourself–or you can pull their branch down and perform a merge (e.g.
git merge user/master), retaining both author and committer.
Cherry picking commits is easier–unless you want/need to make adjustments to them (in which case the SHAs would change anyway)–and results in linear history (no merges) with the downside of having repetitive commits (with different committers) across the project network, thus confusing GitHub’s Network Graph (or anything that displays the history of multiple branches) and making it more difficult to find un-applied patches (as the same patch may exist with multiple SHAs).
Merging changes locally is more difficult, but the github gem makes it easier by pulling in the entire patch universe with
gh network fetch. Once that’s been done, the combination of
gh network commits, GitX, and the Network Graph make it relatively easy to identify commits ripe for picking.
An advantage of cherry picking is that you have the freedom to amend (
commit --amend) commits before pushing them out as part of your tree. This is a great opportunity to clean things up to match local coding standards (that should already be the case, but YMMV) and to add additional context to the commit message.
Note: You can achieve the same effect as amending commits by using
format-patch -1 469df8 to create a patch, applying it with
git apply, pausing to clean it up, and committing it with
git commit -c 469df8. git ready has a good article on picking out individual commits.
The main problem with cherry picking becomes more acute when there are multiple authoritative forks (which should maintain a consistent public state) constantly passing work back and forth. If the participants periodically merge others’ work, you end up with a number of merge commits, but a relatively coherent history. If one or more participants choose to cherry pick commits instead, merging their branches back will include repeated commits with different SHAs and committer fields. The resultant state of the tree is fine, but the history gets somewhat polluted and becomes more difficult to follow.
This can be mitigated by sending patches via email (or any mechanism by which public repositories don’t change) and repeatedly munging history locally, but that’s often not an option, given the level of coordination required.
I used to see complicated Network Graphs (with lots of merging and branching) as a sign of project activity, but now I consider it more as a measure of contributors’ comfort with
git (as individual contributors may be responsible for multiple branches). I believe that the main reason that projects end up with complicated history is due to (relatively) limited coordination between collaborator and maintainer; if I had to guess, I would expect closed projects using Git to have much more linear histories.
Ultimately, I think complicated histories are a side-effect of Git’s merging prowess promoting and supporting the drive-by contributor model. However, as powerful as Git is, coordination between collaborators still lessens the burden on the person doing the merging, thus the above manifesto.
Get yourself out there, coding whatever and whenever, and contribute back. You’ll feel good and you will have made the world a little better, one patch at a time.