As the only formally distinct class of people found in all open source projects, committers deserve special attention in this book. Committers are an unavoidable concession to discrimination in a system which is otherwise as non-discriminatory as possible. But "discrimination" is not meant as a pejorative here. The function committers perform is utterly necessary, and I do not think a project could succeed without it. Quality control requires, well, control. There are always many people who feel qualified to make changes to a program, and some smaller number who actually are.[125] The project cannot rely on people's own judgement; it must maintain standards and grant commit access only to those who meet those standards. On the other hand, having people who can commit changes directly working side-by-side with people who cannot sets up an obvious power dynamic. That dynamic must be managed so that it does not harm the project.

In the section called “Who Votes?”, we already discussed the mechanics of choosing new committers, as a subset of choosing maintainers generally. Here we will look at the standards by which potential new committers should be judged, and how this process should be presented to the larger community.

Committers vs Maintainers

If you haven't already, please read the section called “Not All Maintainers Are Coders” and take its point to heart.

The discussion here is specifically about committers, not about all maintainers. Because committers are ultimately responsible for the project's code base, and for the quality of its public software releases, the long-term health of the project is inescapably dependent on how they approach their work. This doesn't mean that other kinds of contributors can't also affect the project's health; it just means that if the committers aren't doing their job well, there is no way the project can succeed.

Choosing Committers

A good basis for choosing committers is the Hippocratic Principle: first, do no harm.

The most important criterion is not technical skill or even deep familiarity with the code, but simply that a person show good judgement. Judgement includes knowing what not to take on. Someone might post only small patches, fixing fairly simple problems in the code, but if his patches apply cleanly, do not contain bugs, and are mostly in accord with the project's log message and coding conventions, and there are enough patches to show a clear pattern, then an existing committer should propose him for commit access. If at least (say) three people say yes, and no one objects, then the offer is made. True, there might be no evidence yet that the person is able to solve complex problems in all areas of the codebase, but that is irrelevant: he has made it clear that he is capable of judging his own abilities, and that is the important thing.

When a new committer proposal does provoke a discussion, it is usually not about technical ability, but rather about the person's behavior in the project's discussion forums. Sometimes someone shows technical skill and an ability to meet the project's formal code contribution standards, yet is also consistently belligerent or uncooperative in public forums. That's a serious concern; if the person doesn't seem to shape up over time, even in response to hints, then don't add him as a committer no matter how skilled he is. In an open source project, social skills, or the ability to "play well in the sandbox", are as important as raw technical ability. Because everything is under version control, the penalty for adding a committer you shouldn't have added is not so much the problems it could cause in the code (review would spot those quickly anyway), but that it might eventually force the project to revoke the person's commit access — an action that is never pleasant and can sometimes fragment the whole community.

Some projects insist that a potential committer first demonstrate a certain level of technical expertise and persistence, by submitting some number of nontrivial patches — that is, not only do these projects want to know that the person will do no harm, they want to know that he is likely to do good across the codebase. This isn't always a bad policy, but be careful that it doesn't start to turn committership into a matter of membership in an exclusive club. The question to keep in everyone's mind should be "What will bring the best results for the code?" not "Will we devalue the social status associated with committership by admitting this person?"

The point of commit access is not to reinforce people's self-worth, it's to allow good changes to enter the code with a minimum of fuss. If you have 100 committers, 12 of whom make large changes on a regular basis, and the other 88 of whom just fix typos and small bugs a few times a year, that's still better than having only the 12.

Revoking Commit Access

The first thing to be said about revoking commit access is: try not to be in that situation in the first place. Depending on whose access is being revoked, and why, the discussions around such an action can be very divisive. Even when not divisive, they will be a time-consuming distraction from productive work.

However, if you must do it, the discussion should be had privately among the same people who would be in a position to vote for granting that person whatever flavor of commit access they currently have. The person himself should not be included. This contradicts the usual injunction against secrecy, but in this case it's necessary. First, no one would be able to speak freely otherwise. Second, if the motion fails, you don't necessarily want the person to know it was ever considered, because that could open up questions ("Who was on my side? Who was against me?") that lead to the worst sort of factionalism. In certain rare circumstances, the group may want someone to know that revocation of commit access is or was being considered, as a warning, but this openness should be a decision the group makes. No one should ever, on her own initiative, reveal information from a discussion and ballot that others assumed were secret.

Once someone's access is revoked, that fact is unavoidably public (see the section called “Avoid Mystery”), so try to be as tactful as you can in how it is presented to the outside world.

Partial Commit Access

Some projects offer gradations of commit access. For example, there might be contributors whose commit access gives them free rein in the documentation, but who do not commit to the code itself. Common areas for partial commit access include documentation, translations, binding code to other programming languages, specification files for packaging (e.g., Debian dpkg configuration files, etc.), and other places where a mistake will not result in a problem for the core project.

Since commit access is sometimes not only about committing, but about being part of an electorate (see the section called “Who Votes?”), a question may naturally arise: what can the partial committers vote on?

There is no one right answer; it depends on what sorts of partial commit domains your project has. In the Subversion project things are fairly simple: a partial committer can vote on matters confined exclusively to that committer's domain, and not on anything else. Importantly, the project does have a mechanism for casting advisory votes (essentially, the committer writes "+0" or "+1 (non-binding)" instead of just "+1" on the ballot). There's no reason to silence people just because their vote isn't formally binding.

Full committers can vote on anything, just as they can commit anywhere, and only full committers vote on adding new committers of any kind. In practice, though, the ability to add new partial committers is usually delegated: any full committer can "sponsor" a new partial committer, and partial committers in a domain can often essentially choose new committers for that same domain (this is especially helpful in making translation work run smoothly).

Your project may need a slightly different arrangement, depending on the nature of the work, but the same general principles apply to all projects. Each committer should be able to vote on matters that fall within the scope of her commit access, and not on matters outside that, and votes on procedural questions should default to the full committers, unless there's some reason (as decided by the full committers) to widen the electorate. Remember that voting should be quite rare anyway (see the section called “When To Vote”), except for technical votes such as the change voting described in the section called “Voting on Changes”.

Regarding enforcement of partial commit access: it's often best not to have the version control system enforce partial commit domains, even if it is capable of doing so. See the section called “Authorization” for the reasons why.

Dormant Committers

Some projects automatically remove people's commit access if they go a certain amount of time (say, a year) without committing anything. I think this is usually unhelpful and even counterproductive, for two reasons.

First, it may tempt some people into committing acceptable but unnecessary changes, just to prevent their commit access from expiring. Second, it doesn't really serve any purpose. If the main criterion for granting commit access is good judgement, then why assume someone's judgement would deteriorate just because she's been away from the project for a while? Even if she completely vanishes for years, not looking at the code or following development discussions, when she reappears she'll know how out of touch she is, and act accordingly. You trusted her judgement before, so why not trust it always? If high school diplomas do not expire, then commit access certainly shouldn't.

Sometimes a committer may ask to be removed, or to be explicitly marked as dormant in the list of committers (see the section called “Avoid Mystery” for more about that list). In these cases, the project should accede to the person's wishes, of course.

Avoid Mystery

Although the discussions around adding any particular new committer must be confidential, the rules and procedures themselves need not be secret. In fact, it's best to publish them, so people realize that the committers are not some mysterious Star Chamber, closed off to mere mortals, but that anyone can join simply by posting good patches and knowing how to handle herself in the community. In the Subversion project, we put this information right in the developer guidelines document, since the people most likely to be interested in how commit access is granted are those thinking of contributing code to the project.

In addition to publishing the procedures, publish the actual list of committers. It often goes in a file called MAINTAINERS or COMMITTERS or something like that, in the top level of the project's source code tree. It should list all the full committers first, followed by the various partial commit domains and the members of each domain. Each person should be listed by name and identifying handle(s).

Since the distinction between full commit and partial commit access is obvious and well defined, it is proper for the list to make that distinction too. Beyond that, the list should not try to indicate the informal distinctions that inevitably arise in a project, such as who is particularly influential and how. It is a public record, not an acknowledgements file. List committers either in alphabetical order, or in the order in which they arrived.

[125] Even an experienced developer is often not immediately qualified to make changes in a project when still new to that project. One of the signs of an experienced developer, in fact, is when they themselves recognize that and make sure to get the help they need to learn their way around.