When I look at open source projects, I divide the people involved into three categories: the investors, the contributors, and the users. The contributors do the work on the project, while the investors (if any) support the contributors in some way. The users are those who simply use the project without contributing to it.

For example, in sourmash, the investors are (primarily) the Moore Foundation, because they support most of the people working on the project via the Moore grant that I have. There are the contributors - myself, Luiz Irber, and many others in and out of my lab - who have submitted code, documentation, tutorials, or bug reports. And then there are the users, who have used the project and not contributed to it. (Projects can have many investors, many contributors, and many users, of course.)

I consider anybody who used sourmash and then contacted us - with a bug report, a question, or a suggestion - as a contributor. They may have made a small contribution, but it is a contribution nonetheless. I should add that those who cite us or build on us are contributing back in a reasonably significant way, by providing a formal indication that they found our code useful. This is a good signal of utility that is quite helpful when discussing new investments.

Users are interesting, because they contribute nothing to the project but also cost us nothing. If someone downloads sourmash, installs it, runs it, and gets a result, but for whatever reason never publishes their use and cites us, then they are a zero-cost user. If they file a bug report, that’s potentially a small burden on the project (someone has to pay attention to it), but - especially if they file a good bug report that makes it easy to track down the bug - then I think they are contributing back to the project, by helping us meet our long-term goals of less-buggy / more correct code.

Some (rare) contributors are more burden than help. They are the contributors who discover an interesting project, try it out, find that it doesn’t quite fit their needs, and then ask the developers to adjust it for them without putting any effort into it. Or, they ask many questions via private e-mail, consuming the time and energy of developers in private without contributing to the public discussion of the software’s scope and functionality. Or, they argue passionately about planned features without putting any other time into the project themselves. I call these extractive contributors.

These extractive contributors are far more of a burden then you might think. They consume the effort of the project with no gain to the project. Sometimes feature requests, questions, and high-energy discussions lead the project in new, worthwhile directions, but quite often they’re simply a waste of time and energy for everyone involved. (We don’t have any such contributors in sourmash, incidentally, but I’ve seen them in many other projects - the more well known and useful your project is, the more likely you are to have people who demand things of the project.) Quote from a friend: “They don’t contribute much code, but boy do they have strong opinions!"

You could certainly imagine an extractive contributor who implements some big new feature and then dumps it on the project with a request to merge (these are often called “code bombs”). If the feature was discussed beforehand and aligns with the direction of the project, that’s great! But sometimes people submit a merge request that simply won’t get merged - perhaps it’s misaligned with the project’s roadmap, or it adds a significant maintenance burden. Or, perhaps the project developers don’t know and trust the submitter enough to merge their code without a lot of review. Again, this is not a problem we’ve had in sourmash, but I know this happens with some frequency in the bigger Python projects.

You could even imagine a significant regular code contributor being extractive if they are not contributing to the maintenance of the code. If someone is working for a company, for example, and that company is asking them to implement features X, Y, and Z in a project, but not giving them time to contribute to the overall project maintenance and infrastructure as part of the core team, then they may be extracting more from the project than they are putting in. Again, on the big projects, I’m told this is a serious problem. To quote a friend, “sometimes pull requests are more effort than they are worth."

I don’t know what the number or cost of extractive contributors is on big projects, but at least by legend they are a significant part of the software sustainability problem. Part of the problem is on the side of the core maintainers of any project, of course, who don’t protect their own time - in the open source world, developers are taught to value all users, and will often bend over backwards to meet user’s needs. But a larger part of the problem is on the side of the extractive contributors, who are effectively sapping valuable effort from the project’s contributors.

I don’t think it’s necessarily easy to identify extractive contributors, nor do I think it’s straightforward to draw well-considered boundaries around an open project in which you indicate exactly which contributions are welcome, and how. And some extractive contributors can turn into net positive contributors with a little bit of mentoring and effort; we could think of such an effort as incurring contributor debt that could be recouped if more "effort" is brought into the project than is lost, over the long term.

Looking at things through this lens, some features of the Python core dev group come into sharp focus. Python has a ‘python-ideas’ list where potentially crackpot ideas can be floated and killed without much effort if they are misaligned with the project. If an idea passes some threshold of critical review there, it can potentially move into a formal suggestion for python implementation via a Python Enhancement Proposal, which must follow certain formatting and content guidelines before it can even be considered. These two mechanisms seem to me to be progressive gating mechanisms that serve to block extractive users from sapping effort from the project: before a major change request will be taken seriously, first the low threshold of a successful python-ideas discussion has to be met, and then the significant burden of writing a PEP needs to be undertaken.

A few (many?) years ago, I seem to recall Martin von Löwis offering to review one externally contributed patch for every ten other patches reviewed by the submitter. (I can’t find the link, sorry!) This imposes work requirements on would-be contributors that obligate them to contribute substantively to the project maintenance, before their pet feature gets implemented.

Projects can also decrease the cost of extractive contributors by lowering the cost of engagement. For example, the “pull request hack” makes it possible for anyone who has made a small "minimally viable" contribution to a project to become a committer on the project. While it probably wouldn't work for big complex projects, on smaller projects you could imagine it working well, especially for bug fixes and documentation-centric issues.

Another mechanism of blocking extractive contributors is to gate contributions on tests: in sourmash and khmer, as in many other open source projects, we don’t even consider reviewing pull requests until they pass the continuous integration tests. We do help people who are having trouble with them, in general, but I almost never ask Luiz to review my own PRs until they pass tests. When applied to potential contributors, this imposes a minimum level of engagement and effort on the part of that contributor before they consume the time and energy of the central project.

I suspect there are actually a bunch of techniques that are used in this way, even if they serve purposes beyond gating contributors (we also care if our tests pass!). I’d be really interested in hearing from people if they have encountered strategies that seem to be aimed at blocking or lowering the cost of extractive contributors.

How does this connect with the title, "How open is too open?" Well, this question of sustainability and "extractive" contributors seems to apply to all putatively "open" projects, but techniques aimed at blocking extractive contributors seem to trading openness for sustainability. And I’m curious if that’s something we need to pay attention to when building open communities, and how we should measure and evaluate the tradeoffs, and what clever social hacks people have for doing this.

—titus