In The importance of bad code (or, WordPress and why I am a psychic), Marco Tabini proposes the idea that we need bad code. Or at least that we should be tolerant of bad code in open source projects because that invites participants that might otherwise not contribute.

This is an interesting idea that struck me as novel. But after thinking more about it, I believe it’s not a radical departure from what we’re all implicitly accepting, no matter how fanatical we might be about clean code.

Luke Welling’s comment to the blog post is particularly enlightening and worth quoting in full:

I’d argue that bad code is often a sign and a side effect of a thriving, welcoming user community around a project.

The OSS projects with good code tend to have a relatively small group of committers doing nearly all the work. There is a big learning curve to
working within the project’s (probably unwritten) architectural guidelines, and a big reputation curve that a new person has to climb
to get their patches accepted.

Bad code is often a sign of welcoming new contributors, taking patches that do something useful even if the approach is ugly.

We  all know the problems bad code brings, but I would argue that some  projects are not just successful in spite of bad code, but successful  because they allow bad code.

I commented:

If  we’re looking for the optimal strategy (which is likely to depend a lot  on the specific project), the question may be what parts of the code  need to be held to high quality standards, and what parts don’t require such strictness. And how to separate the two. Security is one of the key issues, since bugs can hide in bad code, and some of those will be security bugs.

Perhaps even more important is the question of whether and how to keep a clean separation between good and bad code. Bad code becomes a problem to me mainly when I need to maintain bad code written by others. Not that I dislike it so much; I sometimes enjoy cleaning up messes, but it slows me down. But if the person who wrote it is maintaining it, it doesn’t affect me much. So a clean separation would be helpful.

That also makes the whole issue clearer to me. Most of us use operating systems, library software and applications that aren’t necessarily up to our coding standards. Having lower code quality in parts of a project is not much different in principle. In fact, it may be less of a problem in some cases. When you a program library that has code of poor quality, the good code is dependent on that bad code. If you are programming the core of an open-source project and someone else is adding bad code in the form of an extension, the bad code is dependent on the good code, making it even less likely that the bad code can affect the good code.

In Domain-Driven Design, there is a pattern called Anti-Corruption Layer which can be helpful in preventing the bad code from having an undue influence on the structure of the good code. It’s worth thinking about, especially when the bad code has an illogical and confusing API.