Yes, there has been one settled suit and lots more settled out of court, but this php plug-in issue is relatively speaking an edge case.

The answer to the first question is clearly “no.” The answer to the second question is “probably not, at least I’ve never heard of it happening.”

Code that can stand alone, and be used separately from GPL’d works, can have its own license, yes?

So, let’s say you have a hypothetical class library that lets you communicate with some sort of network service (like IM, Twitter, a weather service, etc). The class library is stand-alone — anybody could write code that runs against the interface, it’s not dependent on WordPress in any way. If I write such a class, I can license it however I want, including a private, purchase-only, no-redistribution without permission license. We’re all agreed there, right?

If I write a WordPress plugin that implements that interface (brings in the class and calls its methods), the *plugin* code, if I distribute it, is supposed to be GPL. But the class can’t be forced to be GPL, right? [1]

Now, somebody else could feel free to write a work-alike class implementing the same interfaces, and make it GPL. But they’d have to be careful not to copy the original class code wholesale, or risk violating its copyright. Instead, they (theoretically) would be obligated to only work from the interfaces exposed in the GPL’d plugin code, and reverse engineer based on that (which might not give them the full set of interfaces actually available in the non-GPL library).

[1] This is the point I’m not absolutely sure of. Does GPL somehow forbid you from distributing “non-GPL-compatible” code along with GPL code? The whole “fork/exec” vs “shared structures” argument gets really fuzzy here I think. If my class can be a black-box, it shouldn’t matter how it’s called. I, as the code creator, should be able to determine what is or is-not acceptable usage, and control redistribution rights. But that’s just my common sense talking, not any analysis of what the GPL actually claims. Somone please correct me if common sense doesn’t apply here.

My point was that if the code is not “distributed”, the GPL doesn’t apply. I know there’s some debate over whether this should be the case, hence the GNU Affero GPL licence.

Personally I support open source licensing, I think it makes economic as well as “social” sense. I’d like to see more of WordPress.com openly available for example.

That doesn’t mean you can’t “charge for the code”, but it certainly does complicate a business model based on false scarcity. That’s why there is so much creativity around business models (and customer satisfaction) in the world of Open Source business.

It might be worth reading up on Marten Mickos’ well-stated “time vs. money” thoughts about the MySQL business model, which is deeply relevant to this discussion (open core, paid consulting and services, etc).