@lightweight When it comes to plugins, plugins are almost always derivative works. Wordpress thinks the same: https://wordpress.org/about/license/ If the pro/premium license is additional plugin functionality also under the GPLv2, but only provided if you pay, that's allowed.
If that's not the case, as wordpress plugins appear to be tightly integrated with wordpress, it's time to start GPLv2+ enforcement against such profit driven copyright violation - I'm happy to assist provided a listing of plugins to inspect.
@alilly >Non-GPL Linux modules exist and one would expect them to be in a similar situation, yet the kernel has express technical functionality to support them - maybe look for the existing legal debates about that? That's really an entirely different case. In most cases, I would say that non-GPLv2 modules are copyright infringement (but sadly a lot of Linux copyright holders don't seem to enforce their license).
In Linux, there is an exception model known as EXPORT_MODULE_GPL() and EXPORT_MODULE(). Copyright holders can except the requirements of the GPLv2, but such exception only stands if such exception is agreed to by *all* relevant copyright holders. You can do EXPORT_MODULE() to except the requirements of the GPLv2 under your copyright, but unless all other copyright holders that your code is a derivative work of have made an exceptions as well, the GPLv2 still stands and you doing EXPORT_MODULE() is misleading. It's quite frankly ridiculous to say that you can make exceptions to copyrights that you don't hold.
@alilly Hmm - linked languages like C and levels of linking at, say, an API interaction level are much more loosely coupled. In PHP (in which both Drupal and WP are authored) plugins are, I believe, much more tightly integrated than that kernel-level integration, especially if some API-like linking is being employed to allow for the incompatibly licensed components to interact... @conservancy
Non-GPL Linux modules exist and one would expect them to be in a similar situation, yet the kernel has express technical functionality to support them - maybe look for the existing legal debates about that?
@alilly ok - yeah, as a longtime Drupal developer (which, like WordPress is GPL'd) the idea is that plugins and modules which have no useful function without the platform core (Drupal or WordPress core respectively), they are derivative works and must adhere to the GPL.
@alilly@conservancy given that WordPress plugins/themes are 100% dependent on WordPress core, which is GPL'd, their works are derivative works and therefore obliged to also be GPL'd... I would've thought that'd restrict their ability to offer a second license on the same code - expressly prohibited by the GPL... Am I mistaken?
@lightweight@conservancy The original author of a work has unlimited rights, including the right to license as they see fit to different groups. The developer of a GPLed program is not bound by the GPL and can combine the GPL code with non-GPL code and distribute it under a non-GPL license.
This would be a problem if you mean to accept contributions, as those contributions would be GPL and not your work, unless you make contributors sign a CLA that assigns copyright of the contributions to you
Hello @conservancy - been spending a bit of time in the WordPress (GPLv2+) plugin/theme ecosystem & am amazed how most have "pro/premium licenses" (they use that term) on their code *in addition to the required GPL license*. They're all 'open core' rather than FOSS, from what I can see, contravening the GPL with an additional license. Is this something you're already aware of? Am I right that its a widespread contravention of the GPL? If so, is anything being done to redress it?