Writing WordPress plugins? Read this.

[nakki]

Since the topic of WordPress plugins & licensing came up in couple of other threads, I thought I should make a topic for it.

The issue is, that some people on GFY are writing plugins for WordPress, which is of course the fabulous open source blogging software that's all the rage these days. The problem is that WordPress is licensed under the GPL license, which basically says that if you use any of the functions, variables etc. of the blogging software in your plugin - AND distribute (read: sell) that plugin, the plugin must be released under a GPL-compatible license.

This basically means that if your plugin uses any of the WordPress variables or functions (and I can't think of any useful plugin that wouldn't) and you're distributing that said plugin, you are obliged to also release the source code to that plugin.

Now, I'm not about to sue anyone for not distributing the source code of their plugin. I'm just giving you guys a heads up - when dealing with open source software, you have to be extra careful with licensing. Although the GPL has never been properly tested in court, not paying attention to the licenses might bite you in the ass in the future if you're not careful.

[Trax]

good post

[Veterans Day]

hmmmmmmmmmmmmmmmmm

[nakki]

Heh.. damn, I seem to have forgotten rule #1 of GFY: "Never discuss business".

Really though. Any opinions or thoughts on this?

[griffin]

not true.

[Screaming]

not true.

What makes you say that?

[griffin]

A plugin is not modifying any part of the wordpress source code, it is not a derivative work of wordpress, it is a standalone piece of software that uses the provided interface. There is nothing in the GPL prohibiting any license from utilizing an interface provided by a piece of GPL'd software.

[Brujah]

Some interesting links regarding this topic.
http://www.fsf.org/licensing/licenses/gpl-faq.html

Does the GPL require that source code of modified versions be posted to the public?
http://www.fsf.org/licensing/license...cePostedPublic

If I use a piece of software that has been obtained under the GNU GPL, am I allowed to modify the original code into a new program, then distribute and sell that new program commercially?
http://www.fsf.org/licensing/license...PLCommercially

Can I release a modified version of a GPL-covered program in binary form only?
http://www.fsf.org/licensing/license...fiedJustBinary

If I add a module to a GPL-covered program, do I have to use the GPL as the license for my module?
http://www.fsf.org/licensing/license...LModuleLicense

If a program released under the GPL uses plug-ins, what are the requirements for the licenses of a plug-in?
http://www.fsf.org/licensing/license...#GPLAndPlugins

What should I do if I discover a possible violation of the GPL?
http://www.fsf.org/licensing/license...rtingViolation

[nakki]

A plugin is not modifying any part of the wordpress source code, it is not a derivative work of wordpress, it is a standalone piece of software that uses the provided interface. There is nothing in the GPL prohibiting any license from utilizing an interface provided by a piece of GPL'd software.

You might want to read this FAQ answer. Also, the WordPress Codex says that:

You do not need to license your plugin under the terms of the GPL (http://www.gnu.org/copyleft/gpl.html); but any license you choose to use must be compatible with the GPL (http://www.fsf.org/licensing/license...tibleLicenses).

The GPL pretty clearly says that anything linking to the GPL-licensed code should also be licensed under a compatible license.

Although plugins are somewhat (or, sometimes) in the gray territory, there are some cases of companies distributing the original software and their custom plugins as a single package, in which case (in my opinion) it should definitely be considered a derivative work of the original software.

[nakki]

Sorry, my last URL should be http://www.fsf.org/licensing/license...atibleLicenses

[Brujah]

But, this seems to allow for some seperation depending how the plugin is used/called.
http://www.fsf.org/licensing/license...#GPLAndPlugins

[nakki]

But, this seems to allow for some seperation depending how the plugin is used/called.
http://www.fsf.org/licensing/license...#GPLAndPlugins

Yeah, things get messy when talking about plugins and the GPL. My reading of this is, though, that any useful (WordPress) plugin needs to use a lot of the functions and data structures of the host program to do anything intelligent. But of course there are exceptions.

[twan]

GPL is a virus..