8

I want to write a plugin for an open-source software which is not GPL, but has a GPL-compatible license (MIT/BSD). I would like the plugin to use a GPL library.

Can I do this?

My rationale:

  1. Since the plugin links with a GPL library, the plugin is of course also GPL, which is fine.
  2. In order to comply with GPL, all the components used to produce my plugin binaries need to be open-source with a GPL-compatible license.
  3. In order to build my plugin I also need to link with the host interface library (i.e. my plugin depends on this library).
  4. Because (and only because) this host interface library is also open-source under a GPL-compatible license (MIT), then I'm fine and my plugin can safely be distributed also under the GPL.

Is this reasoning correct?

glopes
  • 181
  • 4
  • 2
    Is the plugin going to distributed separately from the main software? If so it doesn't really matter how either of them are licensed. – curiousdannii Nov 14 '15 at 02:27
  • 1
    Yes, the plugin is going to be distributed separately. That was my original intuition, but I wanted to double check because of a plugin's dependency to the host API. In this case I think it's safe because the host API is MIT-licensed. – glopes Nov 14 '15 at 09:05
  • You use the library through its API, and if that is GPL the result must be GPL. Perhaps just the plugin. But this is murky at best, as far as I know, there are no binding court decisions or laws on the matter. – vonbrand Nov 15 '15 at 13:29
  • 1
    Yes, the plugin itself most definitely needs to be GPL. I was mostly concerned whether there was something about the host dependency that created problems. In this case, since the host is MIT, I'm becoming more and more convinced that it is absolutely fine. – glopes Nov 15 '15 at 14:39
  • See also Can plugins for closed source software use GPL'd libraries? – Martin Schröder Nov 16 '15 at 23:29
  • Yes, I read that one before I posted. I believe the difference lies in the "liberty or death" clause of GPL when attaching to the host. Because my host is licensed with a GPL-compatible license, I believe in this case I can safely pick "liberty". However, I still ask because with GPL you never know... – glopes Nov 16 '15 at 23:42
  • @glopes if the API for the plugin is specific to it, GPL might propagate to the plugin-ee – vonbrand Dec 28 '15 at 22:48
  • @vonbrand Would be curious to hear under what conditions this could happen (with references). Also it seems strange to have a plugin API that is specific to a single plugin. That seems to be contradictory to a plugin architecture. Fortunately, it's not the case at all here. – glopes Dec 29 '15 at 03:11
  • @curiousdannii Why does it matter whether or not the plugin is going to be distributed separately or not? – Venemo May 11 '17 at 10:49
  • @curiousdannii From what I understand, the GPL license is all about how code (and binaries) are distributed. It very much matters what exactly is being distributed together and under what license. Specifically, if you make derivative works out of a GPL license, everything that is distributed together as part of that derivative work must be GPL. However, in this case, the derivative work is simply a plugin and I have no way of changing the original host software, which is distributed separately (under the MIT license). The question was whether it was still possible to distribute this plugin. – glopes May 11 '17 at 23:35

1 Answers1

1

As the license is GPL-compatible there should be no problems (if the license has no share-alike condition).

If you are still unsure you could simply contact the creator of the software you want to make your plugin for.

Info-Screen
  • 244
  • 1
  • 6