[QGIS-Developer] license requirements for QGIS plugin

[Olivier Dalang]

Hi !

We tried our best to convince some partners to base some of their work on
QGIS, but they are not ready for open-source yet.

Thus, I started looking into license requirements for QGIS plugins. But the
more I read, the more I get confused.

I found this blog post [1] which very clearly states plugins must comply to
GPL-2.
This is confirmed by the gpl faq [2] since I think a QGIS plugin and QGIS
have a fairly "intimate" relationship in terms of "exchanging complex data
structures back and forth" (sounds hot :-D ).

Then, I found this [3] saying it's possible to use closed external tools,
such as file based exchanges from/to external applications.

So if they build a GPL-licensed plugin calling a proprietary executable,
how external would that latter executable need to be to comply to GPL ?
- could it be shipped with the plugin, in the plugin repo ?
- if not, could it be dynamically downloaded by the plugin in the
background ?
- if not, could it be downloaded by the plugin with some kind of user
interaction (e.g. copy/paste a link) ?
- if not, could it be manually downloaded by the user and placed somewhere ?

And then, as far as I understand GPL-2, the requirements only apply when
you distribute the software, which means you can keep all the code for
yourself. When is it considered that the software is distributed ?
- if they distribute it only to users inside their organization ?
- if they distribute it only to users from partner organizations ?
- if it's not considered distributed when it's done only internally, can
they have internal agreements to prevent internal users from distributing
the software ?

Thank you very much in advance for these clarifications !

And sorry if this is not the best place to ask basic GPL questions... But
the topic is very complex, and it seems integrating GPL/propritery software
is always an edge case. Maybe we could add some vulgarized information
about this in the pyqgis cookbook ?

Kind regards,

Olivier


[1] http://blog.qgis.org/2016/05/29/licensing-requirements-for-qgis-plugins/
[2]
https://www.gnu.org/licenses/old-licenses/gpl-2.0-faq.en.html#GPLAndPlugins
[3] https://gis.stackexchange.com/a/61069
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