[QGIS-Developer] Plugin licensing requirements

[Vincent Picavet (ml)]

Hi,

On 07/01/2021 10:43, Nyall Dawson wrote:
> On Thu, 7 Jan 2021 at 19:13, Topi Tjukanov <topi at gispo.fi> wrote:
[..]
>> So if this really is a requirement, should this be enforced somehow and
>> checked when plugins are accepted to the official repository?
> 
> Agreed, but keep in mind that it's a little tricky sometimes. A plugin ONLY
> has to make the modules which import QGIS classes GPL (and consequently any
> other modules which import these modules). It is entirely possible to
> separate plugins into two isolated components, a non-GPL "core" layer which
> does NOT use any QGIS modules, and a GPL layer which imports both the QGIS
> modules and the non-gpl core. (This is how the licensed SLYR plugin works,
> for reference).

I would not bet any cent on these assertions. Would you have any serious
references supporting this ?

The GPL licence makes the code "viral" through the notion of "link". For Python
module, it is through import. A link is bidirectionnal, and therefore your whole
package if distributed is considered GPL.

As far as I know, the only way to have a GPL/proprietary coexistence is to have
distinct processes and inter-process communication ( through files, web
interfaces... ). And it can be even trickier if there are strong dependencies
between modules, which can be interpreted as "derived product" or "link", even
if there is no link as in "library link" between the modules.

Best regards,
Vincent


> 
> So to enforce this in some circumstances you'd need to check file-by-file,
> which is going to be time-consuming.
> 
> Nyall
> 
> 
>> 
>> Kind regards, Topi Tjukanov Gispo Oy 
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