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Re: [DotGNU]Qt Theming being a GPL violation

From: Rhys Weatherley
Subject: Re: [DotGNU]Qt Theming being a GPL violation
Date: Sun, 20 Jun 2004 07:50:50 +1000
User-agent: KMail/1.4.3

On Sunday 20 June 2004 02:33 am, Simon Guindon wrote:

> I read the log from the meeting last night and I see some issues have been
> brought up.  Apparently including Qt software into pnetlib can cause GPL
> violations.  Gopal suggested we talk about it on this list and try and come
> to some sort of a conclusion.

There isn't a violation per se.  The issue is that Qt itself is under the full 
GPL, not "GPL plus linking exception" like the rest of pnetlib.  Hence, if we 
were to put the Qt themer inside the core pnetlib assemblies (e.g. 
System.Windows.Forms.dll), we'd get the following effect:

   Qt (GPL) => themer (GPL) => SWF (GPL) => all apps (GPL)

i.e. it would no longer be possible for non-GPL apps to use SWF, as the 
transitivity of the license would promote "GPL plus linking exception" to 
full GPL.  (Technically, GPL has more restrictions than "GPL plus linking 
exception", and the license with the most restrictions wins).

However, putting the Qt themer in a separate assembly, as I believe that you 
have done, should be OK.  Then, the GPL transitivity will only apply if 
someone turns the Qt themer on.  If they don't turn it on, then everything is 
as it is now.

> As I said, I don't know much about licenses but if thats how it is legally,
> then theres not much I can do obviously, but theres some unsure talk if that
> is the issue at all, because if a user builds a non-gpl app, its not really
> linking to qt itself, pnetlib is,which is GPL'd.

It doesn't matter.  If any GPL component is used to run an application, no 
matter how buried the component is in the system, then everything becomes 
GPL.  Even if you don't link against it directly.

The moral of the story is this: we need to add some information to the 
documentation that the Qt themer can only be used with applications whose 
licenses are compatible with the GPL.  If a user uses the Qt themer to run a 
non-compatible application, then the user has caused a violation to occur.

I will verify this with my friends at Trolltech just to be sure.



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