Re: Q: Combining proprietary code and GPL for in-house use

[Walter Landry <landry@physics.utah.edu>]

> My program works well without the GPL library. Now if I sell this program,
> and add a module that the customer may link with the GPL library, would I
> violate the GPL of the library, and why ? If the customer linked in the
> module, would he violate the GPL, and why (he's in the same situation as I
> was: linking a GPL module with proprietary code is not forbidden, only the
> distribution thereof).
> 
> Now what happened if the customer paid somebody else for linking the GPL
> library with the module of my program (the consultant would do this on the
> machine of the customer, FWTW). Would somebody violate the GPL here. Who and
> why ?

If you write a program that uses no GPL'd code, you can distribute it
under any license you want.  Even if it is completely broken and
useless without additional libraries.  Even if you encourage other
people to take GPL'd code and write plugins.

The problem occurs when you want to distribute the plugin (or almost
any kind of interface between the proprietary bits and the GPL'd (not
LGPL'd) library).  Since, to write the plugin, you had to rely on
proprietary and GPL'd code, you can't distribute the resulting
executable.  You can distribute the sources, though.  You can even
make it easy to compile the sources.  But you can't distribute the
executable, and neither can the customer.

If it sounds like a loophole, it sort of is.  But the practical
difficulties of making sure that the client has all of the requisite
development tools is significant, especially for mass-market software.
Also, people who want to use the GPL and not give back generally want
to integrate the code a bit more deeply than just an add-on module.  If
they needed the GPL code in order to compile their own application at
all, then this trick doesn't work.

Regards,
Walter Landry
landry@physics.utah.edu