EPL (Eclipse Public License), GPL (GNU Public License)/LGPL (Lesser GPL) and license exceptions?
The Free Software Foundation considers EPL and GPL to be incompatible. Based on my reading of their reasoning, it would seem that the LGPL would be similarly affected -- IANAL, please correct me if that reading is incorrect. Now, there is a guide for the copyright holder of the GPL-ed code to provide exceptions allowing for the code to be linked against incompatible libraries, but it'd still preclude linking to GPL-ed code from others (if the code is already linked against an EPL library), and the situation with linking a GPL-ed program against an EPL and another LGPL library seems unclear.
I'd like to know the answer to several questions:
- What exactly is the restriction against linking a GPL-ed product against both an EPL library and an LGPL library? Is it not allowed without the LGPL copyright holder's explicit permission, as it would be with GPL, or is it allowed?
- Would an exception granted by the EPL copyright holder be sufficient? Such an exception was considered safe by Trolltech (now part of Nokia), when it used to license the Qt library using its own Qt Public License which is GPL-incompatible; and by the KDE project, whose libraries link against Qt and are released under the LGPL, while KDE apps are generally released under the GPL. The FSF's objection is due to "weak copyleft" and "choice of law clause" -- the former seems unobjectionable, if the EPL license holder grants an exception, but what sort of exception granted by the EPL copyright holder would satisfy the "choice of law clause" objection?
Answer
The above diagram shows the relationships between licenses. Though not comprehensive, if there is an arrow then it is compatible.
From the Eclipse website it states:
The EPL and the GPL are not compatible in any combination where the result would be considered either: (a) a "derivative work" (which Eclipse interprets consistent with the definition of that term in the U.S. Copyright Act ) or (b) a work "based on" the GPL code, as that phrase is used in the GPLv2, GPLv3 or the GPL FAQ as applicable. Further, you may not combine EPL and GPL code in any scenario where source code under those licenses are both the same source code module.
Based upon the position of the Free Software Foundation, you may not combine EPL and GPL code in any scenario where linking exists between code made available under those licenses. The above applies to both GPL version 2 and GPL version 3.
In my opinion, unless an exception is made - LGPL and EPL code should not be combined. In fact, a lot of software is dual-licensed under LGPL and EPL.