2012/6/28 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
Hi,
I had a look too, and the FAQ really confuses me, especially the
requirements 2 and 3 of this entry
http://www.mozilla.org/MPL/2.0/FAQ.html#mpl-and-lgpl:
2 - The Larger Work must be "a combination of Covered Software with a
work governed by one or more Secondary Licenses." So you can't just
say "I really prefer (L)GPL" - you must have a need to combine with
another, existing GPL work. (This is different from a traditional
dual-license, which does not require you to combine, and instead
allows you to simply say "I've decided to be GPL-only.")
3 - You must "additionally distribute" under (L)GPL. In other words,
you must make the MPL-licensed source code available to your
recipients under both MPL and (L)GPL. Someone downstream from your
recipients can then take under (L)GPL-only or MPL-only. This is
different from a traditional dual-license, which never requires
publication under both licenses, and so always gives you the option of
releasing incompatibly-licensed code.
Does that means if someone combines MPL2 code and LGPL code to build
an app, then the app can be either MPL2 or LGPL?? This does not make
sense to me.
No. That's the whole point here: the MPL2 is trying to strike a
balance between GPL compatibility, and fixing the loophole whereby
people can take MPL code, improve it, and only release the
improvements under GPL-only. This is a compromise between two really
hard-to-reconcile opposite things, which is why it's complicated.
So here's how it works, in my understanding. If someone combines
MPL2-licensed Eigen with their (L)GPL code, then they MUST offer the
result under MPL, but they are also allowed to dual-license it with
one of the Secondary Licenses. So for example, they can dual-license
MPL/GPL. A third-party can then take it and drop either license, but
they can't directly do it themselves. So the loophole still exists (if
they can find a complacent/fake "third-party" to drop the MPL license
for them), but it's a lot more inconvenient/dangerous to exploit.