LGPL 2.1 + GPL 3 = problems?

[Philippe Verdy]

Arnoud Engelfriet wrote:
> Jesse Hannah wrote:
> > Would using (linking, including/redistributing unmodified) a library
> > that's licensed under the LGPL version 2.1 with a program that's
> > licensed under the GPL version 3 cause any weird problems? My initial
> 
> My initial thought is that you can't do that, or at least you can't
> distribute the result.
> 
> GPLv3 defines any linked libraries as being part of the
> Corresponding Source, assuming the GPLv3 program "is specifically
> designed to require" this LGPLv21 library.
> 
> Article 5c of GPLv3 says that "You must license the entire work,
> as a whole, under this License to anyone who comes into possession
> of a copy."
> 
> The problem is that you can't license the LGPLv21 parts under
> GPLv3.
> 
> LGPLv21 has an automatic compatibility provision with GPLv2,
> so in the past this was never a problem.

You can do that if the library was licensed explicitly under LGPL 2 "or
later", meaning that it can be distributed under the terms of LGPL v3.
The GPLv3 contains the wordings necessary that explicitly says that linking
it with LGPLv3 is creating a combined work that is covered by GPLv3 as
whole, but whose individual components remain under their respective
licences.

In other words, the library used in your GPLv3-licensed product will remain
licensed now under LGPL v3 by its original author(s), as allowed by the
LGPLv2 licence from that(these) author(s)...