[Pkg-mpd-maintainers] Bug#767504: Bug#767504: mpd: licence clash with libmp4v2 (MPL) and mpd GPL-+2

[Simon McVittie]

retitle 767504 mpd: GPL-2+ incompatible with libmp4v2 which is MPL-1.1

On Fri, 31 Oct 2014 at 17:20:27 +0100, grossepoubelle at free.fr wrote:
> On Fri, Oct 31, 2014 at 03:27:47PM +0100, grossepoubelle at free.fr wrote:
> >> You can't link GPL packages against MPL packages.
> >IANAL, but I read in MPL1.1 section 6.2 that I can choose to use the
> >code under a newer version of the license, such as MPL2.0 which is
> >deemed compatible with the GPL by the FSF.
> 
> IANAL too, but you can find several pages saying that MPL isn't compatible  
> with GPL like this one :
>                         
> http://www.tomhull.com/ocston/docs/mozgpl.html

Sorry, but the bug submitter appears to be correct here. MPL-1.1 §6.2 says

      Once Covered Code has been published under a particular version of the
      License, You may always continue to use it under the terms of that
      version. You may also choose to use such Covered Code under the terms
      of any subsequent version of the License published by Netscape.

So yes, you can opt to use libmp4v2 under MPL-2.0. However,
MPL-2.0 is only compatible with the GPL via MPL-2.0 §3.3, which does
not apply if the Covered Software is "Incompatible With Secondary Licenses".
According to MPL-2.0 §1.5, anything "made available under the terms of
version 1.1 or earlier of the License" is indeed "Incompatible With Secondary
Licenses".

The FSF's license list does make this explicit:

    Software under previous versions of the MPL can be upgraded to
    version 2.0, but any software that isn't already available under
    one of the listed GNU licenses must be marked as Incompatible With
    Secondary Licenses. This means that software that's only available
    under previous versions of the MPL is still incompatible with the
    GPL and AGPL.

Unfortunately, the MPL-2.0 effectively behaves like two separate licenses:
"MPL-2.0 Incompatible With Secondary Licenses" and plain MPL-2.0.
The former is incompatible with the GPL, the latter is compatible.

Regards,
    S