Re: Unclear license information regarding copyleft

[Walter Landry <wlandry@caltech.edu>]

Sven Bartscher <sven.bartscher@weltraumschlangen.de> writes:
> Greetings,
>
> (Please excuse if the below analysis is partly or even completely wrong,
> reading about licensing and copyright issues often makes me quite confused)
>
> I'm the maintainer of the package dwarf-fortress in non-free. The
> package as a whole is clearly non-free as the license states that „you
> may redistribute the *unmodified* binary and accompanying files“ and the
> source code to the contained executable is not provided.
>
> The package also contains a shared library called libgraphics.so and the
> corresponding source code. The library links to (among others) SDL and
> GTK which are licensed under the LGPL-2.1, AIUI this means that
> libgraphics.so and its source code have to licensed under the LGPL. (due
> to condition 2, correct?)

As I understand it, libgraphics.so is not modifying SDL.  In general,
the LGPL only requires that you not get rid of the ability to
dynamically link in a new version of SDL.  So this is probably OK.

> I could not find an explicit statement in the upstream tarball that
> clarifies what license applies to the library in question. There is a
> file called 'sdl license.txt' that contains a copy of the LGPL-2.1,
> which hints that the author is aware that their work is in some way
> affected by this license.
>
> As there are some problems[1] with the compiled shared library as
> distributed by upstream (and because compiling things ourselves is
> always nicer) I would like to rebuild the library when building the
> Debian package, though I'm not sure if it is clear in the given
> situation that it is legal to recompile the library and distribute the
> resulting shared library. But maybe someone smarter than me can
> enlighten me.

I think you have to ask upstream about this (i.e. Tarn Adams).  Absent
any other information, I would think that you could not recompile the
source into a new binary.  It is probably just an oversight on the part
of the Dwarf Fortress developers.

I would phrase it as asking what license that part is under.  There are
a few obvious choices: LGPL 2.1 or later (to match SDL), MIT, or
Apache.  Please do not suggest a custom license.

Cheers,
Walter Landry