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Re: Unclear license information regarding copyleft

On Tue, 15 May 2018 at 19:22:54 +0200, Sven Bartscher wrote:
> 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?)

No. glibc is LGPL-licensed, the same as GTK[1], so if your interpretation
was correct, the dwarf-fortress developer would not be allowed to
distribute their proprietary executable that is linked to glibc.

The main difference between each version of the GPL and the corresponding
version of the LGPL is that you can link (possibly proprietary) objects
to a LGPL library without being obliged to release source for those
objects under the (L)GPL.

If the dwarf-fortress developer is the copyright holder of everything in
libgraphics, then the choice of license is up to them, as long as they
meet the conditions in LGPL-2.1 §6. They are under no obligation to
provide source code for it (under LGPL or otherwise), because LGPL-2.1
§5 and §6 apply to it.

> 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.

The dwarf-fortress developer doesn't seem to have given you permission
to compile g_src into a replacement libgraphics.so and distribute the
result, so you can't; but it seems to be their intention that you can
(otherwise they wouldn't have released source code), so if you ask nicely,
it seems likely that they will give you that permission.


[1] I don't know whether it's the same version of the LGPL, but the
    differences between versions are not particularly relevant here

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