Re: Lua and GNU readline linking

[Lefteris Chatzibarbas <lefcha@...>]

On Mon, Feb 20, 2006 at 02:53:40PM +0100, Mike Pall wrote:
> Hi,
> 
> Please do not spread FUD. The discussion is as old as this line
> in the GPL FAQ. You can read about it in many mailing list
> archives.

Sorry, I'm not trying to spread anything, I thought that there may be
something wrong with Lua (consider it a bug report) and I just reported
it here.

> It's not the license that spreads, it's the license terms
> ("providing source code") that spread. And even this has been
> debated at length, too. Consult a lawyer if you are in doubt.

Yes, maybe consulting the lawyers at licensing@gnu.org may be a good
idea, they are also representing the FSF ie. the copyright holders of
GNU readline, but it's not something I will do, it's something the
developers of Lua may want to do if they are in doubt.  As I said I
just wanted to make sure this isn't a bug...

> Some things to consider:
> 
> - The Lua readline support depends on the readline API, but not
>   on the readline library. It can be linked to libedit, too
>   (BSD license).
>   In fact precisely this happens on Mac OS X when one
>   links with -lreadline (which is a symlink to libedit).

So IIUC, the lua libraries aren't affected at all, and if one uses the
Lua provided lua_readline() API and manually link his program with GNU
readline by adding the necessary -lreadline, only then he can end up
linking to GNU readline and thus affected by the GPL? I think I got this
now...

Considering the availability of the NetBSD editline library as an
alternative that uses the same Lua readline API, this makes sense...
Because I'm not so sure that the FSF would accept this
API-only-not-linking, if GNU readline was the only library compatible
with the API...

> - Lua is only distributed in source form by the authors.
>   And it's under a "GPL compatible" license.

Although, as stated in another reply, the website of GNU readline seems
to mention something about other software GPL-compatible, I wouldn't
consider it a legal document; the legal document is the licensing terms
included in the GNU readline source code distribution.

In these terms nothing is mentioned about GPL-compatibility, in the
contrary a mail from Richard M. Stallman is included in the USAGE file,
and it empasizes that there is no difference between static/dynamic
linking and that software that links either way to the GNU readline
becomes a larger work that is subject to the GNU GPL conditions.

And as stated in the GNU GPL, GPL'd software may link with free and GPL
compatible software, but software that isn't itself GPL'd may NOT link
with GPL software despite being free and GPL-compatible.  Unless it's
license is changed to the GPL, the program is in violation when
distributed...

> - Anyone distributing a Lua binary linked to readline also
>   provides the source (e.g. Debian or LuaBinaries).

This isn't enough according to the GPL.  That's why I Cc: this to the
Debian packager.  I also thought this was a bug of Debian and maybe the
debian-legal@ team could clarify this...

So although, as I now understand it, I agree that the Lua library is
unaffected by the GPL, but how about the Lua interpreter (src/lua.c)?
Some link it to GNU readline and distribute it, but the interpreter is
released under the MIT license.


Better be safe than sorry, although if something is not right with all
the legal nonsense, the sky won't fall, still...

I just wanted to raise awareness of the fact that GNU readline has
caused problems to a LOT of software out there, being a GPL'd library,
and I saw that it was "included" in some way in Lua 5.1.

I'm sure everyone has better things to do, such as hacking Lua, instead
of messing around with this license hell, so I won't annoy the list
about this anymore...

Regards,
Lefteris Chatzibarbas