[darcs-users] how to redistribute darcs+Eclipse (was: Darcs API?)

[zooko at zooko.com]

> I've read over the CPL (http://www.eclipse.org/legal/cpl-v10.html), and
> have no objection to dual-licensing darcs.  The CPL is indeed quite similar
> in spirit to the GPL.  I don't see any loopholes, and I suspect the IBM
> lawyers put some thought into making it enforceable.

The CPL is similar to the LGPL, in that it allows use of the CPL'ed code as a 
module in a larger program even if that larger program is proprietary.

There are at least three alternatives:

1.  Do nothing, therefore continuing to distribute darcs under "GPL v2 or (at
your option) any later version".  The possible drawback to this is that someday
someone might come up with a good idea for darcs which involves CPL'ed code,
and the CPL/GPL incompatibility (if it still exists at that juncture) would
prevent that.  For motivating examples, think perhaps of a darcs GUI written
with the "SWT" GUI toolkit, or a larger program containing code from darcs and
from Eclipse.

2.  Dual-license under GPL/CPL.  This would enable derived works comprised of 
darcs and CPL'ed code, but it would also enable derived works comprised of 
darcs and proprietary code.  As per your (David Roundy's) message [1], I think 
that this is not what you want.

[1] http://www.abridgegame.org/pipermail/darcs-users/2005-April/007035.html

3.  Add the following text to the license:

"As a special exception, you have permission to link this program
 with code which is licensed under the Common Public Licence or the Eclipse
 Public Licence, as long as you follow the requirements of the GNU GPL in 
 regard to all of the software in the executable aside from the software which
 is licensed under the Common Public License or the Eclipse Public License."

This would allow the redistribution of works which combined darcs and CPL'ed
code, but it would not allow the redistribution of works which combined darcs
and proprietary code.

That special exception text is derived from the Free Software Foundation's
suggested special exception text to deal with the Q Public License.  See [2]
for historical details.

[2] http://www.fsf.org/licensing/licenses/license-list.html#GPLIncompatibleLicenses


> I'm also not really clear as to why this is an important issue.  What sort
> of eclipse interface would you imagine that would need to be more closely
> integrated with darcs than the current interface allows?

The reason I care about it in *general* is that there someday may be an
opportunity to create a useful tool that by combining darcs and CPL'ed code
someday, and by that time it may be too late to relicense darcs.

The reason I care about it in specific is that I downloaded the darcs eclipse 
plugin yesterday.  It came with a note "For license reasons, Darcs itself is 
not included in this software. In order to use the plugin, you need an 
executable installed on your system. You can download Darcs at
http://darcs.net".

This also means that if I hook up darcs and the darcs eclipse plugin together
(which has so far proved to be a non-trivial task...), I am technically
forbidden to give the resulting setup to a friend.

Now, obviously it isn't a big deal for my friend to download and install darcs
himself, but there is something unsettling about it.  These are supposed to be
Free Software packages, which give me the freedom to use them in my own way.
But I am not allowed to combine them and give them to a friend.  That doesn't
seem right.


> Also, since the
> CPL (according to FAQ #19 quoted above) allows non-CPL modules, why
> couldn't a hypothetical darcs eclipse plugin be licensed under the GPL?

If it were, it would be illegal for The Eclipse Project folks to include the
darcs plugin in the standard Eclipse distribution.


> In summary, if you (or anyone else) wanted to contact all the darcs
> contributors to get agreement to dual-license darcs under both GPL and CPL,
> I'd agree.  But it's not something that greatly interests me, and I'm not
> going to go to the trouble myself.

I am willing to do the "contacting authors" work.


Regards,

Zooko