Re: draft for new Vim license

[Richard Stallman <rms@gnu.org>]

    I have attempted to add the possibility to allow people to distribute a
    modified Vim, under the condition that they include the source code.

This is a free software license, and I think it is better than the
current Vim license.  So I encourage you to switch to this license.
It is not GPL-compatible, though, because of a few details.

	2) A user of the modified Vim must be able to see that it was modified, at
	   least in the version information and in the intro screen.

The GPL has a similar kind of requirement, but this is more specific,
hence not GPL-compatible.

	3) The modified Vim must be distributed in one of the following four ways:

It's sufficient if one of these ways, or a combination of them, allows
what the GPL allows.  However, that is not so.

	   a) If you make changes to Vim, you must clearly mention in the
	      distribution how to contact you.  When the maintainer asks you (in
	      any way) for a copy of the modified Vim you distributed, you must
	      make the changes, including source code, available to the
	      maintainer.

This clearly isn't GPL-compatible (and isn't trying to be).

	   c) Provide the changes, including source code, with every copy of the
	      modified Vim you distribute.

I think this is trying to be GPL-compatible, but does not succeed.
The reason is that this is somewhat more restrictive than the GPL
actually is.

If you want to make this license GPL-compatible, the easiest way is by
making two changes: first, add an alternative 3e which specifically
allows release under the GPL, and second, change 2 a little so it
isn't more specific than what the GPL requires.

Here is more explanation about what it means to be GPL-compatible:

    > > If the license were GPL-compatible, I could license my changes under
    > > the GPL, and never talk to the Vim maintainer.  However, one of the
    > > things that Bram wants to be able to do is relicense the whole thing
    > > under a proprietary license.  This is exactly the sort of thing that
    > > the GPL is designed to prevent.  So a GPL patch would restrict future
    > > official Vim distributions.
    > 
    > Ah yes, I missed that last part.  So it does seem to me that it is not
    > GPL compatible, as long as it wants to reserve the right to include
    > changes in future vim distributions, which themselves might be
    > released under nonfree terms.

    But so long as changes are only included using the Vim license, would
    there be any problem?  Thus isn't the license GPL-compatible for as
    long as no incompatible-licensed changes have been included?

The question is what licenses I could use for modified versions of
Vim.  Specifically, could I release a modified version of Vim under
the GPL?  A license is GPL-compatible if it permits that; otherwise,
it is not GPL-compatible.

If I am required to use a license which permits you to rerelease my
changes under the Vim license, then the GPL does not qualify (since it
does not permit that), so the requirement is incompatible with the
GPL.