Can a Mercurial fork change its license to AGPL?

[Matt Mackall]

On Sat, 2015-02-28 at 03:08 +0100, Mads Kiilerich wrote:
> On 02/28/2015 02:21 AM, Matt Mackall wrote:
> > On Sat, 2015-02-28 at 09:26 +0900, Kaz Nishimura wrote:
> >> I found a fork of Mercurial named Quicksilver <
> >> http://hg.quicksilver-vcs.org/quicksilver> is being licenced under the GNU
> >> AGPL.  Is it permitted to change a fork to the AGPL by the Mercurial
> >> copyright holder(s)?
> > Nope. Generally speaking you can't remove restrictions from a license..
> > or else copyright would be meaningless. The GPL says "we give you the
> > privilege to copy.. but you lose that if you try to restrict your
> > changes".
> 
> I'm not so sure it is that clear. From some point of view, the AGPL is 
> more Free than GPL; it will be argued that AGPL adds a freedom, not a 
> restriction.

That's why I wrote "generally speaking you can't remove restrictions
from a license.. or else copyright would be meaningless." I could simply
take a GPL program and remove restrictions until it was BSD otherwise or
the default copyright terms on a book and remove restrictions until it
was public domain. So you're not allowed to remove restrictions (or add
freedoms).

Given the GPL's additional provision that you're not allowed to add
restrictions (or remove freedoms) without giving up the freedoms granted
by the GPL, you effectively can't change the license.

There is one exception here with the AGPL and the GPLv3 (section 13 of
both licenses), which is that you're allowed to combine works (aka
"linking") _and leave the license intact on both pieces_. But that's not
what's happening here at all. This is just a wholesale change of the
license (with additional bogus assertions of copyright claims in every
file) and no functional changes.

-- 
Mathematics is the supreme nostalgia of our time.