Can a Mercurial fork change its license to AGPL?

[Mike Hommey]

On Fri, Feb 27, 2015 at 07:21:09PM -0600, 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".
> 
> Sigh. I'll pass this on to the lawyers.

Or, you know, you could ask the forker(s) before doing anything else.

That being said, Mercurial is under GPL v2 or later. Which means it can
be "relicensed" to GPL v3. And GPL v3 says that the AGPL v3 applies to
a combination of GPL v3 and AGPL v3 code, which, in some way could be
misinterpreted as being able to relicense to AGPL v3 if you don't read
the actual GPL text, which a lot of people don't do. So this could very
well be a simple case of "I know AGPLv3 is compatible with GPLv3, that
must mean I can relicense", combined with the fact that they want their
own changes under the AGPL.

Mike