Hi Georgiy (and everyone else),
On Wed, 24 Jun 2015, Georgiy Tugai wrote:
(3) Multiple high-profile projects have run into copyright issues in the past; I believe that most of these stemmed from actions which legally require the consent of all contributors (who have contributed anything over 10 lines of code or equivalent) --- for example, relicensing from GPL to LGPL --- in combination with past contributors being out of contact for one reason or another, so their consent cannot be obtained.
Yes, this was something I mentioned in my message earlier today. I know a little bit about this, because I helped the Mercurial project track down some old contributors in 2009. They needed to change their license from GPL2 to GPL2+, I think. I forgot why exactly.
Anyway, some of those old contributors, dating from like 2005, were never tracked down. I remember going to considerable effort to try to locate someone from Singapore who was one of Mercurial's earliest significant contributors as of 2005, but without success. However, I believe they changed the license anyway.
See also https://mercurial.selenic.com/wiki/Relicensing
I thought (and said earlier) that Mercurial requested a copyright assignment from contributors, but I think I must have been mistaken. I see no signs of this. However, that does not make it a bad idea for the Clasp project,
It is worth noting that the legal umbrella for the Mercurial project is the Software Freedom Conservancy (https://sfconservancy.org/), loosely affiliated with the FSF (Bradley Kuhn is associated with both organizations in a senior capacity). Presumably the Conservancy advises them on such issues.
Chris, I'd recommend talking to them at some point. They could be a useful resource on legal matters.
Regards, Faheem Mitha