Licensing of Mercurial: "GPL" (any), "GPLv2" or "GPLV2 or later"?

[Sean E. Russell]

On Monday 04 August 2008, Matt Mackall wrote:
> Some small components of Mercurial (especially those borrowed from other
> sources) are licensed under the GPLv2+ in deference to their authors'
> original wishes. The bulk are GPLv2 only. Thus the only license that's
> valid for the combined work is GPLv2.

Interesting.  Then it would appear that any GPLv3 plugin (or any other 
low-level hook) is incompatible Mercurial:

http://www.gnu.org/philosophy/license-list.html#GPLCompatibleLicenses

Under the section "GNU General Public License (GPL) version 2" says:

"Please note that GPLv2 is, by itself, not compatible with GPLv3.  However, 
most software released under GPLv2 allows you to use the terms of later 
versions of the GPL as well. When this is the case, you can use the code 
under GPLv3 to make the desired combination."

Therefore, if parts of Mercurial are, as you state, GPLv2 and not GPLv2+; and 
if those parts aren't entirely disjoint from the rest of Mercurial; then 
*all* of Mercurial is GPLv2, regardless of what those other parts say.  I 
think that's pretty clearly implied by the verbiage in the quote.  Or does 
hooking into those GPLv2+ parts with GPLv3 code somehow doesn't violate the 
linking clause?

I'm curious to know how else this could be interpreted so that this isn't the 
case.

-- 
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