The FSF clearly promulgated the GPL with the intent of prohibiting the
bundling of GPL code with proprietary code. The way the GPL does this
is by putting conditions on distribution: if you "distribute" a
program "based on" a GPL program, the whole program must be licensed
under the GPL.
Clearly, the crux of the matter is the meaning of "distribute" and
"based on". The FSF takes a maximalist view of this, so that (for
example) distributing R together with additional components (libraries
/ packages / whatever), even if they are in separate files and loaded
dynamically, would require that the additional components be licensed
under GPL (and therefore that their source be released). The
additional libraries need not be derived works of the original; this
is not a copyright issue, but a licensing issue.
I am not a lawyer, so can't judge this professionally, but it seems to
me that the copyright owner is within his rights to impose conditions
like this on distribution -- just as he could arbitrarily decide that
he will only license his code to people whose names begin with 'T'.
The logic is not: "I require you to release your code under GPL" but:
"I will only license my GPL code to you for this application if you
release your code under GPL".
On the other hand, the GPL explicitly allows *users* of the code to do
what they want, including mixing it with proprietary code, as long as
they don't distribute the result. And I do not believe the copyright
holder has any way of preventing a third party from distributing
*separately* code that can be run on top of R. In fact the FSF itself
has been quite clear that they don't consider that the license for a
language implementation restricts the code that can be run on top of
it in any way.
All that being said, the entity that must enforce these conditions is
not the FSF, but the copyright owner, in this case the R Foundation
and the copyright holders of any other packages redistributed by the
bundler. So it would be useful to know what the R Foundation's
position is. Regardless of what the license says, it is up to the R
Foundation to decide what *its* interpretation of the license is and
under what circumstances it would ask a distributor of its code to
cease and desist -- and that failing, sue.
-s