> One view is that GPL does not propagate, because the Guile language does
> not link.

This would be a very dangerous interpretation and clearly go against the
spirit of the GPL: any proprietary software could use any GPL software
if they were written in a language that doesn't link. There is a lot of
python code, for example, under the GPL and it would have no protection
against being used in proprietary programs.

> If Guix’ GPL would propagate, then the GPL2 of libgit2 would propagate
> to Guix.

Libgit2 defines an exception that it may be linked against programs
under any license, and I would consider FFI or whatever Guile uses to
interact with the compiled libgit2 library to qualify as linking.

I feel like Guix' GPL would propagate, but you could ask
licensing@fsf.org what they think about it.