substitute derivation: also substitute grafts?

[Ricardo Wurmus]

Hi Guix,

I really like the fact that Guix can substitute derivations.  It’s a
great way to transfer a profile from one powerful machine to a weak
machine without having to set up SSH for “guix copy” first.

I just build a profile on machine A, and then on the weak machine B I do

  guix build --substitute-urls="http://A:8000"; /gnu/store/…-profile.drv

and all items for that profile are copied to B.

Did I say *all items*?  Well, … grafts are not included, because graft
derivations are marked as not substitutable.

Can we change that conditionally?  I would really like to avoid having
to build grafts on B when they have already been built on A.

-- 
Ricardo

PS: please keep me in Cc as I’m not subscribed to guix-devel at the moment.