I am right now in the process of updating pari-gp to version 2.9.3.
After building it on a git check-out of three days ago, which went smoothly,
I rebased my patch on today's master and was pleased to see that no rebuild
$ ./pre-inst-env guix build pari-gp -n
However, once the -n dropped, the gd package gets built.
And then it is starting ruby, which has no connection to pari-gp:
ruby-2.4.1.tar.xz 9.5MiB 22KiB/s 00:06 [ ] 1.3%^