Hello,

I believe there's still something wrong here.
The bug (the new one, described below) occurs after adding 
#:use-module (gnu packages avr) to the firmware.scm file.
Attached the diff file of my package below.

I'm packaging qmk-firmware and here's what happens running guix build:

error: binutils: unbound variable
hint: Did you forget a `use-modules' form?

error: googletest: unbound variable
hint: Did you forget a `use-modules' form?

error: bzip2: unbound variable
hint: Did you forget a `use-modules' form?

error: gcc-4.9: unbound variable
hint: Did you forget a `use-modules' form?

error: perl-module-build: unbound variable
hint: Did you forget a `use-modules' form?

error: python2-numpy: unbound variable
hint: Did you forget a `use-modules' form?

error: gzip: unbound variable
hint: Did you forget a `use-modules' form?

error: xcb-proto: unbound variable
hint: Did you forget a `use-modules' form?

error: gnu-make: unbound variable
hint: Did you forget a `use-modules' form?

error: unzip: unbound variable
hint: Did you forget a `use-modules' form?

error: curl: unbound variable
hint: Did you forget a `use-modules' form?

error: binutils: unbound variable
hint: Did you forget a `use-modules' form?

error: pjproject: unbound variable
hint: Did you forget a `use-modules' form?

error: xorg-server: unbound variable
hint: Did you forget a `use-modules' form?

error: libdvdnav: unbound variable
hint: Did you forget a `use-modules' form?

error: perl: unbound variable
hint: Did you forget a `use-modules' form?

error: coreutils: unbound variable
hint: Did you forget a `use-modules' form?

error: libetpan: unbound variable
hint: Did you forget a `use-modules' form?

Throw to key `unbound-variable' with args `("resolve-interface" "no
binding `~A' in module ~A" (python (gnu packages python)) #f)'.
Backtrace: In ice-9/boot-9.scm:
  1736:10 19 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   631:22 18 (thunk)
   1299:8 17 (call-with-build-handler #<procedure 7fd7f867b420 at g…> …)
In guix/scripts/build.scm:
    817:2 16 (_)
In srfi/srfi-1.scm:
   673:15 15 (append-map _ _ . _)
   586:17 14 (map1 ((argument . "qmk-firmware") (build-mode . 0) # …))
In guix/scripts/build.scm:
   837:30 13 (_ _)
In gnu/packages.scm:
    477:2 12 (%find-package "qmk-firmware" "qmk-firmware" #f)
    362:6 11 (find-best-packages-by-name _ _)
   292:55 10 (_ "qmk-firmware" _)
In unknown file:
           9 (force #<promise #<procedure 7fd7f9172a00 at gnu/packag…>)
In gnu/packages.scm:
   239:33  8 (fold-packages #<procedure 7fd7f76d6f18 at gnu/package…> …)
In guix/discovery.scm:
   153:11  7 (all-modules _ #:warn _)
In srfi/srfi-1.scm:
   460:18  6 (fold #<procedure 7fd7f8626300 at guix/discovery.scm:1…> …)
In guix/discovery.scm:
   143:19  5 (_ _ ())
In srfi/srfi-1.scm:
   691:23  4 (filter-map #<procedure 7fd7f86262c0 at guix/discove…> . #)
In guix/discovery.scm:
   118:22  3 (_ . _)
In guix/ui.scm:
    329:2  2 (report-unbound-variable-error _ #:frame _)
In ice-9/boot-9.scm:
  1669:16  1 (raise-exception _ #:continuable? _)
  1669:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1669:16: In procedure raise-exception:
Throw to key `match-error' with args `("match" "no matching pattern"
(unbound-variable "resolve-interface" "no binding `~A' in module ~A"
(python (gnu packages python)) #f))'.



Jan Wielkiewicz