bug#35242: Backtrace on building with load path

[brettg]

Hi all. I am trying to build custom packages, and today a regression may 
have been introduced either on guix-master or in my own channel. I am 
trying to find out where the issue lies.

address@hidden ~/Repos/guix-system [env]$ guix build fstar -L .
Backtrace:
In guix/store.scm:
   613:10 19 (call-with-store #<procedure 14f3f40 at 
guix/scripts/build.scm:889:8…>)
In guix/scripts/build.scm:
   895:26 18 (_ #<store-connection 256.99 103fdc0>)
In ice-9/boot-9.scm:
    829:9 17 (catch unbound-variable #<procedure 14fac00 at 
guix/ui.scm:499:4 ()> …)
In guix/ui.scm:
    500:6 16 (_)
In guix/scripts/build.scm:
   863:22 15 (_)
In srfi/srfi-1.scm:
   679:15 14 (append-map _ _ . _)
   592:17 13 (map1 ((argument . "fstar") (system . "x86_64-linux") (# . 
0) (. #) …))
In guix/scripts/build.scm:
   791:30 12 (_ _)
In gnu/packages.scm:
    477:2 11 (%find-package "fstar" "fstar" #f)
    383:6 10 (find-best-packages-by-name _ _)
   313:55  9 (_ "fstar" _)
In unknown file:
           8 (force #<promise #<procedure 7fa491ff4638 at 
gnu/packages.scm:303:18…>)
In gnu/packages.scm:
   260:33  7 (fold-packages #<procedure 7fa491ff5cf0 at 
gnu/packages.scm:304:35 …> …)
In srfi/srfi-1.scm:
   466:18  6 (fold #<procedure 14fc100 at guix/discovery.scm:133:8 (spec 
result)> …)
In guix/discovery.scm:
   136:31  5 (_ "." ())
   116:14  4 (scheme-modules _ _ #:warn _)
In srfi/srfi-1.scm:
   501:18  3 (fold-right #<procedure 14fc0c0 at guix/discovery.scm:56:14 
(entr…> . #)
In guix/discovery.scm:
    66:32  2 (_ _ ("./channels.scm" "./non-gnu/packages/coq-extend.scm" 
"./non…" …))
In srfi/srfi-1.scm:
   501:18  1 (fold-right #<procedure 16566c0 at guix/discovery.scm:56:14 
(entr…> . #)
In unknown file:
           0 (append #<unspecified> ())


address@hidden ~/Repos/guix-system [env]$ guix describe
Generation 38   Apr 11 2019 22:56:24    (current)
  guix-system 796b205
    repository URL: https://git.sr.ht/~brettgilio/guix-system
    branch: master
    commit: 796b205ddc019fd366b0025800aa3a0e91b0fa2e
  guix 89647ff
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 89647ff1d4abc4674973392cb7e08d14898e3ac9


Thanks!