Subject: bug#70717: uninformative guix deploy error

From: [email-masked]
Date: Thu, 02 May 2024 13:33:53 +0000

No idea what causes this and the error is not very helpful.
`guix deploy deploy.scm` works
`guix deploy -x deploy.scm -- herd restart unipi` produces this error:
```
guix deploy: sending 0 store items (0 MiB) to 'localhost'...
Backtrace:
In ice-9/boot-9.scm:
  1752:10 18 (with-exception-handler _ _ #:unwind? _ # _)
In unknown file:
          17 (apply-smob/0 #<thunk 7f0e1baa32a0>)
In ice-9/boot-9.scm:
    724:2 16 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
    619:8 15 (_ #(#(#<directory (guile-user) 7f0e1baa8c80>)))
In guix/ui.scm:
   2324:7 14 (run-guix . _)
  2287:10 13 (run-guix-command _ . _)
In ice-9/boot-9.scm:
  1752:10 12 (with-exception-handler _ _ #:unwind? _ # _)
In guix/status.scm:
    839:4 11 (call-with-status-report _ _)
In ice-9/boot-9.scm:
  1752:10 10 (with-exception-handler _ _ #:unwind? _ # _)
In guix/store.scm:
   661:37  9 (thunk)
   1300:8  8 (call-with-build-handler _ _)
   1300:8  7 (call-with-build-handler #<procedure 7f0dfec20a20 at g…> …)
In guix/scripts/deploy.scm:
   274:23  6 (_)
In srfi/srfi-1.scm:
   460:18  5 (fold #<procedure 7f0dfec27740 at guix/scripts/deploy.…> …)
In guix/scripts/deploy.scm:
    214:2  4 (_ #<<machine> operating-system: #<<operating-system> …> …)
In guix/store.scm:
  2180:25  3 (run-with-store #<store-connection 256.99 7f0dfec11eb0> …)
In guix/remote.scm:
    84:17  2 (_ _)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
ERROR:
  1. &inferior-exception:
      arguments: (unbound-variable #f "Unbound variable: ~S"
#f)
      inferior: #f
      stack: ()
```