Errors with (display) when building derivations from the REPL.

[Brian Cully <bjc@spork.org>]

I’m trying to do some work on Guix with Emacs and Geiser, and 
while a lot of things work fairly well, I consistently run into 
problems when trying to build derivations from the Geiser 
REPL. From what I can tell by looking at where it’s breaking, it 
seems to me like the output of the build process is supposed to be 
captured for display by the client, but (for whatever reason) the 
output port its supposed to go to is closed. The failing line 
appears to be these (found in guix/store.scm:758):

--8<---------------cut here---------------start------------->8---
           (let ((s (read-maybe-utf8-string p)))
             (display s (current-build-output-port))
--8<---------------cut here---------------end--------------->8---

I don’t know if this is an actual bug, or if I’m expected to set 
up the output port myself before attempting to do a build from the 
REPL. If it is an actual bug, I’ll be happy to submit this to the 
issue tracker. If it’s not, can someone tell me what I’m supposed 
to be doing for this to work? Also, is there a reason that the 
build’s output port doesn’t just default to standard output so no 
setup would be necessary?

Sample code:

--8<---------------cut here---------------start------------->8---
(define-module (bjc repltest)
  #:use-module (guix derivations)
  #:use-module (guix gexp)
  #:use-module (guix monads)
  #:use-module (guix store))

(define (m)
  (with-store store
    (run-with-store store
      (mlet %store-monad ((drv (lower-object
                                (computed-file "test"
                                               #~(mkdir 
                                               #$output)))))
        (mbegin %store-monad
          (built-derivations (list drv)))))))
--8<---------------cut here---------------end--------------->8---

Backtrace:

--8<---------------cut here---------------start------------->8---
scheme@(bjc repltest)> (m)
ice-9/boot-9.scm:1685:16: In procedure raise-exception:
In procedure display: Wrong type argument in position 2: #<closed: 
string 7f38350291c0>

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to 
continue.
scheme@(bjc repltest) [1]> ,bt
In ice-9/boot-9.scm:
  1752:10  8 (with-exception-handler _ _ #:unwind? _ 
  #:unwind-for-type _)
In guix/store.scm:
   658:37  7 (thunk)
In guix/monads.scm:
    560:2  6 (run-with-store #<store-connection 256.99 
    7f382193fb90> _ #:guile-for-build _ #:system _ #:target _)
In guix/store.scm:
  2001:38  5 (_ #<store-connection 256.99 7f3822eae9b0>)
  1421:15  4 (_ #<store-connection 256.99 7f3822eae9b0> _ _)
   759:14  3 (process-stderr _ _)
In unknown file:
           2 (display "substitute: \r" #<closed: string 
           7f38350291c0>)
In ice-9/boot-9.scm:
  1685:16  1 (raise-exception _ #:continuable? _)
  1685:16  0 (raise-exception _ #:continuable? _)
--8<---------------cut here---------------end--------------->8---


-bjc