GWL 0.5 fails with plain packages

[Liliana Marie Prikler <liliana.prikler@ist.tugraz.at>]

Hi Guix,

using this rather simple workflow

--8<---------------cut here---------------start------------->8---
use-modules : gnu packages base

process greet
  packages hello
  # { hello }

workflow simple-wisp
  processes
    list greet
--8<---------------cut here---------------end--------------->8---

I get the following error:

--8<---------------cut here---------------start------------->8---
Backtrace:
In guix/gexp.scm:
    893:4 19 (_ _)
In guix/store.scm:
  2053:12 18 (_ #<store-connection 256.99 7f0d3e5eef00>)
  1380:11 17 (map/accumulate-builds #<store-connection 256.99 7f0d3…>
…)
   1298:8 16 (call-with-build-handler #<procedure 7f0d3d783990 at g…>
…)
  2168:25 15 (run-with-store #<store-connection 256.99 7f0d3e5eef00> …)
In guix/gexp.scm:
   898:13 14 (_ _)
In guix/store.scm:
   1996:8 13 (_ _)
In guix/gexp.scm:
   300:22 12 (_ _)
In guix/profiles.scm:
   1935:2 11 (_ _)
In guix/store.scm:
  2053:12 10 (_ #<store-connection 256.99 7f0d3e5eef00>)
  1380:11  9 (map/accumulate-builds #<store-connection 256.99 7f0d3…>
…)
   1298:8  8 (call-with-build-handler #<procedure 7f0d3d7fb900 at g…>
…)
  2168:25  7 (run-with-store #<store-connection 256.99 7f0d3e5eef00> …)
In guix/gexp.scm:
   1181:2  6 (_ _)
   1047:2  5 (_ _)
   1388:2  4 (_ _)
In guix/monads.scm:
    471:9  3 (_ _)
    471:9  2 (_ _)
In guix/gexp.scm:
   332:25  1 (_ _)
In ice-9/boot-9.scm:
  1685:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1685:16: In procedure raise-exception:
ERROR:
  1. &derivation-missing-output-error:
      derivation: #<derivation
/gnu/store/1mzvmkh3a81xm4xz6g2l0b0vgzpl52c5-hello-2.12.1.drv =>
/gnu/store/s5pd3rnzymliafb4la5sca63j86xs0y0-hello-2.12.1 7f0d3ba40af0>
      output: #f
--8<---------------cut here---------------end--------------->8---

I'd hazard a guess this has to do with the recently added support for
outputs.  Note that attempting to specify an output

--8<---------------cut here---------------start------------->8---
process greet
  packages
    list : list hello "out"
  # { hello }
--8<---------------cut here---------------end--------------->8---

results in a different error

--8<---------------cut here---------------start------------->8---
ice-9/boot-9.scm:1752:10: error: type error: expected one of
`<package>' `<inferior-package>' `<string>', but got `<pair>' in
`(#<package hello@2.12.1 gnu/packages/base.scm:86 7fd084ba76e0> out)'
--8<---------------cut here---------------end--------------->8---

Thus, there is no way to use plain packages with GWL 0.5.

Cheers