bug#34637: inferiors example yields error from guix package

[Martin Flack]

I'm getting an error trying the example here:

https://www.gnu.org/software/guix/manual/en/html_node/Inferiors.html

```

(use-modules (guix inferior) (guix channels)

             (srfi srfi-1))   ;for 'first'

(define channels

  ;; This is the old revision from which we want to

  ;; extract guile-json.

  (list (channel

         (name 'guix)

         (url "https://git.savannah.gnu.org/git/guix.git")

         (commit

          "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

(define inferior

  ;; An inferior representing the above revision.

  (inferior-for-channels channels))

;; Now create a manifest with the current "guile" package

;; and the old "guile-json" package.

(packages->manifest

 (list (first (lookup-inferior-packages inferior "guile-json"))

       (specification->package "guile")))

```

```

$ guix --version

guix (GNU Guix) 0964671086fb9e372894e788038aee75098e61a6

Copyright (C) 2019 the Guix authors

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

```

```

$ guix package -n -m example-inferior.scm

Updating channel 'guix' from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...

Computing Guix derivation for 'x86_64-linux'... |

substitute: updating substitutes from 'https://bayfront.guixsd.org'... 100.0%

The following derivation will be built:

   /gnu/store/zxrm9a410iywcdm71crjbg2j4ggpvdbv-profile.drv

The following profile hook will be built:

   /gnu/store/gkhfa4z16x4336pbi1ha7njgdpm680yf-guix-package-cache.drv

guix package: error: exception thrown: #<condition &store-protocol-error [message: "build of `/gnu/store/zxrm9a410iywcdm71crjbg2j4ggpvdbv-profile.drv' failed" status: 100] 1f80de0>

```

I'm running guix on ubuntu 18.04.2.

I noticed bug 34402 was similar - I think I'm at the latest version of guix today.

--

Martin