bug#51463: Lack of error message in several guix subcommands

[Alice BRENON <alice.brenon@ens-lyon.fr>]

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Hi list,

I was giving guix shell a try today and noticed this annoying lack of
relevant feedback from the tool: when running on a particularly
malformed guix.scm, either by auto-loading or by explicitely passing -f
guix.scm, guix shell returned in error ($? == 1) without printing any
error message, which is a bit unhelpful.

The particular malformed guix.scm simply contains an extra parenthesis
after the package definition. Compare to the case when the package
definition lacks the final parenthesis, which yields a helpful message
like this:

/tmp/bug/guix.scm:25:1: missing closing parenthesis

This is not specific to guix shell because I could then reproduce this
behaviour with other commands like guix environment or guix build.

Find attached the file I've been using to reproduce the bug, which is
essentially the "hello" package example from the manual[1] without the
(define-public …) layer, in order for the top-level expression
contained in the file to be directly a package usable by -f (-l for
guix environment) and not have to put hello on the last line. The
version attached is correct and will allow guix shell -f guix.scm to
enter an environment where hello is installed. Remove a parenthesis,
you should have the above message. Add one, on the contrary, and you
should get nothing but silence.

I'm using guix on Guix System, and pulled this morning:

guix 5cbf9a4
  URL du dépôt : https://git.savannah.gnu.org/git/guix.git
  branche : master
  commit : 5cbf9a48d766191d8f17b2e9d1cf7b7db69b99ea


Regards,

Alice


[1]
https://guix.gnu.org/manual/devel/en/html_node/Defining-Packages.html

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(define-module (gnu packages hello)
  #:use-module (guix packages)
  #:use-module (guix download)
  #:use-module (guix build-system gnu)
  #:use-module (guix licenses)
  #:use-module (gnu packages gawk))

(package
  (name "hello")
  (version "2.10")
  (source (origin
            (method url-fetch)
            (uri (string-append "mirror://gnu/hello/hello-" version
                                ".tar.gz"))
            (sha256
             (base32
              "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
  (build-system gnu-build-system)
  (arguments '(#:configure-flags '("--enable-silent-rules")))
  (inputs `(("gawk" ,gawk)))
  (synopsis "Hello, GNU world: An example GNU package")
  (description "Guess what GNU Hello prints!")
  (home-page "https://www.gnu.org/software/hello/")
  (license gpl3+)))