challenge: Really exit with non-zero upon hash mismatch.

Reported by John Darrington.

* guix/scripts/challenge.scm (guix-challenge): Add an explicit 'exit'
call when ISSUES is empty.
* scripts/guix.in: Add comment about 'exit'.
* doc/guix.texi (Invoking guix challenge): Mention the behavior and exit
code.

1 files changed, 6 insertions, 1 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index aeeec617e0..a16422261a 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -5582,7 +5582,7 @@ $ guix challenge @var{package}
 
 @noindent
 where @var{package} is a package specification such as
-@code{guile-2.0} or @code{glibc:debug}.
+@code{guile@@2.0} or @code{glibc:debug}.
 
 The general syntax is:
 
@@ -5590,6 +5590,11 @@ The general syntax is:
 guix challenge @var{options} [@var{packages}@dots{}]
 @end example
 
+When a difference is found between the hash of a locally-built item and
+that of a server-provided substitute, or among substitutes provided by
+different servers, the command displays it as in the example above and
+exits with a non-zero return code.
+
 The one option that matters is:
 
 @table @code