build: svn: Fix handle fetch errors.

This fixes the revert 1ec67d5220.

* guix/build/svn.scm (svn-fetch): Add 'guard' to handle errors.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

guix/build/svn.scm

@@ -2,6 +2,7 @@
 ;;; Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014 Sree Harsha Totakura <sreeharsha@totakura.in>
 ;;; Copyright © 2018 Mark H Weaver <mhw@netris.org>
+;;; Copyright © 2020 Simon Tournier <zimon.toutoune@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -20,6 +21,8 @@
 
 (define-module (guix build svn)
   #:use-module (guix build utils)
+  #:use-module (srfi srfi-34)
+  #:use-module (ice-9 format)
   #:export (svn-fetch))
 
 ;;; Commentary:
@@ -36,6 +39,15 @@
                     (password #f))
   "Fetch REVISION from URL into DIRECTORY.  REVISION must be an integer, and a
 valid Subversion revision.  Return #t on success, #f otherwise."
+  (guard (c ((invoke-error? c)
+             (format (current-error-port)
+                     "svn-fetch: '~a~{ ~a~}' failed with exit code ~a~%"
+                     (invoke-error-program c)
+                     (invoke-error-arguments c)
+                     (or (invoke-error-exit-status c)
+                         (invoke-error-stop-signal c)
+                         (invoke-error-term-signal c)))
+             #f))
     (apply invoke svn-command
            "export" "--non-interactive"
            ;; Trust the server certificate.  This is OK as we
@@ -50,6 +62,6 @@ valid Subversion revision.  Return #t on success, #f otherwise."
                    '()
                    (list "--ignore-externals"))
              ,url ,directory))
-  #t)
+    #t))
 
 ;;; svn.scm ends here