channels: Print backtrace when generating package cache fails.

* guix/channels.scm (package-cache-file): Add a throw handler around
the generate-package-cache call, and print backtrace in it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/guix/channels.scm b/guix/channels.scm
index 5f47834c10..ce1a60436f 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -907,7 +907,14 @@ be used as a profile hook."
                 (format (current-error-port)
                         "Generating package cache for '~a'...~%"
                         #$profile)
-                (generate-package-cache #$output))
+                ;; This script runs through (primitive-load), which by default
+                ;; doesn't print backtraces when it encounters an exception,
+                ;; so manually do it.  Use with-throw-handler because it is
+                ;; supported by all Guile versions.
+                (with-throw-handler #t
+                  (lambda () (generate-package-cache #$output))
+                  (lambda (key . args)
+                      (backtrace))))
               (mkdir #$output))))
 
     (gexp->derivation-in-inferior "guix-package-cache" build