Subject: [bug#55911] [PATCH] channels: Print backtrace when generating package cache fails.

From: Josselin Poiret <[email-masked]>
Date: Sat, 11 Jun 2022 18:30:31 +0200

* guix/channels.scm (package-cache-file): Add a throw handler around
the generate-package-cache call, and print backtrace in it.
---
 guix/channels.scm | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/guix/channels.scm b/guix/channels.scm
index 20f347d34f..e3a4daf7b3 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -911,7 +911,17 @@ (define build
                 (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 #$output))
+                  (lambda (key . args)
+                    ;; Guile 1 prints the whole backtrace, and would need a
+                    ;; fluid set for the backtrace procedure to work, so ignore.
+                    (unless (string-prefix? "1" (version))
+                      (backtrace)))))
               (mkdir #$output))))
 
     (gexp->derivation-in-inferior "guix-package-cache" build
-- 
2.36.1