Add a new utils module, containing a with-time-logging syntax rule

Makefile.am

@@ -70,6 +70,7 @@ SOURCES =									\
   guix-data-service/comparison.scm						\
   guix-data-service/config.scm							\
   guix-data-service/database.scm						\
+  guix-data-service/utils.scm						\
   guix-data-service/data-deletion.scm						\
   guix-data-service/jobs.scm							\
   guix-data-service/jobs/load-new-guix-revision.scm				\

guix-data-service/utils.scm

@@ -0,0 +1,33 @@
+;;; Guix Data Service -- Information about Guix over time
+;;; Copyright © 2020 Christopher Baines <mail@cbaines.net>
+;;;
+;;; This program is free software: you can redistribute it and/or
+;;; modify it under the terms of the GNU Affero General Public License
+;;; as published by the Free Software Foundation, either version 3 of
+;;; the License, or (at your option) any later version.
+;;;
+;;; This program is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; Affero General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Affero General Public
+;;; License along with this program.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(define-module (guix-data-service utils)
+  #:export (call-with-time-logging
+            with-time-logging))
+
+(define (call-with-time-logging action thunk)
+  (simple-format #t "debug: Starting ~A\n" action)
+  (let* ((start-time (current-time))
+         (result (thunk))
+         (time-taken (- (current-time) start-time)))
+    (simple-format #t "debug: Finished ~A, took ~A seconds\n"
+                   action time-taken)
+    result))
+
+(define-syntax-rule (with-time-logging action exp ...)
+  "Log under NAME the time taken to evaluate EXP."
+  (call-with-time-logging action (lambda () exp ...)))