extensions-tool: Add common option to silence errors

Error reporting is useful when used interactively, but often undesirable
when used in scripts. Account for that with a common --quiet option,
which is more convenient than redirection stderr to /dev/null.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/2391

subprojects/extensions-tool/src/main.c

@@ -49,6 +49,39 @@ extension_state_to_string (ExtensionState state)
   return "UNKNOWN";
 }
 
+static void
+print_nothing (const char *message)
+{
+}
+
+static gboolean
+quiet_cb (const gchar  *option_name,
+          const gchar  *value,
+          gpointer      data,
+          GError      **error)
+{
+  g_set_printerr_handler (print_nothing);
+  return TRUE;
+}
+
+GOptionGroup *
+get_option_group ()
+{
+  GOptionEntry entries[] = {
+    { .long_name = "quiet", .short_name = 'q',
+      .description = _("Do not print error messages"),
+      .arg = G_OPTION_ARG_CALLBACK, .arg_data = &quiet_cb,
+      .flags = G_OPTION_FLAG_NO_ARG | G_OPTION_FLAG_IN_MAIN },
+    { NULL }
+  };
+  GOptionGroup *group;
+
+  group = g_option_group_new ("Common", "common options", "common options", NULL, NULL);
+  g_option_group_add_entries (group, entries);
+
+  return group;
+}
+
 void
 show_help (GOptionContext *context, const char *message)
 {