[gnome-panel] clock: fix timezone offset in calendar popup

[Alberts Muktupāvels <muktupavels src gnome org>]

commit fb24302e460461509434ad614b232fe171ea48dd
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Thu Mar 3 10:50:18 2022 +0200

    clock: fix timezone offset in calendar popup
    
    One more regression from cd1a0db671b6... Before that commit
    clock_location_get_offset returned timezone offset in seconds
    relative to system timezone.

 modules/clock/clock-location.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)
---
diff --git a/modules/clock/clock-location.c b/modules/clock/clock-location.c
index 99ffd7af7..6a448e195 100644
--- a/modules/clock/clock-location.c
+++ b/modules/clock/clock-location.c
@@ -362,7 +362,26 @@ clock_location_is_current (ClockLocation *loc)
 glong
 clock_location_get_offset (ClockLocation *loc)
 {
-       return gweather_timezone_get_offset (loc->priv->wtz);
+  GDateTime *datetime;
+  gint64 now;
+  GTimeZone *timezone;
+  int interval;
+  gint32 system_offset;
+  gint32 location_offset;
+
+  datetime = g_date_time_new_now_local ();
+  now = g_date_time_to_unix (datetime);
+  g_date_time_unref (datetime);
+
+  timezone = gnome_wall_clock_get_timezone (loc->priv->wall_clock);
+  interval = g_time_zone_find_interval (timezone, G_TIME_TYPE_STANDARD, now);
+  system_offset = g_time_zone_get_offset (timezone, interval);
+
+  timezone = loc->priv->tz;
+  interval = g_time_zone_find_interval (timezone, G_TIME_TYPE_STANDARD, now);
+  location_offset = g_time_zone_get_offset (timezone, interval);
+
+  return system_offset - location_offset;
 }
 
 typedef struct {