[FIX] calendar: comparing timezoned datetimes

We transform the rrule stored as a string into a real
rrule object using 'rrule.rrulestr'. The 'UNTIL' parameter
of the rrule might not be timezoned. So the '_until' property
of the rrule object will be a naive datetime.

Later in the '_get_recurrent_date_by_event', we add the recurring
date in the '_exdate' property, but those dates are timezoned.

When iterating on the rrule set (its a set since forceset=True), the
until date and exdate are compared, but it cause crashes as we can not
compare offset-naive and offset-aware datetimes.

This commit make the rrule use only naive or aware datetimes for its
'until' and '_exdate' properties depending on the 'until' property
of calendar.event rrule field.

opw-1825679
closes #24010

addons/calendar/models/calendar.py

@@ -608,7 +608,8 @@ class Meeting(models.Model):
         if not event_date:
             event_date = datetime.now()
 
-        if self.allday and self.rrule and 'UNTIL' in self.rrule and 'Z' not in self.rrule:
+        use_naive_datetime = self.allday and self.rrule and 'UNTIL' in self.rrule and 'Z' not in self.rrule
+        if use_naive_datetime:
             rset1 = rrule.rrulestr(str(self.rrule), dtstart=event_date.replace(tzinfo=None), forceset=True, ignoretz=True)
         else:
             # Convert the event date to saved timezone (or context tz) as it'll
@@ -616,9 +617,13 @@ class Meeting(models.Model):
             event_date = event_date.astimezone(timezone)  # transform "+hh:mm" timezone
             rset1 = rrule.rrulestr(str(self.rrule), dtstart=event_date, forceset=True, tzinfos={})
         recurring_meetings = self.search([('recurrent_id', '=', self.id), '|', ('active', '=', False), ('active', '=', True)])
-
         for meeting in recurring_meetings:
-            rset1._exdate.append(todate(meeting.recurrent_id_date))
+            recurring_date = fields.Datetime.from_string(meeting.recurrent_id_date)
+            if use_naive_datetime:
+                recurring_date = recurring_date.replace(tzinfo=None)
+            else:
+                recurring_date = todate(meeting.recurrent_id_date)
+            rset1.exdate(recurring_date)
         return [d.astimezone(pytz.UTC) if d.tzinfo else d for d in rset1]
 
     @api.multi