Avoid fatal errors when setting recurrence until date for tasks (#4852)

plugins/libkolab/lib/kolab_format_task.php

@@ -116,6 +116,20 @@ class kolab_format_task extends kolab_format_xcal
         return $this->data;
     }
 
+    /**
+     * Return the reference date for recurrence and alarms
+     *
+     * @return mixed DateTime instance of null if no refdate is available
+     */
+    public function get_reference_date()
+    {
+        if ($this->data['due'] && $this->data['due'] instanceof DateTime) {
+            return $this->data['due'];
+        }
+
+        return self::php_datetime($this->obj->due()) ?: parent::get_reference_date();
+    }
+
     /**
      * Callback for kolab_storage_cache to get object specific tags to cache
      *

plugins/libkolab/lib/kolab_format_xcal.php

@@ -184,7 +184,10 @@ abstract class kolab_format_xcal extends kolab_format
                 $object['recurrence']['COUNT'] = $count;
             }
             else if ($until = self::php_datetime($rr->end())) {
-                $until->setTime($object['start']->format('G'), $object['start']->format('i'), 0);
+                $refdate = $this->get_reference_date();
+                if ($refdate && $refdate instanceof DateTime && !$refdate->_dateonly) {
+                    $until->setTime($refdate->format('G'), $refdate->format('i'), 0);
+                }
                 $object['recurrence']['UNTIL'] = $until;
             }
 
@@ -567,6 +570,20 @@ abstract class kolab_format_xcal extends kolab_format
         $this->set_attachments($object);
     }
 
+    /**
+     * Return the reference date for recurrence and alarms
+     *
+     * @return mixed DateTime instance of null if no refdate is available
+     */
+    public function get_reference_date()
+    {
+        if ($this->data['start'] && $this->data['start'] instanceof DateTime) {
+            return $this->data['start'];
+        }
+
+        return self::php_datetime($this->obj->start());
+    }
+
     /**
      * Callback for kolab_storage_cache to get words to index for fulltext search
      *