Empty date fields causes missing deltas

I originally posted this concern in http://drupal.org/node/522558#comment-4825090, thinking it was something wrong with multigroups, but having traced the code (thank goodness for NetBeans and xdebug!), I think I found the issue in function date_element_empty in the date_elements.inc file.

With the patch in the above-noted issues, multigroups makes sure that every element in a multigroup has a '_weight' and a '_remove' element set, and the '_weight' element is particularly important for maintaining deltas across all row elements of a multigroup.

Now, if a date element is empty in a particular row, during form validation, and in particular in the function date_combo_validate, when the element is found to be empty, the function calls date_element_empty, which creates a new $item array and then completely overwrites what was in $form_state (through function form_set_value) as follows:

  $item = array();
  $item['value'] = NULL;
  $item['value2']   = NULL;
  $item['timezone']   = NULL;
  $item['offset'] = NULL;
  $item['offset2'] = NULL;
  $item['rrule'] = NULL;
  form_set_value($element, $item, $form_state);
  return $item;

This of course means that the '_weight' attribute is gone from $form_state, and then later on when the field goes through a sort to deal with table-drag stuff, without those '_weight' attributes for each empty date field, the order of the resulting array (which is really the reassignment of deltas) is out-of-whack.

To solve this, I made a slight change in function date_element_empty as follows:

function date_element_empty($element, &$form_state) {
//  PATCH:  Multigroups needs _weight and _remove attributes to maintain deltas properly.
//          Alter the definition of $item here to preserve that.
//  $item = array();
  $item = isset($form_state['values'][$element['#field_name']]['rrule'])
                  ? $form_state['values'][$element['#field_name']]
                  : $form_state['values'][$element['#field_name']][$element['#delta']];
  $item['value'] = NULL;
  $item['value2']   = NULL;
  $item['timezone']   = NULL;
  $item['offset'] = NULL;
  $item['offset2'] = NULL;
  $item['rrule'] = NULL;
  form_set_value($element, $item, $form_state);
  return $item;
}

This seems to be working now for me, preserving the proper deltas, and still only storing non-empty date values in the database.

Would love some feedback on this. I've attached a patch.

Shawn