Add dynamic TCA field eval configuration

gistfile1.txt

ext_localconf.php
--------------------
$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_tceforms.php']['getSingleFieldClass'][$_EXTKEY] =
   'EXT:' . $_EXTKEY . '/Classes/Hooks/Tceforms.php:Tx_Calendar_Hooks_Tceforms';


Classes/Hooks/Tceforms.php
--------------------
class Tx_Calendar_Hooks_Tceforms
{

   public function getSingleField_beforeRender($table, $field, &$row, &$PA)
   {
       if ($table === 'tx_calendar_domain_model_event' && ($field == 'event_start' || $field == 'event_end')) {
           if ($row['full_day']) {
               $PA['fieldConf']['config']['eval'] = 'date,required';
           } else {
               $PA['fieldConf']['config']['eval'] = 'datetime,required';
           }
       }
   }
}