TYPO3 Core

The correct way to add a required evaluation of the field would be:

TCEFORM.pages.lastUpdated.config.eval = required

Unfortunatly this can't work, because it's simply not allowed to change this attribute in the override matrix.

$this->allowOverrideMatrix = array(
'input' => array('size', 'max'),
'text' => array('cols', 'rows', 'wrap'),
'check' => array('cols', 'showIfRTE'),
'select' => array('size', 'autoSizeMax', 'maxitems', 'minitems'),
'group' => array('size', 'autoSizeMax', 'max_size', 'show_thumbs', 'maxitems', 'minitems', 'disable_controls'),
'inline' => array('appearance', 'behaviour', 'foreign_label', 'foreign_selector', 'foreign_unique', 'maxitems', 'minitems', 'size', 'autoSizeMax', 'symmetric_label'),
);

It's possible to overwrite this TCA setting in extTables.php (site wide).

IMHO we should try to add this to the override matrix. If it works without side effects, we should just add most of the eval keys.

Agree with Philipp.

This can be very convenient, f.i. for content elements.

For one CType you can make a certain field mandatory and for another CType optional, using conditions in pageTSconfig. More and more agencies are developing their own content elements. For one CE the header field might be mandatory, for the other one not. I don't expect any side effects when adding eval to the override matrix, for fields where eval is allowed.

I found out it can be done using the hook $TYPO3_CONF_VARS['SC_OPTIONS']['t3lib/class.t3lib_tceforms.php']['getSingleFieldClass']

$this->allowOverrideMatrix can be changed using this hook. Therefor it is not necessary adding more options to this variable.

We are not able to use #note-7 anymore, since that hook is removed by breaking change #63846

As there doesn't seem to be any possibility to manipulate the allowOverrideMatrix after the getMainFieldsClass hook was removed with breaking change #63846 (https://docs.typo3.org/typo3cms/extensions/core/Changelog/7.5/Breaking-69568-FormEngine.html), even not in current master (as of 18-11-08), we currently use Reflection as a workaround.

E.g. to allow overriding 'eval'-config on an input tca field with TCEFORM.pages.lastUpdated.config.eval = required the following code placed in an extensions ext_localconf.php does the job for us:

    $reflectionClassFormEngineUtility = new ReflectionClass(\TYPO3\CMS\Backend\Form\Utility\FormEngineUtility::class);
    $reflectionPropertyAllowOverrideMatrix = $reflectionClassFormEngineUtility->getProperty('allowOverrideMatrix');
    $reflectionPropertyAllowOverrideMatrix->setAccessible(true); // make protected property accessible
    $allowOverrideMatrix = $reflectionPropertyAllowOverrideMatrix->getValue();
    $allowOverrideMatrix['input'][] = 'eval';
    $reflectionPropertyAllowOverrideMatrix->setValue($allowOverrideMatrix);

Tested with TYPO3 7.6.31 and PHP 5.6.