We are upgrading our sites one at a time from Drupal 8 to Drupal 9 and there is one line of code in our custom theme that is the last of our problems.
We get the following error on View that uses an exposed filter:
Drupal\Core\Security\UntrustedCallbackException: Render #pre_render callbacks must be methods of a class that implements \Drupal\Core\Security\TrustedCallbackInterface or be an anonymous function. The callback was MYSITE_form_alter_views_exposed_form_MYVIEW_pre_render. See https://www.drupal.org/node/2966725 in Drupal\Core\Render\Renderer->doTrustedCallback() (line 96 of core/lib/Drupal/Core/Security/DoTrustedCallbackTrait.php).
In the OURTHEME.theme file, we have this function:
/**
* Custom form alter for events.
*/
function OURTHEME_form_alter_views_exposed_form_events_pre_render($form) {
$fields = [
'field_start_date_value',
'field_end_date_value',
'field_address_locality',
];
foreach ($fields as $field) {
$form[$field]['#title_display'] = 'after';
}
$form['field_date_range_end_value']['#prefix'] = '<div class="event-exposed-form">';
$form['field_event_address_locality']['#suffix'] = '</div>';
return $form;
}
And the function is called here (just a snippet of the code in this function):
/**
* These are the alterations to forms variables before they are rendered.
*/
function OURTHEME_form_alter(&$form, &$form_state, $form_id) {
if ($form_id == 'views_exposed_form' && strpos($form['#id'], 'views-exposed-form-events-') === 0) {
$form['#pre_render'][] = 'OURTHEME_form_alter_views_exposed_form_events_pre_render';
}
return $form;
}
From what I could divine from the research I've done so far, it seems that normally whatever class these kinds of functions are utilized in have implemented Drupal's TrustedCallbackInterface. Unfortunately, the only information I have found has been throughout the various patches being applied to projects throughout Drupal.org, so I'm trying to cobble together a methodology from random applications of it.
Of course, there's the Drupal API page, but that's not especially helpful when it comes to actually putting the pieces together into a useful methodology without knowing the rest of the API like the back of your hand.
Does anyone know if there's any documentation on how to apply the TrustedCallbackInterface to a function that previously used $form['#pre_render'][], especially in THEME.theme which is not set up the same as any old custom class in a Module?
