function system_form_alter

Implements hook_form_alter().

File

core/modules/system/system.module, line 773

Code

function system_form_alter(&$form, FormStateInterface $form_state) {
    // If the page that's being built is cacheable, set the 'immutable' flag, to
    // ensure that when the form is used, a new form build ID is generated when
    // appropriate, to prevent information disclosure.
    // Note: This code just wants to know whether cache response headers are set,
    // not whether page_cache module will be active.
    // \Drupal\Core\EventSubscriber\FinishResponseSubscriber::onRespond will
    // send those headers, in case $request_policy->check($request) succeeds. In
    // that case we need to ensure that the immutable flag is sot, so future POST
    // request won't take over the form state of another user.
    
    /** @var \Drupal\Core\PageCache\RequestPolicyInterface $request_policy */
    $request_policy = \Drupal::service('page_cache_request_policy');
    $request = \Drupal::requestStack()->getCurrentRequest();
    $request_is_cacheable = $request_policy->check($request) === RequestPolicyInterface::ALLOW;
    if ($request_is_cacheable) {
        $form_state->addBuildInfo('immutable', TRUE);
    }
}