ErrorHandlerSubscriber.php

<?php

namespace Drupal\devel\EventSubscriber;

use Drupal\Core\Session\AccountProxyInterface;
use Symfony\Component\EventDispatcher\Event;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Listener for handling PHP errors.
 */
class ErrorHandlerSubscriber implements EventSubscriberInterface {
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountProxyInterface
     */
    protected $account;
    
    /**
     * ErrorHandlerSubscriber constructor.
     *
     * @param \Drupal\Core\Session\AccountProxyInterface $account
     *   The current user.
     */
    public function __construct(AccountProxyInterface $account) {
        $this->account = $account;
    }
    
    /**
     * Register devel error handler.
     *
     * @param \Symfony\Component\EventDispatcher\Event $event
     *   The event to process.
     */
    public function registerErrorHandler(Event $event = NULL) {
        if ($this->account && $this->account
            ->hasPermission('access devel information')) {
            devel_set_handler(devel_get_handlers());
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() {
        // Runs as soon as possible in the request but after
        // AuthenticationSubscriber (priority 300) because you need to access to
        // the current user for determine whether register the devel error handler
        // or not.
        $events[KernelEvents::REQUEST][] = [
            'registerErrorHandler',
            256,
        ];
        return $events;
    }

}