D8_rplf/modules/colorbox/colorbox.install

<?php

/**
 * @file
 * Install, update and uninstall functions for the colorbox module.
 */

/**
 * Implements hook_requirements().
 */
function colorbox_requirements($phase) {
  if ($phase != 'runtime') {
    return array();
  }

  $library = \Drupal::service('library.discovery')->getLibraryByName('colorbox', 'colorbox');
  $library_exists = file_exists(DRUPAL_ROOT . '/' . $library['js'][0]['data']);

  return [
    'colorbox_library_downloaded' => [
      'title' => t('Colorbox library'),
      'value' => $library_exists ? t('Installed') : t('Not installed'),
      'description' => $library_exists ? '' : t('The Colorbox library needs to be <a href="@url">downloaded</a> and extracted into the /libraries/colorbox folder in your Drupal installation directory.', ['@url' => 'https://github.com/jackmoore/colorbox/archive/master.zip']),
      'severity' => $library_exists ? REQUIREMENT_OK : REQUIREMENT_ERROR,
    ],
  ];
}