Issue #3270093 by Grevil, Anybody: Implement hook_requirements in combination...

    "issues": "https://www.drupal.org/project/issues/drowl_admin_dashboard",

    "source": "http://cgit.drupalcode.org/drowl_admin_dashboard"

  },

  "require": {

    "npm-asset/drowl-admin-iconset": "^1.0"

  "suggest": {

    "npm-asset/drowl-admin-iconset": "Required to use drupal/drowl_admin_dashboard. Expected version: ^1.0"

  }

}

<?php

/**

 * @file

 * Install, update and uninstall functions for the drowl_admin_dashboard module.

 */

/**

 * Implements hook_requirements().

 */

function drowl_admin_dashboard_requirements($phase) {

  if ($phase != 'runtime') {

    return [];

  }

  $requirements = [];

  $drowlAdminIconsetLibrary = \Drupal::service('library.discovery')->getLibraryByName('drowl_admin_dashboard', 'admin_iconset');

  if (empty($drowlAdminIconsetLibrary)) {

    throw new Exception("Required libraries for the drowl_admin_dashboard module are not defined in the appropriate libraries.yml file.");

  }

  $drowlAdminIconsExist = file_exists(DRUPAL_ROOT . '/' . $drowlAdminIconsetLibrary['css'][0]['data']);

  $requirements['drowl_admin_iconset'] = [

    'title' => t('Drowl Admin Dashboard: Missing Drowl Admin Iconset library'),

    'value' => $drowlAdminIconsExist ? t('Installed') : t('Not installed'),

    'description' => $drowlAdminIconsExist ? '' : t('To use the drowl_admin_dashboard module, the drowl admin iconset library needs to be required via composer, using "composer require npm-asset/drowl-admin-iconset". NOTE, that you need to set up the "asset-packagist" repository in your projects composer.json file.<br>See <a href="https://www.drupal.org/docs/develop/using-composer/using-composer-to-install-drupal-and-manage-dependencies#third-party-libraries">here</a> on how to do it.'),

    'severity' => $drowlAdminIconsExist ? REQUIREMENT_OK : REQUIREMENT_ERROR,

  ];

  return $requirements;

}