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

Issue #3270093 by Grevil, Anybody: Implement hook_requirements in combination with composer "suggest" for "npm-asset" libraries

composer.json

@@ -10,7 +10,7 @@
     "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"
   }
 }

drowl_admin_dashboard.install

+<?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;
+}