Issue #3057399 by quietone, Akhil Babu, kristiaanvandeneynde, alexpott,...

Issue #3057399 by quietone, Akhil Babu, kristiaanvandeneynde, alexpott, pradhumanjain2311, smustgrave, catch, poker10, longwave, jimafisk, Newb_Druper, robpowell, dpi, tomdewild: Add user_requirements to check for missing anonymous user

core/modules/user/tests/src/Functional/UserRequirementsTest.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\user\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the requirements checks of the User module.
+ *
+ * @group user
+ */
+class UserRequirementsTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that the requirements check can detect a missing anonymous user.
+   */
+  public function testAnonymousUser(): void {
+    // Remove the anonymous user.
+    \Drupal::database()
+      ->delete('users')
+      ->condition('uid', 0)
+      ->execute();
+
+    $this->drupalLogin($this->rootUser);
+    $this->drupalGet('/admin/reports/status');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains("The anonymous user does not exist.");
+  }
+
+}

core/modules/user/user.install

@@ -93,6 +93,34 @@ function user_install() {
     ->save();
 }
 
+/**
+ * Implements hook_requirements().
+ */
+function user_requirements($phase): array {
+  if ($phase !== 'runtime') {
+    return [];
+  }
+
+  $result = (bool) \Drupal::entityQuery('user')
+    ->accessCheck(FALSE)
+    ->condition('uid', 0)
+    ->range(0, 1)
+    ->execute();
+
+  if ($result === FALSE) {
+    return [
+      'anonymous user' => [
+        'title' => t('Anonymous user'),
+        'description' => t('The anonymous user does not exist. See the <a href=":url">restore the anonymous (user ID 0) user record</a> for more information', [
+          ':url' => 'https://www.drupal.org/node/1029506',
+        ]),
+        'severity' => REQUIREMENT_WARNING,
+      ],
+    ];
+  }
+  return [];
+}
+
 /**
  * Implements hook_update_last_removed().
  */