Issue #3063134 by heddn, tatarbj: Backport PendingDbUpdates

ReadinessCheckers/PendingDbUpdates.php

+<?php
+
+/**
+ * Pending database updates checker.
+ */
+class PendingDbUpdates implements ReadinessCheckerInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function run() {
+    $messages = [];
+
+    if (static::areDbUpdatesPending()) {
+      $messages[] = t('There are pending database updates, therefore updates cannot be applied. Please run update.php.');
+    }
+    return $messages;
+  }
+
+  /**
+   * Checks if there are pending database updates.
+   *
+   * @return bool
+   *   TRUE if there are pending updates, otherwise FALSE.
+   */
+  protected static function areDbUpdatesPending() {
+    require_once DRUPAL_ROOT . '/includes/install.inc';
+    require_once DRUPAL_ROOT . '/includes/update.inc';
+    drupal_load_updates();
+    return (bool) update_get_update_list();
+  }
+
+}

ReadinessCheckers/ReadinessCheckerManager.php

@@ -28,6 +28,7 @@ class ReadinessCheckerManager {
     static::$checkers['warning'][0][] = 'ModifiedFiles';
     static::$checkers['warning'][0][] = 'PhpSapi';
     static::$checkers['error'][0][] = 'DiskSpace';
+    static::$checkers['error'][0][] = 'PendingDbUpdates';
     static::$checkers['error'][0][] = 'ReadOnlyFilesystem';
 
     return static::$checkers;

automatic_updates.info

@@ -15,5 +15,6 @@ files[] = ReadinessCheckers/DiskSpace.php
 files[] = ReadinessCheckers/FileOwnership.php
 files[] = ReadinessCheckers/MissingProjectInfo.php
 files[] = ReadinessCheckers/ModifiedFiles.php
+files[] = ReadinessCheckers/PendingDbUpdates.php
 files[] = ReadinessCheckers/PhpSapi.php
 files[] = ReadinessCheckers/ReadOnlyFilesystem.php