Issue #3230507: Create build tests for case where site is using core recommended Composer project

src/Updater.php

@@ -8,6 +8,7 @@ use Drupal\automatic_updates\Event\PreStartEvent;
 use Drupal\automatic_updates\Event\UpdateEvent;
 use Drupal\automatic_updates\Exception\UpdateException;
 use Drupal\Component\FileSystem\FileSystem;
+use Drupal\Component\Serialization\Json;
 use Drupal\Core\State\StateInterface;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
 use Drupal\Core\StringTranslation\TranslationInterface;
@@ -167,7 +168,7 @@ class Updater {
       throw new \InvalidArgumentException("Currently only updates to Drupal core are supported.");
     }
     $packages = [
-      'drupal/core' => $project_versions['drupal'],
+      $this->getCorePackageName() => $project_versions['drupal'],
     ];
     $stage_key = $this->createActiveStage($packages);
     /** @var \Drupal\automatic_updates\Event\PreStartEvent $event */
@@ -176,6 +177,46 @@ class Updater {
     return $stage_key;
   }
 
+  /**
+   * Determines the name of the core package in the project composer.json.
+   *
+   * This makes the following assumptions:
+   * - The vendor directory is next to the project composer.json.
+   * - The project composer.json contains a requirement for a core package.
+   * - That requirement is either for drupal/core or drupal/core-recommended.
+   *
+   * @return string
+   *   The name of the core package (either drupal/core or
+   *   drupal/core-recommended).
+   *
+   * @throws \RuntimeException
+   *   If the project composer.json is not found.
+   * @throws \LogicException
+   *   If the project composer.json does not contain one of the supported core
+   *   packages.
+   *
+   * @todo Move this to an update validator, or use a more robust method of
+   *   detecting the core package.
+   */
+  protected function getCorePackageName(): string {
+    $composer = realpath(static::getVendorDirectory() . '/../composer.json');
+
+    if (empty($composer) || !file_exists($composer)) {
+      throw new \RuntimeException("Could not find project-level composer.json");
+    }
+
+    $composer = file_get_contents($composer);
+    $composer = Json::decode($composer);
+
+    if (isset($composer['require']['drupal/core'])) {
+      return 'drupal/core';
+    }
+    elseif (isset($composer['require']['drupal/core-recommended'])) {
+        return 'drupal/core-recommended';
+    }
+    throw new \LogicException("Could not determine the Drupal core package in the project-level composer.json.");
+  }
+
   /**
    * Gets the excluded paths collected by an event object.
    *