Issue #3104922 by greg.1.anderson, Mile23, alexpott: Guard against changes to Scaffold Plugin that might cause upgrade problems

(cherry picked from commit 61fa1bf27cbe173b777b345dc2b3f123b6bd5532)

Author: alexpott

Handler.php

@@ -7,7 +7,6 @@
 use Composer\Installer\PackageEvent;
 use Composer\IO\IOInterface;
 use Composer\Package\PackageInterface;
-use Composer\Plugin\CommandEvent;
 use Composer\Util\Filesystem;
 use Drupal\Composer\Plugin\Scaffold\Operations\OperationData;
 use Drupal\Composer\Plugin\Scaffold\Operations\OperationFactory;
@@ -82,14 +81,9 @@ public function __construct(Composer $composer, IOInterface $io) {
  }
 
  /**
- * Registers post-package events before any 'require' event runs.
- *
- * This method is called by composer prior to doing a 'require' command.
- *
- * @param \Composer\Plugin\CommandEvent $event
- * The Composer Command event.
+ * Registers post-package events if the 'require' command was called.
  */
- public function beforeRequire(CommandEvent $event) {
+ public function requireWasCalled() {
  // In order to differentiate between post-package events called after
  // 'composer require' vs. the same events called at other times, we will
  // only install our handler when a 'require' event is detected.

Plugin.php

@@ -21,22 +21,41 @@
  */
 class Plugin implements PluginInterface, EventSubscriberInterface, Capable {
 
+ /**
+ * The Composer service.
+ *
+ * @var \Composer\Composer
+ */
+ protected $composer;
+
+ /**
+ * Composer's I/O service.
+ *
+ * @var \Composer\IO\IOInterface
+ */
+ protected $io;
+
  /**
  * The Composer Scaffold handler.
  *
  * @var \Drupal\Composer\Plugin\Scaffold\Handler
  */
  protected $handler;
 
+ /**
+ * Record whether the 'require' command was called.
+ *
+ * @param bool
+ */
+ protected $requireWasCalled;
+
  /**
  * {@inheritdoc}
  */
  public function activate(Composer $composer, IOInterface $io) {
- // We use a Handler object to separate the main functionality
- // of this plugin from the Composer API. This also avoids some
- // debug issues with the plugin being copied on initialisation.
- // @see \Composer\Plugin\PluginManager::registerPackage()
- $this->handler = new Handler($composer, $io);
+ $this->composer = $composer;
+ $this->io = $io;
+ $this->requireWasCalled = FALSE;
  }
 
  /**
@@ -50,6 +69,7 @@ public function getCapabilities() {
  * {@inheritdoc}
  */
  public static function getSubscribedEvents() {
+ // Important note: We only instantiate our handler on "post" events.
  return [
  ScriptEvents::POST_UPDATE_CMD => 'postCmd',
  ScriptEvents::POST_INSTALL_CMD => 'postCmd',
@@ -65,7 +85,7 @@ public static function getSubscribedEvents() {
  * The Composer event.
  */
  public function postCmd(Event $event) {
- $this->handler->scaffold();
+ $this->handler()->scaffold();
  }
 
  /**
@@ -75,7 +95,7 @@ public function postCmd(Event $event) {
  * Composer package event sent on install/update/remove.
  */
  public function postPackage(PackageEvent $event) {
- $this->handler->onPostPackageEvent($event);
+ $this->handler()->onPostPackageEvent($event);
  }
 
  /**
@@ -86,8 +106,28 @@ public function postPackage(PackageEvent $event) {
  */
  public function onCommand(CommandEvent $event) {
  if ($event->getCommandName() == 'require') {
- $this->handler->beforeRequire($event);
+ if ($this->handler) {
+ throw new \Error('Core Scaffold Plugin handler instantiated too early. See https://www.drupal.org/project/drupal/issues/3104922');
+ }
+ $this->requireWasCalled = TRUE;
+ }
+ }
+
+ /**
+ * Lazy-instantiate the handler object. It is dangerous to update a Composer
+ * plugin if it loads any classes prior to the `composer update` operation,
+ * and later tries to use them in a post-update hook.
+ */
+ protected function handler() {
+ if (!$this->handler) {
+ $this->handler = new Handler($this->composer, $this->io);
+ // On instantiation of our handler, notify it if the 'require' command
+ // was executed.
+ if ($this->requireWasCalled) {
+ $this->handler->requireWasCalled();
+ }
  }
+ return $this->handler;
  }
 
 }