Issue #3218660 by alexpott: help_topics module can break during module uninstall

core/lib/Drupal/Core/Extension/ModuleInstaller.php

@@ -523,12 +523,12 @@ class ModuleInstaller implements ModuleInstallerInterface {
       // into its statically cached list.
       \Drupal::service('extension.list.module')->reset();
 
-      // Clear plugin manager caches.
-      \Drupal::getContainer()->get('plugin.cache_clearer')->clearCachedDefinitions();
-
       // Update the kernel to exclude the uninstalled modules.
       $this->updateKernel($module_filenames);
 
+      // Clear plugin manager caches.
+      \Drupal::getContainer()->get('plugin.cache_clearer')->clearCachedDefinitions();
+
       // Update the theme registry to remove the newly uninstalled module.
       drupal_theme_rebuild();
 

core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php

@@ -263,6 +263,28 @@ class HelpTopicSearchTest extends HelpTopicTranslatedTestBase {
     $this->assertSession()->statusCodeEquals(200);
   }
 
+  /**
+   * Tests uninstalling the search module.
+   */
+  public function testUninstallSearch() {
+    // Ensure we can uninstall search and use the help system without
+    // breaking.
+    $this->drupalLogin($this->rootUser);
+    $edit = [];
+    $edit['uninstall[search]'] = TRUE;
+    $this->drupalGet('admin/modules/uninstall');
+    $this->submitForm($edit, 'Uninstall');
+    $this->submitForm([], 'Uninstall');
+    $this->assertSession()->pageTextContains('The selected modules have been uninstalled.');
+    $this->drupalGet('admin/help');
+    $this->assertSession()->statusCodeEquals(200);
+
+    // Rebuild the container to reflect the latest changes.
+    $this->rebuildContainer();
+    $this->assertTrue(\Drupal::moduleHandler()->moduleExists('help_topics'), 'The help_topics module is still installed.');
+    $this->assertFalse(\Drupal::moduleHandler()->moduleExists('search'), 'The search module is uninstalled.');
+  }
+
   /**
    * Asserts that help search returned the expected number of results.
    *

core/modules/system/tests/modules/module_test/module_test.services.yml

@@ -0,0 +1,7 @@
+services:
+  # Tests module uninstall
+  plugin.manager.module_test.cache_clear_test:
+    class: Drupal\module_test\PluginManagerCacheClearer
+    arguments: ['@state', '@?logger.dblog']
+    tags:
+      - { name: plugin_manager_cache_clear }

core/modules/system/tests/modules/module_test/src/PluginManagerCacheClearer.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\module_test;
+
+use Drupal\Core\Plugin\DefaultPluginManager;
+use Drupal\Core\State\StateInterface;
+
+/**
+ * Helps test module uninstall.
+ */
+class PluginManagerCacheClearer extends DefaultPluginManager {
+
+  /**
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * An optional service dependency.
+   *
+   * @var object|null
+   */
+  protected $optionalService;
+
+  /**
+   * PluginManagerCacheClearer constructor.
+   *
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service for recording what happens.
+   * @param null $optional_service
+   *   An optional service for testing.
+   */
+  public function __construct(StateInterface $state, $optional_service = NULL) {
+    $this->state = $state;
+    $this->optionalService = $optional_service;
+  }
+
+  /**
+   * Tests call to CachedDiscoveryInterface::clearCachedDefinitions().
+   *
+   * @see \Drupal\Component\Plugin\Discovery\CachedDiscoveryInterface::clearCachedDefinitions()
+   */
+  public function clearCachedDefinitions() {
+    $this->state->set(self::class, isset($this->optionalService));
+  }
+
+}

core/modules/system/tests/src/Kernel/Installer/UninstallKernelTest.php

@@ -3,6 +3,7 @@
 namespace Drupal\Tests\system\Kernel\Installer;
 
 use Drupal\KernelTests\KernelTestBase;
+use Drupal\module_test\PluginManagerCacheClearer;
 
 /**
  * Tests the uninstallation of modules.
@@ -48,4 +49,24 @@ class UninstallKernelTest extends KernelTestBase {
     \Drupal::service('module_installer')->uninstall(['file']);
   }
 
+  /**
+   * Tests uninstalling a module with a plugin cache clearer service.
+   */
+  public function testUninstallPluginCacheClear() {
+    \Drupal::service('module_installer')->install(['module_test']);
+    $this->assertFalse($this->container->get('state')->get(PluginManagerCacheClearer::class));
+    \Drupal::service('module_installer')->install(['dblog']);
+    $this->assertTrue($this->container->get('state')->get(PluginManagerCacheClearer::class));
+
+    // The plugin cache clearer service should be called during dblog uninstall
+    // without the dependency.
+    \Drupal::service('module_installer')->uninstall(['dblog']);
+    $this->assertFalse($this->container->get('state')->get(PluginManagerCacheClearer::class));
+
+    // The service should not be called during module_test uninstall.
+    $this->container->get('state')->delete(PluginManagerCacheClearer::class);
+    \Drupal::service('module_installer')->uninstall(['module_test']);
+    $this->assertNull($this->container->get('state')->get(PluginManagerCacheClearer::class));
+  }
+
 }