Issue #3000677 by catch, Shane Birley, featherbelly, alexpott: Fatal error...

Issue #3000677 by catch, Shane Birley, featherbelly, alexpott: Fatal error after upgrade to 8.6x [due to regression in extension system]

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

@@ -747,7 +747,13 @@ public function getModuleDirectories() {
    * {@inheritdoc}
    */
   public function getName($module) {
-    return \Drupal::service('extension.list.module')->getName($module);
+    try {
+      return \Drupal::service('extension.list.module')->getName($module);
+    }
+    catch (UnknownExtensionException $e) {
+      @trigger_error('Calling ModuleHandler::getName() with an unknown module is deprecated in Drupal 8.7.0 and support for this will be removed in Drupal 9.0.0, check that the module exists before calling this method. See https://www.drupal.org/node/3024541.', E_USER_DEPRECATED);
+      return $module;
+    }
   }
 
 }

core/tests/Drupal/KernelTests/Core/Extension/ModuleHandlerTest.php

+<?php
+
+namespace Drupal\KernelTests\Core\Extension;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Extension\ModuleHandler
+ *
+ * @group Extension
+ */
+class ModuleHandlerTest extends KernelTestBase {
+
+  /**
+   * Tests requesting the name of an invalid module.
+   *
+   * @covers ::getName
+   * @group legacy
+   * @expectedDeprecation Calling ModuleHandler::getName() with an unknown module is deprecated in Drupal 8.7.0 and support for this will be removed in Drupal 9.0.0, check that the module exists before calling this method. See https://www.drupal.org/node/3024541.
+   */
+  public function testInvalidGetName() {
+    $module_handler = $this->container->get('module_handler');
+    $this->assertSame('module_nonsense', $module_handler->getName('module_nonsense'));
+  }
+
+}