Issue #2820411 by Akhil Babu, smustgrave, larowlan, joachim, quietone: Improve...

Issue #2820411 by Akhil Babu, smustgrave, larowlan, joachim, quietone: Improve the exception message when an entity handler class does not exist

core/lib/Drupal/Core/Entity/EntityTypeManager.php

@@ -253,7 +253,11 @@ public function getHandler($entity_type_id, $handler_type) {
       $definition = $this->getDefinition($entity_type_id);
       $class = $definition->getHandlerClass($handler_type);
       if (!$class) {
-        throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The "%s" entity type did not specify a %s handler.', $entity_type_id, $handler_type));
+        $handlers = $definition->getHandlerClasses();
+        if (!isset($handlers[$handler_type])) {
+          throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The "%s" entity type did not specify a %s handler.', $entity_type_id, $handler_type));
+        }
+        throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The %s handler of the "%s" entity type specifies a non-existent class "%s".', $handler_type, $entity_type_id, $handlers[$handler_type]));
       }
       $this->handlers[$handler_type][$entity_type_id] = $this->createHandlerInstance($class, $definition);
     }

core/tests/Drupal/Tests/Core/Entity/EntityTypeManagerTest.php

@@ -280,17 +280,49 @@ public function testGetHandler() {
     $this->assertInstanceOf(TranslationInterface::class, $apple_controller->stringTranslation);
   }
 
+  /**
+   * Provides test data for testGetHandlerMissingHandler().
+   *
+   * @return array
+   *   Test data.
+   */
+  public function provideMissingHandlerData() : array {
+    return [
+      'missing_handler' => [
+        'test_entity_type',
+        'storage',
+        '',
+        'The "test_entity_type" entity type did not specify a storage handler.',
+      ],
+      'missing_handler_class' => [
+        'test_entity_type',
+        'storage',
+        'Non_Existing_Class',
+        'The storage handler of the "test_entity_type" entity type specifies a non-existent class "Non_Existing_Class".',
+      ],
+    ];
+  }
+
   /**
    * Tests the getHandler() method when no controller is defined.
    *
    * @covers ::getHandler
+   *
+   * @dataProvider provideMissingHandlerData
    */
-  public function testGetHandlerMissingHandler() {
+  public function testGetHandlerMissingHandler(string $entity_type, string $handler_name, string $handler_class, $exception_message) : void {
     $entity = $this->prophesize(EntityTypeInterface::class);
-    $entity->getHandlerClass('storage')->willReturn('');
-    $this->setUpEntityTypeDefinitions(['test_entity_type' => $entity]);
+    $entity->getHandlerClass($handler_name)->willReturn(NULL);
+    if (!$handler_class) {
+      $entity->getHandlerClasses()->willReturn([]);
+    }
+    else {
+      $entity->getHandlerClasses()->willReturn([$handler_name => $handler_class]);
+    }
+    $this->setUpEntityTypeDefinitions([$entity_type => $entity]);
     $this->expectException(InvalidPluginDefinitionException::class);
-    $this->entityTypeManager->getHandler('test_entity_type', 'storage');
+    $this->expectExceptionMessage($exception_message);
+    $this->entityTypeManager->getHandler($entity_type, $handler_name);
   }
 
   /**