Issue #3418298 by Akhil Babu, Kanchan Bhogade: Improve the exception message...

Issue #3418298 by Akhil Babu, Kanchan Bhogade: Improve the exception message when an entity form class does not exist

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

@@ -207,7 +207,11 @@ public function getListBuilder($entity_type_id) {
    */
   public function getFormObject($entity_type_id, $operation) {
     if (!$class = $this->getDefinition($entity_type_id, TRUE)->getFormClass($operation)) {
-      throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The "%s" entity type did not specify a "%s" form class.', $entity_type_id, $operation));
+      $handlers = $this->getDefinition($entity_type_id, TRUE)->getHandlerClasses();
+      if (!isset($handlers['form'][$operation])) {
+        throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The "%s" entity type did not specify a "%s" form class.', $entity_type_id, $operation));
+      }
+      throw new InvalidPluginDefinitionException($entity_type_id, sprintf('The "%s" form handler of the "%s" entity type specifies a non-existent class "%s".', $operation, $entity_type_id, $handlers['form'][$operation]));
     }
 
     $form_object = $this->classResolver->getInstanceFromDefinition($class);

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

@@ -248,18 +248,52 @@ public function testGetFormObject() {
     $this->assertEquals('yellow', $banana_form->color);
   }
 
+  /**
+   * Provides test data for testGetFormObjectInvalidOperation().
+   *
+   * @return array
+   *   Test data.
+   */
+  public function provideFormObjectInvalidOperationData(): array {
+    return [
+      'missing_form_handler' => [
+        'test_entity_type',
+        'edit',
+        '',
+        'The "test_entity_type" entity type did not specify a "edit" form class.',
+      ],
+      'missing_form_handler_class' => [
+        'test_entity_type',
+        'edit',
+        'Drupal\test_entity_type\Form\NonExistingClass',
+        'The "edit" form handler of the "test_entity_type" entity type specifies a non-existent class "Drupal\test_entity_type\Form\NonExistingClass".',
+      ],
+    ];
+  }
+
   /**
    * Tests the getFormObject() method with an invalid operation.
    *
    * @covers ::getFormObject
+   *
+   * @dataProvider provideFormObjectInvalidOperationData
    */
-  public function testGetFormObjectInvalidOperation() {
+  public function testGetFormObjectInvalidOperation(string $entity_type_id, string $operation, string $form_class, string $exception_message): void {
     $entity = $this->prophesize(EntityTypeInterface::class);
-    $entity->getFormClass('edit')->willReturn('');
-    $this->setUpEntityTypeDefinitions(['test_entity_type' => $entity]);
+    $entity->getFormClass($operation)->willReturn(NULL);
+    if (!$form_class) {
+      $entity->getHandlerClasses()->willReturn([]);
+    }
+    else {
+      $entity->getHandlerClasses()->willReturn([
+        'form' => [$operation => $form_class],
+      ]);
+    }
+    $this->setUpEntityTypeDefinitions([$entity_type_id => $entity]);
 
     $this->expectException(InvalidPluginDefinitionException::class);
-    $this->entityTypeManager->getFormObject('test_entity_type', 'edit');
+    $this->expectExceptionMessage($exception_message);
+    $this->entityTypeManager->getFormObject($entity_type_id, $operation);
   }
 
   /**