Issue #2923915 by tstoeckler, heddn: Stubbing content entities with required fields with a default value is broken

core/modules/migrate/src/Plugin/migrate/destination/EntityContentBase.php

@@ -275,7 +275,7 @@ class EntityContentBase extends Entity implements HighestIdInterface {
       if ($field_definition->isRequired() && is_null($row->getDestinationProperty($field_name))) {
         // Use the configured default value for this specific field, if any.
         if ($default_value = $field_definition->getDefaultValueLiteral()) {
-          $values[] = $default_value;
+          $values = $default_value;
         }
         else {
           // Otherwise, ask the field type to generate a sample value.

core/modules/migrate/tests/src/Kernel/MigrateEntityContentBaseTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\migrate\Kernel;
 
+use Drupal\entity_test\Entity\EntityTestMul;
 use Drupal\KernelTests\KernelTestBase;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\migrate\MigrateExecutable;
@@ -44,6 +45,11 @@ class MigrateEntityContentBaseTest extends KernelTestBase {
    */
   protected function setUp() {
     parent::setUp();
+
+    // Enable two required fields with default values: a single-value field and
+    // a multi-value field.
+    \Drupal::state()->set('entity_test.required_default_field', TRUE);
+    \Drupal::state()->set('entity_test.required_multi_default_field', TRUE);
     $this->installEntitySchema('entity_test_mul');
 
     ConfigurableLanguage::createFromLangcode('en')->save();
@@ -265,4 +271,34 @@ class MigrateEntityContentBaseTest extends KernelTestBase {
     $this->assertNull($entity->version->value);
   }
 
+  /**
+   * Tests stub rows.
+   */
+  public function testStubRows() {
+    // Create a destination.
+    $this->createDestination([]);
+
+    // Import a stub row.
+    $row = new Row([], [], TRUE);
+    $row->setDestinationProperty('type', 'test');
+    $ids = $this->destination->import($row);
+    $this->assertCount(1, $ids);
+
+    // Make sure the entity was saved.
+    $entity = EntityTestMul::load(reset($ids));
+    $this->assertInstanceOf(EntityTestMul::class, $entity);
+    // Make sure the default value was applied to the required fields.
+    $single_field_name = 'required_default_field';
+    $single_default_value = $entity->getFieldDefinition($single_field_name)->getDefaultValueLiteral();
+    $this->assertSame($single_default_value, $entity->get($single_field_name)->getValue());
+
+    $multi_field_name = 'required_multi_default_field';
+    $multi_default_value = $entity->getFieldDefinition($multi_field_name)->getDefaultValueLiteral();
+    $count = 3;
+    $this->assertCount($count, $multi_default_value);
+    for ($i = 0; $i < $count; ++$i) {
+      $this->assertSame($multi_default_value[$i], $entity->get($multi_field_name)->get($i)->getValue());
+    }
+  }
+
 }

core/modules/system/tests/modules/entity_test/entity_test.module

@@ -114,6 +114,23 @@ function entity_test_entity_base_field_info(EntityTypeInterface $entity_type) {
       ->setLabel('Internal field')
       ->setInternal(TRUE);
   }
+  if ($entity_type->id() === 'entity_test_mul' && \Drupal::state()->get('entity_test.required_default_field')) {
+    $fields['required_default_field'] = BaseFieldDefinition::create('string')
+      ->setLabel('Required field with default value')
+      ->setRequired(TRUE)
+      ->setDefaultValue('this is a default value');
+  }
+  if ($entity_type->id() === 'entity_test_mul' && \Drupal::state()->get('entity_test.required_multi_default_field')) {
+    $fields['required_multi_default_field'] = BaseFieldDefinition::create('string')
+      ->setLabel('Required field with default value')
+      ->setRequired(TRUE)
+      ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)
+      ->setDefaultValue([
+        ['value' => 'this is the first default field item'],
+        ['value' => 'this is the second default value'],
+        ['value' => 'you get the idea...'],
+      ]);
+  }
   if ($entity_type->id() == 'entity_test_mulrev' && \Drupal::state()->get('entity_test.field_test_item')) {
     $fields['field_test_item'] = BaseFieldDefinition::create('field_test')
       ->setLabel(t('Field test'))