Issue #2850022 by Sam152, Berdir: Duplicating a non-default revision should produce a default revision for a newly created entity

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

@@ -312,7 +312,9 @@ abstract class ContentEntityBase extends Entity implements \IteratorAggregate, C
     if (isset($new_value)) {
       $this->isDefaultRevision = (bool) $new_value;
     }
-    return $return;
+    // New entities should always ensure at least one default revision exists,
+    // creating an entity without a default revision is an invalid state.
+    return $this->isNew() || $return;
   }
 
   /**

core/tests/Drupal/KernelTests/Core/Entity/EntityDuplicateTest.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Entity;
+
+use Drupal\entity_test\Entity\EntityTestRev;
+
+/**
+ * Test entity duplication.
+ *
+ * @group Entity
+ */
+class EntityDuplicateTest extends EntityKernelTestBase {
+
+  /**
+   * @var \Drupal\Core\Entity\ContentEntityStorageInterface
+   */
+  protected $entityTestRevStorage;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->installEntitySchema('entity_test_rev');
+    $this->entityTestRevStorage = $this->container->get('entity_type.manager')->getStorage('entity_test_rev');
+  }
+
+  /**
+   * Test duplicating a non-default revision.
+   */
+  public function testDuplicateNonDefaultRevision() {
+    $entity = EntityTestRev::create([
+      'name' => 'First Revision',
+    ]);
+    $entity->save();
+    $first_revision_id = $entity->getRevisionId();
+
+    $entity->setNewRevision(TRUE);
+    $entity->name = 'Second Revision';
+    $entity->save();
+
+    $duplicate_first_revision = $this->entityTestRevStorage->loadRevision($first_revision_id)->createDuplicate();
+    $this->assertTrue($duplicate_first_revision->isDefaultRevision(), 'Duplicating a non-default revision creates a default revision.');
+    $this->assertEquals($duplicate_first_revision->label(), 'First Revision');
+    $duplicate_first_revision->save();
+
+    $duplicate_first_revision->name = 'Updated name';
+    $duplicate_first_revision->save();
+
+    $this->entityTestRevStorage->resetCache();
+    $duplicate_first_revision = EntityTestRev::load($duplicate_first_revision->id());
+    $this->assertEquals('Updated name', $duplicate_first_revision->label());
+  }
+
+}

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

@@ -182,8 +182,8 @@ class ContentEntityBaseUnitTest extends UnitTestCase {
       ->method('getFieldDefinitions')
       ->with($this->entityTypeId, $this->bundle)
       ->will($this->returnValue($this->fieldDefinitions));
-    $this->entity = $this->getMockForAbstractClass('\Drupal\Core\Entity\ContentEntityBase', array($values, $this->entityTypeId, $this->bundle));
 
+    $this->entity = $this->getMockForAbstractClass('\Drupal\Core\Entity\ContentEntityBase', array($values, $this->entityTypeId, $this->bundle), '', TRUE, TRUE, TRUE, ['isNew']);
     $values['defaultLangcode'] = array(LanguageInterface::LANGCODE_DEFAULT => LanguageInterface::LANGCODE_NOT_SPECIFIED);
     $this->entityUnd = $this->getMockForAbstractClass('\Drupal\Core\Entity\ContentEntityBase', array($values, $this->entityTypeId, $this->bundle));
   }
@@ -262,6 +262,12 @@ class ContentEntityBaseUnitTest extends UnitTestCase {
     $this->assertTrue($this->entity->isDefaultRevision(FALSE));
     // The last call changed the return value for this call.
     $this->assertFalse($this->entity->isDefaultRevision());
+    // The revision for a new entity should always be the default revision.
+    $this->entity->expects($this->any())
+      ->method('isNew')
+      ->will($this->returnValue(TRUE));
+    $this->entity->isDefaultRevision(FALSE);
+    $this->assertTrue($this->entity->isDefaultRevision());
   }
 
   /**