Issue #2933306 by gnuget, jian he, heddn: EntityLookup fatal error on config entity type

src/Plugin/migrate/process/EntityLookup.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\migrate_plus\Plugin\migrate\process;
 
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManagerInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
@@ -275,7 +276,8 @@ class EntityLookup extends ProcessPluginBase implements ContainerFactoryPluginIn
     if (!$ignoreCase) {
       // Returns the entity's identifier.
       foreach ($results as $k => $identifier) {
-        $result_value = $this->entityManager->getStorage($this->lookupEntityType)->load($identifier)->{$this->lookupValueKey}->value;
+        $entity = $this->entityManager->getStorage($this->lookupEntityType)->load($identifier);
+        $result_value = $entity instanceof ConfigEntityInterface ? $entity->get($this->lookupValueKey) : $entity->get($this->lookupValueKey)->value;
         if (($multiple && !in_array($result_value, $value, TRUE)) || (!$multiple && $result_value !== $value)) {
           unset($results[$k]);
         }

tests/src/Kernel/Plugin/migrate/process/EntityGenerateTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\migrate_plus\Kernel\Plugin\migrate\process;
 
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\field\Tests\EntityReference\EntityReferenceTestTrait;
@@ -183,7 +184,9 @@ class EntityGenerateTest extends KernelTestBase implements MigrateMessageInterfa
                   }
                 }
                 elseif ($entity->{$property}->getValue()) {
-                  $this->assertEquals($expectedValue, $entity->{$property}[0]->entity->$key->value);
+                  $referenced_entity = $entity->{$property}[0]->entity;
+                  $result_value = $referenced_entity instanceof ConfigEntityInterface ? $referenced_entity->get($key) : $referenced_entity->get($key)->value;
+                  $this->assertEquals($expectedValue, $result_value);
                 }
                 else {
                   $this->fail("Expected value: $expectedValue does not exist in $property.");
@@ -708,6 +711,53 @@ class EntityGenerateTest extends KernelTestBase implements MigrateMessageInterfa
           ],
         ],
       ],
+      'lookup config entity' => [
+        'definition' => [
+          'source' => [
+            'plugin' => 'embedded_data',
+            'data_rows' => [
+              [
+                'id' => 1,
+                'name' => 'user 1',
+                'mail' => 'user1@user1.com',
+                'roles' => ['role_1'],
+              ],
+            ],
+            'ids' => [
+              'id' => ['type' => 'integer'],
+            ],
+          ],
+          'process' => [
+            'id' => 'id',
+            'name' => 'name',
+            'roles' => [
+              'plugin' => 'entity_lookup',
+              'entity_type' => 'user_role',
+              'value_key' => 'id',
+              'source' => 'roles',
+            ],
+          ],
+          'destination' => [
+            'plugin' => 'entity:user',
+          ],
+        ],
+        'expected' => [
+          'row 1' => [
+            'id' => 1,
+            'name' => 'user 1',
+            'roles' => [
+              'id' => 'role_1',
+              'label' => 'Role 1',
+            ],
+          ],
+        ],
+        'pre seed' => [
+          'user_role' => [
+            'id' => 'role_1',
+            'label' => 'Role 1',
+          ],
+        ],
+      ],
     ];
   }