Issue #3081123 by quietone, alexpott: Add checkrequirements to VariableTranslation source plugin

(cherry picked from commit de2072c9fa)

core/modules/migrate_drupal/src/Plugin/migrate/source/d6/VariableTranslation.php

@@ -4,6 +4,7 @@ namespace Drupal\migrate_drupal\Plugin\migrate\source\d6;
 
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\State\StateInterface;
+use Drupal\migrate\Exception\RequirementsException;
 use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
 
@@ -12,7 +13,7 @@ use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
  *
  * @MigrateSource(
  *   id = "d6_variable_translation",
- *   source_module = "system",
+ *   source_module = "i18n",
  * )
  */
 class VariableTranslation extends DrupalSqlBase {
@@ -98,4 +99,14 @@ class VariableTranslation extends DrupalSqlBase {
     return $ids;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function checkRequirements() {
+    if (!$this->getDatabase()->schema()->tableExists('i18n_variable')) {
+      throw new RequirementsException("Source database table 'i18n_variable' does not exist");
+    }
+    parent::checkRequirements();
+  }
+
 }

core/modules/migrate_drupal/tests/src/Kernel/d6/VariableTranslationCheckRequirementsTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\Tests\migrate_drupal\Kernel\d6;
+
+use Drupal\migrate\Exception\RequirementsException;
+
+/**
+ * Tests check requirements for variable translation source plugin.
+ *
+ * @group migrate_drupal
+ */
+class VariableTranslationCheckRequirementsTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['config_translation'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setup() {
+    parent::setUp();
+    $this->sourceDatabase->schema()->dropTable('i18n_variable');
+  }
+
+  /**
+   * Tests exception in thrown when the i18n_variable table does not exist.
+   */
+  public function testCheckRequirements() {
+    $this->expectException(RequirementsException::class);
+    $this->expectExceptionMessage("Source database table 'i18n_variable' does not exist");
+    $this->getMigration('d6_system_maintenance_translation')
+      ->getSourcePlugin()
+      ->checkRequirements();
+  }
+
+}