Resolve #3232488 "Deprecate transliteration plugin"

src/Plugin/migrate/process/Service.php

@@ -9,7 +9,7 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
 /**
  * Provides a plugin to use a callable from a service class.
  *
- * Example:
+ * Examples:
  *
  * @code
  * process:
@@ -20,6 +20,27 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
  *     source: filename
  * @endcode
  *
+ * @code
+ * source:
+ *   # plugin ...
+ *   constants:
+ *     langcode: en
+ *     slash: /
+ * process:
+ *   transliterated_value:
+ *     plugin: service
+ *     service: transliteration
+ *     method: transliterate
+ *     unpack_source: true
+ *     source:
+ *       - original_value
+ *       - constants/langcode
+ *       - constants/slash
+ * @endcode
+ *
+ * Since Drupal 9.2.0, it is possible to supply multiple arguments using
+ * unpack_source property. See: https://www.drupal.org/node/3205079
+ *
  * All options for the callback plugin can be used, except for 'callable',
  * which will be ignored.
  *

src/Plugin/migrate/process/Transliteration.php

@@ -34,6 +34,11 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
  * @MigrateProcessPlugin(
  *   id = "transliteration"
  * )
+ *
+ * @deprecated in migrate_plus:8.x-5.3 and is removed from migrate_plus:6.0.0.
+ * Use 'service' process plugin instead. See https://www.drupal.org/node/3255994
+ *
+ * @see https://www.drupal.org/node/3255994
  */
 class Transliteration extends ProcessPluginBase implements ContainerFactoryPluginInterface {
 
@@ -57,6 +62,7 @@ class Transliteration extends ProcessPluginBase implements ContainerFactoryPlugi
    *   The transliteration service.
    */
   public function __construct(array $configuration, $plugin_id, $plugin_definition, TransliterationInterface $transliteration) {
+    @trigger_error(__CLASS__ . ' is deprecated in migrate_plus:8.x-5.3 and is removed from migrate_plus:6.0.0. Use Drupal\migrate_plus\Plugin\migrate\process\Service process plugin instead. See https://www.drupal.org/node/3255994', E_USER_DEPRECATED);
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->transliteration = $transliteration;
   }

tests/src/Unit/process/TransliterationTest.php

@@ -48,4 +48,14 @@ class TransliterationTest extends MigrateProcessTestCase {
     $this->assertEquals($expected_result, $value);
   }
 
+  /**
+   * Tests deprecation notice of Transliteration process plugin.
+   *
+   * @group legacy
+   */
+  public function testDeprecationMessage() {
+    $this->expectDeprecation("Drupal\migrate_plus\Plugin\migrate\process\Transliteration is deprecated in migrate_plus:8.x-5.3 and is removed from migrate_plus:6.0.0. Use Drupal\migrate_plus\Plugin\migrate\process\Service process plugin instead. See https://www.drupal.org/node/3255994");
+    new Transliteration([], 'transliteration', [], $this->transliteration);
+  }
+
 }