Issue #2844181 by maxocub, Alex Bukach, alexpott: PluralTranslatableMarkup serialization error

core/lib/Drupal/Core/StringTranslation/PluralTranslatableMarkup.php

@@ -157,4 +157,11 @@ protected function getPluralIndex() {
     return -1;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function __sleep() {
+    return array_merge(parent::__sleep(), array('count'));
+  }
+
 }

core/tests/Drupal/Tests/Core/StringTranslation/PluralTranslatableMarkupTest.php

+<?php
+
+namespace Drupal\Tests\Core\StringTranslation;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\StringTranslation\PluralTranslatableMarkup;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests the TranslatableMarkup class.
+ *
+ * @coversDefaultClass \Drupal\Core\StringTranslation\PluralTranslatableMarkup
+ * @group StringTranslation
+ */
+class PluralTranslatableMarkupTest extends UnitTestCase {
+
+  /**
+   * Tests serialization of PluralTranslatableMarkup().
+   *
+   * @dataProvider providerPluralTranslatableMarkupSerialization
+   */
+  public function testPluralTranslatableMarkupSerialization($count, $expected_text) {
+    // Add a mock string translation service to the container.
+    $container = new ContainerBuilder();
+    $container->set('string_translation', $this->getStringTranslationStub());
+    \Drupal::setContainer($container);
+
+    // Create an object to serialize and unserialize.
+    $markup = new PluralTranslatableMarkup($count, 'singular @count', 'plural @count');
+    $serialized_markup = unserialize(serialize($markup));
+    $this->assertEquals($expected_text, $serialized_markup->render());
+  }
+
+  /**
+   * Data provider for ::testPluralTranslatableMarkupSerialization().
+   */
+  public function providerPluralTranslatableMarkupSerialization() {
+    return [
+      [1, 'singular 1'],
+      [2, 'plural 2'],
+    ];
+  }
+
+}