Issue #2505263 by maxocub, tstoeckler: Session language switch links are (sometimes) broken

core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationSession.php

@@ -144,7 +144,10 @@ public function getLanguageSwitchLinks(Request $request, $type, Url $url) {
     foreach ($this->languageManager->getNativeLanguages() as $language) {
       $langcode = $language->getId();
       $links[$langcode] = array(
-        'url' => $url,
+        // We need to clone the $url object to avoid using the same one for all links.
+        // When the links are rendered, options are set on the $url object,
+        // so if we use the same one, they would be set for all links.
+        'url' => clone $url,
         'title' => $language->getName(),
         'attributes' => array('class' => array('language-link')),
         'query' => $query,

core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php

@@ -200,7 +200,10 @@ public function getLanguageSwitchLinks(Request $request, $type, Url $url) {
 
     foreach ($this->languageManager->getNativeLanguages() as $language) {
       $links[$language->getId()] = array(
-        'url' => $url,
+        // We need to clone the $url object to avoid using the same one for all links.
+        // When the links are rendered, options are set on the $url object,
+        // so if we use the same one, they would be set for all links.
+        'url' => clone $url,
         'title' => $language->getName(),
         'language' => $language,
         'attributes' => array('class' => array('language-link')),

core/modules/language/src/Tests/LanguageSwitchingTest.php

@@ -9,6 +9,7 @@
 
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
+use Drupal\menu_link_content\Entity\MenuLinkContent;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 
@@ -24,7 +25,7 @@ class LanguageSwitchingTest extends WebTestBase {
    *
    * @var array
    */
-  public static $modules = array('locale', 'language', 'block', 'language_test');
+  public static $modules = array('locale', 'language', 'block', 'language_test', 'menu_ui');
 
   protected function setUp() {
     parent::setUp();
@@ -392,6 +393,58 @@ protected function doTestLanguageLinkActiveClassAnonymous() {
     $this->assertTrue(isset($links[0]), t('A link generated by :function to the current :language page with langcode :langcode is marked active.', array(':function' => $function_name, ':language' => $current_language, ':langcode' => $langcode)));
   }
 
+  /**
+   * Test language switcher links for session based negotiation.
+   */
+  function testLanguageSessionSwitchLinks() {
+    // Add language.
+    $edit = array(
+      'predefined_langcode' => 'fr',
+    );
+    $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add language'));
+
+    // Enable session language detection and selection.
+    $edit = array(
+      'language_interface[enabled][language-url]' => FALSE,
+      'language_interface[enabled][language-session]' => TRUE,
+    );
+    $this->drupalPostForm('admin/config/regional/language/detection', $edit, t('Save settings'));
+
+    // Enable the language switching block.
+    $this->drupalPlaceBlock('language_block:' . LanguageInterface::TYPE_INTERFACE, array(
+      'id' => 'test_language_block',
+    ));
+
+    // Enable the main menu block.
+    $this->drupalPlaceBlock('system_menu_block:main', array(
+      'id' => 'test_menu',
+    ));
+
+    // Add a link to the homepage.
+    $link = MenuLinkContent::create([
+      'title' => 'Home',
+      'menu_name' => 'main',
+      'bundle' => 'menu_link_content',
+      'link' => [['uri' => 'entity:user/2']],
+    ]);
+    $link->save();
+
+    // Go to the homepage.
+    $this->drupalGet('');
+    // Click on the French link.
+    $this->clickLink(t('French'));
+    // There should be a query parameter to set the session language.
+    $this->assertUrl('user/2', ['query' => ['language' => 'fr']]);
+    // Click on the 'Home' Link.
+    $this->clickLink(t('Home'));
+    // There should be no query parameter.
+    $this->assertUrl('user/2');
+    // Click on the French link.
+    $this->clickLink(t('French'));
+    // There should be no query parameter.
+    $this->assertUrl('user/2');
+  }
+
   /**
    * Saves the native name of a language entity in configuration as a label.
    *