Issue #2528482 by googletorp, mpdonadio, TR: Fix notice in Date::processDate

core/lib/Drupal/Core/Render/Element/Date.php

@@ -40,6 +40,8 @@ class Date extends FormElement {
       '#process' => [[$class, 'processDate']],
       '#pre_render' => [[$class, 'preRenderDate']],
       '#theme_wrappers' => ['form_element'],
+      '#attributes' => ['type' => 'date'],
+      '#date_date_format' => 'Y-m-d',
     ];
   }
 

core/modules/system/src/Tests/Form/FormTest.php

@@ -533,7 +533,7 @@ class FormTest extends WebTestBase {
     // All the elements should be marked as disabled, including the ones below
     // the disabled container.
     $actual_count = count($disabled_elements);
-    $expected_count = 41;
+    $expected_count = 42;
     $this->assertEqual($actual_count, $expected_count, SafeMarkup::format('Found @actual elements with disabled property (expected @expected).', array(
       '@actual' => count($disabled_elements),
       '@expected' => $expected_count,

core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php

@@ -142,6 +142,15 @@ class FormTestDisabledElementsForm extends FormBase {
       '#date_timezone' => 'Europe/Berlin',
     );
 
+    $form['disabled_container']['disabled_container_date'] = array(
+      '#type' => 'date',
+      '#title' => 'date',
+      '#default_value' => '2001-01-13',
+      '#expected_value' => '2001-01-13',
+      '#test_hijack_value' => '2013-01-01',
+      '#date_timezone' => 'Europe/Berlin',
+    );
+
 
     // Try to hijack the email field with a valid email.
     $form['disabled_container']['disabled_container_email'] = array(