Issue #2412805 by mondrake: View preview does not attach assets provided by plugins

core/modules/views_ui/src/Tests/PreviewTest.php

@@ -213,6 +213,9 @@ public function testPreviewAdditionalInfo() {
     // @see views_ui_test.module
     $elements = $this->xpath('//div[@id="views-live-preview"]/div[contains(@class, views-query-info)]//td[text()=:text]', array(':text' => t('Test row count')));
     $this->assertEqual(count($elements), 1, 'Views Query Preview Info area altered.');
+    // Check that additional assets are attached.
+    $this->assertTrue(strpos($this->getDrupalSettings()['ajaxPageState']['libraries'], 'views_ui_test/views_ui_test.test') !== FALSE, 'Attached library found.');
+    $this->assertRaw('css/views_ui_test.test.css', 'Attached CSS asset found.');
   }
 
   /**

core/modules/views_ui/src/ViewPreviewForm.php

@@ -68,7 +68,7 @@ public function form(array $form, FormStateInterface $form_state) {
         '#weight' => 110,
         '#theme_wrappers' => array('container'),
         '#attributes' => array('id' => 'views-live-preview'),
-        '#markup' => $view->renderPreview($this->displayID, $args),
+        'preview' => $view->renderPreview($this->displayID, $args),
       );
     }
     $uri = $view->urlInfo('preview-form');

core/modules/views_ui/src/ViewUI.php

@@ -577,7 +577,6 @@ public function renderPreview($display_id, $args = array()) {
     $combined = $show_query && $show_stats;
 
     $rows = array('query' => array(), 'statistics' => array());
-    $output = '';
 
     $errors = $this->executable->validate();
     $this->executable->destroy();
@@ -599,7 +598,9 @@ public function renderPreview($display_id, $args = array()) {
       $this->executable->setExposedInput($exposed_input);
 
       if (!$this->executable->setDisplay($display_id)) {
-        return t('Invalid display id @display', array('@display' => $display_id));
+        return [
+          '#markup' => t('Invalid display id @display', array('@display' => $display_id)),
+        ];
       }
 
       $this->executable->setArguments($args);
@@ -644,7 +645,6 @@ public function renderPreview($display_id, $args = array()) {
 
       // Execute/get the view preview.
       $preview = $this->executable->preview($display_id, $args);
-      $preview = drupal_render($preview);
 
       if ($show_additional_queries) {
         $this->endQueryCapture();
@@ -769,10 +769,16 @@ public function renderPreview($display_id, $args = array()) {
     }
 
     if ($show_location === 'above' || $show_stats === 'above') {
-      $output .= drupal_render($table) . $preview;
+      $output = [
+        'table' => $table,
+        'preview' => $preview,
+      ];
     }
     elseif ($show_location === 'below' || $show_stats === 'below') {
-      $output .= $preview . drupal_render($table);
+      $output = [
+        'preview' => $preview,
+        'table' => $table,
+      ];
     }
 
     // Ensure that we just remove an additional request we pushed earlier.

core/modules/views_ui/tests/modules/views_ui_test/css/views_ui_test.test.css

+/**
+ * @file
+ * Just a placeholder file for the test.
+ */

core/modules/views_ui/tests/modules/views_ui_test/views_ui_test.libraries.yml

+views_ui_test.test:
+  css:
+    component:
+      css/views_ui_test.test.css: {}

core/modules/views_ui/tests/modules/views_ui_test/views_ui_test.module

@@ -11,7 +11,7 @@
  * Add a row count row to the live preview area.
  */
 function views_ui_test_views_preview_info_alter(&$rows, $view) {
-  $rows['query'][] = array(
-    t('Test row count'), count($view->result),
-  );
+  $data = ['#markup' => t('Test row count')];
+  $data['#attached']['library'][] = 'views_ui_test/views_ui_test.test';
+  $rows['query'][] = [['data' => $data], count($view->result)];
 }