Let ViewExecutable->preview() return a render array

There might be an issue here as the preview is used with an AJAX command, and that will expect the result to be rendered. This could be moved somewhere else, just a warning :)

Working on this one.

We may have to do something like this, which I'm not sure about.

Just a few notes:

-    $output = $view->preview();
+    $preview = $view->preview();
+    $output = drupal_render($preview);

Lots of these, what about

     $output = $view->preview();
+    $output = drupal_render($output);

instead?

+++ b/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.php
@@ -202,20 +202,24 @@ public function optionsSummary(&$categories, &$options) {
-    return new Response($this->view->render(), 200, array('Content-type' => $this->getMimeType()));
+   $output = $this->view->render();
+    return new Response(drupal_render($output), 200, array('Content-type' => $this->getMimeType()));

Indentation.

+++ b/core/modules/views/lib/Drupal/views/Plugin/views/area/View.php
@@ -81,14 +81,10 @@ function render($empty = FALSE) {
         // Current $view->preview() does not return a render array, so we have
         // to build a markup out if it.

Obsolete.

Thanks for the review! Much appreciated.

Here are those changes, let's see how this gets on. In a bit of a rush so if there are some missing I will have to fi them later :)

And the interdiff..

Spotted a couple of things.

Fixing this bunch of silly mistakes :)

Thanks! I did say I ran out of time :)

Forgot to set the patch rtbc

RTBC+1

#9: drupal-1938380-9.patch queued for re-testing.

+++ b/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.phpundefined
@@ -202,20 +202,24 @@ public function optionsSummary(&$categories, &$options) {
   /**
    * Overrides \Drupal\views\Plugin\views\display\DisplayPluginBase::render().
    */
   public function render() {
-    $output = $this->view->style_plugin->render();
+    $build = array();
+    $build['#markup'] = $this->view->style_plugin->render();
 
+    // Wrap the output in a pre tag if this is for a live preview.
     if (!empty($this->view->live_preview)) {
-      return '<pre>' . $output . '</pre>';
+      $build['#prefix'] = '<pre>';
+      $build['#suffix'] = '</pre>';
     }
 
-    return $output;
+    return $build;

So Alex and I talked at length about this method, since it was setting a value in #markup rather than returning a "true" render array. However, in this particular case, the contents of the #markup isn't actually markup at all--it's a string representation of the REST response, getting wrapped in a <pre> tag for display to the user.

I did notice that we are calling drupal_render() in StylePluginBase::render_grouping_sets() -- Is that a requirement, or is that something we're planning to clean up later? Out of scope here in any case.

So we agree that this is commit-ready once it finishes testing.

Opened a follow up: #1962836: Don't use drupal_render in StylePluginBase::render_grouping_sets()

Committed and pushed to 8.x. Thanks!