Respect format configuration on REST views display

Ah this makes sense!
Can we fix the test coverage?

.

StyleSerializerTest::testLivePreview() is already testing this, so you could add it there or do something similar?

This one is probably blocked until Live preview for REST display is fixed #2443119: Views preview not working for REST display.

Added tests for this.

+++ b/core/modules/rest/src/Plugin/views/style/Serializer.php
@@ -125,10 +125,10 @@ public function render() {
-    $content_type = $this->displayHandler->getContentType();
-    if (!empty($this->view->live_preview)) {
-      $content_type = $this->options['formats'] ? reset($this->options['formats']) : 'json';
-    }
+    // Get the content type configured in the display or fallback to the
+    // default.
+    $default_content_type = empty($this->view->live_preview) ? $this->displayHandler->getContentType() : 'json';
+    $content_type = $this->options['formats'] ? reset($this->options['formats']) : $default_content_type;
 
     return $this->serializer->serialize($rows, $content_type);

So what we do here, sounds a bit of a bug. Does that mean if we setup one of the formats, even if multiple, we never respect the requested format from the request, see RestExport::init(), that sounds wrong, to be honest

Yes we where actually ignoring the requested format, this should fix that.
I guess we will need extra test coverage there.

Added extra test coverage.

Ah the problem is the default request format in RestExport

  /**
   * Overrides the content type of the data response, if needed.
   *
   * @var string
   */
  protected $contentType = 'json';

Will check how to fix this later this weekend.

This should fix that test failure, it seems like there should be a better way to do this though.

Bit better

This looks perfect now, thank you a lot!

Setting to RTBC

Reroll

Setting RTBC as per #29

This issue is a normal bug fix, and doesn't include any disruptive changes, so it is allowed per https://www.drupal.org/core/beta-changes. Committed 6e83e1f and pushed to 8.0.x. Thanks!

Thanks for adding the beta evaluation to the issue summary.