diff --git a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
index b47ff0c..cd796a1 100644
--- a/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
+++ b/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
@@ -142,11 +142,9 @@ public function processAttachments(AttachmentsInterface $response) {
     // placeholder for it, we can safely avoid processing the render array if
     // it's not present.
     if (!empty($placeholders['head'])) {
-      // 'feed' is a special case of 'html_head_link'. We create an
-      // 'html_head_link' for the RSS feed and merge it.
+      // 'feed' is a special case of 'html_head_link'. We process them into
+      // 'html_head_link' entries and merge them.
       if (!empty($attached['feed'])) {
-        // Since mergeBubbleableMetadata() requires a complete render array, we
-        // have to add the '#attached' key.
         $attached = BubbleableMetadata::mergeAttachments(
           $attached,
           $this->processFeed($attached['feed'])
@@ -160,8 +158,7 @@ public function processAttachments(AttachmentsInterface $response) {
       if (!empty($attached['html_head_link'])) {
         // Merge the processed 'html_head_link' into $attached so that its
         // 'html_head' and 'http_header' values are present for further
-        // processing. The merge requires a full render array, so we have to add
-        // '#attached' keys.
+        // processing.
         $attached = BubbleableMetadata::mergeAttachments(
           $attached,
           $this->processHtmlHeadLink($attached['html_head_link'])
diff --git a/core/modules/system/src/Tests/Common/RenderTest.php b/core/modules/system/src/Tests/Common/RenderTest.php
index 11bb96a..a6aa89e 100644
--- a/core/modules/system/src/Tests/Common/RenderTest.php
+++ b/core/modules/system/src/Tests/Common/RenderTest.php
@@ -53,14 +53,15 @@ function testDrupalRenderThemePreprocessAttached() {
   }
 
   /**
-   * Tests drupal_process_attached().
+   * Tests whether the render process allows invalid attachment types.
    */
-  public function testDrupalProcessAttached() {
+  public function testProcessAttached() {
     // Specify invalid attachments in a render array.
     $build['#attached']['library'][] = 'core/drupal.states';
     $build['#attached']['drupal_process_states'][] = [];
+    $renderer = $this->container->get('bare_html_page_renderer');
     try {
-      drupal_process_attached($build);
+      $renderer->renderBarePage($build, '', $this->container->get('theme.manager')->getActiveTheme()->getName());
       $this->fail("Invalid #attachment 'drupal_process_states' allowed");
     }
     catch (\Exception $e) {