Half Pipe WIP

half-pipe.php

<?php

// ...

    if (!empty($half_pipe_placeholders)) {
      $extra_attachments = $this->doHalfPipe($page_parts[0], $half_pipe_placeholders);
      // Print the extra attachments.
      if (!empty($extra_attachments['library']) || !empty($extra_attachments['drupalSettings'])) {
        $all_attachments = BubbleableMetadata::mergeAttachments($attachments, $extra_attachments);

        // Update the extra libraries using the Response's ajax page state.
        // In the ideal case this will be empty and all libraries have been
        // to the bottom js section already.
        $variables_extra = $this->htmlResponseAttachmentsProcessor->processAssetLibraries($extra_attachments, [ 'scripts' => 'TRUE', 'styles' => TRUE ], $this->ajaxPageState);
        if (!empty($variables_extra['styles'])) {
          print $this->renderer->renderRoot($variables_extra['styles']);
        }
        if (!empty($variables_extra['styles'])) {
          print $this->renderer->renderRoot($variables_extra['scripts']);
        }

        // Update the bottom attachments with no ajax page state.
        $variables = $this->htmlResponseAttachmentsProcessor->processAssetLibraries($all_attachments, [ 'scripts_bottom' => TRUE ]);
        $scripts_bottom = $this->renderer->renderRoot($variables['scripts_bottom']);
      }
    }