core/core.services.yml                             |  1 +
 core/lib/Drupal/Core/Template/TwigExtension.php    | 41 ++++++++++++++++++++++
 .../twig_extension_test.services.yml               |  1 +
 .../Tests/Core/Template/TwigExtensionTest.php      |  3 +-
 core/themes/bartik/bartik.libraries.yml            |  7 +++-
 .../bartik/templates/status-messages.html.twig     |  1 +
 6 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/core/core.services.yml b/core/core.services.yml
index ca74a8c..48a3991 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1212,6 +1212,7 @@ services:
       - { name: service_collector, tag: 'twig.extension', call: addExtension }
   twig.extension:
     class: Drupal\Core\Template\TwigExtension
+    arguments: ['@renderer']
     tags:
       - { name: twig.extension, priority: 100 }
     calls:
diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 551e3cb..625aa0e 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -12,6 +12,7 @@
 
 namespace Drupal\Core\Template;
 
+use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\Core\Url;
 use Drupal\Core\Utility\LinkGeneratorInterface;
@@ -40,10 +41,29 @@ class TwigExtension extends \Twig_Extension {
   protected $linkGenerator;
 
   /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
    * Constructs \Drupal\Core\Template\TwigExtension.
    *
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer.
+   */
+  public function __construct(RendererInterface $renderer) {
+    $this->renderer = $renderer;
+  }
+
+  /**
+   * Sets the URL generator.
+   *
    * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
    *   The URL generator.
+   *
+   * @return $this
    */
   public function setGenerators(UrlGeneratorInterface $url_generator) {
     $this->urlGenerator = $url_generator;
@@ -77,6 +97,7 @@ public function getFunctions() {
       new \Twig_SimpleFunction('url_from_path', array($this, 'getUrlFromPath'), array('is_safe_callback' => array($this, 'isUrlGenerationSafe'))),
       new \Twig_SimpleFunction('link', array($this, 'getLink')),
       new \Twig_SimpleFunction('file_url', 'file_create_url'),
+      new \Twig_SimpleFunction('attach_library', array($this, 'attachLibrary'))
     );
   }
 
@@ -257,4 +278,24 @@ public function isUrlGenerationSafe(\Twig_Node $args_node) {
     return array();
   }
 
+  /**
+   * Attaches an asset library to the template, and hence to the response.
+   *
+   * Allows Twig templates to attach asset libraries using
+   * @code
+   * {{ attach_library('extension/library_name') }}
+   * @endcode
+   *
+   * This makes for a much better TX.
+   *
+   * @param string $library
+   *   An asset library.
+   */
+  public function attachLibrary($library) {
+    // Use Renderer::render() on a temporary render array to get additional
+    // bubbleable metadata on the render stack.
+    $template_attached = ['#attached' => ['library' => [$library]]];
+    $this->renderer->render($template_attached);
+  }
+
 }
diff --git a/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.services.yml b/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.services.yml
index 8784c0f..491d1e8 100644
--- a/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.services.yml
+++ b/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.services.yml
@@ -1,5 +1,6 @@
 services:
   twig_extension_test.twig.test_extension:
+    arguments: ['@renderer']
     class: Drupal\twig_extension_test\TwigExtension\TestExtension
     tags:
       - { name: twig.extension }
diff --git a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
index 31352a6..3866965 100644
--- a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -25,13 +25,14 @@ class TwigExtensionTest extends UnitTestCase {
    * @dataProvider providerTestEscaping
    */
   public function testEscaping($template, $expected) {
+    $renderer = $this->getMock('\Drupal\Core\Render\RendererInterface');
     $twig = new \Twig_Environment(NULL, array(
       'debug' => TRUE,
       'cache' => FALSE,
       'autoescape' => TRUE,
       'optimizations' => 0
     ));
-    $twig->addExtension((new TwigExtension())->setGenerators($this->getMock('Drupal\Core\Routing\UrlGeneratorInterface')));
+    $twig->addExtension((new TwigExtension($renderer))->setGenerators($this->getMock('Drupal\Core\Routing\UrlGeneratorInterface')));
 
     $nodes = $twig->parse($twig->tokenize($template));
 
diff --git a/core/themes/bartik/bartik.libraries.yml b/core/themes/bartik/bartik.libraries.yml
index 23ba491..f796093 100644
--- a/core/themes/bartik/bartik.libraries.yml
+++ b/core/themes/bartik/bartik.libraries.yml
@@ -22,7 +22,6 @@ global-styling:
       css/components/region-help.css: {}
       css/components/item-list.css: {}
       css/components/list-group.css: {}
-      css/components/messages.css: {}
       css/components/node-preview.css: {}
       css/components/pager.css: {}
       css/components/panel.css: {}
@@ -46,6 +45,12 @@ global-styling:
       css/colors.css: {}
       css/print.css: { media: print }
 
+messages:
+  version: VERSION
+  css:
+    theme:
+      css/components/messages.css: {}
+
 color.preview:
   version: VERSION
   css:
diff --git a/core/themes/bartik/templates/status-messages.html.twig b/core/themes/bartik/templates/status-messages.html.twig
index a3b5d49..96188d3 100644
--- a/core/themes/bartik/templates/status-messages.html.twig
+++ b/core/themes/bartik/templates/status-messages.html.twig
@@ -24,6 +24,7 @@
 #}
 {% block messages %}
   {% if message_list is not empty %}
+    {{ attach_library('bartik/messages') }}
     <div id="messages">
       <div class="section clearfix">
         {{ parent() }}