core/includes/theme.inc                            | 60 -------------------
 core/lib/Drupal/Core/Theme/ThemeSettings.php       | 10 +++-
 core/modules/comment/comment.module                |  1 -
 core/modules/node/node.module                      |  1 -
 core/modules/shortcut/shortcut.module              |  1 -
 .../src/EventSubscriber/ThemeSettingsCacheTag.php  | 67 ++++++++++++++++++++++
 .../src/Plugin/Block/SystemBrandingBlock.php       |  3 -
 core/modules/system/system.module                  |  1 -
 core/modules/system/system.services.yml            |  5 ++
 core/modules/user/user.module                      |  1 -
 core/themes/bartik/bartik.theme                    |  1 -
 11 files changed, 80 insertions(+), 71 deletions(-)

diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index cb7581e..3dac164 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -319,63 +319,7 @@ function drupal_find_theme_templates($cache, $extension, $path) {
   return $implementations;
 }
 
-/**
- * For use in preprocess functions only; adds cache tags for theme settings.
- *
- * When a theme setting is used in a preprocess function, it is used to
- * determine whether something should be visible or not. Hence the cache tags
- * associated with that theme setting must *always* be added.
- *
- * Whenever theme_get_setting() is used in a preprocess function, this must also
- * be called, to ensure that the rendered HTML (and the render cache items that
- * contain this HTML) are tagged with the necessary cache tags.
- *
- * E.g.:
- * @code
- * theme_add_setting_cache_tag();
- * if (theme_get_setting('features.node_user_picture')) {
- *   $variables['author_picture'] = user_view($node->getOwner(), 'compact');
- * }
- * @endcode
- *
- * @see theme_get_setting()
- */
-function theme_add_setting_cache_tag() {
-  $build = [
-    '#cache' => [
-      'tags' => theme_setting_get_cache_tags(),
-    ],
-  ];
-  drupal_render($build);
-}
 
-/**
- * Returns the cache tags to be used when using a theme setting.
- *
- * If a render array depends on a theme setting, then these cache tags should be
- * associated with the render array.
- *
- * E.g.:
- * @code
- * $logo = theme_get_setting('logo');
- * $build['site_logo'] = array(
- *   '#theme' => 'image',
- *   '#uri' => $logo['url'],
- *   '#alt' => t('Home'),
- *   '#access' => $this->configuration['use_site_logo'],
- *   '#cache' => [
- *     'tags' => theme_setting_get_cache_tags(),
- *   ],
- * );
- * @endcode
- *
- * There's no efficient way to figure out if it was the global theme setting
- * or a theme-specific overriding setting, so we return cache tags for both.
- *
- * @return string[]
- *
- * @see theme_get_setting()
- */
 function theme_setting_get_cache_tags() {
   $theme = \Drupal::theme()->getActiveTheme()->getName();
   return [
@@ -400,9 +344,6 @@ function theme_setting_get_cache_tags() {
  *
  * @return
  *   The value of the requested setting, NULL if the setting does not exist.
- *
- * @see theme_setting_get_cache_tags()
- * @see theme_add_setting_cache_tag()
  */
 function theme_get_setting($setting_name, $theme = NULL) {
   /** @var \Drupal\Core\Theme\ThemeSettings[] $cache */
@@ -1501,7 +1442,6 @@ function template_preprocess_page(&$variables) {
     }
   }
 
-  theme_add_setting_cache_tag();
   $variables['base_path']         = base_path();
   $variables['front_page']        = \Drupal::url('<front>');
   $variables['language']          = $language_interface;
diff --git a/core/lib/Drupal/Core/Theme/ThemeSettings.php b/core/lib/Drupal/Core/Theme/ThemeSettings.php
index a43d3f8..ab0d081 100644
--- a/core/lib/Drupal/Core/Theme/ThemeSettings.php
+++ b/core/lib/Drupal/Core/Theme/ThemeSettings.php
@@ -17,8 +17,6 @@
  * not persisted.
  *
  * @see theme_get_setting()
- * @see theme_add_setting_cache_tag()
- * @see theme_setting_get_cache_tags()
  */
 class ThemeSettings extends ConfigBase {
 
@@ -48,4 +46,12 @@ public function __construct($theme) {
   public function getTheme() {
     return $this->theme;
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheTags() {
+    return ['rendered'];
+  }
+
 }
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index f3724a6..d9f9674 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -708,7 +708,6 @@ function template_preprocess_comment(&$variables) {
     $variables['changed'] = format_date($comment->getChangedTime());
   }
 
-  theme_add_setting_cache_tag();
   if (theme_get_setting('features.comment_user_picture')) {
     // To change user picture settings (e.g., image style), edit the 'compact'
     // view mode on the User entity.
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index 0e709a0..918e738 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -604,7 +604,6 @@ function template_preprocess_node(&$variables) {
   $variables['author_attributes'] = new Attribute();
   $variables['display_submitted'] = $node_type->displaySubmitted();
   if ($variables['display_submitted']) {
-    theme_add_setting_cache_tag();
     if (theme_get_setting('features.node_user_picture')) {
       // To change user picture settings (e.g. image style), edit the 'compact'
       // view mode on the User entity. Note that the 'compact' view mode might
diff --git a/core/modules/shortcut/shortcut.module b/core/modules/shortcut/shortcut.module
index 526f0da..ba9c43d 100644
--- a/core/modules/shortcut/shortcut.module
+++ b/core/modules/shortcut/shortcut.module
@@ -330,7 +330,6 @@ function shortcut_preprocess_page(&$variables) {
       $route_parameters = array('shortcut' => $shortcut_id);
     }
 
-    theme_add_setting_cache_tag();
     if (theme_get_setting('third_party_settings.shortcut.module_link')) {
       $variables['title_suffix']['add_or_remove_shortcut'] = array(
         '#attached' => array(
diff --git a/core/modules/system/src/EventSubscriber/ThemeSettingsCacheTag.php b/core/modules/system/src/EventSubscriber/ThemeSettingsCacheTag.php
new file mode 100644
index 0000000..bfabb2d
--- /dev/null
+++ b/core/modules/system/src/EventSubscriber/ThemeSettingsCacheTag.php
@@ -0,0 +1,67 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\EventSubscriber\ThemeSettingsCacheTag.
+ */
+
+namespace Drupal\system\EventSubscriber;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Config\ConfigCrudEvent;
+use Drupal\Core\Config\ConfigEvents;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * A subscriber invalidating the 'rendered' cache tag when saving theme settings.
+ */
+class ThemeSettingsCacheTag implements EventSubscriberInterface {
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * Constructs a configuration object.
+   *
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler
+   */
+  public function __construct(ThemeHandlerInterface $theme_handler) {
+    $this->themeHandler = $theme_handler;
+  }
+
+  /**
+   * Invalidate the 'rendered' cache tag whenever a theme setting is modified.
+   *
+   * @param \Drupal\Core\Config\ConfigCrudEvent $event
+   *   The Event to process.
+   */
+  public function onSave(ConfigCrudEvent $event) {
+    // Global theme settings.
+    if ($event->getConfig()->getName() === 'system.theme.global') {
+      Cache::invalidateTags(['rendered']);
+    }
+
+    // Theme-specific settings.
+    $matches = [];
+    if (preg_match('/(.*)\.settings$/', $event->getConfig()->getName(), $matches)) {
+      if (in_array($matches[1], array_keys($this->themeHandler->listInfo()))) {
+        Cache::invalidateTags(['rendered']);
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    $events[ConfigEvents::SAVE][] = ['onSave'];
+    return $events;
+  }
+
+}
diff --git a/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php b/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
index dfddabf..6d10aff 100644
--- a/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemBrandingBlock.php
@@ -170,9 +170,6 @@ public function build() {
       '#uri' => $logo['url'],
       '#alt' => t('Home'),
       '#access' => $this->configuration['use_site_logo'],
-      '#cache' => [
-        'tags' => theme_setting_get_cache_tags(),
-      ],
     );
 
     $build['site_name'] = array(
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 1d9b1eb..8f2a8ab 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -530,7 +530,6 @@ function system_page_attachments(array &$page) {
   }
 
   // Attach favicon.
-  theme_add_setting_cache_tag();
   if (theme_get_setting('features.favicon')) {
     $favicon = theme_get_setting('favicon.url');
     $type = theme_get_setting('favicon.mimetype');
diff --git a/core/modules/system/system.services.yml b/core/modules/system/system.services.yml
index e95c91d..97cd4b9 100644
--- a/core/modules/system/system.services.yml
+++ b/core/modules/system/system.services.yml
@@ -42,3 +42,8 @@ services:
     arguments: ['@cron', '@config.factory', '@state']
     tags:
       - { name: event_subscriber }
+  system.theme_settings_cache_tag:
+    class: Drupal\system\EventSubscriber\ThemeSettingsCacheTag
+    arguments: ['@theme_handler']
+    tags:
+      - { name: event_subscriber }
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index c23ab68..a02d098 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -535,7 +535,6 @@ function template_preprocess_username(&$variables) {
   $variables['extra'] = '';
   $variables['uid'] = $account->id();
   if (empty($variables['uid'])) {
-    theme_add_setting_cache_tag();
     if (theme_get_setting('features.comment_user_verification')) {
       $variables['extra'] = ' (' . t('not verified') . ')';
     }
diff --git a/core/themes/bartik/bartik.theme b/core/themes/bartik/bartik.theme
index 6700652..4d6ef3a 100644
--- a/core/themes/bartik/bartik.theme
+++ b/core/themes/bartik/bartik.theme
@@ -143,7 +143,6 @@ function _bartik_process_page(&$variables) {
   $site_config = \Drupal::config('system.site');
   // Always print the site name and slogan, but if they are toggled off, we'll
   // just hide them visually.
-  theme_add_setting_cache_tag();
   $variables['hide_site_name']   = theme_get_setting('features.name') ? FALSE : TRUE;
   $variables['hide_site_slogan'] = theme_get_setting('features.slogan') ? FALSE : TRUE;
   if ($variables['hide_site_name']) {