Issue #1829224 by alexpott, pfrenssen, vijaycs85, lirantal: Convert the...

Issue #1829224 by alexpott, pfrenssen, vijaycs85, lirantal: Convert the 'theme_default()' variable to CMI.

core/includes/ajax.inc

@@ -411,7 +411,7 @@ function ajax_base_page_theme() {
     // to see the default theme, token validation isn't required for that, and
     // bypassing it allows most use-cases to work even when accessed from the
     // page cache.
-    if ($theme === variable_get('theme_default', 'stark') || drupal_valid_token($token, $theme)) {
+    if ($theme === config('system.theme')->get('default') || drupal_valid_token($token, $theme)) {
       return $theme;
     }
   }

core/includes/theme.inc

@@ -90,7 +90,7 @@ function drupal_theme_initialize() {
 
   // Only select the user selected theme if it is available in the
   // list of themes that can be accessed.
-  $theme = !empty($user->theme) && drupal_theme_access($user->theme) ? $user->theme : variable_get('theme_default', 'stark');
+  $theme = !empty($user->theme) && drupal_theme_access($user->theme) ? $user->theme : config('system.theme')->get('default');
 
   // Allow modules to override the theme. Validation has already been performed
   // inside menu_get_custom_theme(), so we do not need to check it again here.
@@ -1530,7 +1530,7 @@ function theme_enable($theme_list) {
  */
 function theme_disable($theme_list) {
   // Don't disable the default theme.
-  if ($pos = array_search(variable_get('theme_default', 'stark'), $theme_list) !== FALSE) {
+  if ($pos = array_search(config('system.theme')->get('default'), $theme_list) !== FALSE) {
     unset($theme_list[$pos]);
     if (empty($theme_list)) {
       return;

core/includes/theme.maintenance.inc

@@ -50,7 +50,7 @@ function _drupal_maintenance_theme() {
     //   Stark otherwise. Since there is no low-level access to configuration
     //   currently, we only consult settings.php and fall back to Bartik
     //   otherwise, as it looks generic enough and way more user-friendly.
-    $custom_theme = variable_get('maintenance_theme', variable_get('theme_default', 'bartik'));
+    $custom_theme = variable_get('maintenance_theme', config('system.theme')->get('default')) ?: 'bartik';
   }
 
   // Ensure that system.module is loaded.

core/modules/block/block.admin.inc

@@ -70,7 +70,7 @@ function block_admin_edit(Block $entity) {
   $theme = $themes[$theme_key];
   // Use meaningful titles for the main site and administrative themes.
   $theme_title = $theme->info['name'];
-  if ($theme_key == variable_get('theme_default', 'stark')) {
+  if ($theme_key == config('system.theme')->get('default')) {
     $theme_title = t('!theme (default theme)', array('!theme' => $theme_title));
   }
   elseif ($admin_theme && $theme_key == $admin_theme) {

core/modules/block/block.module

@@ -59,7 +59,7 @@ function block_help($path, $arg) {
       $output .= '<dd>' . t('Blocks can be configured to be visible only on certain pages, only to users of certain roles, or only on pages displaying certain <a href="@content-type">content types</a>. Some dynamic blocks, such as those generated by modules, will be displayed only on certain pages.', array('@content-type' => url('admin/structure/types'), '@user' => url('user'))) . '</dd>';
       if (module_exists('custom_block')) {
         $output .= '<dt>' . t('Creating custom blocks') . '</dt>';
-        $output .= '<dd>' . t('Users with the <em>Administer blocks</em> permission can <a href="@block-add">add custom blocks</a>, which are then listed on the <a href="@blocks">Blocks administration page</a>. Once created, custom blocks behave just like default and module-generated blocks.', array('@blocks' => url('admin/structure/block'), '@block-add' => url('admin/structure/block/list/block_plugin_ui:' . variable_get('theme_default', 'stark') . '/add/custom_blocks'))) . '</dd>';
+        $output .= '<dd>' . t('Users with the <em>Administer blocks</em> permission can <a href="@block-add">add custom blocks</a>, which are then listed on the <a href="@blocks">Blocks administration page</a>. Once created, custom blocks behave just like default and module-generated blocks.', array('@blocks' => url('admin/structure/block'), '@block-add' => url('admin/structure/block/list/block_plugin_ui:' . config('system.theme')->get('default') . '/add/custom_blocks'))) . '</dd>';
       }
       $output .= '</dl>';
       return $output;
@@ -69,7 +69,7 @@ function block_help($path, $arg) {
       list(, $demo_theme) = explode(':', $arg[4]);
     }
     else {
-      $demo_theme = variable_get('theme_default', 'stark');
+      $demo_theme = config('system.theme')->get('default');
     }
     $themes = list_themes();
     $output = '<p>' . t('This page provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions. Since not all themes implement the same regions, or display regions in the same way, blocks are positioned on a per-theme basis. Remember that your changes will not be saved until you click the <em>Save blocks</em> button at the bottom of the page. Click the <em>configure</em> link next to each block to configure its specific title and visibility settings.') . '</p>';
@@ -112,7 +112,7 @@ function block_permission() {
  * @todo Clarify the documentation for the per-plugin block admin links.
  */
 function block_menu() {
-  $default_theme = variable_get('theme_default', 'stark');
+  $default_theme = config('system.theme')->get('default');
   $items['admin/structure/block'] = array(
     'title' => 'Blocks',
     'description' => 'Configure what block content appears in your site\'s sidebars and other regions.',
@@ -267,7 +267,7 @@ function block_page_build(&$page) {
       $page['page_top']['backlink'] = array(
         '#type' => 'link',
         '#title' => t('Exit block region demonstration'),
-        '#href' => 'admin/structure/block' . (variable_get('theme_default', 'stark') == $theme ? '' : '/list/' . $theme),
+        '#href' => 'admin/structure/block' . (config('system.theme')->get('default') == $theme ? '' : '/list/' . $theme),
         // Add the "overlay-restore" class to indicate this link should restore
         // the context in which the region demonstration page was opened.
         '#options' => array('attributes' => array('class' => array('block-demo-backlink', 'overlay-restore'))),
@@ -363,7 +363,7 @@ function _block_get_renderable_region($list = array()) {
  *   Blocks currently exported by modules.
  */
 function _block_rehash($theme = NULL) {
-  $theme = $theme ? $theme : variable_get('theme_default', 'stark');
+  $theme = $theme ? $theme : config('system.theme')->get('default');
   $regions = system_region_list($theme);
   $blocks = entity_load_multiple_by_properties('block', array('theme' => $theme));
   foreach ($blocks as $block_id => $block) {
@@ -412,7 +412,7 @@ function block_theme_initialize($theme) {
   // Initialize theme's blocks if none already registered.
   $has_blocks = entity_load_multiple_by_properties('block', array('theme' => $theme));
   if (!$has_blocks) {
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     // Apply only to new theme's visible regions.
     $regions = system_region_list($theme, REGIONS_VISIBLE);
     $default_theme_blocks = entity_load_multiple_by_properties('block', array('theme' => $default_theme));

core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockFormController.php

@@ -182,7 +182,7 @@ public function save(array $form, array &$form_state) {
           $form_state['redirect'] = 'admin/structure/block/add/custom_block:' . $block->uuid->value . '/' . $theme;
         }
         else {
-          $form_state['redirect'] = 'admin/structure/block/add/custom_block:' . $block->uuid->value . '/' . variable_get('theme_default', 'stark');
+          $form_state['redirect'] = 'admin/structure/block/add/custom_block:' . $block->uuid->value . '/' . config('system.theme')->get('default');
         }
       }
       else {

core/modules/block/lib/Drupal/block/Tests/BlockHiddenRegionTest.php

@@ -61,7 +61,9 @@ public function testBlockNotInHiddenRegion() {
     // Enable "block_test_theme" and set it as the default theme.
     $theme = 'block_test_theme';
     theme_enable(array($theme));
-    variable_set('theme_default', $theme);
+    config('system.theme')
+      ->set('default', $theme)
+      ->save();
     menu_router_rebuild();
 
     // Ensure that "block_test_theme" is set as the default theme.

core/modules/block/lib/Drupal/block/Tests/BlockLanguageTest.php

@@ -54,7 +54,7 @@ function setUp() {
    */
   public function testLanguageBlockVisibility() {
     // Check if the visibility setting is available.
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     $this->drupalGet('admin/structure/block/add/system_powered_by_block' . '/' . $default_theme);
 
     $this->assertField('visibility[language][langcodes][en]', 'Language visibility field is visible.');

core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php

@@ -40,7 +40,7 @@ function testBlockThemeHookSuggestions() {
     $block = entity_create('block', array(
       'plugin' => 'system_menu_block:menu-admin',
       'region' => 'footer',
-      'id' => variable_get('theme_default', 'stark') . '.machinename',
+      'id' => config('system.theme')->get('default') . '.machinename',
     ));
 
     $variables = array();

core/modules/block/lib/Drupal/block/Tests/BlockTest.php

@@ -65,7 +65,7 @@ function setUp() {
    * Test creating custom block, moving it to a specific region and then deleting it.
    */
   public function testCustomBlock() {
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
 
     // Clear the block cache to load the Custom Block module's block definitions.
     $this->container->get('plugin.manager.block')->clearCachedDefinitions();
@@ -150,7 +150,7 @@ public function testCustomBlock() {
    * Test creating custom block using Full HTML.
    */
   public function testCustomBlockFormat() {
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
 
     // Add a new custom block by filling out the input form on block/add/basic.
     $info = strtolower($this->randomName(8));
@@ -200,7 +200,7 @@ function testBlockVisibility() {
     // Create a random title for the block.
     $title = $this->randomName(8);
     // Enable a standard block.
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     $edit = array(
       'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
@@ -240,7 +240,7 @@ function testBlockVisibilityListedEmpty() {
     // Create a random title for the block.
     $title = $this->randomName(8);
     // Enable a standard block.
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     $edit = array(
       'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
@@ -273,7 +273,7 @@ function testBlock() {
     $block['id'] = 'system_powered_by_block';
     $block['label'] = $this->randomName(8);
     $block['machine_name'] = strtolower($this->randomName(8));
-    $block['theme'] = variable_get('theme_default', 'stark');
+    $block['theme'] = config('system.theme')->get('default');
     $block['region'] = 'header';
 
     // Set block title to confirm that interface works and override any custom titles.
@@ -320,7 +320,7 @@ function testBlock() {
    */
   function moveBlockToRegion(array $block, $region) {
     // Set the created block to a specific region.
-    $block += array('theme' => variable_get('theme_default', 'stark'));
+    $block += array('theme' => config('system.theme')->get('default'));
     $edit = array();
     $edit['blocks[' . $block['theme'] . '.' . $block['machine_name'] . '][region]'] = $region;
     $this->drupalPost('admin/structure/block', $edit, t('Save blocks'));
@@ -354,7 +354,7 @@ function testBlockRehash() {
     $block = array();
     $block['id'] = 'test_cache';
     $block['machine_name'] = strtolower($this->randomName(8));
-    $block['theme'] = variable_get('theme_default', 'stark');
+    $block['theme'] = config('system.theme')->get('default');
     $block['region'] = 'header';
     $block = $this->drupalPlaceBlock('test_cache', array('region' => 'header'));
 
@@ -413,7 +413,7 @@ function testBlockModuleDisable() {
     }
 
     // Ensure that the disabled module's block plugin is no longer available.
-    $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . variable_get('theme_default', 'stark') . '/add');
+    $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . config('system.theme')->get('default') . '/add');
     $this->assertNoText(t('Test block caching'));
 
     // Confirm that the block is no longer displayed on the front page.

core/modules/block/lib/Drupal/block/Tests/BlockTitleXSSTest.php

@@ -47,7 +47,7 @@ function testXSSInTitle() {
     $this->assertNoRaw('<script>alert("XSS label");</script>', 'The block title was properly sanitized when rendered.');
 
     $this->drupalLogin($this->drupalCreateUser(array('administer blocks', 'access administration pages')));
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . $default_theme . '/add');
     $this->assertNoRaw("<script>alert('XSS subject');</script>", 'The block title was properly sanitized in Block Plugin UI Admin page.');
   }

core/modules/block/lib/Drupal/block/Tests/NewDefaultThemeBlocksTest.php

@@ -33,7 +33,7 @@ public static function getInfo() {
    * Check the enabled Bartik blocks are correctly copied over.
    */
   function testNewDefaultThemeBlocks() {
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
 
     // Add several block instances.
     $this->adminUser = $this->drupalCreateUser(array('administer blocks'));
@@ -51,7 +51,9 @@ function testNewDefaultThemeBlocks() {
     $new_theme = 'bartik';
     $this->assertFalse($new_theme == $default_theme, 'The new theme is different from the previous default theme.');
     theme_enable(array($new_theme));
-    variable_set('theme_default', $new_theme);
+    config('system.theme')
+      ->set('default', $new_theme)
+      ->save();
 
     // Ensure that the new theme has all the blocks as the previous default.
     // @todo Replace the string manipulation below once the configuration

core/modules/block/lib/Drupal/block/Tests/Views/DisplayBlockTest.php

@@ -142,7 +142,7 @@ protected function testDeleteBlockDisplay() {
    */
   public function testViewsBlockForm() {
     $this->drupalLogin($this->drupalCreateUser(array('administer blocks')));
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
     $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
     $elements = $this->xpath('//input[@name="label"]');
     $this->assertTrue(empty($elements), 'The label field is not found for Views blocks.');

core/modules/ckeditor/ckeditor.module

@@ -97,7 +97,7 @@ function ckeditor_theme() {
 function _ckeditor_theme_css($theme = NULL) {
   $css = array();
   if (!isset($theme)) {
-    $theme = variable_get('theme_default');
+    $theme = config('system.theme')->get('default');
   }
   if ($theme_path = drupal_get_path('theme', $theme)) {
     $info = system_get_info('theme', $theme);

core/modules/color/lib/Drupal/color/Tests/ColorTest.php

@@ -76,7 +76,9 @@ function testColor() {
    * Tests the Color module functionality using the given theme.
    */
   function _testColor($theme, $test_values) {
-    variable_set('theme_default', $theme);
+    config('system.theme')
+      ->set('default', $theme)
+      ->save();
     $settings_path = 'admin/appearance/settings/' . $theme;
 
     $this->drupalLogin($this->big_user);
@@ -122,7 +124,9 @@ function _testColor($theme, $test_values) {
    * Tests whether the provided color is valid.
    */
   function testValidColor() {
-    variable_set('theme_default', 'bartik');
+    config('system.theme')
+      ->set('default', 'bartik')
+      ->save();
     $settings_path = 'admin/appearance/settings/bartik';
 
     $this->drupalLogin($this->big_user);

core/modules/comment/lib/Drupal/comment/Tests/CommentLinksTest.php

@@ -35,7 +35,9 @@ public static function getInfo() {
   function testCommentLinks() {
     // Bartik theme alters comment links, so use a different theme.
     theme_enable(array('stark'));
-    variable_set('theme_default', 'stark');
+    config('system.theme')
+      ->set('default', 'stark')
+      ->save();
 
     // Remove additional user permissions from $this->web_user added by setUp(),
     // since this test is limited to anonymous and authenticated roles only.

core/modules/menu/lib/Drupal/menu/Tests/MenuTest.php

@@ -157,7 +157,7 @@ function addCustomMenu() {
     // Enable the custom menu block.
     $menu_name = 'menu-' . $menu_name; // Drupal prepends the name with 'menu-'.
     // Confirm that the custom menu block is available.
-    $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . variable_get('theme_default', 'stark') . '/add');
+    $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . config('system.theme')->get('default') . '/add');
     $this->assertText($label);
 
     // Enable the block.

core/modules/php/php.module

@@ -61,16 +61,16 @@ function php_permission() {
  * @see php_filter_info()
  */
 function php_eval($code) {
-  global $theme_path, $theme_info, $conf;
+  global $theme_path, $theme_info;
 
   // Store current theme path.
   $old_theme_path = $theme_path;
 
   // Restore theme_path to the theme, as long as php_eval() executes,
   // so code evaluated will not see the caller module as the current theme.
-  // If theme info is not initialized get the path from theme_default.
+  // If theme info is not initialized get the path from default theme.
   if (!isset($theme_info)) {
-    $theme_path = drupal_get_path('theme', $conf['theme_default']);
+    $theme_path = drupal_get_path('theme', config('system.theme')->get('default'));
   }
   else {
     $theme_path = dirname($theme_info->filename);

core/modules/shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php

@@ -136,7 +136,9 @@ function testShortcutLinkDelete() {
    */
   function testNoShortcutLink() {
     // Change to a theme that displays shortcuts.
-    variable_set('theme_default', 'seven');
+    config('system.theme')
+      ->set('default', 'seven')
+      ->save();
 
     $this->drupalGet('page-that-does-not-exist');
     $this->assertNoRaw('add-shortcut', 'Add to shortcuts link was not shown on a page not found.');

core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php

@@ -119,6 +119,8 @@ protected function setUp() {
     $modules = array_reverse($modules);
     $modules = call_user_func_array('array_merge_recursive', $modules);
     $this->enableModules($modules, FALSE);
+    // In order to use theme functions default theme config needs to exist.
+    config('system.theme')->set('default', 'stark');
   }
 
   protected function tearDown() {

core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php

@@ -376,7 +376,7 @@ protected function drupalPlaceBlock($plugin_id, array $values = array(), array $
       'plugin' => $plugin_id,
       'label' => $this->randomName(8),
       'region' => 'sidebar_first',
-      'theme' => variable_get('theme_default', 'stark'),
+      'theme' => config('system.theme')->get('default'),
       'machine_name' => strtolower($this->randomName(8)),
       'settings' => $settings,
     );

core/modules/system/config/system.theme.yml

 admin: '0'
 enabled:
   stark: '0'
+default: stark

core/modules/system/lib/Drupal/system/Tests/Ajax/FrameworkTest.php

@@ -157,7 +157,9 @@ function testLazyLoadOverriddenCSS() {
     // The test theme overrides system.base.css without an implementation,
     // thereby removing it.
     theme_enable(array('test_theme'));
-    variable_set('theme_default', 'test_theme');
+    config('system.theme')
+      ->set('default', 'test_theme')
+      ->save();
 
     // This gets the form, and emulates an Ajax submission on it, including
     // adding markup to the HEAD and BODY for any lazy loaded JS/CSS files.

core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php

@@ -35,7 +35,9 @@ public static function getInfo() {
   function testBatchProgressPageTheme() {
     // Make sure that the page which starts the batch (an administrative page)
     // is using a different theme than would normally be used by the batch API.
-    variable_set('theme_default', 'bartik');
+    config('system.theme')
+      ->set('default', 'bartik')
+      ->save();
     theme_enable(array('seven'));
     config('system.theme')->set('admin', 'seven')->save();
     // Log in as an administrator who can see the administrative theme.

core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php

@@ -60,8 +60,10 @@ function setUp() {
     $this->admin_theme = 'seven';
     $this->alternate_theme = 'stark';
     theme_enable(array($this->default_theme));
-    variable_set('theme_default', $this->default_theme);
-    config('system.theme')->set('admin', $this->admin_theme)->save();
+    config('system.theme')
+      ->set('default', $this->default_theme)
+      ->set('admin', $this->admin_theme)
+      ->save();
     theme_disable(array($this->alternate_theme));
     $this->drupalPlaceBlock('system_menu_block:menu-tools');
   }

core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php

@@ -205,7 +205,9 @@ function testAdministrationTheme() {
     $this->assertRaw('core/themes/stark', 'Site default theme used on the add content page.');
 
     // Reset to the default theme settings.
-    variable_set('theme_default', 'bartik');
+    config('system.theme')
+      ->set('default', 'bartik')
+      ->save();
     $edit = array(
       'admin_theme' => '0',
       'node_admin_theme' => FALSE,
@@ -227,7 +229,7 @@ function testSwitchDefaultTheme() {
     theme_enable(array('bartik'));
     $this->drupalGet('admin/appearance');
     $this->clickLink(t('Set default'));
-    $this->assertEqual(variable_get('theme_default', ''), 'bartik');
+    $this->assertEqual(config('system.theme')->get('default'), 'bartik');
 
     // Test the default theme on the secondary links (blocks admin page).
     $this->drupalGet('admin/structure/block');

core/modules/system/lib/Drupal/system/Tests/Theme/EntityFilteringThemeTest.php

@@ -130,7 +130,9 @@ function testThemedEntity() {
 
     // Check each path in all available themes.
     foreach ($this->themes as $theme) {
-      variable_set('theme_default', $theme);
+      config('system.theme')
+        ->set('default', $theme)
+        ->save();
       foreach ($paths as $path) {
         $this->drupalGet($path);
         $this->assertResponse(200);

core/modules/system/lib/Drupal/system/Tests/Theme/ThemeInfoStylesTest.php

@@ -34,7 +34,9 @@ public static function getInfo() {
    */
   function testStylesheets() {
     theme_enable(array('test_basetheme', 'test_subtheme'));
-    variable_set('theme_default', 'test_subtheme');
+    config('system.theme')
+      ->set('default', 'test_subtheme')
+      ->save();
 
     $base = drupal_get_path('theme', 'test_basetheme');
     // Unlike test_basetheme (and the original module CSS), the subtheme decides

core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTest.php

@@ -132,7 +132,9 @@ function testCSSOverride() {
    * Ensures a themes template is overrideable based on the 'template' filename.
    */
   function testTemplateOverride() {
-    variable_set('theme_default', 'test_theme');
+    config('system.theme')
+      ->set('default', 'test_theme')
+      ->save();
     $this->drupalGet('theme-test/template-test');
     $this->assertText('Success: Template overridden.', 'Template overridden by defined \'template\' filename.');
   }

core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php

@@ -38,7 +38,9 @@ function setUp() {
    * Ensures a themes template is overrideable based on the 'template' filename.
    */
   function testTemplateOverride() {
-    variable_set('theme_default', 'test_theme_twig');
+    config('system.theme')
+      ->set('default', 'test_theme_twig')
+      ->save();
     $this->drupalGet('theme-test/template-test');
     $this->assertText('Success: Template overridden.', t('Template overridden by defined \'template\' filename.'));
   }

core/modules/system/lib/Drupal/system/Tests/Theme/TwigDebugMarkupTest.php

@@ -35,7 +35,7 @@ public static function getInfo() {
   function testTwigDebugMarkup() {
     $extension = twig_extension();
     theme_enable(array('test_theme_twig'));
-    variable_set('theme_default', 'test_theme_twig');
+    config('system.theme')->set('default', 'test_theme_twig')->save();
     // Enable debug, rebuild the service container, and clear all caches.
     $this->settingsSet('twig_debug', TRUE);
     $this->rebuildContainer();

core/modules/system/lib/Drupal/system/Tests/Upgrade/BlockUpgradePathTest.php

@@ -46,7 +46,7 @@ public function testBlockUpgradeTitleLength() {
       'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
     );
-    $this->drupalPost('admin/structure/block/add/system_powered_by_block/' . variable_get('theme_default', 'stark'), $settings, t('Save block'));
+    $this->drupalPost('admin/structure/block/add/system_powered_by_block/' . config('system.theme')->get('default'), $settings, t('Save block'));
     $this->assertText($settings['label'], 'Block with title longer than 64 characters successfully created.');
 
     // Try to add a block with a title over 255 characters.
@@ -55,7 +55,7 @@ public function testBlockUpgradeTitleLength() {
       'machine_name' => strtolower($this->randomName(8)),
       'region' => 'sidebar_first',
     );
-    $this->drupalPost('admin/structure/block/add/system_powered_by_block/' . variable_get('theme_default', 'stark'), $settings, t('Save block'));
+    $this->drupalPost('admin/structure/block/add/system_powered_by_block/' . config('system.theme')->get('default'), $settings, t('Save block'));
 
     // Confirm that the custom block cannot be created with title longer than
     // the maximum number of characters.

core/modules/system/system.admin.inc

@@ -124,7 +124,7 @@ function system_themes_page() {
   $themes = system_rebuild_theme_data();
   uasort($themes, 'system_sort_modules_by_info_name');
 
-  $theme_default = variable_get('theme_default', 'stark');
+  $theme_default = config('system.theme')->get('default');
   $theme_groups  = array();
   $admin_theme = config('system.theme')->get('admin');
 
@@ -315,7 +315,7 @@ function system_theme_disable() {
     // Check if the specified theme is one recognized by the system.
     if (!empty($themes[$theme])) {
       // Do not disable the default or admin theme.
-      if ($theme == variable_get('theme_default', 'stark') || $theme == config('system.theme')->get('admin')) {
+      if ($theme === config('system.theme')->get('default') || $theme === config('system.theme')->get('admin')) {
         drupal_set_message(t('%theme is the default theme and cannot be disabled.', array('%theme' => $themes[$theme]->info['name'])), 'error');
       }
       else {
@@ -347,7 +347,9 @@ function system_theme_default() {
        theme_enable(array($theme));
       }
       // Set the default theme.
-      variable_set('theme_default', $theme);
+      config('system.theme')
+        ->set('default', $theme)
+        ->save();
 
       // Rebuild the menu. This duplicates the menu_router_rebuild() in
       // theme_enable(). However, modules must know the current default theme in

core/modules/system/system.install

@@ -521,10 +521,12 @@ function system_requirements($phase) {
  * Implements hook_install().
  */
 function system_install() {
-  // Enable the default theme. Can't use theme_enable() this early in
+  // Enable and set the default theme. Can't use theme_enable() this early in
   // installation.
-  variable_set('theme_default', 'stark');
   config_install_default_config('theme', 'stark');
+  config('system.theme')
+    ->set('default', 'stark')
+    ->save();
 
   // Populate the cron key state variable.
   $cron_key = drupal_hash_base64(drupal_random_bytes(55));
@@ -1972,7 +1974,8 @@ function system_update_8040() {
  */
 function system_update_8041() {
   update_variables_to_config('system.theme', array(
-    'admin_theme' => 'admin'
+    'admin_theme' => 'admin',
+    'theme_default' => 'default'
   ));
 }
 

core/modules/system/tests/modules/design_test/design_test.module

@@ -98,7 +98,7 @@ function design_test_menu_local_tasks_alter(&$data, $router_item, $root_path) {
     $actions = &$data['actions']['output'];
     // Determine the currently selected theme, if any.
     $selected_theme = drupal_container()->get('request')->query->get('theme');
-    $default_theme = variable_get('theme_default', 'stark');
+    $default_theme = config('system.theme')->get('default');
 
     // Expand all enabled themes into action links.
     $themes = list_themes();

core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php

@@ -25,7 +25,9 @@ function setUp() {