Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/lib/Drupal/Core/Theme/ActiveTheme.php

@@ -80,6 +80,13 @@ class ActiveTheme {
    */
   protected $regions;
 
+  /**
+   * The libraries or library assets overridden by the theme.
+   *
+   * @var array
+   */
+  protected $librariesOverride;
+
   /**
    * Constructs an ActiveTheme object.
    *
@@ -96,6 +103,8 @@ class ActiveTheme {
       'extension' => 'html.twig',
       'base_themes' => [],
       'regions' => [],
+      'libraries_override' => [],
+      'libraries_extend' => [],
     ];
 
     $this->name = $values['name'];
@@ -107,6 +116,8 @@ class ActiveTheme {
     $this->extension = $values['extension'];
     $this->baseThemes = $values['base_themes'];
     $this->regions = $values['regions'];
+    $this->librariesOverride = $values['libraries_override'];
+    $this->librariesExtend = $values['libraries_extend'];
   }
 
   /**
@@ -169,6 +180,8 @@ class ActiveTheme {
    * Returns the removed stylesheets by the theme.
    *
    * @return mixed
+   *
+   * @deprecated in Drupal 8.0.0, will be removed before Drupal 9.0.0.
    */
   public function getStyleSheetsRemove() {
     return $this->styleSheetsRemove;
@@ -198,4 +211,24 @@ class ActiveTheme {
     return array_keys($this->regions);
   }
 
+  /**
+   * Returns the libraries or library assets overridden by the active theme.
+   *
+   * @return array
+   *   The list of libraries overrides.
+   */
+  public function getLibrariesOverride() {
+    return $this->librariesOverride;
+  }
+
+  /**
+   * Returns the libraries extended by the active theme.
+   *
+   * @return array
+   *   The list of libraries-extend definitions.
+   */
+  public function getLibrariesExtend() {
+    return $this->librariesExtend;
+  }
+
 }

core/lib/Drupal/Core/Theme/Registry.php

@@ -472,12 +472,14 @@ class Registry implements DestructableInterface {
         // A template file is the default implementation for a theme hook, but
         // if the theme hook specifies a function callback instead, check to
         // ensure the function actually exists.
-        if (isset($info['function']) && !function_exists($info['function'])) {
-          throw new \BadFunctionCallException(sprintf(
-            'Theme hook "%s" refers to a theme function callback that does not exist: "%s"',
-            $hook,
-            $info['function']
-          ));
+        if (isset($info['function'])) {
+          if (!function_exists($info['function'])) {
+            throw new \BadFunctionCallException(sprintf(
+              'Theme hook "%s" refers to a theme function callback that does not exist: "%s"',
+              $hook,
+              $info['function']
+            ));
+          }
         }
         // Provide a default naming convention for 'template' based on the
         // hook used. If the template does not exist, the theme engine used

core/lib/Drupal/Core/Theme/ThemeInitialization.php

@@ -161,27 +161,56 @@ class ThemeInitialization implements ThemeInitializationInterface {
     $values['path'] = $theme_path;
     $values['name'] = $theme->getName();
 
-    // Prepare stylesheets from this theme as well as all ancestor themes.
-    // We work it this way so that we can have child themes remove CSS files
-    // easily from parent.
-    $values['stylesheets_remove'] = array();
+    // @todo Remove in Drupal 9.0.x.
+    $values['stylesheets_remove'] = $this->prepareStylesheetsRemove($theme, $base_themes);
 
-    // Grab stylesheets from base theme.
+    // Prepare libraries overrides from this theme and ancestor themes. This
+    // allows child themes to easily remove CSS files from base themes and
+    // modules.
+    $values['libraries_override'] = [];
+
+    // Get libraries overrides declared by base themes.
     foreach ($base_themes as $base) {
-      $base_theme_path = $base->getPath();
-      if (!empty($base->info['stylesheets-remove'])) {
-        foreach ($base->info['stylesheets-remove'] as $css_file) {
-          $css_file = $this->resolveStyleSheetPlaceholders($css_file);
-          $values['stylesheets_remove'][$css_file] = $css_file;
+      if (!empty($base->info['libraries-override'])) {
+        foreach ($base->info['libraries-override'] as $library => $override) {
+          $values['libraries_override'][$base->getPath()][$library] = $override;
         }
       }
     }
 
-    // Add stylesheets used by this theme.
-    if (!empty($theme->info['stylesheets-remove'])) {
-      foreach ($theme->info['stylesheets-remove'] as $css_file) {
-        $css_file = $this->resolveStyleSheetPlaceholders($css_file);
-        $values['stylesheets_remove'][$css_file] = $css_file;
+    // Add libraries overrides declared by this theme.
+    if (!empty($theme->info['libraries-override'])) {
+      foreach ($theme->info['libraries-override'] as $library => $override) {
+        $values['libraries_override'][$theme->getPath()][$library] = $override;
+      }
+    }
+
+    // Get libraries extensions declared by base themes.
+    foreach ($base_themes as $base) {
+      if (!empty($base->info['libraries-extend'])) {
+        foreach ($base->info['libraries-extend'] as $library => $extend) {
+          if (isset($values['libraries_extend'][$library])) {
+            // Merge if libraries-extend has already been defined for this
+            // library.
+            $values['libraries_extend'][$library] = array_merge($values['libraries_extend'][$library], $extend);
+          }
+          else {
+            $values['libraries_extend'][$library] = $extend;
+          }
+        }
+      }
+    }
+    // Add libraries extensions declared by this theme.
+    if (!empty($theme->info['libraries-extend'])) {
+      foreach ($theme->info['libraries-extend'] as $library => $extend) {
+        if (isset($values['libraries_extend'][$library])) {
+          // Merge if libraries-extend has already been defined for this
+          // library.
+          $values['libraries_extend'][$library] = array_merge($values['libraries_extend'][$library], $extend);
+        }
+        else {
+          $values['libraries_extend'][$library] = $extend;
+        }
       }
     }
 
@@ -241,6 +270,8 @@ class ThemeInitialization implements ThemeInitializationInterface {
    *
    * @return string
    *   CSS file where placeholders are replaced.
+   *
+   * @todo Remove in Drupal 9.0.x.
    */
   protected function resolveStyleSheetPlaceholders($css_file) {
     $token_candidate = explode('/', $css_file)[0];
@@ -256,4 +287,44 @@ class ThemeInitialization implements ThemeInitializationInterface {
       return str_replace($token_candidate, $extensions[$token]->getPath(), $css_file);
     }
   }
+
+  /**
+   * Prepares stylesheets-remove specified in the *.info.yml file.
+   *
+   * @param \Drupal\Core\Extension\Extension $theme
+   *   The theme extension object.
+   * @param \Drupal\Core\Extension\Extension[] $base_themes
+   *   An array of base themes.
+   *
+   * @return string[]
+   *   The list of stylesheets-remove specified in the *.info.yml file.
+   *
+   * @todo Remove in Drupal 9.0.x.
+   */
+  protected function prepareStylesheetsRemove(Extension $theme, $base_themes) {
+    // Prepare stylesheets from this theme as well as all ancestor themes.
+    // We work it this way so that we can have child themes remove CSS files
+    // easily from parent.
+    $stylesheets_remove = array();
+    // Grab stylesheets from base theme.
+    foreach ($base_themes as $base) {
+      $base_theme_path = $base->getPath();
+      if (!empty($base->info['stylesheets-remove'])) {
+        foreach ($base->info['stylesheets-remove'] as $css_file) {
+          $css_file = $this->resolveStyleSheetPlaceholders($css_file);
+          $stylesheets_remove[$css_file] = $css_file;
+        }
+      }
+    }
+
+    // Add stylesheets used by this theme.
+    if (!empty($theme->info['stylesheets-remove'])) {
+      foreach ($theme->info['stylesheets-remove'] as $css_file) {
+        $css_file = $this->resolveStyleSheetPlaceholders($css_file);
+        $stylesheets_remove[$css_file] = $css_file;
+      }
+    }
+    return $stylesheets_remove;
+  }
+
 }

core/lib/Drupal/Core/Theme/ThemeManager.php

@@ -7,8 +7,8 @@
 
 namespace Drupal\Core\Theme;
 
-use Drupal\Component\Utility\SafeStringInterface;
-use Drupal\Core\Render\SafeString;
+use Drupal\Component\Render\MarkupInterface;
+use Drupal\Core\Render\Markup;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Routing\StackedRouteMatchInterface;
 use Symfony\Component\HttpFoundation\RequestStack;
@@ -319,7 +319,7 @@ class ThemeManager implements ThemeManagerInterface {
         // Theme functions do not render via the theme engine, so the output is
         // not autoescaped. However, we can only presume that the theme function
         // has been written correctly and that the markup is safe.
-        $output = SafeString::create($info['function']($variables));
+        $output = Markup::create($info['function']($variables));
       }
     }
     else {
@@ -389,7 +389,7 @@ class ThemeManager implements ThemeManagerInterface {
       $output = $render_function($template_file, $variables);
     }
 
-    return ($output instanceof SafeStringInterface) ? $output : (string) $output;
+    return ($output instanceof MarkupInterface) ? $output : (string) $output;
   }
 
   /**

core/lib/Drupal/Core/Theme/ThemeManagerInterface.php

@@ -26,8 +26,8 @@ interface ThemeManagerInterface {
    * @param array $variables
    *   An associative array of theme variables.
    *
-   * @return string|\Drupal\Component\Utility\SafeStringInterface
-   *   The rendered output, or a SafeString object.
+   * @return string|\Drupal\Component\Render\MarkupInterface
+   *   The rendered output, or a Markup object.
    */
   public function render($hook, array $variables);