ThemeManager::render

public ThemeManager::render($hook, array $variables)

public function render($hook, array $variables) {
  static $default_attributes;

  $active_theme = $this->getActiveTheme();

  // If called before all modules are loaded, we do not necessarily have a
  // full theme registry to work with, and therefore cannot process the theme
  // request properly. See also \Drupal\Core\Theme\Registry::get().
  if (!$this->moduleHandler->isLoaded() && !defined('MAINTENANCE_MODE')) {
    throw new \Exception('The theme implementations may not be rendered until all modules are loaded.');
  }

  $theme_registry = $this->themeRegistry->getRuntime();

  // If an array of hook candidates were passed, use the first one that has an
  // implementation.
  if (is_array($hook)) {
    foreach ($hook as $candidate) {
      if ($theme_registry->has($candidate)) {
        break;
      }
    }
    $hook = $candidate;
  }
  // Save the original theme hook, so it can be supplied to theme variable
  // preprocess callbacks.
  $original_hook = $hook;

  // If there's no implementation, check for more generic fallbacks.
  // If there's still no implementation, log an error and return an empty
  // string.
  if (!$theme_registry->has($hook)) {
    // Iteratively strip everything after the last '__' delimiter, until an
    // implementation is found.
    while ($pos = strrpos($hook, '__')) {
      $hook = substr($hook, 0, $pos);
      if ($theme_registry->has($hook)) {
        break;
      }
    }
    if (!$theme_registry->has($hook)) {
      // Only log a message when not trying theme suggestions ($hook being an
      // array).
      if (!isset($candidate)) {
        \Drupal::logger('theme')->warning('Theme hook %hook not found.', array('%hook' => $hook));
      }
      // There is no theme implementation for the hook passed. Return FALSE so
      // the function calling
      // \Drupal\Core\Theme\ThemeManagerInterface::render() can differentiate
      // between a hook that exists and renders an empty string, and a hook
      // that is not implemented.
      return FALSE;
    }
  }

  $info = $theme_registry->get($hook);

  // If a renderable array is passed as $variables, then set $variables to
  // the arguments expected by the theme function.
  if (isset($variables['#theme']) || isset($variables['#theme_wrappers'])) {
    $element = $variables;
    $variables = array();
    if (isset($info['variables'])) {
      foreach (array_keys($info['variables']) as $name) {
        if (isset($element["#$name"]) || array_key_exists("#$name", $element)) {
          $variables[$name] = $element["#$name"];
        }
      }
    }
    else {
      $variables[$info['render element']] = $element;
      // Give a hint to render engines to prevent infinite recursion.
      $variables[$info['render element']]['#render_children'] = TRUE;
    }
  }

  // Merge in argument defaults.
  if (!empty($info['variables'])) {
    $variables += $info['variables'];
  }
  elseif (!empty($info['render element'])) {
    $variables += array($info['render element'] => array());
  }
  // Supply original caller info.
  $variables += array(
    'theme_hook_original' => $original_hook,
  );

  // Set base hook for later use. For example if '#theme' => 'node__article'
  // is called, we run hook_theme_suggestions_node_alter() rather than
  // hook_theme_suggestions_node__article_alter(), and also pass in the base
  // hook as the last parameter to the suggestions alter hooks.
  if (isset($info['base hook'])) {
    $base_theme_hook = $info['base hook'];
  }
  else {
    $base_theme_hook = $hook;
  }

  // Invoke hook_theme_suggestions_HOOK().
  $suggestions = $this->moduleHandler->invokeAll('theme_suggestions_' . $base_theme_hook, array($variables));
  // If the theme implementation was invoked with a direct theme suggestion
  // like '#theme' => 'node__article', add it to the suggestions array before
  // invoking suggestion alter hooks.
  if (isset($info['base hook'])) {
    $suggestions[] = $hook;
  }

  // Invoke hook_theme_suggestions_alter() and
  // hook_theme_suggestions_HOOK_alter().
  $hooks = array(
    'theme_suggestions',
    'theme_suggestions_' . $base_theme_hook,
  );
  $this->moduleHandler->alter($hooks, $suggestions, $variables, $base_theme_hook);
  $this->alter($hooks, $suggestions, $variables, $base_theme_hook);

  // Check if each suggestion exists in the theme registry, and if so,
  // use it instead of the base hook. For example, a function may use
  // '#theme' => 'node', but a module can add 'node__article' as a suggestion
  // via hook_theme_suggestions_HOOK_alter(), enabling a theme to have
  // an alternate template file for article nodes.
  foreach (array_reverse($suggestions) as $suggestion) {
    if ($theme_registry->has($suggestion)) {
      $info = $theme_registry->get($suggestion);
      break;
    }
  }

  // Include a file if the theme function or variable preprocessor is held
  // elsewhere.
  if (!empty($info['includes'])) {
    foreach ($info['includes'] as $include_file) {
      include_once $this->root . '/' . $include_file;
    }
  }

  // Invoke the variable preprocessors, if any.
  if (isset($info['base hook'])) {
    $base_hook = $info['base hook'];
    $base_hook_info = $theme_registry->get($base_hook);
    // Include files required by the base hook, since its variable
    // preprocessors might reside there.
    if (!empty($base_hook_info['includes'])) {
      foreach ($base_hook_info['includes'] as $include_file) {
        include_once $this->root . '/' . $include_file;
      }
    }
    if (isset($base_hook_info['preprocess functions'])) {
      // Set a variable for the 'theme_hook_suggestion'. This is used to
      // maintain backwards compatibility with template engines.
      $theme_hook_suggestion = $hook;
    }
  }
  if (isset($info['preprocess functions'])) {
    foreach ($info['preprocess functions'] as $preprocessor_function) {
      if (function_exists($preprocessor_function)) {
        $preprocessor_function($variables, $hook, $info);
      }
    }
    // Allow theme preprocess functions to set $variables['#attached'] and
    // $variables['#cache'] and use them like the corresponding element
    // properties on render arrays. In Drupal 8, this is the (only) officially
    // supported method of attaching bubbleable metadata from preprocess
    // functions. Assets attached here should be associated with the template
    // that we are preprocessing variables for.
    $preprocess_bubbleable = [];
    foreach (['#attached', '#cache'] as $key) {
      if (isset($variables[$key])) {
        $preprocess_bubbleable[$key] = $variables[$key];
      }
    }
    // We do not allow preprocess functions to define cacheable elements.
    unset($preprocess_bubbleable['#cache']['keys']);
    if ($preprocess_bubbleable) {
      // @todo Inject the Renderer in https://www.drupal.org/node/2529438.
      drupal_render($preprocess_bubbleable);
    }
  }

  // Generate the output using either a function or a template.
  $output = '';
  if (isset($info['function'])) {
    if (function_exists($info['function'])) {
      // 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.
      $output = Markup::create($info['function']($variables));
    }
  }
  else {
    $render_function = 'twig_render_template';
    $extension = '.html.twig';

    // The theme engine may use a different extension and a different
    // renderer.
    $theme_engine = $active_theme->getEngine();
    if (isset($theme_engine)) {
      if ($info['type'] != 'module') {
        if (function_exists($theme_engine . '_render_template')) {
          $render_function = $theme_engine . '_render_template';
        }
        $extension_function = $theme_engine . '_extension';
        if (function_exists($extension_function)) {
          $extension = $extension_function();
        }
      }
    }

    // In some cases, a template implementation may not have had
    // template_preprocess() run (for example, if the default implementation
    // is a function, but a template overrides that default implementation).
    // In these cases, a template should still be able to expect to have
    // access to the variables provided by template_preprocess(), so we add
    // them here if they don't already exist. We don't want the overhead of
    // running template_preprocess() twice, so we use the 'directory' variable
    // to determine if it has already run, which while not completely
    // intuitive, is reasonably safe, and allows us to save on the overhead of
    // adding some new variable to track that.
    if (!isset($variables['directory'])) {
      $default_template_variables = array();
      template_preprocess($default_template_variables, $hook, $info);
      $variables += $default_template_variables;
    }
    if (!isset($default_attributes)) {
      $default_attributes = new Attribute();
    }
    foreach (array('attributes', 'title_attributes', 'content_attributes') as $key) {
      if (isset($variables[$key]) && !($variables[$key] instanceof Attribute)) {
        if ($variables[$key]) {
          $variables[$key] = new Attribute($variables[$key]);
        }
        else {
          // Create empty attributes.
          $variables[$key] = clone $default_attributes;
        }
      }
    }

    // Render the output using the template file.
    $template_file = $info['template'] . $extension;
    if (isset($info['path'])) {
      $template_file = $info['path'] . '/' . $template_file;
    }
    // Add the theme suggestions to the variables array just before rendering
    // the template for backwards compatibility with template engines.
    $variables['theme_hook_suggestions'] = $suggestions;
    // For backwards compatibility, pass 'theme_hook_suggestion' on to the
    // template engine. This is only set when calling a direct suggestion like
    // '#theme' => 'menu__shortcut_default' when the template exists in the
    // current theme.
    if (isset($theme_hook_suggestion)) {
      $variables['theme_hook_suggestion'] = $theme_hook_suggestion;
    }
    $output = $render_function($template_file, $variables);
  }

  return ($output instanceof MarkupInterface) ? $output : (string) $output;
}