drupal/core/themes/engines/twig/twig.engine

<?php

/**
 * @file
 * Handles integration of Twig templates with the Drupal theme system.
 */

use Drupal\Component\Utility\Html;
use Drupal\Core\Render\Markup;
use Twig\Error\RuntimeError;

/**
 * Implements hook_theme().
 */
function twig_theme($existing, $type, $theme, $path) {
  return drupal_find_theme_templates($existing, '.html.twig', $path);
}

/**
 * Implements hook_extension().
 */
function twig_extension() {
  return '.html.twig';
}

/**
 * Implements hook_render_template().
 */
function twig_render_template($template_file, array $variables) {
  /** @var \Twig\Environment $twig_service */
  $twig_service = \Drupal::service('twig');
  $output = [
    'debug_prefix' => '',
    'debug_info' => '',
    'rendered_markup' => '',
    'debug_suffix' => '',
  ];
  try {
    $output['rendered_markup'] = $twig_service->load($template_file)->render($variables);
  }
  catch (RuntimeError $e) {
    // In case there is a previous exception, re-throw the previous exception,
    // so that the original exception is shown, rather than
    // \Twig\Template::displayWithErrorHandling()'s exception.
    $previous_exception = $e->getPrevious();
    if ($previous_exception) {
      throw $previous_exception;
    }
    throw $e;
  }
  if ($twig_service->isDebug()) {
    $output['debug_prefix'] .= "\n\n<!-- THEME DEBUG -->";
    $output['debug_prefix'] .= "\n<!-- THEME HOOK: '" . Html::escape($variables['theme_hook_original']) . "' -->";
    // If there are theme suggestions, reverse the array so more specific
    // suggestions are shown first.
    if (!empty($variables['theme_hook_suggestions'])) {
      $variables['theme_hook_suggestions'] = array_reverse($variables['theme_hook_suggestions']);
    }
    // Add debug output for directly called suggestions like
    // '#theme' => 'comment__node__article'.
    if (str_contains($variables['theme_hook_original'], '__')) {
      $derived_suggestions[] = $hook = $variables['theme_hook_original'];
      while ($pos = strrpos($hook, '__')) {
        $hook = substr($hook, 0, $pos);
        $derived_suggestions[] = $hook;
      }
      // Get the value of the base hook (last derived suggestion) and append it
      // to the end of all theme suggestions.
      $base_hook = array_pop($derived_suggestions);
      $variables['theme_hook_suggestions'] = array_merge($derived_suggestions, $variables['theme_hook_suggestions']);
      $variables['theme_hook_suggestions'][] = $base_hook;
    }
    if (!empty($variables['theme_hook_suggestions'])) {
      $extension = twig_extension();
      $current_template = basename($template_file);
      $suggestions = $variables['theme_hook_suggestions'];
      // Only add the original theme hook if it wasn't a directly called
      // suggestion.
      if (!str_contains($variables['theme_hook_original'], '__')) {
        $suggestions[] = $variables['theme_hook_original'];
      }
      $invalid_suggestions = [];
      $base_hook = $base_hook ?? $variables['theme_hook_original'];
      foreach ($suggestions as $key => &$suggestion) {
        // Valid suggestions are $base_hook, $base_hook__*, and contain no hyphens.
        if (($suggestion !== $base_hook && !str_starts_with($suggestion, $base_hook . '__')) || str_contains($suggestion, '-')) {
          $invalid_suggestions[] = $suggestion;
          unset($suggestions[$key]);
          continue;
        }
        $template = strtr($suggestion, '_', '-') . $extension;
        $prefix = ($template == $current_template) ? '✅' : '▪️';
        $suggestion = $prefix . ' ' . $template;
      }
      $output['debug_info'] .= "\n<!-- FILE NAME SUGGESTIONS:\n   " . Html::escape(implode("\n   ", $suggestions)) . "\n-->";

      if (!empty($invalid_suggestions)) {
        $output['debug_info'] .= "\n<!-- INVALID FILE NAME SUGGESTIONS:";
        $output['debug_info'] .= "\n   See https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Render!theme.api.php/function/hook_theme_suggestions_alter";
        $output['debug_info'] .= "\n   " . Html::escape(implode("\n   ", $invalid_suggestions));
        $output['debug_info'] .= "\n-->";
      }
    }
    // Check if the template_file belongs to a custom theme
    $template_override_status_output = "BEGIN OUTPUT";
    $template_override_suffix_output = "END OUTPUT";
    if (str_starts_with($template_file, $variables['directory'])) {
      $template_override_status_output = "💡 BEGIN CUSTOM TEMPLATE OUTPUT";
      $template_override_suffix_output = "END CUSTOM TEMPLATE OUTPUT";
    }
    $output['debug_info']   .= "\n<!-- " . $template_override_status_output . " from '" . Html::escape($template_file) . "' -->\n";
    $output['debug_suffix'] .= "\n<!-- " . $template_override_suffix_output . " from '" . Html::escape($template_file) . "' -->\n\n";
  }
  // This output has already been rendered and is therefore considered safe.
  return Markup::create(implode('', $output));
}