class YamlFileLoader

1. 8.x drupal/core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php \Drupal\Core\DependencyInjection\YamlFileLoader
2. 8.x drupal/core/vendor/symfony/routing/Symfony/Component/Routing/Loader/YamlFileLoader.php \Symfony\Component\Routing\Loader\YamlFileLoader
3. 8.x drupal/core/vendor/symfony/dependency-injection/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php \Symfony\Component\DependencyInjection\Loader\YamlFileLoader
4. 8.x drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php \Symfony\Component\Validator\Mapping\Loader\YamlFileLoader

YamlFileLoaderTest.php in drupal/core/vendor/symfony/routing/Symfony/Component/Routing/Tests/Loader/YamlFileLoaderTest.php

class YamlFileLoader extends FileLoader {
  private static $availableKeys = array(
    'resource',
    'type',
    'prefix',
    'pattern',
    'path',
    'host',
    'schemes',
    'methods',
    'defaults',
    'requirements',
    'options',
  );
  private $yamlParser;

  /**
   * Loads a Yaml file.
   *
   * @param string      $file A Yaml file path
   * @param string|null $type The resource type
   *
   * @return RouteCollection A RouteCollection instance
   *
   * @throws \InvalidArgumentException When a route can't be parsed because YAML is invalid
   *
   * @api
   */
  public function load($file, $type = null) {
    $path = $this->locator
      ->locate($file);
    if (!stream_is_local($path)) {
      throw new \InvalidArgumentException(sprintf('This is not a local file "%s".', $path));
    }
    if (!file_exists($path)) {
      throw new \InvalidArgumentException(sprintf('File "%s" not found.', $path));
    }
    if (null === $this->yamlParser) {
      $this->yamlParser = new YamlParser();
    }
    $config = $this->yamlParser
      ->parse(file_get_contents($path));
    $collection = new RouteCollection();
    $collection
      ->addResource(new FileResource($path));

    // empty file
    if (null === $config) {
      return $collection;
    }

    // not an array
    if (!is_array($config)) {
      throw new \InvalidArgumentException(sprintf('The file "%s" must contain a YAML array.', $path));
    }
    foreach ($config as $name => $config) {
      if (isset($config['pattern'])) {
        if (isset($config['path'])) {
          throw new \InvalidArgumentException(sprintf('The file "%s" cannot define both a "path" and a "pattern" attribute. Use only "path".', $path));
        }
        $config['path'] = $config['pattern'];
        unset($config['pattern']);
      }
      $this
        ->validate($config, $name, $path);
      if (isset($config['resource'])) {
        $this
          ->parseImport($collection, $config, $path, $file);
      }
      else {
        $this
          ->parseRoute($collection, $name, $config, $path);
      }
    }
    return $collection;
  }

  /**
   * {@inheritdoc}
   *
   * @api
   */
  public function supports($resource, $type = null) {
    return is_string($resource) && 'yml' === pathinfo($resource, PATHINFO_EXTENSION) && (!$type || 'yaml' === $type);
  }

  /**
   * Parses a route and adds it to the RouteCollection.
   *
   * @param RouteCollection $collection A RouteCollection instance
   * @param string          $name       Route name
   * @param array           $config     Route definition
   * @param string          $path       Full path of the YAML file being processed
   */
  protected function parseRoute(RouteCollection $collection, $name, array $config, $path) {
    $defaults = isset($config['defaults']) ? $config['defaults'] : array();
    $requirements = isset($config['requirements']) ? $config['requirements'] : array();
    $options = isset($config['options']) ? $config['options'] : array();
    $host = isset($config['host']) ? $config['host'] : '';
    $schemes = isset($config['schemes']) ? $config['schemes'] : array();
    $methods = isset($config['methods']) ? $config['methods'] : array();
    $route = new Route($config['path'], $defaults, $requirements, $options, $host, $schemes, $methods);
    $collection
      ->add($name, $route);
  }

  /**
   * Parses an import and adds the routes in the resource to the RouteCollection.
   *
   * @param RouteCollection $collection A RouteCollection instance
   * @param array           $config     Route definition
   * @param string          $path       Full path of the YAML file being processed
   * @param string          $file       Loaded file name
   */
  protected function parseImport(RouteCollection $collection, array $config, $path, $file) {
    $type = isset($config['type']) ? $config['type'] : null;
    $prefix = isset($config['prefix']) ? $config['prefix'] : '';
    $defaults = isset($config['defaults']) ? $config['defaults'] : array();
    $requirements = isset($config['requirements']) ? $config['requirements'] : array();
    $options = isset($config['options']) ? $config['options'] : array();
    $host = isset($config['host']) ? $config['host'] : null;
    $schemes = isset($config['schemes']) ? $config['schemes'] : null;
    $methods = isset($config['methods']) ? $config['methods'] : null;
    $this
      ->setCurrentDir(dirname($path));
    $subCollection = $this
      ->import($config['resource'], $type, false, $file);

    /* @var $subCollection RouteCollection */
    $subCollection
      ->addPrefix($prefix);
    if (null !== $host) {
      $subCollection
        ->setHost($host);
    }
    if (null !== $schemes) {
      $subCollection
        ->setSchemes($schemes);
    }
    if (null !== $methods) {
      $subCollection
        ->setMethods($methods);
    }
    $subCollection
      ->addDefaults($defaults);
    $subCollection
      ->addRequirements($requirements);
    $subCollection
      ->addOptions($options);
    $collection
      ->addCollection($subCollection);
  }

  /**
   * Validates the route configuration.
   *
   * @param array  $config A resource config
   * @param string $name   The config key
   * @param string $path   The loaded file path
   *
   * @throws \InvalidArgumentException If one of the provided config keys is not supported,
   *                                   something is missing or the combination is nonsense
   */
  protected function validate($config, $name, $path) {
    if (!is_array($config)) {
      throw new \InvalidArgumentException(sprintf('The definition of "%s" in "%s" must be a YAML array.', $name, $path));
    }
    if ($extraKeys = array_diff(array_keys($config), self::$availableKeys)) {
      throw new \InvalidArgumentException(sprintf('The routing file "%s" contains unsupported keys for "%s": "%s". Expected one of: "%s".', $path, $name, implode('", "', $extraKeys), implode('", "', self::$availableKeys)));
    }
    if (isset($config['resource']) && isset($config['path'])) {
      throw new \InvalidArgumentException(sprintf('The routing file "%s" must not specify both the "resource" key and the "path" key for "%s". Choose between an import and a route definition.', $path, $name));
    }
    if (!isset($config['resource']) && isset($config['type'])) {
      throw new \InvalidArgumentException(sprintf('The "type" key for the route definition "%s" in "%s" is unsupported. It is only available for imports in combination with the "resource" key.', $name, $path));
    }
    if (!isset($config['resource']) && !isset($config['path'])) {
      throw new \InvalidArgumentException(sprintf('You must define a "path" for the route "%s" in file "%s".', $name, $path));
    }
  }

}