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

ValidatorBuilder.php in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/ValidatorBuilder.php

YamlFileLoaderTest.php in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Tests/Mapping/Loader/YamlFileLoaderTest.php

class YamlFileLoader extends FileLoader {
  private $yamlParser;

  /**
   * An array of YAML class descriptions
   *
   * @var array
   */
  protected $classes = null;

  /**
   * {@inheritDoc}
   */
  public function loadClassMetadata(ClassMetadata $metadata) {
    if (null === $this->classes) {
      if (!stream_is_local($this->file)) {
        throw new \InvalidArgumentException(sprintf('This is not a local file "%s".', $this->file));
      }
      if (!file_exists($this->file)) {
        throw new \InvalidArgumentException(sprintf('File "%s" not found.', $this->file));
      }
      if (null === $this->yamlParser) {
        $this->yamlParser = new YamlParser();
      }
      $this->classes = $this->yamlParser
        ->parse(file_get_contents($this->file));

      // empty file
      if (null === $this->classes) {
        return false;
      }

      // not an array
      if (!is_array($this->classes)) {
        throw new \InvalidArgumentException(sprintf('The file "%s" must contain a YAML array.', $this->file));
      }
      if (isset($this->classes['namespaces'])) {
        foreach ($this->classes['namespaces'] as $alias => $namespace) {
          $this
            ->addNamespaceAlias($alias, $namespace);
        }
        unset($this->classes['namespaces']);
      }
    }

    // TODO validation
    if (isset($this->classes[$metadata
      ->getClassName()])) {
      $yaml = $this->classes[$metadata
        ->getClassName()];
      if (isset($yaml['group_sequence_provider'])) {
        $metadata
          ->setGroupSequenceProvider((bool) $yaml['group_sequence_provider']);
      }
      if (isset($yaml['group_sequence'])) {
        $metadata
          ->setGroupSequence($yaml['group_sequence']);
      }
      if (isset($yaml['constraints']) && is_array($yaml['constraints'])) {
        foreach ($this
          ->parseNodes($yaml['constraints']) as $constraint) {
          $metadata
            ->addConstraint($constraint);
        }
      }
      if (isset($yaml['properties']) && is_array($yaml['properties'])) {
        foreach ($yaml['properties'] as $property => $constraints) {
          if (null !== $constraints) {
            foreach ($this
              ->parseNodes($constraints) as $constraint) {
              $metadata
                ->addPropertyConstraint($property, $constraint);
            }
          }
        }
      }
      if (isset($yaml['getters']) && is_array($yaml['getters'])) {
        foreach ($yaml['getters'] as $getter => $constraints) {
          if (null !== $constraints) {
            foreach ($this
              ->parseNodes($constraints) as $constraint) {
              $metadata
                ->addGetterConstraint($getter, $constraint);
            }
          }
        }
      }
      return true;
    }
    return false;
  }

  /**
   * Parses a collection of YAML nodes
   *
   * @param array $nodes The YAML nodes
   *
   * @return array An array of values or Constraint instances
   */
  protected function parseNodes(array $nodes) {
    $values = array();
    foreach ($nodes as $name => $childNodes) {
      if (is_numeric($name) && is_array($childNodes) && count($childNodes) == 1) {
        $options = current($childNodes);
        if (is_array($options)) {
          $options = $this
            ->parseNodes($options);
        }
        $values[] = $this
          ->newConstraint(key($childNodes), $options);
      }
      else {
        if (is_array($childNodes)) {
          $childNodes = $this
            ->parseNodes($childNodes);
        }
        $values[$name] = $childNodes;
      }
    }
    return $values;
  }

}