Separate applies and build logic for breadcrumb builders

Updated: Comment #N

Problem/Motivation

Currently the BreadcrumbBuilderInterface consists of just a build() method. This means the logic that decides whether the breadcrumb builder applies on a certain page and the actual building of the breadcrumb live in build(). So we rely on that returning NULL to determine whether or not it applies. The build() method should be for...building.

Proposed resolution

Add an applies() method to BreadcrumbBuilderInterface so the applies logic can live there instead. Then we have a nice separation between the two, and therefore (I think) a better API. This is more in line with access checkers etc..

So, for example, CommnetBreacrumbBuilder looks like this:

  /**
   * {@inheritdoc}
   */
  public function build(array $attributes) {
    if (isset($attributes[RouteObjectInterface::ROUTE_NAME]) && $attributes[RouteObjectInterface::ROUTE_NAME] == 'comment.reply'
      && isset($attributes['entity_type'])
      && isset($attributes['entity_id'])
      && isset($attributes['field_name'])
      ) {
      $breadcrumb[] = $this->l($this->t('Home'), '<front>');
      $entity = $this->entityManager
        ->getStorageController($attributes['entity_type'])
        ->load($attributes['entity_id']);
      $uri = $entity->uri();
      $breadcrumb[] = l($entity->label(), $uri['path'], $uri['options']);
      return $breadcrumb;
    }
  }

when it could look like:

  /**
   * {@inheritdoc}
   */
  public function applies(array $attributes) {
    return isset($attributes[RouteObjectInterface::ROUTE_NAME]) && $attributes[RouteObjectInterface::ROUTE_NAME] == 'comment.reply'
    && isset($attributes['entity_type'])
    && isset($attributes['entity_id'])
    && isset($attributes['field_name']);
  }

  /**
   * {@inheritdoc}
   */
  public function build(array $attributes) {
    $breadcrumb[] = $this->l($this->t('Home'), '<front>');
    $entity = $this->entityManager
      ->getStorageController($attributes['entity_type'])
      ->load($attributes['entity_id']);
    $uri = $entity->uri();
    $breadcrumb[] = l($entity->label(), $uri['path'], $uri['options']);
    return $breadcrumb;
  }

IMO, that is much much better.

Remaining tasks

Conversion patch

User interface changes

None.

API changes

Addition of applies() method to BreadcrumbBuilderInterface