Skip link headers for non-canonicalizable entities

[adam-vessey]

What does this Pull Request do?

Addresses Islandora/documentation#1551, allowing for content making reference to non-canonicalizable entities (such as blocks) to be manipulated and viewed.

What's new?

We use Entity::toUrl() to generate the URL, and catch its UndefinedLinkTemplateException exception.

How should this be tested?

• Create a node bundle which can make references to blocks with an entity reference field
• Make a node with a reference to a block

In 1.1.1--prior to this change--you might experience uncaught exceptions, such as:

Symfony\Component\Routing\Exception\RouteNotFoundException: Route "entity.block.canonical" does not exist. in Drupal\Core\Routing\RouteProvider->getRouteByName() (line 208 of /opt/www/drupal/core/lib/Drupal/Core/Routing/RouteProvider.php).

With the new URL generation, we catch the more-specific UndefinedLinkTemplateException exception, and skip attempting to create a link entry for it.

Additional Notes:

The docs on EntityInterface::toUrl() indicate:

If the path is not set in the links array, the uri_callback function is used for setting the path. If this does not exist and the link relationship type is canonical, the path is set using the default template: entity/entityType/id.

... This does not appear to happen, with the exception being thrown instead of whatever "default template" being used, despite the nearby inline documentation.

Interested parties

@Islandora/8-x-committers

[dannylamb]

Works as described. Thanks @adam-vessey! 🙇‍♂️