Spots where dependency injection is impossible because type hinting expects implementations, not interfaces

[qadan]

This originally cropped up when enabling the webprofiler submodule of the Devel module. webprofiler implements a whole bunch of interfaces to inject, including an EntityManagerWrapper which is put in place of the standard EntityTypeManager. It doesn't extend the EntityTypeManager however, it only implements EntityTypeManagerInterface.

There's a bunch of examples of where this would trip things up in Islandora; I'll just pull the first one:

NodeLinkHeaderSubscriber takes an @entity_type.manager as its first argument, and in the actual implementation inherited from LinkHeaderSubscriber, it's type hinted to use Drupal\Core\Entity\EntityTypeManager.

So, webprofiler tries to inject its EntityManagerWrapper as the @entity_type.manager, but the type hint is looking for an actual EntityTypeManager or subclass thereof, which EntityManagerWrapper is not one of, so it goes boom.

The Drupal docs on dependency injection are disappointingly unclear on what they want you to do here ... the services.yaml definition says to use "the default class that provides the service, or if the service uses a factory class, the interface for the service" ... but they often document the default class instead of the interface, like with @entity_type.manager.

Anyway, that's all just an aside I guess. In practice modules use the interface providing a service to type hint (content_sync and search_api_solr both have examples of this specific service being implemented using the interface instead of the class), and we should follow suit to properly facilitate dependency injection. Even in Drupal\islandora\EventSubscriber\LinkHeaderSubscriber, the @entity_type.manager and @entity_field.manager don't type hint the interface, but then other stuff like @access_manager and @current_user do, so consistency is also a factor here.

Logging this issue specifically to look at auditing the codebase for spots where type hinting is going to reduce or prevent our ability to dependency inject, as this reduces our ability to extend Islandora 8 via contrib modules. EntityTypeManager is one example, but suspect others may exist. Logging the issue also to perhaps make a hard rule for development to use interface type hinting.

[dannylamb]

I did a quick audit and it looks like we are injecting the EntityTypeManager, EntityFieldManager, and FileSystem services without using their interfaces. Some vim -> grep -> %s action should take care of this...

[whikloj]

Resolved with Islandora/islandora@0d9019b