Implements ObjectWithPluginCollectionInterface

Problem/Motivation

We are defining some classes with properties being plugins attachments/collections:

• display_builder/DisplayBuilder config entity type (which may be renamed "Profile"):
  • Islands plugins in island property
• display_builder/PatternPreset config entity type:
  • UI Patterns Sources plugins in sources property
• display_builder_page_layout/PageLayout config entity type:
  • UI Patterns Sources plugins in sources property
  • Conditions plugins in conditions property (this one is already managed by ConditionPluginCollection, so PageLayout already implement EntityWithPluginCollectionInterface)
• display_builder_views/DisplayBuilderDisplayExtender ViewsDisplayExtender plugin :
  • UI Patterns Sources plugins in sources property

There is a Drupal mechanism to attach collections of plugins in a config entity in a standardized way:

• implementing ObjectWithPluginCollectionInterface (or the more specific EntityWithPluginCollectionInterface)
• and moving the logic related to this attachment to a class extending DefaultLazyPluginCollection (if multiple plugins) or DefaultSingleLazyPluginCollection (if only one plugin)

This may brings the following benefits:

• make the plugin attachments obvious among other properties
• move the specific logic to a distinct, reusable, class
• the lazy loading may improve performance
• ConfigEntityBase is doing some nice stuff like calculating automatically the dependencies
• ConfigEntityBase and EntityForm are managing some aspects of the values saving

Proposed resolution

Create an IslandPluginCollection:

• use it in DisplayBuilder config entity
• add DisplayBuilderInterface::getIslands() method
• move part of this logic scope to IslandPluginCollection: getIslandEnabled(), getIslandConfigurations(), getIslandConfiguration(), setIslandConfiguration()?

Create an SourcePluginCollection:

• use it in PatternPreset and PageLayout config entities and maybe in DisplayBuilderDisplayExtender plugin. It may also useful for display_builder_entity_view/EntityViewDisplay even if we work with third party settings here.
• is it also the opportunity of centralizing some logic here?