HookDiscovery.php

<?php

namespace Drupal\Core\Plugin\Discovery;

use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
use Drupal\Component\Plugin\Discovery\DiscoveryTrait;
use Drupal\Core\Extension\ModuleHandlerInterface;

/**
 * Provides a hook-based plugin discovery class.
 */
class HookDiscovery implements DiscoveryInterface {
    use DiscoveryTrait;
    
    /**
     * The name of the hook that will be implemented by this discovery instance.
     *
     * @var string
     */
    protected $hook;
    
    /**
     * The module handler used to find and execute the plugin hook.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * Constructs a Drupal\Core\Plugin\Discovery\HookDiscovery object.
     *
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param string $hook
     *   The Drupal hook that a module can implement in order to interface to
     *   this discovery class.
     */
    public function __construct(ModuleHandlerInterface $module_handler, $hook) {
        $this->moduleHandler = $module_handler;
        $this->hook = $hook;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDefinitions() {
        $definitions = [];
        foreach ($this->moduleHandler
            ->getImplementations($this->hook) as $module) {
            $result = $this->moduleHandler
                ->invoke($module, $this->hook);
            foreach ($result as $plugin_id => $definition) {
                $definition['provider'] = $module;
                $definitions[$plugin_id] = $definition;
            }
        }
        return $definitions;
    }

}