Allow plugin definition to be aliased

Closes #3467425

core/lib/Drupal/Component/Plugin/Discovery/DiscoveryCachedTrait.php

@@ -2,6 +2,10 @@
 
 namespace Drupal\Component\Plugin\Discovery;
 
+use Drupal\Component\Plugin\Definition\DerivablePluginDefinitionInterface;
+use Drupal\Component\Plugin\Definition\PluginDefinitionInterface;
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+
 trait DiscoveryCachedTrait {
 
   use DiscoveryTrait;
@@ -13,6 +17,8 @@ trait DiscoveryCachedTrait {
    */
   protected $definitions;
 
+  protected $aliasDefinitions;
+
   /**
    * {@inheritdoc}
    */
@@ -22,7 +28,47 @@ public function getDefinition($plugin_id, $exception_on_invalid = TRUE) {
       $this->getDefinitions();
     }
 
-    return $this->doGetDefinition($this->definitions, $plugin_id, $exception_on_invalid);
+    try {
+      return $this->doGetDefinition($this->definitions, $plugin_id, TRUE);
+    }
+    catch (PluginNotFoundException $e) {
+      $aliases = $this->getAliasDefinitions();
+      if (isset($aliases[$plugin_id])) {
+        return $this->doGetDefinition($this->definitions, $aliases[$plugin_id], $exception_on_invalid);
+      }
+
+      return $exception_on_invalid ? throw $e : NULL;
+    }
+  }
+
+  public function getAliasDefinitions(): array {
+    if (isset($this->aliasDefinitions)) {
+      return $this->aliasDefinitions;
+    }
+
+    $this->aliasDefinitions = [];
+
+    $definitions = $this->getDefinitions();
+    foreach ($definitions as $id => $definition) {
+      if ($definition instanceof PluginDefinitionInterface) {
+        if ($definition instanceof DerivablePluginDefinitionInterface && $definition->getDeriver()) {
+          continue;
+        }
+
+        $this->aliasDefinitions[$definition->getClass()] = $definition->id();
+        continue;
+      }
+
+      if ($definition['deriver'] ?? FALSE) {
+        continue;
+      }
+
+      if ($definition['class'] ?? FALSE) {
+        $this->aliasDefinitions[$definition['class']] = $definition['id'] ?? $id;
+      }
+    }
+
+    return $this->aliasDefinitions;
   }
 
 }