Issue #3432347: Add tokens for reference fields

Closes #3432347

message_plus.tokens.inc

@@ -5,6 +5,7 @@
  * Provides Token integration for Message Plus.
  */
 
+use Drupal\Core\Render\BubbleableMetadata;
 use Drupal\message\MessageInterface;
 
 /**
@@ -48,7 +49,8 @@ function message_plus_token_info() {
 /**
  * Implements hook_tokens().
  */
-function message_plus_tokens($type, $tokens, array $data) {
+function message_plus_tokens($type, $tokens, array $data, array $options, BubbleableMetadata $bubbleable_metadata) {
+  $token_service = \Drupal::token();
   $replacements = [];
 
   if ($type != 'message' || !($message = $data['message'] ?? NULL) instanceof MessageInterface) {
@@ -61,7 +63,24 @@ function message_plus_tokens($type, $tokens, array $data) {
       continue;
     }
 
-    foreach (['_name', '_link'] as $string_ending) {
+    // Process reference field tokens.
+    $matches = [];
+    preg_match('/(?<=field_)(.*)(?=_reference)/', $name, $matches);
+    $entity_type_id = $matches[0] ?? NULL;
+
+    if (
+      $entity_type_id &&
+      ($field_name = 'field_' . $entity_type_id . '_reference') &&
+      $message->hasField($field_name) &&
+      $entity_tokens = $token_service->findWithPrefix($tokens, $field_name)
+    ) {
+      $replacements += $token_service->generate($entity_type_id, $entity_tokens, [
+        $entity_type_id => $message->get($field_name)->entity,
+      ], $options, $bubbleable_metadata);
+    }
+
+    // Process reference field name and link.
+    foreach (['name', 'link'] as $string_ending) {
       if (!str_ends_with($name, $string_ending)) {
         continue;
       }