Important patch updates:

• Moved all tag parsing to Yaml class.
• Implemented string translation context.
• Updated two other recipes for translation.
• Handled yaml validation properly with Type(['string', Stringable::class])
• Fixed arguments types in ConsoleInputCollector.

Closes #3313863

core/lib/Drupal/Component/Serialization/Yaml.php

@@ -5,6 +5,7 @@
 use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
 use Symfony\Component\Yaml\Dumper;
 use Symfony\Component\Yaml\Parser;
+use Symfony\Component\Yaml\Tag\TaggedValue;
 use Symfony\Component\Yaml\Yaml as SymfonyYaml;
 
 /**
@@ -51,4 +52,39 @@ public static function getFileExtension() {
     return 'yml';
   }
 
+  /**
+   * Parses custom YAML tags and convert values to primitive types.
+   *
+   * Tag objects will be replaced by their raw value or, if a callback
+   * exists for that tag it will be used.
+   *
+   * The only tag custom tag supported by default is the '!translate' tag.
+   *
+   * @param mixed $data
+   *   Parsed YAML data.
+   * @param callable[] $tag_callbacks
+   *   Optional callbacks for tag value, indexed by tag.
+   *
+   * @return mixed
+   *   Parsed data with parsed tag values.
+   */
+  public static function decodeTags($data, array $tag_callbacks = []) {
+    if (is_array($data)) {
+      foreach ($data as $key => $value) {
+        if (is_object($value) && $value instanceof TaggedValue) {
+          if (isset($tag_callbacks[$value->getTag()])) {
+            $data[$key] = call_user_func($tag_callbacks[$value->getTag()], $value);
+          }
+          else {
+            $data[$key] = $value->getValue();
+          }
+        }
+        elseif (is_array($value)) {
+          $data[$key] = static::decodeTags($value, $tag_callbacks);
+        }
+      }
+    }
+    return $data;
+  }
+
 }