Add theme hook form_required_marker (#128)

src/Theme/Registry.php

@@ -61,6 +61,13 @@ protected function processExtension(array &$cache, $name, $type, $theme, $path):
                 $cache[$theme_hook]['path'] = '@retrofit';
             }
         }
+
+        $cache['form_required_marker'] = [
+            'render element' => 'element',
+            'type' => 'module',
+            'template' => 'theme-function',
+            'path' => '@retrofit',
+        ];
     }
 
     /**

src/functions/form.php

@@ -103,3 +103,16 @@ function form_get_errors()
         return $form;
     }
 }
+
+/**
+ * @param mixed[] $variables
+ */
+function theme_form_required_marker(array $variables): string
+{
+    $attributes = [
+        'class' => ['form-item__label', 'form-required'],
+        'style' => 'display: inline',
+        'title' => (string) t('This field is required.'),
+    ];
+    return '<span' . drupal_attributes($attributes) . '></span>';
+}