Issue #3377671: Disable already mapped fields on the mapping add form.

modules/feeds_migrate_ui/src/Form/MigrationMappingFormBase.php

@@ -6,6 +6,7 @@ use Drupal\Core\Entity\EntityFieldManager;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Form\SubformState;
+use Drupal\Core\Security\TrustedCallbackInterface;
 use Drupal\Core\Url;
 use Drupal\feeds_migrate\MappingFieldFormManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -15,7 +16,7 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
  *
  * @package Drupal\feeds_migrate\Form
  */
-class MigrationMappingFormBase extends EntityForm {
+class MigrationMappingFormBase extends EntityForm implements TrustedCallbackInterface {
 
   const CUSTOM_DESTINATION_KEY = '_custom';
 
@@ -80,6 +81,13 @@ class MigrationMappingFormBase extends EntityForm {
     );
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public static function trustedCallbacks(): array {
+    return ['postRender'];
+  }
+
   /**
    * Gets the label for the destination field - if any.
    *
@@ -157,6 +165,8 @@ class MigrationMappingFormBase extends EntityForm {
         'effect' => 'fade',
         'progress' => 'throbber',
       ],
+      '#post_render' => [[$this, 'postRender']],
+      '#description' => $this->t('Note: fields that are disabled in the selection list are already mapped.'),
     ];
 
     $form['general']['destination_key'] = [
@@ -201,6 +211,23 @@ class MigrationMappingFormBase extends EntityForm {
     return $form;
   }
 
+  /**
+   * Post render callback: disables already mapped destination fields.
+   */
+  public function postRender($rendered, $element) {
+    // Disable already mapped fields.
+    $mappings = $this->entity->getMappings();
+    if (empty($mappings)) {
+      return $rendered;
+    }
+    foreach (array_keys($mappings) as $destination_field_id) {
+      $search[] = '<option value="' . $destination_field_id . '">';
+      $replace[] = '<option value="' . $destination_field_id . '" disabled="disabled">';
+    }
+    $rendered = str_replace($search, $replace, $rendered);
+    return $rendered;
+  }
+
   /**
    * Overrides Drupal\Core\Entity\EntityFormController::actions().
    *
@@ -380,7 +407,10 @@ class MigrationMappingFormBase extends EntityForm {
     /** @var \Drupal\Core\Field\FieldDefinitionInterface[] $fields */
     $fields = $this->entity->getDestinationFields();
     foreach ($fields as $field_name => $field) {
-      $options[$field->getName()] = $field->getLabel();
+      $options[$field->getName()] = $this->t('@label (@id)', [
+        '@label' => $field->getLabel(),
+        '@id' => $field->getName(),
+      ]);
     }
 
     return $options;