Issue #2611758 by swentel, webflo, zuuperman: Field UI table is broken for nested elements

core/modules/field_ui/src/Element/FieldUiTable.php

@@ -85,11 +85,12 @@ class FieldUiTable extends Table {
           if ($depth = count($parents[$name])) {
             $children = Element::children($row);
             $cell = current($children);
-            $row[$cell]['#prefix'] = [
+            $indentation = [
               '#theme' => 'indentation',
               '#size' => $depth,
               '#suffix' => isset($row[$cell]['#prefix']) ? $row[$cell]['#prefix'] : '',
             ];
+            $row[$cell]['#prefix'] = \Drupal::service('renderer')->render($indentation);
           }
 
           // Add row id and associate JS settings.

core/modules/field_ui/src/Tests/FieldUIIndentationTest.php

@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\field_ui\Tests\FieldUIIndentationTest.
+ */
+
+namespace Drupal\field_ui\Tests;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests indentation on Field UI.
+ *
+ * @group field_ui
+ */
+class FieldUIIndentationTest extends WebTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  public static $modules = array('node', 'field_ui', 'field_ui_test');
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    // Create a test user.
+    $admin_user = $this->drupalCreateUser(array('access content', 'administer content types', 'administer node display'));
+    $this->drupalLogin($admin_user);
+
+    // Create Basic page node type.
+    $this->drupalCreateContentType(array('type' => 'page', 'name' => 'Basic page'));
+
+  }
+
+  function testIndentation() {
+    $this->drupalGet('admin/structure/types/manage/page/display');
+    $this->assertRaw('js-indentation indentation');
+  }
+}

core/modules/field_ui/tests/modules/field_ui_test/field_ui_test.info.yml

@@ -0,0 +1,6 @@
+name: 'Field UI test'
+type: module
+description: 'Support module for Field UI tests.'
+core: 8.x
+package: Testing
+version: VERSION

core/modules/field_ui/tests/modules/field_ui_test/field_ui_test.module

@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * @file
+ * Field UI test module.
+ */
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Render\Element;
+
+/**
+ * Implements hook_form_FORM_BASE_ID_alter().
+ */
+function field_ui_test_form_entity_view_display_edit_form_alter(&$form, FormStateInterface $form_state) {
+  $table = &$form['fields'];
+
+  foreach (Element::children($table) as $name) {
+    $table[$name]['parent_wrapper']['parent']['#options'] = array('indent' => 'Indent');
+    $table[$name]['parent_wrapper']['parent']['#default_value'] = 'indent';
+  }
+
+  $table['indent'] = [
+    '#attributes' => array('class' => array('draggable', 'field-group'), 'id' => 'indent-id'),
+    '#row_type' => 'group',
+    '#region_callback' => 'field_ui_test_region_callback',
+    '#js_settings' => array('rowHandler' => 'group'),
+    'human_name' => array(
+      '#markup' => 'Indent',
+      '#prefix' => '<span class="group-label">',
+      '#suffix' => '</span>',
+    ),
+    'weight' => array(
+      '#type' => 'textfield',
+      '#default_value' => 0,
+      '#size' => 3,
+      '#attributes' => array('class' => array('field-weight')),
+    ),
+    'parent_wrapper' => array(
+      'parent' => array(
+        '#type' => 'select',
+        '#options' =>  array('indent' => 'Indent'),
+        '#empty_value' => '',
+        '#default_value' => '',
+        '#attributes' => array('class' => array('field-parent')),
+        '#parents' => array('fields', 'indent', 'parent'),
+      ),
+      'hidden_name' => array(
+        '#type' => 'hidden',
+        '#default_value' => 'indent',
+        '#attributes' => array('class' => array('field-name')),
+      ),
+    ),
+  ];
+
+}
+
+function field_ui_test_region_callback($row) {
+  return 'content';
+}