Issue #2870410 by tim.plunkett: Field UI should show fields with unknown regions in the "Disabled" section

core/modules/field_layout/tests/modules/field_layout_test/field_layout_test.module

@@ -0,0 +1,16 @@
+<?php
+
+/**
+ * @file
+ * Contains hook implementations for field_layout_test.
+ */
+
+/**
+ * Implements hook_layout_alter().
+ */
+function field_layout_test_layout_alter(&$definitions) {
+  /** @var \Drupal\Core\Layout\LayoutDefinition[] $definitions */
+  if (\Drupal::state()->get('field_layout_test.alter_regions') && isset($definitions['layout_onecol'])) {
+    $definitions['layout_onecol']->setRegions(['foo' => ['label' => 'Foo']]);
+  }
+}

core/modules/field_layout/tests/src/Functional/FieldLayoutTest.php

@@ -14,7 +14,7 @@ class FieldLayoutTest extends BrowserTestBase {
   /**
    * {@inheritdoc}
    */
-  public static $modules = ['field_layout', 'field_ui', 'node'];
+  public static $modules = ['field_layout', 'field_ui', 'node', 'field_layout_test'];
 
   /**
    * {@inheritdoc}
@@ -57,6 +57,22 @@ class FieldLayoutTest extends BrowserTestBase {
     $this->assertSession()->optionExists('fields[body][region]', 'content');
   }
 
+  /**
+   * Tests that changes to the regions still leave the fields visible.
+   */
+  public function testRegionChanges() {
+    $this->drupalGet('admin/structure/types/manage/article/display');
+    $this->assertEquals(['Content', 'Disabled'], $this->getRegionTitles());
+    $this->assertSession()->optionExists('fields[body][region]', 'content');
+
+    \Drupal::state()->set('field_layout_test.alter_regions', TRUE);
+    \Drupal::service('plugin.cache_clearer')->clearCachedDefinitions();
+
+    $this->drupalGet('admin/structure/types/manage/article/display');
+    $this->assertEquals(['Foo', 'Disabled'], $this->getRegionTitles());
+    $this->assertSession()->optionExists('fields[body][region]', 'hidden');
+  }
+
   /**
    * Gets the region titles on the page.
    *

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

@@ -67,7 +67,7 @@ class FieldUiTable extends Table {
           unset($list[$name]);
 
           // Determine the region for the row.
-          $region_name = call_user_func($row['#region_callback'], $row);
+          $region_name = call_user_func_array($row['#region_callback'], [&$row]);
 
           // Add the element in the tree.
           $target = &$trees[$region_name][''];

core/modules/field_ui/src/Form/EntityDisplayFormBase.php

@@ -817,12 +817,12 @@ abstract class EntityDisplayFormBase extends EntityForm {
    * @return string|null
    *   The region name this row belongs to.
    */
-  public function getRowRegion($row) {
+  public function getRowRegion(&$row) {
-    switch ($row['#row_type']) {
+    $regions = $this->getRegions();
-      case 'field':
+    if (!isset($regions[$row['region']['#value']])) {
-      case 'extra_field':
+      $row['region']['#value'] = 'hidden';
-        return $row['region']['#value'] ?: 'hidden';
     }
+    return $row['region']['#value'];
   }
 
   /**