Issue #3144010 by danflanagan8, ravi.shankar, tim.plunkett, chrisolof, sorlov: New pseudo-fields cannot be removed, InvalidArgumentException thrown

core/misc/cspell/dictionary.txt

@@ -572,6 +572,7 @@ fieldblock
 fieldbody
 fieldgroups
 fielditem
+fieldlayout
 fieldlinks
 fieldnames
 fieldsets

core/modules/layout_builder/src/EventSubscriber/PrepareLayout.php

@@ -69,13 +69,16 @@ class PrepareLayout implements EventSubscriberInterface {
     if ($this->layoutTempstoreRepository->has($section_storage)) {
       $this->messenger->addWarning($this->t('You have unsaved changes.'));
     }
-    // If the layout is an override that has not yet been overridden, copy the
-    // sections from the corresponding default.
-    elseif ($section_storage instanceof OverridesSectionStorageInterface && !$section_storage->isOverridden()) {
-      $sections = $section_storage->getDefaultSectionStorage()->getSections();
-      foreach ($sections as $section) {
-        $section_storage->appendSection($section);
+    else {
+      // If the layout is an override that has not yet been overridden, copy the
+      // sections from the corresponding default.
+      if ($section_storage instanceof OverridesSectionStorageInterface && !$section_storage->isOverridden()) {
+        $sections = $section_storage->getDefaultSectionStorage()->getSections();
+        foreach ($sections as $section) {
+          $section_storage->appendSection($section);
+        }
       }
+      // Add storage to tempstore regardless of what the storage is.
       $this->layoutTempstoreRepository->set($section_storage);
     }
   }

core/modules/layout_builder/tests/modules/layout_builder_extra_field_test/layout_builder_extra_field_test.info.yml

@@ -0,0 +1,5 @@
+name: 'Layout Builder Extra Field test'
+type: module
+description: 'Support module for testing layout building.'
+package: Testing
+version: VERSION

core/modules/layout_builder/tests/modules/layout_builder_extra_field_test/layout_builder_extra_field_test.module

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * @file
+ * Provides hook implementations for Layout Builder tests.
+ */
+
+use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
+use Drupal\Core\Entity\EntityInterface;
+
+/**
+ * Implements hook_entity_extra_field_info().
+ */
+function layout_builder_extra_field_test_entity_extra_field_info() {
+  $extra['node']['bundle_with_section_field']['display']['layout_builder_extra_field_test'] = [
+    'label' => t('New Extra Field'),
+    'description' => t('New Extra Field description'),
+    'weight' => 0,
+  ];
+  return $extra;
+}
+
+/**
+ * Implements hook_entity_node_view().
+ */
+function layout_builder_extra_field_test_node_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {
+  if ($display->getComponent('layout_builder_extra_field_test')) {
+    $build['layout_builder_extra_field_test'] = [
+      '#markup' => 'A new extra field.',
+    ];
+  }
+}

core/modules/layout_builder/tests/src/FunctionalJavascript/LayoutBuilderUiTest.php

@@ -240,6 +240,30 @@ class LayoutBuilderUiTest extends WebDriverTestBase {
     $this->assertHighlightNotExists();
   }
 
+  /**
+   * Tests removing newly added extra field.
+   */
+  public function testNewExtraField() {
+    $assert_session = $this->assertSession();
+    $page = $this->getSession()->getPage();
+
+    // At this point layout builder has been enabled for the test content type.
+    // Install a test module that creates a new extra field then clear cache.
+    \Drupal::service('module_installer')->install(['layout_builder_extra_field_test']);
+    \Drupal::service('entity_field.manager')->clearCachedFieldDefinitions();
+
+    // View the layout and try to remove the new extra field.
+    $this->drupalGet(static::FIELD_UI_PREFIX . '/display/default/layout');
+    $assert_session->pageTextContains('New Extra Field');
+    $this->clickContextualLink('.block-extra-field-blocknodebundle-with-section-fieldlayout-builder-extra-field-test', 'Remove block');
+    $this->assertNotEmpty($assert_session->waitForElementVisible('css', '#drupal-off-canvas'));
+    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->pageTextContains('Are you sure you want to remove');
+    $page->pressButton('Remove');
+    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->pageTextNotContains('New Extra Field');
+  }
+
   /**
    * Confirms the presence of the 'is-layout-builder-highlighted' class.
    *