Issue #3007973 by tim.plunkett, lukasss, xopoc, bnjmnm, stompersly: Layout builder prevents the rendering of extra fields (like Links) on pages not using Layout Builder

(cherry picked from commit fea6c51)

Author: xjm

modules/layout_builder/layout_builder.module

@@ -7,14 +7,14 @@
 
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Render\Element;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Url;
 use Drupal\field\FieldConfigInterface;
 use Drupal\layout_builder\Entity\LayoutBuilderEntityViewDisplay;
 use Drupal\layout_builder\Entity\LayoutBuilderEntityViewDisplayStorage;
 use Drupal\layout_builder\Form\LayoutBuilderEntityViewDisplayForm;
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
-use Drupal\layout_builder\Entity\LayoutEntityDisplayInterface;
 use Drupal\layout_builder\Plugin\Block\ExtraFieldBlock;
 use Drupal\layout_builder\InlineBlockEntityOperations;
 use Drupal\Core\Session\AccountInterface;
@@ -106,7 +106,9 @@ function layout_builder_field_config_delete(FieldConfigInterface $field_config)
  * @see layout_builder_module_implements_alter()
  */
 function layout_builder_entity_view_alter(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display) {
-  if ($display instanceof LayoutEntityDisplayInterface) {
+  // Only replace extra fields when Layout Builder has been used to alter the
+  // build. See \Drupal\layout_builder\Entity\LayoutBuilderEntityViewDisplay::buildMultiple().
+  if (isset($build['_layout_builder']) && !Element::isEmpty($build['_layout_builder'])) {
     /** @var \Drupal\Core\Entity\EntityFieldManagerInterface $field_manager */
     $field_manager = \Drupal::service('entity_field.manager');
     $extra_fields = $field_manager->getExtraFields($entity->getEntityTypeId(), $entity->bundle());

modules/layout_builder/tests/src/Functional/LayoutBuilderTest.php

@@ -482,6 +482,23 @@ public function testLayoutBuilderChooseBlocksAlter() {
     $assert_session->linkExists('Changed');
   }
 
+  /**
+   * Tests that extra fields work before and after enabling Layout Builder.
+   */
+  public function testExtraFields() {
+    $assert_session = $this->assertSession();
+
+    $this->drupalLogin($this->drupalCreateUser(['administer node display']));
+
+    $this->drupalGet('node');
+    $assert_session->linkExists('Read more');
+
+    $this->drupalPostForm('admin/structure/types/manage/bundle_with_section_field/display/default', ['layout[enabled]' => TRUE], 'Save');
+
+    $this->drupalGet('node');
+    $assert_session->linkExists('Read more');
+  }
+
   /**
    * Tests that deleting a View block used in Layout Builder works.
    */