Issue #2992410 by tim.plunkett, scottsawyer, sugaroverflow, phenaproxima:...

Issue #2992410 by tim.plunkett, scottsawyer, sugaroverflow, phenaproxima: Provide placeholders for empty blocks (for example, an empty Views listing)

core/lib/Drupal/Core/Block/BlockBase.php

@@ -11,6 +11,7 @@
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Plugin\PluginWithFormsInterface;
 use Drupal\Core\Plugin\PluginWithFormsTrait;
+use Drupal\Core\Render\PlaceholderInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Component\Transliteration\TransliterationInterface;
 
@@ -23,7 +24,7 @@
  *
  * @ingroup block_api
  */
-abstract class BlockBase extends ContextAwarePluginBase implements BlockPluginInterface, PluginWithFormsInterface {
+abstract class BlockBase extends ContextAwarePluginBase implements BlockPluginInterface, PluginWithFormsInterface, PlaceholderInterface {
 
   use ContextAwarePluginAssignmentTrait;
   use MessengerTrait;
@@ -252,6 +253,13 @@ public function getMachineNameSuggestion() {
     return $transliterated;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getPlaceholderString() {
+    return $this->t('Placeholder for the "@block" block', ['@block' => $this->label()]);
+  }
+
   /**
    * Wraps the transliteration service.
    *

core/lib/Drupal/Core/Entity/Entity/EntityViewDisplay.php

@@ -8,6 +8,7 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Entity\EntityDisplayBase;
+use Drupal\Core\Render\Element;
 use Drupal\Core\TypedData\TranslatableInterface as TranslatableDataInterface;
 
 /**
@@ -269,7 +270,7 @@ public function buildMultiple(array $entities) {
     foreach ($entities as $id => $entity) {
       // Assign the configured weights.
       foreach ($this->getComponents() as $name => $options) {
-        if (isset($build_list[$id][$name])) {
+        if (isset($build_list[$id][$name]) && !Element::isEmpty($build_list[$id][$name])) {
           $build_list[$id][$name]['#weight'] = $options['weight'];
         }
       }

core/lib/Drupal/Core/Render/PlaceholderInterface.php

+<?php
+
+namespace Drupal\Core\Render;
+
+/**
+ * Allows an element to provide a placeholder representation of itself.
+ */
+interface PlaceholderInterface {
+
+  /**
+   * Returns a string to be used as a placeholder.
+   *
+   * This is typically used when an element has no output and must be displayed,
+   * for example during configuration.
+   *
+   * @return string|\Drupal\Core\StringTranslation\TranslatableMarkup
+   *   A placeholder string for this element.
+   */
+  public function getPlaceholderString();
+
+}

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

@@ -5,6 +5,8 @@
 use Drupal\block_content\Access\RefinableDependentAccessInterface;
 use Drupal\Core\Access\AccessResult;
 use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Render\Element;
+use Drupal\Core\Render\PlaceholderInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\layout_builder\Access\LayoutPreviewAccessAllowed;
 use Drupal\layout_builder\Event\SectionComponentBuildRenderArrayEvent;
@@ -98,6 +100,9 @@ public function onBuildRender(SectionComponentBuildRenderArrayEvent $event) {
         '#weight' => $event->getComponent()->getWeight(),
         'content' => $block->build(),
       ];
+      if ($event->inPreview() && Element::isEmpty($build['content']) && $block instanceof PlaceholderInterface) {
+        $build['content']['#markup'] = $block->getPlaceholderString();
+      }
       $event->setBuild($build);
     }
   }

core/modules/layout_builder/src/Plugin/Block/ExtraFieldBlock.php

@@ -130,13 +130,22 @@ public function build() {
         // render array. If the hook is invoked the placeholder will be
         // replaced.
         // @see ::replaceFieldPlaceholder()
-        '#markup' => new TranslatableMarkup('Placeholder for the "@field" field', ['@field' => $extra_fields['display'][$this->fieldName]['label']]),
+        '#markup' => $this->getPlaceholderString(),
       ];
     }
     CacheableMetadata::createFromObject($this)->applyTo($build);
     return $build;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getPlaceholderString() {
+    $entity = $this->getEntity();
+    $extra_fields = $this->entityFieldManager->getExtraFields($entity->getEntityTypeId(), $entity->bundle());
+    return new TranslatableMarkup('Placeholder for the "@field" field', ['@field' => $extra_fields['display'][$this->fieldName]['label']]);
+  }
+
   /**
    * Replaces all placeholders for a given field.
    *

core/modules/layout_builder/src/Plugin/Block/FieldBlock.php

@@ -17,7 +17,6 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Plugin\ContextAwarePluginInterface;
-use Drupal\Core\Render\Element;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
 use Psr\Log\LoggerInterface;
@@ -160,13 +159,17 @@ public function build() {
       $build = [];
       $this->logger->warning('The field "%field" failed to render with the error of "%error".', ['%field' => $this->fieldName, '%error' => $e->getMessage()]);
     }
-    if (!empty($entity->in_preview) && !Element::getVisibleChildren($build)) {
-      $build['content']['#markup'] = new TranslatableMarkup('Placeholder for the "@field" field', ['@field' => $this->getFieldDefinition()->getLabel()]);
-    }
     CacheableMetadata::createFromObject($this)->applyTo($build);
     return $build;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getPlaceholderString() {
+    return new TranslatableMarkup('Placeholder for the "@field" field', ['@field' => $this->getFieldDefinition()->getLabel()]);
+  }
+
   /**
    * {@inheritdoc}
    */

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

@@ -22,6 +22,7 @@ class LayoutBuilderTest extends BrowserTestBase {
     'layout_builder_views_test',
     'layout_test',
     'block',
+    'block_test',
     'node',
     'layout_builder_test',
   ];
@@ -482,6 +483,49 @@ public function testDeletedView() {
     $assert_session->pageTextNotContains('Test Block View');
   }
 
+  /**
+   * Tests the usage of placeholders for empty blocks.
+   *
+   * @see \Drupal\Core\Block\BlockPluginInterface::getPlaceholderString()
+   * @see \Drupal\layout_builder\EventSubscriber\BlockComponentRenderArray::onBuildRender()
+   */
+  public function testBlockPlaceholder() {
+    $assert_session = $this->assertSession();
+    $page = $this->getSession()->getPage();
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'configure any layout',
+      'administer node display',
+    ]));
+
+    $field_ui_prefix = 'admin/structure/types/manage/bundle_with_section_field';
+    $this->drupalPostForm("$field_ui_prefix/display/default", ['layout[enabled]' => TRUE], 'Save');
+
+    // Customize the default view mode.
+    $this->drupalGet("$field_ui_prefix/display-layout/default");
+
+    // Add a block whose content is controlled by state and is empty by default.
+    $this->clickLink('Add Block');
+    $this->clickLink('Test block caching');
+    $page->fillField('settings[label]', 'The block label');
+    $page->pressButton('Add Block');
+
+    $block_content = 'I am content';
+    $placeholder_content = 'Placeholder for the "The block label" block';
+
+    // The block placeholder is displayed and there is no content.
+    $assert_session->pageTextContains($placeholder_content);
+    $assert_session->pageTextNotContains($block_content);
+
+    // Set block content and reload the page.
+    \Drupal::state()->set('block_test.content', $block_content);
+    $this->getSession()->reload();
+
+    // The block placeholder is no longer displayed and the content is visible.
+    $assert_session->pageTextNotContains($placeholder_content);
+    $assert_session->pageTextContains($block_content);
+  }
+
   /**
    * Asserts that a text string only appears once on the page.
    *

core/modules/layout_builder/tests/src/Kernel/FieldBlockTest.php

@@ -230,11 +230,10 @@ protected function getTestBlock(ProphecyInterface $entity_prophecy, array $confi
    * @covers ::build
    * @dataProvider providerTestBuild
    */
-  public function testBuild(PromiseInterface $promise, $in_preview, $expected_markup, $log_message = '', $log_arguments = []) {
+  public function testBuild(PromiseInterface $promise, $expected_markup, $log_message = '', $log_arguments = []) {
     $entity = $this->prophesize(FieldableEntityInterface::class);
     $field = $this->prophesize(FieldItemListInterface::class);
     $entity->get('the_field_name')->willReturn($field->reveal());
-    $entity->in_preview = $in_preview;
     $field->view(Argument::type('array'))->will($promise);
 
     $field_definition = $this->prophesize(FieldDefinitionInterface::class);
@@ -269,40 +268,20 @@ public function testBuild(PromiseInterface $promise, $in_preview, $expected_mark
    */
   public function providerTestBuild() {
     $data = [];
-    $data['array, no preview'] = [
+    $data['array'] = [
       new ReturnPromise([['content' => ['#markup' => 'The field value']]]),
-      FALSE,
-      'The field value',
-    ];
-    $data['array, preview'] = [
-      new ReturnPromise([['content' => ['#markup' => 'The field value']]]),
-      TRUE,
       'The field value',
     ];
-    $data['empty array, no preview'] = [
+    $data['empty array'] = [
       new ReturnPromise([[]]),
-      FALSE,
       '',
     ];
-    $data['empty array, preview'] = [
-      new ReturnPromise([[]]),
-      TRUE,
-      'Placeholder for the "The Field Label" field',
-    ];
-    $data['exception, no preview'] = [
+    $data['exception'] = [
       new ThrowPromise(new \Exception('The exception message')),
-      FALSE,
       '',
       'The field "%field" failed to render with the error of "%error".',
       ['%field' => 'the_field_name', '%error' => 'The exception message'],
     ];
-    $data['exception, preview'] = [
-      new ThrowPromise(new \Exception('The exception message')),
-      TRUE,
-      'Placeholder for the "The Field Label" field',
-      'The field "%field" failed to render with the error of "%error".',
-      ['%field' => 'the_field_name', '%error' => 'The exception message'],
-    ];
     return $data;
   }
 

core/modules/views/src/Plugin/Block/ViewsBlockBase.php

@@ -105,6 +105,13 @@ public function defaultConfiguration() {
     return ['views_label' => ''];
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getPlaceholderString() {
+    return $this->t('Placeholder for the "@view" views block', ['@view' => $this->view->storage->label()]);
+  }
+
   /**
    * {@inheritdoc}
    */