Issue #3162699 by tim.plunkett, smustgrave, nicxvan, sam152, lauriii: Improve...

Issue #3162699 by tim.plunkett, smustgrave, nicxvan, sam152, lauriii: Improve debugability of block plugins returning NULL in Layout Builder

core/modules/block/tests/modules/block_test/src/Plugin/Block/TestEmptyBlock.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block that returns an empty array.
+ */
+#[Block(
+  id: "test_empty",
+  admin_label: new TranslatableMarkup("Test Empty block"),
+)]
+class TestEmptyBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [];
+  }
+
+}

core/modules/block/tests/src/Kernel/BlockViewBuilderTest.php

@@ -69,6 +69,27 @@ protected function setUp(): void {
     $this->renderer = $this->container->get('renderer');
   }
 
+  /**
+   * Tests rendering a block plugin that returns an empty array.
+   */
+  public function testEmptyRender(): void {
+    \Drupal::keyValue('block_test')->set('content', '');
+
+    $entity = $this->controller->create([
+      'id' => 'test_block1',
+      'theme' => 'stark',
+      'plugin' => 'test_empty',
+    ]);
+    $entity->save();
+
+    // Test the rendering of a block.
+    $entity = Block::load('test_block1');
+    $builder = \Drupal::entityTypeManager()->getViewBuilder('block');
+    $output = $builder->view($entity, 'block');
+    $expected_output = '';
+    $this->assertSame($expected_output, (string) $this->renderer->renderRoot($output));
+  }
+
   /**
    * Tests the rendering of blocks.
    */

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

@@ -104,6 +104,10 @@ public function onBuildRender(SectionComponentBuildRenderArrayEvent $event) {
       }
 
       $content = $block->build();
+      // @todo Remove when https://www.drupal.org/node/3164389 is resolved.
+      if (!is_array($content)) {
+        throw new \UnexpectedValueException(sprintf('The block "%s" did not return an array', get_class($block)));
+      }
 
       // We don't output the block render data if there are no render elements
       // found, but we want to capture the cache metadata from the block

core/modules/layout_builder/tests/src/Unit/BlockComponentRenderArrayTest.php

@@ -499,6 +499,29 @@ public function testOnBuildRenderEmptyBuildWithCacheTags(): void {
     $this->assertEqualsCanonicalizing($expected_cache, $result);
   }
 
+  /**
+   * @covers ::onBuildRender
+   */
+  public function testOnBuildRenderNullBuild(): void {
+    $block = $this->prophesize(BlockPluginInterface::class);
+
+    $access_result = AccessResult::allowed();
+    $block->access($this->account->reveal(), TRUE)->willReturn($access_result)->shouldBeCalled();
+    $block->getCacheContexts()->willReturn([]);
+    $block->getCacheTags()->willReturn(['test']);
+    $block->getCacheMaxAge()->willReturn(Cache::PERMANENT);
+
+    $block->build()->willReturn(NULL);
+    $this->expectException(\UnexpectedValueException::class);
+    $this->expectExceptionMessage(sprintf('The block "%s" did not return an array', get_class($block->reveal())));
+    $this->blockManager->createInstance('some_block_id', ['id' => 'some_block_id'])->willReturn($block->reveal());
+
+    $component = new SectionComponent('some-uuid', 'some-region', ['id' => 'some_block_id']);
+    $event = new SectionComponentBuildRenderArrayEvent($component, [], FALSE);
+    $subscriber = new BlockComponentRenderArray($this->account->reveal());
+    $subscriber->onBuildRender($event);
+  }
+
   /**
    * @covers ::onBuildRender
    */