Issue #1994146 by larowlan, kim.pepper: Fixed WSOD after deleting a custom block content entity.

core/modules/block/custom_block/custom_block.pages.inc

@@ -92,6 +92,14 @@ function custom_block_delete_form($form, &$form_state, CustomBlock $block) {
     '#value' => $block->id(),
   );
 
+  $instances = $block->getInstances();
+
+  $form['message'] = array(
+    '#type' => 'markup',
+    '#markup' => format_plural(count($instances), 'This will also remove 1 placed block instance.', 'This will also remove @count placed block instances.'),
+    '#access' => !empty($instances),
+  );
+
   return confirm_form(
     $form,
     t('Are you sure you want to delete %label?', array('%label' => $block->label())),
@@ -105,7 +113,6 @@ function custom_block_delete_form($form, &$form_state, CustomBlock $block) {
  * Form submission handler for custom_block_delete_form().
  */
 function custom_block_delete_form_submit($form, &$form_state) {
-  // @todo Delete all configured instances of the block.
   $block = $form_state['custom_block'];
   $block->delete();
 

core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockInterface.php

@@ -38,4 +38,12 @@ public function setTheme($theme);
    */
   public function getTheme();
 
+  /**
+   * Gets the configured instances of this custom block.
+   *
+   * @return array
+   *   Array of Drupal\block\Core\Plugin\Entity\Block entities.
+   */
+  public function getInstances();
+
 }

core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Core/Entity/CustomBlock.php

@@ -180,4 +180,22 @@ public function uri() {
       )
     );
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getInstances() {
+    return entity_load_multiple_by_properties('block', array('plugin' => 'custom_block:' . $this->uuid->value));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function delete() {
+    foreach ($this->getInstances() as $instance) {
+      $instance->delete();
+    }
+    parent::delete();
+  }
+
 }

core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockCreationTest.php

@@ -102,4 +102,64 @@ public function testFailedBlockCreation() {
       $this->assertTrue(count($records) > 0, 'Transactions not supported, and rollback error logged to watchdog.');
     }
   }
+
+  /**
+   * Test deleting a block.
+   */
+  public function testBlockDelete() {
+    // Create a block.
+    $edit = array();
+    $langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $edit['info'] = $this->randomName(8);
+    $body = $this->randomName(16);
+    $edit["block_body[$langcode][0][value]"] = $body;
+    $this->drupalPost('block/add/basic', $edit, t('Save'));
+
+    // Place the block.
+    $instance = array(
+      'machine_name' => drupal_strtolower($edit['info']),
+      'settings[label]' => $edit['info'],
+      'region' => 'sidebar_first',
+    );
+    $this->drupalPost(NULL, $instance, t('Save block'));
+
+    $block = custom_block_load(1);
+
+    // Test getInstances method.
+    $this->assertEqual(1, count($block->getInstances()));
+
+    // Navigate to home page.
+    $this->drupalGet('');
+    $this->assertText($body);
+
+    // Delete the block.
+    $this->drupalGet('block/1/delete');
+    $this->assertText(format_plural(1, 'This will also remove 1 placed block instance.', 'This will also remove @count placed block instance.'));
+
+    $this->drupalPost(NULL, array(), 'Delete');
+    $this->assertRaw(t('Custom block %name has been deleted.', array('%name' => $edit['info'])));
+
+    // Create another block and force the plugin cache to flush.
+    $edit2 = array();
+    $langcode = Language::LANGCODE_NOT_SPECIFIED;
+    $edit2['info'] = $this->randomName(8);
+    $body2 = $this->randomName(16);
+    $edit2["block_body[$langcode][0][value]"] = $body2;
+    $this->drupalPost('block/add/basic', $edit2, t('Save'));
+
+    $this->assertNoRaw('Error message');
+
+    // Create another block with no instances, and test we don't get a
+    // confirmation message about deleting instances.
+    $edit3 = array();
+    $edit3['info'] = $this->randomName(8);
+    $body = $this->randomName(16);
+    $edit3["block_body[$langcode][0][value]"] = $body;
+    $this->drupalPost('block/add/basic', $edit3, t('Save'));
+
+    // Show the delete confirm form.
+    $this->drupalGet('block/3/delete');
+    $this->assertNoText('This will also remove');
+  }
+
 }