Issue #3269276 by RenatoG: Create a route to delete block class by id with confirmationForm

  requirements:

    _permission: 'administer block classes'

block_class.confirm_deletion:

  path: '/admin/config/content/block-class/delete/{bid}'

  defaults:

    _form: '\Drupal\block_class\Form\BlockClassConfirmDeletionForm'

    _title: 'Confirm Deletion'

  requirements:

    _permission: 'administer block classes'

block_class.list:

  path: '/admin/config/content/block-class/list'

  defaults:

<?php

namespace Drupal\block_class\Form;

use Drupal\Core\Form\ConfirmFormBase;

use Drupal\Core\Form\FormStateInterface;

use Drupal\Core\Url;

use Drupal\block\Entity\Block;

use Symfony\Component\HttpFoundation\RedirectResponse;

/**

 * Form for Block Class Confirm Bulk Operation.

 */

class BlockClassConfirmDeletionForm extends ConfirmFormBase {

  /**

   * Block ID.

   *

   * @var string

   */

  protected $bid;

  /**

   * {@inheritdoc}

   */

  // @codingStandardsIgnoreLine

  public function buildForm(array $form, FormStateInterface $form_state, $bid = NULL) {

    $this->bid = $bid;

    $message_to_confirm = (string) $this->getQuestion();

    $form['message_to_confirm'] = [

      '#type' => 'item',

      '#markup' => $message_to_confirm,

    ];

    return parent::buildForm($form, $form_state);

  }

  /**

   * {@inheritdoc}

   */

  public function submitForm(array &$form, FormStateInterface $form_state) {

    // Load block. Todo: We'll implements DI here @codingStandardsIgnoreLine

    $block = Block::load($this->bid);

    // If there is ThirdPartySetting remove that.

    $block->unsetThirdPartySetting('block_class', 'classes');

    // Block save.

    $block->save();

    // Set a messsage.

    \Drupal::messenger()->addStatus($this->t('Block Class deleted'));

    // Get the block class list path.

    $block_class_list_path = Url::fromRoute('block_class.list')->toString();

    // Get response.

    $response = new RedirectResponse($block_class_list_path);

    // Send to confirmation.

    $response->send();

    exit;

  }

  /**

   * {@inheritdoc}

   */

  public function getFormId() : string {

    return "block_class_confirm_deletion_form";

  }

  /**

   * {@inheritdoc}

   */

  public function getCancelUrl() {

    return Url::fromRoute('block_class.list');

  }

  /**

   * {@inheritdoc}

   */

  public function getQuestion() {

    $message_to_confirm = $this->t('Are you sure?');

    return $message_to_confirm;

  }

}