BlockLibraryController::listBlocks

public BlockLibraryController::listBlocks(Request $request, $theme)

public function listBlocks(Request $request, $theme) {
  // Since modals do not render any other part of the page, we need to render
  // them manually as part of this listing.
  if ($request->query->get(MainContentViewSubscriber::WRAPPER_FORMAT) === 'drupal_modal') {
    $build['local_actions'] = $this->buildLocalActions();
  }

  $headers = [
    ['data' => $this->t('Block')],
    ['data' => $this->t('Category')],
    ['data' => $this->t('Operations')],
  ];

  // Only add blocks which work without any available context.
  $definitions = $this->blockManager->getDefinitionsForContexts($this->contextRepository->getAvailableContexts());
  // Order by category, and then by admin label.
  $definitions = $this->blockManager->getSortedDefinitions($definitions);

  $region = $request->query->get('region');
  $weight = $request->query->get('weight');
  $rows = [];
  foreach ($definitions as $plugin_id => $plugin_definition) {
    $row = [];
    $row['title']['data'] = [
      '#type' => 'inline_template',
      '#template' => '<div class="block-filter-text-source">{{ label }}</div>',
      '#context' => [
        'label' => $plugin_definition['admin_label'],
      ],
    ];
    $row['category']['data'] = $plugin_definition['category'];
    $links['add'] = [
      'title' => $this->t('Place block'),
      'url' => Url::fromRoute('block.admin_add', ['plugin_id' => $plugin_id, 'theme' => $theme]),
      'attributes' => [
        'class' => ['use-ajax'],
        'data-dialog-type' => 'modal',
        'data-dialog-options' => Json::encode([
          'width' => 700,
        ]),
      ],
    ];
    if ($region) {
      $links['add']['query']['region'] = $region;
    }
    if (isset($weight)) {
      $links['add']['query']['weight'] = $weight;
    }
    $row['operations']['data'] = [
      '#type' => 'operations',
      '#links' => $links,
    ];
    $rows[] = $row;
  }

  $build['#attached']['library'][] = 'block/drupal.block.admin';

  $build['filter'] = [
    '#type' => 'search',
    '#title' => $this->t('Filter'),
    '#title_display' => 'invisible',
    '#size' => 30,
    '#placeholder' => $this->t('Filter by block name'),
    '#attributes' => [
      'class' => ['block-filter-text'],
      'data-element' => '.block-add-table',
      'title' => $this->t('Enter a part of the block name to filter by.'),
    ],
  ];

  $build['blocks'] = [
    '#type' => 'table',
    '#header' => $headers,
    '#rows' => $rows,
    '#empty' => $this->t('No blocks available.'),
    '#attributes' => [
      'class' => ['block-add-table'],
    ],
  ];

  return $build;
}