IndexTidDepthModifier.php

<?php

namespace Drupal\taxonomy\Plugin\views\argument;

use Drupal\Core\Form\FormStateInterface;
use Drupal\views\Attribute\ViewsArgument;
use Drupal\views\Plugin\views\argument\ArgumentPluginBase;

/**
 * Argument handler for to modify depth for a previous term.
 *
 * This handler is actually part of the node table and has some restrictions,
 * because it uses a subquery to find nodes with.
 *
 * @ingroup views_argument_handlers
 */
class IndexTidDepthModifier extends ArgumentPluginBase {
  public function buildOptionsForm(&$form, FormStateInterface $form_state) {
  }
  public function query($group_by = FALSE) {
  }
  public function preQuery() {
    // We don't know our argument yet, but it's based upon our position:
    $argument = $this->view->args[$this->position] ?? NULL;
    if (!is_numeric($argument)) {
      return;
    }
    if ($argument > 10) {
      $argument = 10;
    }
    if ($argument < -10) {
      $argument = -10;
    }
    // Figure out which argument preceded us.
    $keys = array_reverse(array_keys($this->view->argument));
    $skip = TRUE;
    foreach ($keys as $key) {
      if ($key == $this->options['id']) {
        $skip = FALSE;
        continue;
      }
      if ($skip) {
        continue;
      }
      if (empty($this->view->argument[$key])) {
        continue;
      }
      $handler =& $this->view->argument[$key];
      if (empty($handler->definition['accept depth modifier'])) {
        continue;
      }
      // Finally!
      $handler->options['depth'] = $argument;
    }
  }

}