ConfigsList.php

<?php

namespace Drupal\devel\Form;

use Drupal\Component\Utility\Html;
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Url;

/**
 * Form that displays all the config variables to edit them.
 */
class ConfigsList extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'devel_config_system_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, $filter = '') {
        $form['filter'] = [
            '#type' => 'details',
            '#title' => $this->t('Filter variables'),
            '#attributes' => [
                'class' => [
                    'container-inline',
                ],
            ],
            '#open' => isset($filter) && trim($filter) != '',
        ];
        $form['filter']['name'] = [
            '#type' => 'textfield',
            '#title' => $this->t('Variable name'),
            '#title_display' => 'invisible',
            '#default_value' => $filter,
        ];
        $form['filter']['actions'] = [
            '#type' => 'actions',
        ];
        $form['filter']['actions']['show'] = [
            '#type' => 'submit',
            '#value' => $this->t('Filter'),
        ];
        $header = [
            'name' => [
                'data' => $this->t('Name'),
            ],
            'edit' => [
                'data' => $this->t('Operations'),
            ],
        ];
        $rows = [];
        $destination = $this->getDestinationArray();
        // List all the variables filtered if any filter was provided.
        $names = $this->configFactory()
            ->listAll($filter);
        foreach ($names as $config_name) {
            $operations['edit'] = [
                'title' => $this->t('Edit'),
                'url' => Url::fromRoute('devel.config_edit', [
                    'config_name' => $config_name,
                ]),
                'query' => $destination,
            ];
            $rows[] = [
                'name' => $config_name,
                'operation' => [
                    'data' => [
                        '#type' => 'operations',
                        '#links' => $operations,
                    ],
                ],
            ];
        }
        $form['variables'] = [
            '#type' => 'table',
            '#header' => $header,
            '#rows' => $rows,
            '#empty' => $this->t('No variables found'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $filter = $form_state->getValue('name');
        $form_state->setRedirectUrl(Url::FromRoute('devel.configs_list', [
            'filter' => Html::escape($filter),
        ]));
    }

}