form_test.module

<?php

/**
 * @file
 * Helper module for the form API tests.
 */
use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_form_FORM_ID_alter().
 */
function block_form_form_test_alter_form_alter(&$form, FormStateInterface $form_state) {
  \Drupal::messenger()
    ->addStatus('block_form_form_test_alter_form_alter() executed.');
}

/**
 * Implements hook_form_alter().
 */
function form_test_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'form_test_alter_form') {
    \Drupal::messenger()
      ->addStatus('form_test_form_alter() executed.');
  }
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function form_test_form_form_test_alter_form_alter(&$form, FormStateInterface $form_state) {
  \Drupal::messenger()
    ->addStatus('form_test_form_form_test_alter_form_alter() executed.');
}

/**
 * Implements hook_form_FORM_ID_alter().
 */
function system_form_form_test_alter_form_alter(&$form, FormStateInterface $form_state) {
  \Drupal::messenger()
    ->addStatus('system_form_form_test_alter_form_alter() executed.');
}

/**
 * Create a header and options array. Helper function for callbacks.
 */
function _form_test_tableselect_get_data() {
  $header = [
    'one' => t('One'),
    'two' => t('Two'),
    'three' => t('Three'),
    'four' => t('Four'),
  ];
  $options['row1'] = [
    'title' => [
      'data' => [
        '#title' => t('row1'),
      ],
    ],
    'one' => 'row1col1',
    'two' => t('row1col2'),
    'three' => t('row1col3'),
    'four' => t('row1col4'),
  ];
  $options['row2'] = [
    'title' => [
      'data' => [
        '#title' => t('row2'),
      ],
    ],
    'one' => 'row2col1',
    'two' => t('row2col2'),
    'three' => t('row2col3'),
    'four' => t('row2col4'),
  ];
  $options['row3'] = [
    'title' => [
      'data' => [
        '#title' => t('row3'),
      ],
    ],
    'one' => 'row3col1',
    'two' => t('row3col2'),
    'three' => t('row3col3'),
    'four' => t('row3col4'),
  ];
  return [
    $header,
    $options,
  ];
}

/**
 * Implements hook_form_FORM_ID_alter() for the registration form.
 */
function form_test_form_user_register_form_alter(&$form, FormStateInterface $form_state) {
  $form['test_rebuild'] = [
    '#type' => 'submit',
    '#value' => t('Rebuild'),
    '#submit' => [
      'form_test_user_register_form_rebuild',
    ],
  ];
}

/**
 * Submit callback that just lets the form rebuild.
 */
function form_test_user_register_form_rebuild($form, FormStateInterface $form_state) {
  \Drupal::messenger()
    ->addStatus('Form rebuilt.');
  $form_state
    ->setRebuild();
}

/**
 * Implements hook_form_FORM_ID_alter() for form_test_vertical_tabs_access_form().
 */
function form_test_form_form_test_vertical_tabs_access_form_alter(&$form, &$form_state, $form_id) {
  $form['vertical_tabs1']['#access'] = FALSE;
  $form['vertical_tabs2']['#access'] = FALSE;
  $form['tabs3']['#access'] = TRUE;
  $form['fieldset1']['#access'] = FALSE;
  $form['container']['#access'] = FALSE;
}

/**
 * Ajax callback that returns the form element.
 */
function form_test_tableselect_ajax_callback($form, FormStateInterface $form_state) {
  return $form['tableselect'];
}