class Boolean

1. 8.x drupal/core/lib/Drupal/Core/TypedData/Type/Boolean.php \Drupal\Core\TypedData\Type\Boolean
2. 8.x drupal/core/modules/views/lib/Drupal/views/Plugin/views/field/Boolean.php \Drupal\views\Plugin\views\field\Boolean

options_field_info in drupal/core/modules/options/options.module

Implements hook_field_info().

system.data_types.schema.yml in drupal/core/modules/system/config/schema/system.data_types.schema.yml

drupal/core/modules/system/config/schema/system.data_types.schema.yml

system_data_type_info in drupal/core/modules/system/system.module

Implements hook_data_type_info().

TypeValidatorTest::getValidValues in drupal/core/vendor/symfony/validator/Symfony/Component/Validator/Tests/Constraints/TypeValidatorTest.php

views.field.schema.yml in drupal/core/modules/views/config/schema/views.field.schema.yml

drupal/core/modules/views/config/schema/views.field.schema.yml

class Boolean extends FieldPluginBase {
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['type'] = array(
      'default' => 'yes-no',
    );
    $options['type_custom_true'] = array(
      'default' => '',
      'translatable' => TRUE,
    );
    $options['type_custom_false'] = array(
      'default' => '',
      'translatable' => TRUE,
    );
    $options['not'] = array(
      'default' => FALSE,
      'bool' => TRUE,
    );
    return $options;
  }

  /**
   * Overrides \Drupal\views\Plugin\views\field\FieldPluginBase::init().
   */
  public function init(ViewExecutable $view, DisplayPluginBase $display, array &$options = NULL) {
    parent::init($view, $display, $options);
    $default_formats = array(
      'yes-no' => array(
        t('Yes'),
        t('No'),
      ),
      'true-false' => array(
        t('True'),
        t('False'),
      ),
      'on-off' => array(
        t('On'),
        t('Off'),
      ),
      'enabled-disabled' => array(
        t('Enabled'),
        t('Disabled'),
      ),
      'boolean' => array(
        1,
        0,
      ),
      'unicode-yes-no' => array(
        '✔',
        '✖',
      ),
    );
    $output_formats = isset($this->definition['output formats']) ? $this->definition['output formats'] : array();
    $custom_format = array(
      'custom' => array(
        t('Custom'),
      ),
    );
    $this->formats = array_merge($default_formats, $output_formats, $custom_format);
  }
  public function buildOptionsForm(&$form, &$form_state) {
    foreach ($this->formats as $key => $item) {
      $options[$key] = implode('/', $item);
    }
    $form['type'] = array(
      '#type' => 'select',
      '#title' => t('Output format'),
      '#options' => $options,
      '#default_value' => $this->options['type'],
    );
    $form['type_custom_true'] = array(
      '#type' => 'textfield',
      '#title' => t('Custom output for TRUE'),
      '#default_value' => $this->options['type_custom_true'],
      '#states' => array(
        'visible' => array(
          'select[name="options[type]"]' => array(
            'value' => 'custom',
          ),
        ),
      ),
    );
    $form['type_custom_false'] = array(
      '#type' => 'textfield',
      '#title' => t('Custom output for FALSE'),
      '#default_value' => $this->options['type_custom_false'],
      '#states' => array(
        'visible' => array(
          'select[name="options[type]"]' => array(
            'value' => 'custom',
          ),
        ),
      ),
    );
    $form['not'] = array(
      '#type' => 'checkbox',
      '#title' => t('Reverse'),
      '#description' => t('If checked, true will be displayed as false.'),
      '#default_value' => $this->options['not'],
    );
    parent::buildOptionsForm($form, $form_state);
  }
  function render($values) {
    $value = $this
      ->getValue($values);
    if (!empty($this->options['not'])) {
      $value = !$value;
    }
    if ($this->options['type'] == 'custom') {
      return $value ? filter_xss_admin($this->options['type_custom_true']) : filter_xss_admin($this->options['type_custom_false']);
    }
    elseif (isset($this->formats[$this->options['type']])) {
      return $value ? $this->formats[$this->options['type']][0] : $this->formats[$this->options['type']][1];
    }
    else {
      return $value ? $this->formats['yes-no'][0] : $this->formats['yes-no'][1];
    }
  }

}