drupal/core/modules/datetime_range/datetime_range.module

<?php

/**
 * @file
 * Field hooks to implement a datetime field that stores a start and end date.
 */

use Drupal\Core\Url;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\views\Views;
use Drupal\views\ViewEntityInterface;

/**
 * Implements hook_help().
 */
function datetime_range_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.datetime_range':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Datetime Range module provides a Date field that stores start dates and times, as well as end dates and times. See the <a href=":field">Field module help</a> and the <a href=":field_ui">Field UI module help</a> pages for general information on fields and how to create and manage them. For more information, see the <a href=":datetime_do">online documentation for the Datetime Range module</a>.', [':field' => Url::fromRoute('help.page', ['name' => 'field'])->toString(), ':field_ui' => (\Drupal::moduleHandler()->moduleExists('field_ui')) ? Url::fromRoute('help.page', ['name' => 'field_ui'])->toString() : '#', ':datetime_do' => 'https://www.drupal.org/documentation/modules/datetime_range']) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Managing and displaying date fields') . '</dt>';
      $output .= '<dd>' . t('The <em>settings</em> and the <em>display</em> of the Date field can be configured separately. See the <a href=":field_ui">Field UI help</a> for more information on how to manage fields and their display.', [':field_ui' => (\Drupal::moduleHandler()->moduleExists('field_ui')) ? Url::fromRoute('help.page', ['name' => 'field_ui'])->toString() : '#']) . '</dd>';
      $output .= '<dt>' . t('Displaying dates') . '</dt>';
      $output .= '<dd>' . t('Dates can be displayed using the <em>Plain</em> or the <em>Default</em> formatter. The <em>Plain</em> formatter displays the date in the <a href="http://en.wikipedia.org/wiki/ISO_8601">ISO 8601</a> format. If you choose the <em>Default</em> formatter, you can choose a format from a predefined list that can be managed on the <a href=":date_format_list">Date and time formats</a> page.', [':date_format_list' => Url::fromRoute('entity.date_format.collection')->toString()]) . '</dd>';
      $output .= '</dl>';
      return $output;
  }
}

/**
 * Implements hook_ENTITY_TYPE_presave().
 *
 * When a view is saved using the old string or standard plugin format for
 * Datetime Range filters or sorts, they will automatically be updated to
 * Datetime filters or sorts. Old plugins usage must to be considered
 * deprecated and must be converted before 9.0.0, when this updating layer will
 * be removed.
 *
 * @deprecated in Drupal 8.5.x and will be removed before 9.0.0.
 *
 * @see https://www.drupal.org/node/2857691
 */
function datetime_range_view_presave(ViewEntityInterface $view) {
  $config_factory = \Drupal::configFactory();
  $displays = $view->get('display');
  $changed = FALSE;

  foreach ($displays as $display_name => &$display) {

    // Update datetime_range filters.
    if (isset($display['display_options']['filters'])) {
      foreach ($display['display_options']['filters'] as $field_name => &$filter) {
        if ($filter['plugin_id'] === 'string') {
          $table_data = Views::viewsData()->get($filter['table']);
          if (!$table_data) {
            continue;
          }

          // Get field config.
          $filter_views_data = $table_data[$filter['field']]['filter'];
          if (!isset($filter_views_data['entity_type']) || !isset($filter_views_data['field_name'])) {
            continue;
          }
          $field_storage_name = 'field.storage.' . $filter_views_data['entity_type'] . '.' . $filter_views_data['field_name'];
          $field_configuration = $config_factory->get($field_storage_name);

          if ($field_configuration->get('type') === 'daterange') {

            // Set entity_type if missing.
            if (!isset($filter['entity_type'])) {
              $filter['entity_type'] = $filter_views_data['entity_type'];
            }

            // Set datetime plugin_id.
            $filter['plugin_id'] = 'datetime';

            // Create datetime value array.
            $datetime_value = [
              'min' => '',
              'max' => '',
              'value' => $filter['value'],
              'type' => 'date',
            ];

            // Map string operator/value to numeric equivalent.
            switch ($filter['operator']) {
              case '=':
              case 'empty':
              case 'not empty':
                $operator = $filter['operator'];
                break;

              case '!=':
              case 'not':
                $operator = '!=';
                break;

              case 'starts':
                $operator = 'regular_expression';
                $datetime_value['value'] = '^' . preg_quote($datetime_value['value']);
                break;

              case 'ends':
                $operator = 'regular_expression';
                $datetime_value['value'] = preg_quote($datetime_value['value']) . '$';
                break;

              default:
                $operator = 'regular_expression';
                // Add .* to prevent blank regexes.
                if (empty($datetime_value['value'])) {
                  $datetime_value['value'] = '.*';
                }
                else {
                  $datetime_value['value'] = preg_quote($datetime_value['value']);
                }
            }

            // Set value and operator.
            $filter['value'] = $datetime_value;
            $filter['operator'] = $operator;
            $changed = TRUE;
            @trigger_error('Use of string filters for datetime_range fields is deprecated. Use the datetime filters instead. See https://www.drupal.org/node/2857691', E_USER_DEPRECATED);
          }
        }
      }
    }

    // Update datetime_range sort handlers.
    if (isset($display['display_options']['sorts'])) {
      foreach ($display['display_options']['sorts'] as $field_name => &$sort) {
        if ($sort['plugin_id'] === 'standard') {
          $table_data = Views::viewsData()->get($sort['table']);
          if (!$table_data) {
            continue;
          }

          // Get field config.
          $sort_views_data = $table_data[$sort['field']]['sort'];
          if (!isset($sort_views_data['entity_type']) || !isset($sort_views_data['field_name'])) {
            continue;
          }
          $field_storage_name = 'field.storage.' . $sort_views_data['entity_type'] . '.' . $sort_views_data['field_name'];
          $field_configuration = $config_factory->get($field_storage_name);

          if ($field_configuration->get('type') === 'daterange') {

            // Set entity_type if missing.
            if (!isset($sort['entity_type'])) {
              $sort['entity_type'] = $sort_views_data['entity_type'];
            }

            // Set datetime plugin_id.
            $sort['plugin_id'] = 'datetime';
            $changed = TRUE;
            @trigger_error('Use of standard sort handlers for datetime_range fields is deprecated. Use the datetime sort handlers instead. See https://www.drupal.org/node/2857691', E_USER_DEPRECATED);
          }
        }
      }
    }
  }

  if ($changed) {
    $view->set('display', $displays);
  }
}