is2_site_release_info.module

<?php
/**
 * @file
 * Contains the hooks for this module.
 */

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\is2_site_release_info\Callback\PreRenderCallback;

/**
 * Implements hook_help().
 */
function is2_site_release_info_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.is2_site_release_info':
      $output = '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('This module is a lightweight module and reads RELEASE.md file contents (if present) and showcases information in the Drupal toolbar section.') . '</p>';
      return $output;
  }
}

/**
 * Implements hook_toolbar().
 */
function is2_site_release_info_toolbar():array {
  $user = \Drupal::currentUser();
  $items = [];
  $items['release_version'] = [
    '#cache' => [
      'contexts' => [
        'user.permissions',
        'user.roles:anonymous',
      ],
    ],
  ];

  if ($user->hasPermission('access shortcuts')) {
    $items['release_version'] += [
      '#type' => 'toolbar_item',
      'tab' => [
        '#lazy_builder' => [
          'is2_site_release_info.toolbar_data_builder:renderReleaseInformation',
          [],
        ],
        '#create_placeholder' => TRUE,
      ],
      '#wrapper_attributes' => [
        'class' => [
          'toolbar-item',
          'release-info',
        ],
      ],
      '#weight' => 9999,
    ];
  }
  // Remove the attribute field.
  $items['release_version'] += \Drupal::service('plugin.manager.element_info')->getInfo('toolbar_item');
  $items['release_version']['#pre_render'][] = [PreRenderCallback::class, 'removeTabAttributes'];

  return $items;
}