Issue #3283895 by Tim Bozeman: D9!

# Contextual Help

Provides pluggable toolbar help topics. Simply add a plugin to `/src/Plugin/Help/MyHelpTopic.php`.

#### Example plugin

```php

<?php

namespace Drupal\MY_MODULE\Plugin\Help;

use Drupal\contextual_help\HelpInterface;

use Drupal\Core\Routing\RouteMatchInterface;

/**

 * Clear Caches.

 *

 * @help(

 *   id = "clear_caches",

 *   title = @Translation("How to clear caches"),

 *   weight = 10,

 * )

 */

class MyHelpTopic implements HelpInterface {

  /**

   * {@inheritdoc}

   */

  public function applies(RouteMatchInterface $route_match): bool {

    return $route_match->getRouteName() === 'system.admin_content';

  }

  /**

   * {@inheritdoc}

   */

  public function display(): array {

    return [

      '#markup' => t('<p>Navigate Manage > Configuration > Development > Performance and click "Clear all caches".</p>'),

    ];

  }

}

```

name: Contextual Help

type: module

description: 'Provides a contextual user help system.'

core_version_requirement: ^8.8 || ^9

heading:

  version: 1.x

  css:

    theme:

      css/contextual-help.css: {}

<?php

/**

 * @file

 * Provides help items.

 */

use Drupal\Core\Url;

/**

 * Implements hook_toolbar().

 */

function contextual_help_toolbar() {

  $items = [];

  $items['contextual_help'] = [

    '#cache' => [

      'contexts' => [

        'url.path',

      ],

    ],

  ];

  if (!\Drupal::currentUser()->hasPermission('access contextual help')) {

    return $items;

  }

  $help_topics = Drupal::service('contextual_help')->getHelpTopics();

  if ($help_topics) {

    $items['contextual_help'] += [

      '#type' => 'toolbar_item',

      'tab' => [

        '#type' => 'link',

        '#title' => t('Help'),

        '#url' => Url::fromRoute('<front>'),

        '#attributes' => [

          'id' => 'contextual-help',

        ],

      ],

      'tray' => [

        'visible_heading' => ['#markup' => t('<h3 id="contextual-help-heading">Help Topics</h3>')],

        'help' => $help_topics,

      ],

      '#weight' => 90,

      '#wrapper_attributes' => [

        'class' => ['contextual-help-button'],

      ],

      '#attached' => [

        'library' => [

          'contextual_help/heading',

        ],

      ],

    ];

  }

  return $items;

}

access contextual help:

  title: 'Access Contextual Help'