--- /dev/null
+<?php
+
+namespace Drupal\help\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Provides a 'Help' block.
+ *
+ * @Block(
+ * id = "help_block",
+ * admin_label = @Translation("Help")
+ * )
+ */
+class HelpBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+ /**
+ * The module handler.
+ *
+ * @var \Drupal\Core\Extension\ModuleHandlerInterface
+ */
+ protected $moduleHandler;
+
+ /**
+ * The current request.
+ *
+ * @var \Symfony\Component\HttpFoundation\Request
+ */
+ protected $request;
+
+ /**
+ * The current route match.
+ *
+ * @var \Drupal\Core\Routing\RouteMatchInterface
+ */
+ protected $routeMatch;
+
+ /**
+ * Creates a HelpBlock instance.
+ *
+ * @param array $configuration
+ * A configuration array containing information about the plugin instance.
+ * @param string $plugin_id
+ * The plugin_id for the plugin instance.
+ * @param mixed $plugin_definition
+ * The plugin implementation definition.
+ * @param \Symfony\Component\HttpFoundation\Request $request
+ * The current request.
+ * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+ * The module handler.
+ * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+ * The current route match.
+ */
+ public function __construct(array $configuration, $plugin_id, $plugin_definition, Request $request, ModuleHandlerInterface $module_handler, RouteMatchInterface $route_match) {
+ parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+ $this->request = $request;
+ $this->moduleHandler = $module_handler;
+ $this->routeMatch = $route_match;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+ return new static(
+ $configuration,
+ $plugin_id,
+ $plugin_definition,
+ $container->get('request_stack')->getCurrentRequest(),
+ $container->get('module_handler'),
+ $container->get('current_route_match')
+ );
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function build() {
+ // Do not show on a 403 or 404 page.
+ if ($this->request->attributes->has('exception')) {
+ return [];
+ }
+
+ $implementations = $this->moduleHandler->getImplementations('help');
+ $build = [];
+ $args = [
+ $this->routeMatch->getRouteName(),
+ $this->routeMatch,
+ ];
+ foreach ($implementations as $module) {
+ // Don't add empty strings to $build array.
+ if ($help = $this->moduleHandler->invoke($module, 'help', $args)) {
+ // Convert strings to #markup render arrays so that they will XSS admin
+ // filtered.
+ $build[] = is_array($help) ? $help : ['#markup' => $help];
+ }
+ }
+ return $build;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getCacheContexts() {
+ return Cache::mergeContexts(parent::getCacheContexts(), ['route']);
+ }
+
+}