Add a cache tag to invalidate a group's user membership listings

config/schema/og.schema.yml

@@ -193,3 +193,14 @@ condition.plugin.og_group_type:
       type: sequence
       sequence:
         type: string
+
+block.settings.og_member_count:
+  type: block_settings
+  label: 'Group member count block'
+  mapping:
+    count_blocked_users:
+      type: boolean
+      label: 'Count blocked users'
+    count_pending_users:
+      type: boolean
+      label: 'Count pending users'

og.module

@@ -303,6 +303,38 @@ function og_entity_type_alter(array &$entity_types) {
   }
 }
 
+/**
+ * Implements hook_theme().
+ */
+function og_theme($existing, $type, $theme, $path) {
+  return [
+    'og_member_count' => [
+      'variables' => [
+        'count' => 0,
+        'membership_states' => [],
+        'group' => NULL,
+      ],
+    ],
+  ];
+}
+
+/**
+ * Prepares variables for member count templates.
+ *
+ * Default template: og-member-count.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - count: An integer representing the number of members in the group.
+ *   - group: The group, which is a content entity.
+ */
+function template_preprocess_og_member_count(array &$variables) {
+  /** @var \Drupal\Core\Entity\ContentEntityInterface $group */
+  $group = $variables['group'];
+
+  $variables['group_label'] = $group->label();
+}
+
 /**
  * Invalidates group content cache tags for the groups this entity belongs to.
  *

src/Entity/OgMembership.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\og\Entity;
 
+use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\ContentEntityBase;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
@@ -482,6 +483,42 @@ public function save() {
     return $result;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function invalidateTagsOnSave($update) {
+    parent::invalidateTagsOnSave($update);
+
+    // A membership was created or updated: invalidate the membership list cache
+    // tags of its group. An updated membership may start to appear in a group's
+    // membership listings because it now meets those listings' filtering
+    // requirements. A newly created membership may start to appear in listings
+    // because it did not exist before.
+    $group = $this->getGroup();
+    if (!empty($group)) {
+      $tags = Cache::buildTags(OgMembershipInterface::GROUP_MEMBERSHIP_LIST_CACHE_TAG_PREFIX, $group->getCacheTagsToInvalidate());
+      Cache::invalidateTags($tags);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static function invalidateTagsOnDelete(EntityTypeInterface $entity_type, array $entities) {
+    parent::invalidateTagsOnDelete($entity_type, $entities);
+
+    // A membership was deleted: invalidate the list cache tags of its group
+    // membership lists, so that any lists that contain the membership will be
+    // recalculated.
+    $tags = [];
+    foreach ($entities as $entity) {
+      if ($group = $entity->getGroup()) {
+        $tags = Cache::mergeTags(Cache::buildTags(OgMembershipInterface::GROUP_MEMBERSHIP_LIST_CACHE_TAG_PREFIX, $group->getCacheTagsToInvalidate()), $tags);
+      }
+    }
+    Cache::invalidateTags($tags);
+  }
+
   /**
    * {@inheritdoc}
    */

src/MembershipManagerInterface.php

@@ -193,7 +193,7 @@ public function getGroups(EntityInterface $entity, $group_type_id = NULL, $group
    * Returns the number of groups associated with a given group content entity.
    *
    * Do not use this to retrieve the group membership count for a user entity.
-   * Use count(Og::GetEntityGroups()) instead.
+   * Use count(\Drupal\og\MembershipManager::getUserGroupIds()) instead.
    *
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The group content entity for which to count the associated groups.

src/OgMembershipInterface.php

@@ -57,6 +57,11 @@ interface OgMembershipInterface extends ContentEntityInterface, EntityOwnerInter
    */
   const REQUEST_FIELD = 'og_membership_request';
 
+  /**
+   * The prefix that is used to identify group membership list cache tags.
+   */
+  const GROUP_MEMBERSHIP_LIST_CACHE_TAG_PREFIX = 'og-group-membership-list';
+
   /**
    * Gets the membership creation timestamp.
    *

src/Plugin/Block/MemberCountBlock.php

@@ -0,0 +1,166 @@
+<?php
+
+namespace Drupal\og\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\og\MembershipManagerInterface;
+use Drupal\og\OgContextInterface;
+use Drupal\og\OgMembershipInterface;
+use Drupal\og\OgRoleInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a block that shows the number of members in the current group.
+ *
+ * This block is mainly intended to demonstrate the group membership list cache
+ * tag but can also be used to show the number of members on group pages. The
+ * way the text is displayed can be changed by overriding the Twig template.
+ *
+ * @Block(
+ *   id = "og_member_count",
+ *   admin_label = @Translation("Group member count")
+ * )
+ */
+class MemberCountBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The OG context provider.
+   *
+   * @var \Drupal\og\OgContextInterface
+   */
+  protected $ogContext;
+
+  /**
+   * The membership manager.
+   *
+   * @var \Drupal\og\MembershipManagerInterface
+   */
+  protected $membershipManager;
+
+  /**
+   * Constructs a MemberCountBlock object.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param string $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\og\OgContextInterface $og_context
+   *   The OG context provider.
+   * @param \Drupal\og\MembershipManagerInterface $membership_manager
+   *   The membership manager.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, OgContextInterface $og_context, MembershipManagerInterface $membership_manager) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+    $this->ogContext = $og_context;
+    $this->membershipManager = $membership_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('og.context'),
+      $container->get('og.membership_manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'count_blocked_users' => FALSE,
+      'count_pending_users' => FALSE,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    $form['count_blocked_users'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Count blocked users'),
+      '#default_value' => $this->configuration['count_blocked_users'],
+    ];
+
+    $form['count_pending_users'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Count pending users'),
+      '#default_value' => $this->configuration['count_pending_users'],
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockSubmit($form, FormStateInterface $form_state) {
+    foreach (array_keys($this->defaultConfiguration()) as $setting) {
+      $this->configuration[$setting] = $form_state->getValue($setting);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    // Do not render anything if there is no group in the current context.
+    $group = $this->ogContext->getGroup();
+    if (empty($group)) {
+      return [];
+    }
+
+    $states = [OgMembershipInterface::STATE_ACTIVE];
+
+    if ($this->configuration['count_blocked_users']) {
+      $states[] = OgMembershipInterface::STATE_BLOCKED;
+    }
+
+    if ($this->configuration['count_pending_users']) {
+      $states[] = OgMembershipInterface::STATE_PENDING;
+    }
+
+    $membership_ids = $this->membershipManager->getGroupMembershipIdsByRoleNames($group, [OgRoleInterface::AUTHENTICATED], $states);
+
+    return [
+      '#theme' => 'og_member_count',
+      '#count' => count($membership_ids),
+      '#group' => $group,
+      '#membership_states' => $states,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheTags() {
+    $tags = parent::getCacheTags();
+
+    $group = $this->ogContext->getGroup();
+    if (!empty($group)) {
+      $tags = Cache::mergeTags(Cache::buildTags(OgMembershipInterface::GROUP_MEMBERSHIP_LIST_CACHE_TAG_PREFIX, $group->getCacheTagsToInvalidate()), $tags);
+    }
+
+    return $tags;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheContexts() {
+    return Cache::mergeContexts(parent::getCacheContexts(), ['og_group_context']);
+  }
+
+}

templates/og-member-count.html.twig

@@ -0,0 +1,22 @@
+{#
+/**
+ * @file
+ * Default theme implementation to show the member count of a group.
+ *
+ * Available variables:
+ * - count: The number of members in the group.
+ * - membership_states: An array of membership states included in the count.
+ * - group_label: The group label.
+ *
+ * @see \Drupal\og\Plugin\Block\MemberCountBlock
+ *
+ * @ingroup themeable
+ */
+#}
+<p>
+    {% trans %}
+        {{ group_label }} has 1 member.
+    {% plural count %}
+        {{ group_label }} has {{ count }} members.
+    {% endtrans %}
+</p>