TemporaryQueryGuard.php

<?php

namespace Drupal\jsonapi\Access;

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Config\Entity\ConfigEntityTypeInterface;
use Drupal\Core\Entity\EntityFieldManagerInterface;
use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\Core\Entity\Query\QueryInterface;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Field\FieldStorageDefinitionInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\Core\TypedData\DataReferenceDefinitionInterface;
use Drupal\jsonapi\Query\EntityCondition;
use Drupal\jsonapi\Query\EntityConditionGroup;
use Drupal\jsonapi\Query\Filter;

/**
 * Adds sufficient access control to collection queries.
 *
 * This class will be removed when new Drupal core APIs have been put in place
 * to make it obsolete.
 *
 * @internal JSON:API maintains no PHP API. The API is the HTTP API. This class
 *   may change at any time and could break any dependencies on it.
 *
 * @todo These additional security measures should eventually reside in the
 *   Entity API subsystem but were introduced here to address a security
 *   vulnerability. The following two issues should obsolesce this class:
 *
 * @see https://www.drupal.org/project/drupal/issues/2809177
 * @see https://www.drupal.org/project/drupal/issues/777578
 *
 * @see https://www.drupal.org/project/drupal/issues/3032787
 * @see jsonapi.api.php
 */
class TemporaryQueryGuard {
    
    /**
     * The entity field manager.
     *
     * @var \Drupal\Core\Entity\EntityFieldManagerInterface
     */
    protected static $fieldManager;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected static $moduleHandler;
    
    /**
     * Sets the entity field manager.
     *
     * This must be called before calling ::applyAccessControls().
     *
     * @param \Drupal\Core\Entity\EntityFieldManagerInterface $field_manager
     *   The entity field manager.
     */
    public static function setFieldManager(EntityFieldManagerInterface $field_manager) {
        static::$fieldManager = $field_manager;
    }
    
    /**
     * Sets the module handler.
     *
     * This must be called before calling ::applyAccessControls().
     *
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     */
    public static function setModuleHandler(ModuleHandlerInterface $module_handler) {
        static::$moduleHandler = $module_handler;
    }
    
    /**
     * Applies access controls to an entity query.
     *
     * @param \Drupal\jsonapi\Query\Filter $filter
     *   The filters applicable to the query.
     * @param \Drupal\Core\Entity\Query\QueryInterface $query
     *   The query to which access controls should be applied.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     */
    public static function applyAccessControls(Filter $filter, QueryInterface $query, CacheableMetadata $cacheability) {
        assert(static::$fieldManager !== NULL);
        assert(static::$moduleHandler !== NULL);
        $filtered_fields = static::collectFilteredFields($filter->root());
        $field_specifiers = array_map(function ($field) {
            return explode('.', $field);
        }, $filtered_fields);
        static::secureQuery($query, $query->getEntityTypeId(), static::buildTree($field_specifiers), $cacheability);
    }
    
    /**
     * Applies tags, metadata and conditions to secure an entity query.
     *
     * @param \Drupal\Core\Entity\Query\QueryInterface $query
     *   The query to be secured.
     * @param string $entity_type_id
     *   An entity type ID.
     * @param array $tree
     *   A tree of field specifiers in an entity query condition. The tree is a
     *   multi-dimensional array where the keys are field specifiers and the
     *   values are multi-dimensional array of the same form, containing only
     *   subsequent specifiers. @see ::buildTree().
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     * @param string|null $field_prefix
     *   Internal use only. Contains a string representation of the previously
     *   visited field specifiers.
     * @param \Drupal\Core\Field\FieldStorageDefinitionInterface $field_storage_definition
     *   Internal use only. The current field storage definition, if known.
     *
     * @see \Drupal\Core\Database\Query\AlterableInterface::addTag()
     * @see \Drupal\Core\Database\Query\AlterableInterface::addMetaData()
     * @see \Drupal\Core\Database\Query\ConditionInterface
     */
    protected static function secureQuery(QueryInterface $query, $entity_type_id, array $tree, CacheableMetadata $cacheability, $field_prefix = NULL, FieldStorageDefinitionInterface $field_storage_definition = NULL) {
        $entity_type = \Drupal::entityTypeManager()->getDefinition($entity_type_id);
        // Config entity types are not fieldable, therefore they do not have field
        // access restrictions, nor entity references to other entity types.
        if ($entity_type instanceof ConfigEntityTypeInterface) {
            return;
        }
        foreach ($tree as $specifier => $children) {
            // The field path reconstructs the entity condition fields.
            // E.g. `uid.0` would become `uid.0.name` if $specifier === 'name'.
            $child_prefix = is_null($field_prefix) ? $specifier : "{$field_prefix}.{$specifier}";
            if (is_null($field_storage_definition)) {
                // When the field storage definition is NULL, this specifier is the
                // first specifier in an entity query field path or the previous
                // specifier was a data reference that has been traversed. In both
                // cases, the specifier must be a field name.
                $field_storage_definitions = static::$fieldManager->getFieldStorageDefinitions($entity_type_id);
                static::secureQuery($query, $entity_type_id, $children, $cacheability, $child_prefix, $field_storage_definitions[$specifier]);
                // When $field_prefix is NULL, this must be the first specifier in the
                // entity query field path and a condition for the query's base entity
                // type must be applied.
                if (is_null($field_prefix)) {
                    static::applyAccessConditions($query, $entity_type_id, NULL, $cacheability);
                }
            }
            else {
                // When the specifier is an entity reference, it can contain an entity
                // type specifier, like so: `entity:node`. This extracts the `entity`
                // portion. JSON:API will have already validated that the property
                // exists.
                $split_specifier = explode(':', $specifier, 2);
                [
                    $property_name,
                    $target_entity_type_id,
                ] = array_merge($split_specifier, count($split_specifier) === 2 ? [] : [
                    NULL,
                ]);
                // The specifier is either a field property or a delta. If it is a data
                // reference or a delta, then it needs to be traversed to the next
                // specifier. However, if the specific is a simple field property, i.e.
                // it is neither a data reference nor a delta, then there is no need to
                // evaluate the remaining specifiers.
                $property_definition = $field_storage_definition->getPropertyDefinition($property_name);
                if ($property_definition instanceof DataReferenceDefinitionInterface) {
                    // Because the filter is following an entity reference, ensure
                    // access is respected on those targeted entities.
                    // Examples:
                    // - node_query_node_access_alter()
                    $target_entity_type_id = $target_entity_type_id ?: $field_storage_definition->getSetting('target_type');
                    $query->addTag("{$target_entity_type_id}_access");
                    static::applyAccessConditions($query, $target_entity_type_id, $child_prefix, $cacheability);
                    // Keep descending the tree.
                    static::secureQuery($query, $target_entity_type_id, $children, $cacheability, $child_prefix);
                }
                elseif (is_null($property_definition)) {
                    assert(is_numeric($property_name), 'The specifier is not a property name, it must be a delta.');
                    // Keep descending the tree.
                    static::secureQuery($query, $entity_type_id, $children, $cacheability, $child_prefix, $field_storage_definition);
                }
            }
        }
    }
    
    /**
     * Applies access conditions to ensure 'view' access is respected.
     *
     * Since the given entity type might not be the base entity type of the query,
     * the field prefix should be applied to ensure that the conditions are
     * applied to the right subset of entities in the query.
     *
     * @param \Drupal\Core\Entity\Query\QueryInterface $query
     *   The query to which access conditions should be applied.
     * @param string $entity_type_id
     *   The entity type for which to access conditions should be applied.
     * @param string|null $field_prefix
     *   A prefix to add before any query condition fields. NULL if no prefix
     *   should be added.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     */
    protected static function applyAccessConditions(QueryInterface $query, $entity_type_id, $field_prefix, CacheableMetadata $cacheability) {
        $access_condition = static::getAccessCondition($entity_type_id, $cacheability);
        if ($access_condition) {
            $prefixed_condition = !is_null($field_prefix) ? static::addConditionFieldPrefix($access_condition, $field_prefix) : $access_condition;
            $filter = new Filter($prefixed_condition);
            $query->condition($filter->queryCondition($query));
        }
    }
    
    /**
     * Prefixes all fields in an EntityConditionGroup.
     */
    protected static function addConditionFieldPrefix(EntityConditionGroup $group, $field_prefix) {
        $prefixed = [];
        foreach ($group->members() as $member) {
            if ($member instanceof EntityConditionGroup) {
                $prefixed[] = static::addConditionFieldPrefix($member, $field_prefix);
            }
            else {
                $field = !empty($field_prefix) ? "{$field_prefix}." . $member->field() : $member->field();
                $prefixed[] = new EntityCondition($field, $member->value(), $member->operator());
            }
        }
        return new EntityConditionGroup($group->conjunction(), $prefixed);
    }
    
    /**
     * Gets an EntityConditionGroup that filters out inaccessible entities.
     *
     * @param string $entity_type_id
     *   The entity type ID for which to get an EntityConditionGroup.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     *
     * @return \Drupal\jsonapi\Query\EntityConditionGroup|null
     *   An EntityConditionGroup or NULL if no conditions need to be applied to
     *   secure an entity query.
     */
    protected static function getAccessCondition($entity_type_id, CacheableMetadata $cacheability) {
        $current_user = \Drupal::currentUser();
        $entity_type = \Drupal::entityTypeManager()->getDefinition($entity_type_id);
        // Get the condition that handles generic restrictions, such as published
        // and owner.
        $generic_condition = static::getAccessConditionForKnownSubsets($entity_type, $current_user, $cacheability);
        // Some entity types require additional conditions. We don't know what
        // contrib entity types require, so they are responsible for implementing
        // hook_query_ENTITY_TYPE_access_alter(). Some core entity types have
        // logic in their access control handler that isn't mirrored in
        // hook_query_ENTITY_TYPE_access_alter(), so we duplicate that here until
        // that's resolved.
        $specific_condition = NULL;
        switch ($entity_type_id) {
            case 'block_content':
                // Allow access only to reusable blocks.
                // @see \Drupal\block_content\BlockContentAccessControlHandler::checkAccess()
                if (isset(static::$fieldManager->getBaseFieldDefinitions($entity_type_id)['reusable'])) {
                    $specific_condition = new EntityCondition('reusable', 1);
                    $cacheability->addCacheTags($entity_type->getListCacheTags());
                }
                break;
            case 'comment':
                // @see \Drupal\comment\CommentAccessControlHandler::checkAccess()
                $specific_condition = static::getCommentAccessCondition($entity_type, $current_user, $cacheability);
                break;
            case 'entity_test':
                // This case is only necessary for testing comment access controls.
                // @see \Drupal\jsonapi\Tests\Functional\CommentTest::testCollectionFilterAccess()
                $blacklist = \Drupal::state()->get('jsonapi__entity_test_filter_access_blacklist', []);
                $cacheability->addCacheTags([
                    'state:jsonapi__entity_test_filter_access_blacklist',
                ]);
                $specific_conditions = [];
                foreach ($blacklist as $id) {
                    $specific_conditions[] = new EntityCondition('id', $id, '<>');
                }
                if ($specific_conditions) {
                    $specific_condition = new EntityConditionGroup('AND', $specific_conditions);
                }
                break;
            case 'file':
                // Allow access only to public files and files uploaded by the current
                // user.
                // @see \Drupal\file\FileAccessControlHandler::checkAccess()
                $specific_condition = new EntityConditionGroup('OR', [
                    new EntityCondition('uri', 'public://', 'STARTS_WITH'),
                    new EntityCondition('uid', $current_user->id()),
                ]);
                $cacheability->addCacheTags($entity_type->getListCacheTags());
                break;
            case 'shortcut':
                // Unless the user can administer shortcuts, allow access only to the
                // user's currently displayed shortcut set.
                // @see \Drupal\shortcut\ShortcutAccessControlHandler::checkAccess()
                if (!$current_user->hasPermission('administer shortcuts')) {
                    $specific_condition = new EntityCondition('shortcut_set', shortcut_current_displayed_set()->id());
                    $cacheability->addCacheContexts([
                        'user',
                    ]);
                    $cacheability->addCacheTags($entity_type->getListCacheTags());
                }
                break;
            case 'user':
                // Disallow querying values of the anonymous user.
                // @see \Drupal\user\UserAccessControlHandler::checkAccess()
                $specific_condition = new EntityCondition('uid', '0', '!=');
                break;
        }
        // Return a combined condition.
        if ($generic_condition && $specific_condition) {
            return new EntityConditionGroup('AND', [
                $generic_condition,
                $specific_condition,
            ]);
        }
        elseif ($generic_condition) {
            return $generic_condition instanceof EntityConditionGroup ? $generic_condition : new EntityConditionGroup('AND', [
                $generic_condition,
            ]);
        }
        elseif ($specific_condition) {
            return $specific_condition instanceof EntityConditionGroup ? $specific_condition : new EntityConditionGroup('AND', [
                $specific_condition,
            ]);
        }
        return NULL;
    }
    
    /**
     * Gets an access condition for the allowed JSONAPI_FILTER_AMONG_* subsets.
     *
     * If access is allowed for the JSONAPI_FILTER_AMONG_ALL subset, then no
     * conditions are returned. Otherwise, if access is allowed for
     * JSONAPI_FILTER_AMONG_PUBLISHED, JSONAPI_FILTER_AMONG_ENABLED, or
     * JSONAPI_FILTER_AMONG_OWN, then a condition group is returned for the union
     * of allowed subsets. If no subsets are allowed, then static::alwaysFalse()
     * is returned.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type for which to check filter access.
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The account for which to check access.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     *
     * @return \Drupal\jsonapi\Query\EntityConditionGroup|null
     *   An EntityConditionGroup or NULL if no conditions need to be applied to
     *   secure an entity query.
     */
    protected static function getAccessConditionForKnownSubsets(EntityTypeInterface $entity_type, AccountInterface $account, CacheableMetadata $cacheability) {
        // Get the combined access results for each JSONAPI_FILTER_AMONG_* subset.
        $access_results = static::getAccessResultsFromEntityFilterHook($entity_type, $account);
        // No conditions are needed if access is allowed for all entities.
        $cacheability->addCacheableDependency($access_results[JSONAPI_FILTER_AMONG_ALL]);
        if ($access_results[JSONAPI_FILTER_AMONG_ALL]->isAllowed()) {
            return NULL;
        }
        // If filtering is not allowed across all entities, but is allowed for
        // certain subsets, then add conditions that reflect those subsets. These
        // will be grouped in an OR to reflect that access may be granted to
        // more than one subset. If no conditions are added below, then
        // static::alwaysFalse() is returned.
        $conditions = [];
        // The "published" subset.
        $published_field_name = $entity_type->getKey('published');
        if ($published_field_name) {
            $access_result = $access_results[JSONAPI_FILTER_AMONG_PUBLISHED];
            $cacheability->addCacheableDependency($access_result);
            if ($access_result->isAllowed()) {
                $conditions[] = new EntityCondition($published_field_name, 1);
                $cacheability->addCacheTags($entity_type->getListCacheTags());
            }
        }
        // The "enabled" subset.
        // @todo Remove ternary when the 'status' key is added to the User entity type.
        $status_field_name = $entity_type->id() === 'user' ? 'status' : $entity_type->getKey('status');
        if ($status_field_name) {
            $access_result = $access_results[JSONAPI_FILTER_AMONG_ENABLED];
            $cacheability->addCacheableDependency($access_result);
            if ($access_result->isAllowed()) {
                $conditions[] = new EntityCondition($status_field_name, 1);
                $cacheability->addCacheTags($entity_type->getListCacheTags());
            }
        }
        // The "owner" subset.
        // @todo Remove ternary when the 'uid' key is added to the User entity type.
        $owner_field_name = $entity_type->id() === 'user' ? 'uid' : $entity_type->getKey('owner');
        if ($owner_field_name) {
            $access_result = $access_results[JSONAPI_FILTER_AMONG_OWN];
            $cacheability->addCacheableDependency($access_result);
            if ($access_result->isAllowed()) {
                $cacheability->addCacheContexts([
                    'user',
                ]);
                if ($account->isAuthenticated()) {
                    $conditions[] = new EntityCondition($owner_field_name, $account->id());
                    $cacheability->addCacheTags($entity_type->getListCacheTags());
                }
            }
        }
        // If no conditions were added above, then access wasn't granted to any
        // subset, so return alwaysFalse().
        if (empty($conditions)) {
            return static::alwaysFalse($entity_type);
        }
        // If more than one condition was added above, then access was granted to
        // more than one subset, so combine them with an OR.
        if (count($conditions) > 1) {
            return new EntityConditionGroup('OR', $conditions);
        }
        // Otherwise return the single condition.
        return $conditions[0];
    }
    
    /**
     * Gets the combined access result for each JSONAPI_FILTER_AMONG_* subset.
     *
     * This invokes hook_jsonapi_entity_filter_access() and
     * hook_jsonapi_ENTITY_TYPE_filter_access() and combines the results from all
     * of the modules into a single set of results.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type for which to check filter access.
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The account for which to check access.
     *
     * @return \Drupal\Core\Access\AccessResultInterface[]
     *   The array of access results, keyed by subset. See
     *   hook_jsonapi_entity_filter_access() for details.
     */
    protected static function getAccessResultsFromEntityFilterHook(EntityTypeInterface $entity_type, AccountInterface $account) {
        
        /** @var \Drupal\Core\Access\AccessResultInterface[] $combined_access_results */
        $combined_access_results = [
            JSONAPI_FILTER_AMONG_ALL => AccessResult::neutral(),
            JSONAPI_FILTER_AMONG_PUBLISHED => AccessResult::neutral(),
            JSONAPI_FILTER_AMONG_ENABLED => AccessResult::neutral(),
            JSONAPI_FILTER_AMONG_OWN => AccessResult::neutral(),
        ];
        // Invoke hook_jsonapi_entity_filter_access() and
        // hook_jsonapi_ENTITY_TYPE_filter_access() for each module and merge its
        // results with the combined results.
        foreach ([
            'jsonapi_entity_filter_access',
            'jsonapi_' . $entity_type->id() . '_filter_access',
        ] as $hook) {
            static::$moduleHandler->invokeAllWith($hook, function (callable $hook, string $module) use (&$combined_access_results, $entity_type, $account) {
                $module_access_results = $hook($entity_type, $account);
                if ($module_access_results) {
                    foreach ($module_access_results as $subset => $access_result) {
                        $combined_access_results[$subset] = $combined_access_results[$subset]->orIf($access_result);
                    }
                }
            });
        }
        return $combined_access_results;
    }
    
    /**
     * Gets an access condition for a comment entity.
     *
     * Unlike all other core entity types, Comment entities' access control
     * depends on access to a referenced entity. More challenging yet, that entity
     * reference field may target different entity types depending on the comment
     * bundle. This makes the query access conditions sufficiently complex to
     * merit a dedicated method.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $comment_entity_type
     *   The comment entity type object.
     * @param \Drupal\Core\Session\AccountInterface $current_user
     *   The current user.
     * @param \Drupal\Core\Cache\CacheableMetadata $cacheability
     *   Collects cacheability for the query.
     * @param int $depth
     *   Internal use only. The recursion depth. It is possible to have comments
     *   on comments, but since comment access is dependent on access to the
     *   entity on which they live, this method can recurse endlessly.
     *
     * @return \Drupal\jsonapi\Query\EntityConditionGroup|null
     *   An EntityConditionGroup or NULL if no conditions need to be applied to
     *   secure an entity query.
     */
    protected static function getCommentAccessCondition(EntityTypeInterface $comment_entity_type, AccountInterface $current_user, CacheableMetadata $cacheability, $depth = 1) {
        // If a comment is assigned to another entity or author the cache needs to
        // be invalidated.
        $cacheability->addCacheTags($comment_entity_type->getListCacheTags());
        // Constructs a big EntityConditionGroup which will filter comments based on
        // the current user's access to the entities on which each comment lives.
        // This is especially complex because comments of different bundles can
        // live on entities of different entity types.
        $comment_entity_type_id = $comment_entity_type->id();
        $field_map = static::$fieldManager->getFieldMapByFieldType('entity_reference');
        assert(isset($field_map[$comment_entity_type_id]['entity_id']['bundles']), 'Every comment has an `entity_id` field.');
        $bundle_ids_by_target_entity_type_id = [];
        foreach ($field_map[$comment_entity_type_id]['entity_id']['bundles'] as $bundle_id) {
            $field_definitions = static::$fieldManager->getFieldDefinitions($comment_entity_type_id, $bundle_id);
            $commented_entity_field_definition = $field_definitions['entity_id'];
            // Each commented entity field definition has a setting which indicates
            // the entity type of the commented entity reference field. This differs
            // per bundle.
            $target_entity_type_id = $commented_entity_field_definition->getSetting('target_type');
            $bundle_ids_by_target_entity_type_id[$target_entity_type_id][] = $bundle_id;
        }
        $bundle_specific_access_conditions = [];
        foreach ($bundle_ids_by_target_entity_type_id as $target_entity_type_id => $bundle_ids) {
            // Construct a field specifier prefix which targets the commented entity.
            $condition_field_prefix = "entity_id.entity:{$target_entity_type_id}";
            // Ensure that for each possible commented entity type (which varies per
            // bundle), a condition is created that restricts access based on access
            // to the commented entity.
            $bundle_condition = new EntityCondition($comment_entity_type->getKey('bundle'), $bundle_ids, 'IN');
            // Comments on comments can create an infinite recursion! If the target
            // entity type ID is comment, we need special behavior.
            if ($target_entity_type_id === $comment_entity_type_id) {
                $nested_comment_condition = $depth <= 3 ? static::getCommentAccessCondition($comment_entity_type, $current_user, $cacheability, $depth + 1) : static::alwaysFalse($comment_entity_type);
                $prefixed_comment_condition = static::addConditionFieldPrefix($nested_comment_condition, $condition_field_prefix);
                $bundle_specific_access_conditions[$target_entity_type_id] = new EntityConditionGroup('AND', [
                    $bundle_condition,
                    $prefixed_comment_condition,
                ]);
            }
            else {
                $target_condition = static::getAccessCondition($target_entity_type_id, $cacheability);
                $bundle_specific_access_conditions[$target_entity_type_id] = !is_null($target_condition) ? new EntityConditionGroup('AND', [
                    $bundle_condition,
                    static::addConditionFieldPrefix($target_condition, $condition_field_prefix),
                ]) : $bundle_condition;
            }
        }
        // This condition ensures that the user is only permitted to see the
        // comments for which the user is also able to view the entity on which each
        // comment lives.
        $commented_entity_condition = new EntityConditionGroup('OR', array_values($bundle_specific_access_conditions));
        return $commented_entity_condition;
    }
    
    /**
     * Gets an always FALSE entity condition group for the given entity type.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type for which to construct an impossible condition.
     *
     * @return \Drupal\jsonapi\Query\EntityConditionGroup
     *   An EntityConditionGroup which cannot evaluate to TRUE.
     */
    protected static function alwaysFalse(EntityTypeInterface $entity_type) {
        return new EntityConditionGroup('AND', [
            new EntityCondition($entity_type->getKey('id'), 1, '<'),
            new EntityCondition($entity_type->getKey('id'), 1, '>'),
        ]);
    }
    
    /**
     * Recursively collects all entity query condition fields.
     *
     * Entity conditions can be nested within AND and OR groups. This recursively
     * finds all unique fields in an entity query condition.
     *
     * @param \Drupal\jsonapi\Query\EntityConditionGroup $group
     *   The root entity condition group.
     * @param array $fields
     *   Internal use only.
     *
     * @return array
     *   An array of entity query condition field names.
     */
    protected static function collectFilteredFields(EntityConditionGroup $group, array $fields = []) {
        foreach ($group->members() as $member) {
            if ($member instanceof EntityConditionGroup) {
                $fields = static::collectFilteredFields($member, $fields);
            }
            else {
                $fields[] = $member->field();
            }
        }
        return array_unique($fields);
    }
    
    /**
     * Copied from \Drupal\jsonapi\IncludeResolver.
     *
     * @see \Drupal\jsonapi\IncludeResolver::buildTree()
     */
    protected static function buildTree(array $paths) {
        $merged = [];
        foreach ($paths as $parts) {
            // This complex expression is needed to handle the string, "0", which
            // would be evaluated as FALSE.
            if (!is_null($field_name = array_shift($parts))) {
                $previous = $merged[$field_name] ?? [];
                $merged[$field_name] = array_merge($previous, [
                    $parts,
                ]);
            }
        }
        return !empty($merged) ? array_map([
            static::class,
            __FUNCTION__,
        ], $merged) : $merged;
    }

}