update.inc

<?php


/**
 * @file
 * Drupal database update API.
 *
 * This file contains functions to perform database updates for a Drupal
 * installation. It is included and used extensively by update.php.
 */
use Drupal\Component\Graph\Graph;
use Drupal\Core\Extension\Exception\UnknownExtensionException;
use Drupal\Core\Utility\Error;

/**
 * Returns whether the minimum schema requirement has been satisfied.
 *
 * @return array
 *   A requirements info array.
 */
function update_system_schema_requirements() {
    $requirements = [];
    $system_schema = \Drupal::service('update.update_hook_registry')->getInstalledVersion('system');
    $requirements['minimum schema']['title'] = 'Minimum schema version';
    if ($system_schema >= \Drupal::CORE_MINIMUM_SCHEMA_VERSION) {
        $requirements['minimum schema'] += [
            'value' => 'The installed schema version meets the minimum.',
            'description' => 'Schema version: ' . $system_schema,
        ];
    }
    else {
        $requirements['minimum schema'] += [
            'value' => 'The installed schema version does not meet the minimum.',
            'severity' => REQUIREMENT_ERROR,
            'description' => 'Your system schema version is ' . $system_schema . '. Updating directly from a schema version prior to 8000 is not supported. You must upgrade your site to Drupal 8 first, see https://www.drupal.org/docs/8/upgrade.',
        ];
    }
    return $requirements;
}

/**
 * Checks update requirements and reports errors and (optionally) warnings.
 */
function update_check_requirements() {
    // Because this is one of the earliest points in the update process,
    // detect and fix missing schema versions for modules here to ensure
    // it runs on all update code paths.
    _update_fix_missing_schema();
    // Check requirements of all loaded modules.
    $requirements = \Drupal::moduleHandler()->invokeAll('requirements', [
        'update',
    ]);
    \Drupal::moduleHandler()->alter('requirements', $requirements);
    $requirements += update_system_schema_requirements();
    return $requirements;
}

/**
 * Helper to detect and fix 'missing' schema information.
 *
 * Repairs the case where a module has no schema version recorded.
 * This has to be done prior to updates being run, otherwise the update
 * system would detect and attempt to run all historical updates for a
 * module.
 *
 * @todo remove in a major version after
 * https://www.drupal.org/project/drupal/issues/3130037 has been fixed.
 */
function _update_fix_missing_schema() {
    
    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
    $update_registry = \Drupal::service('update.update_hook_registry');
    $versions = $update_registry->getAllInstalledVersions();
    $module_handler = \Drupal::moduleHandler();
    $enabled_modules = $module_handler->getModuleList();
    foreach (array_keys($enabled_modules) as $module) {
        // All modules should have a recorded schema version, but when they
        // don't, detect and fix the problem.
        if (!isset($versions[$module])) {
            // Ensure the .install file is loaded.
            $module_handler->loadInclude($module, 'install');
            $all_updates = $update_registry->getAvailableUpdates($module);
            // If the schema version of a module hasn't been recorded, we cannot
            // know the actual schema version a module is at, because
            // no updates will ever have been run on the site and it was not set
            // correctly when the module was installed, so instead set it to
            // the same as the last update. This means that updates will proceed
            // again the next time the module is updated and a new update is
            // added. Updates added in between the module being installed and the
            // schema version being fixed here (if any have been added) will never
            // be run, but we have no way to identify which updates these are.
            if ($all_updates) {
                $last_update = max($all_updates);
            }
            else {
                $last_update = \Drupal::CORE_MINIMUM_SCHEMA_VERSION;
            }
            // If the module implements hook_update_last_removed() use the
            // value of that if it's higher than the schema versions found so
            // far.
            if ($last_removed = $module_handler->invoke($module, 'update_last_removed')) {
                $last_update = max($last_update, $last_removed);
            }
            $update_registry->setInstalledVersion($module, $last_update);
            $args = [
                '%module' => $module,
                '%last_update_hook' => $module . '_update_' . $last_update . '()',
            ];
            \Drupal::messenger()->addWarning(t('Schema information for module %module was missing from the database. You should manually review the module updates and your database to check if any updates have been skipped up to, and including, %last_update_hook.', $args));
            \Drupal::logger('update')->warning('Schema information for module %module was missing from the database. You should manually review the module updates and your database to check if any updates have been skipped up to, and including, %last_update_hook.', $args);
        }
    }
}

/**
 * Implements callback_batch_operation().
 *
 * Performs one update and stores the results for display on the results page.
 *
 * If an update function completes successfully, it should return a message
 * as a string indicating success, for example:
 * @code
 * return t('New index added successfully.');
 * @endcode
 *
 * Alternatively, it may return nothing. In that case, no message
 * will be displayed at all.
 *
 * If it fails for whatever reason, it should throw an instance of
 * Drupal\Core\Utility\UpdateException with an appropriate error message, for
 * example:
 * @code
 * use Drupal\Core\Utility\UpdateException;
 * throw new UpdateException('Description of what went wrong');
 * @endcode
 *
 * If an exception is thrown, the current update and all updates that depend on
 * it will be aborted. The schema version will not be updated in this case, and
 * all the aborted updates will continue to appear on update.php as updates
 * that have not yet been run.
 *
 * If an update function needs to be re-run as part of a batch process, it
 * should accept the $sandbox array by reference as its first parameter
 * and set the #finished property to the percentage completed that it is, as a
 * fraction of 1.
 *
 * @param $module
 *   The module whose update will be run.
 * @param $number
 *   The update number to run.
 * @param $dependency_map
 *   An array whose keys are the names of all update functions that will be
 *   performed during this batch process, and whose values are arrays of other
 *   update functions that each one depends on.
 * @param $context
 *   The batch context array.
 *
 * @see update_resolve_dependencies()
 */
function update_do_one($module, $number, $dependency_map, &$context) {
    $function = $module . '_update_' . $number;
    // If this update was aborted in a previous step, or has a dependency that
    // was aborted in a previous step, go no further.
    if (!empty($context['results']['#abort']) && array_intersect($context['results']['#abort'], array_merge($dependency_map, [
        $function,
    ]))) {
        return;
    }
    $ret = [];
    if (function_exists($function)) {
        try {
            $ret['results']['query'] = $function($context['sandbox']);
            $ret['results']['success'] = TRUE;
        } catch (Exception $e) {
            $variables = Error::decodeException($e);
            \Drupal::logger('update')->error(Error::DEFAULT_ERROR_MESSAGE, $variables);
            unset($variables['backtrace'], $variables['exception'], $variables['severity_level']);
            $ret['#abort'] = [
                'success' => FALSE,
                'query' => t(Error::DEFAULT_ERROR_MESSAGE, $variables),
            ];
        }
    }
    if (isset($context['sandbox']['#finished'])) {
        $context['finished'] = $context['sandbox']['#finished'];
        unset($context['sandbox']['#finished']);
    }
    if (!isset($context['results'][$module])) {
        $context['results'][$module] = [];
    }
    if (!isset($context['results'][$module][$number])) {
        $context['results'][$module][$number] = [];
    }
    $context['results'][$module][$number] = array_merge($context['results'][$module][$number], $ret);
    if (!empty($ret['#abort'])) {
        // Record this function in the list of updates that were aborted.
        $context['results']['#abort'][] = $function;
    }
    // Record the schema update if it was completed successfully.
    if ($context['finished'] == 1 && empty($ret['#abort'])) {
        \Drupal::service('update.update_hook_registry')->setInstalledVersion($module, $number);
    }
    $context['message'] = t('Updating @module', [
        '@module' => $module,
    ]);
}

/**
 * Executes a single hook_post_update_NAME().
 *
 * @param string $function
 *   The function name, that should be executed.
 * @param array $context
 *   The batch context array.
 */
function update_invoke_post_update($function, &$context) {
    $ret = [];
    // If this update was aborted in a previous step, or has a dependency that was
    // aborted in a previous step, go no further.
    if (!empty($context['results']['#abort'])) {
        return;
    }
    // Ensure extension post update code is loaded.
    [
        $extension,
        $name,
    ] = explode('_post_update_', $function, 2);
    \Drupal::service('update.post_update_registry')->getUpdateFunctions($extension);
    if (function_exists($function)) {
        try {
            $ret['results']['query'] = $function($context['sandbox']);
            $ret['results']['success'] = TRUE;
            if (!isset($context['sandbox']['#finished']) || isset($context['sandbox']['#finished']) && $context['sandbox']['#finished'] >= 1) {
                \Drupal::service('update.post_update_registry')->registerInvokedUpdates([
                    $function,
                ]);
            }
        } catch (Exception $e) {
            $variables = Error::decodeException($e);
            \Drupal::logger('update')->error(Error::DEFAULT_ERROR_MESSAGE, $variables);
            unset($variables['backtrace'], $variables['exception'], $variables['severity_level']);
            $ret['#abort'] = [
                'success' => FALSE,
                'query' => t(Error::DEFAULT_ERROR_MESSAGE, $variables),
            ];
        }
    }
    if (isset($context['sandbox']['#finished'])) {
        $context['finished'] = $context['sandbox']['#finished'];
        unset($context['sandbox']['#finished']);
    }
    if (!isset($context['results'][$extension][$name])) {
        $context['results'][$extension][$name] = [];
    }
    $context['results'][$extension][$name] = array_merge($context['results'][$extension][$name], $ret);
    if (!empty($ret['#abort'])) {
        // Record this function in the list of updates that were aborted.
        $context['results']['#abort'][] = $function;
    }
    $context['message'] = t('Post updating @extension', [
        '@extension' => $extension,
    ]);
}

/**
 * Returns a list of all the pending database updates.
 *
 * @return array
 *   An associative array keyed by module name which contains all information
 *   about database updates that need to be run, and any updates that are not
 *   going to proceed due to missing requirements. The system module will
 *   always be listed first.
 *
 *   The subarray for each module can contain the following keys:
 *   - start: The starting update that is to be processed. If this does not
 *       exist then do not process any updates for this module as there are
 *       other requirements that need to be resolved.
 *   - warning: Any warnings about why this module can not be updated.
 *   - pending: An array of all the pending updates for the module including
 *       the update number and the description from source code comment for
 *       each update function. This array is keyed by the update number.
 */
function update_get_update_list() {
    // Make sure that the system module is first in the list of updates.
    $ret = [
        'system' => [],
    ];
    
    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
    $update_registry = \Drupal::service('update.update_hook_registry');
    $modules = $update_registry->getAllInstalledVersions();
    
    /** @var \Drupal\Core\Extension\ExtensionList $extension_list */
    $extension_list = \Drupal::service('extension.list.module');
    
    /** @var array $installed_module_info */
    $installed_module_info = $extension_list->getAllInstalledInfo();
    foreach ($modules as $module => $schema_version) {
        // Skip uninstalled and incompatible modules.
        try {
            if ($schema_version == $update_registry::SCHEMA_UNINSTALLED || $extension_list->checkIncompatibility($module)) {
                continue;
            }
        } catch (UnknownExtensionException $e) {
            $args = [
                '%name' => $module,
                ':url' => 'https://www.drupal.org/node/3137656',
            ];
            \Drupal::messenger()->addWarning(t('Module %name has an entry in the system.schema key/value storage, but is missing from your site. <a href=":url">More information about this error</a>.', $args));
            \Drupal::logger('system')->notice('Module %name has an entry in the system.schema key/value storage, but is missing from your site. <a href=":url">More information about this error</a>.', $args);
            continue;
        }
        // There might be orphaned entries for modules that are in the filesystem
        // but not installed. Also skip those, but warn site admins about it.
        if (empty($installed_module_info[$module])) {
            $args = [
                '%name' => $module,
                ':url' => 'https://www.drupal.org/node/3137656',
            ];
            \Drupal::messenger()->addWarning(t('Module %name has an entry in the system.schema key/value storage, but is not installed. <a href=":url">More information about this error</a>.', $args));
            \Drupal::logger('system')->notice('Module %name has an entry in the system.schema key/value storage, but is not installed. <a href=":url">More information about this error</a>.', $args);
            continue;
        }
        // Display a requirements error if the user somehow has a schema version
        // from the previous Drupal major version.
        if ($schema_version < \Drupal::CORE_MINIMUM_SCHEMA_VERSION) {
            $ret[$module]['warning'] = '<em>' . $module . '</em> module cannot be updated. Its schema version is ' . $schema_version . ', which is from an earlier major release of Drupal. See the <a href="https://www.drupal.org/docs/upgrading-drupal">Upgrading Drupal guide</a>.';
            continue;
        }
        // Otherwise, get the list of updates defined by this module.
        $updates = $update_registry->getAvailableUpdates($module);
        if ($updates) {
            foreach ($updates as $update) {
                if ($update == \Drupal::CORE_MINIMUM_SCHEMA_VERSION) {
                    $ret[$module]['warning'] = '<em>' . $module . '</em> module cannot be updated. It contains an update numbered as ' . \Drupal::CORE_MINIMUM_SCHEMA_VERSION . ' which is reserved for the earliest installation of a module in Drupal ' . \Drupal::CORE_COMPATIBILITY . ', before any updates. In order to update <em>' . $module . '</em> module, you will need to download a version of the module with valid updates.';
                    continue 2;
                }
                if ($update > $schema_version) {
                    // The description for an update comes from its Doxygen.
                    $func = new ReflectionFunction($module . '_update_' . $update);
                    $patterns = [
                        '/^\\s*[\\/*]*/',
                        '/(\\n\\s*\\**)(.*)/',
                        '/\\/$/',
                        '/^\\s*/',
                    ];
                    $replacements = [
                        '',
                        '$2',
                        '',
                        '',
                    ];
                    $description = preg_replace($patterns, $replacements, $func->getDocComment());
                    $ret[$module]['pending'][$update] = "{$update} - {$description}";
                    if (!isset($ret[$module]['start'])) {
                        $ret[$module]['start'] = $update;
                    }
                }
            }
            if (!isset($ret[$module]['start']) && isset($ret[$module]['pending'])) {
                $ret[$module]['start'] = $schema_version;
            }
        }
    }
    if (empty($ret['system'])) {
        unset($ret['system']);
    }
    return $ret;
}

/**
 * Resolves dependencies in a set of module updates, and orders them correctly.
 *
 * This function receives a list of requested module updates and determines an
 * appropriate order to run them in such that all update dependencies are met.
 * Any updates whose dependencies cannot be met are included in the returned
 * array but have the key 'allowed' set to FALSE; the calling function should
 * take responsibility for ensuring that these updates are ultimately not
 * performed.
 *
 * In addition, the returned array also includes detailed information about the
 * dependency chain for each update, as provided by the depth-first search
 * algorithm in Drupal\Component\Graph\Graph::searchAndSort().
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules with updates to be run
 *   and whose values contain the number of the first requested update for that
 *   module.
 *
 * @return array
 *   An array whose keys are the names of all update functions within the
 *   provided modules that would need to be run in order to fulfill the
 *   request, arranged in the order in which the update functions should be
 *   run. (This includes the provided starting update for each module and all
 *   subsequent updates that are available.) The values are themselves arrays
 *   containing all the keys provided by the
 *   Drupal\Component\Graph\Graph::searchAndSort() algorithm, which encode
 *   detailed information about the dependency chain for this update function
 *   (for example: 'paths', 'reverse_paths', 'weight', and 'component'), as
 *   well as the following additional keys:
 *   - 'allowed': A boolean which is TRUE when the update function's
 *     dependencies are met, and FALSE otherwise. Calling functions should
 *     inspect this value before running the update.
 *   - 'missing_dependencies': An array containing the names of any other
 *     update functions that are required by this one but that are unavailable
 *     to be run. This array will be empty when 'allowed' is TRUE.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see \Drupal\Component\Graph\Graph::searchAndSort()
 */
function update_resolve_dependencies($starting_updates) {
    // Obtain a dependency graph for the requested update functions.
    $update_functions = update_get_update_function_list($starting_updates);
    $graph = update_build_dependency_graph($update_functions);
    // Perform the depth-first search and sort on the results.
    $graph_object = new Graph($graph);
    $graph = $graph_object->searchAndSort();
    uasort($graph, [
        'Drupal\\Component\\Utility\\SortArray',
        'sortByWeightElement',
    ]);
    foreach ($graph as $function => &$data) {
        $module = $data['module'];
        $number = $data['number'];
        // If the update function is missing and has not yet been performed, mark
        // it and everything that ultimately depends on it as disallowed.
        if (update_is_missing($module, $number, $update_functions) && !update_already_performed($module, $number)) {
            $data['allowed'] = FALSE;
            foreach (array_keys($data['paths']) as $dependent) {
                $graph[$dependent]['allowed'] = FALSE;
                $graph[$dependent]['missing_dependencies'][] = $function;
            }
        }
        elseif (!isset($data['allowed'])) {
            $data['allowed'] = TRUE;
            $data['missing_dependencies'] = [];
        }
        // Now that we have finished processing this function, remove it from the
        // graph if it was not part of the original list. This ensures that we
        // never try to run any updates that were not specifically requested.
        if (!isset($update_functions[$module][$number])) {
            unset($graph[$function]);
        }
    }
    return $graph;
}

/**
 * Returns an organized list of update functions for a set of modules.
 *
 * @param $starting_updates
 *   An array whose keys contain the names of modules and whose values contain
 *   the number of the first requested update for that module.
 *
 * @return array
 *   An array containing all the update functions that should be run for each
 *   module, including the provided starting update and all subsequent updates
 *   that are available. The keys of the array contain the module names, and
 *   each value is an ordered array of update functions, keyed by the update
 *   number.
 *
 * @see update_resolve_dependencies()
 */
function update_get_update_function_list($starting_updates) {
    // Go through each module and find all updates that we need (including the
    // first update that was requested and any updates that run after it).
    $update_functions = [];
    
    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
    $update_registry = \Drupal::service('update.update_hook_registry');
    foreach ($starting_updates as $module => $version) {
        $update_functions[$module] = [];
        $updates = $update_registry->getAvailableUpdates($module);
        if ($updates) {
            $max_version = max($updates);
            if ($version <= $max_version) {
                foreach ($updates as $update) {
                    if ($update >= $version) {
                        $update_functions[$module][$update] = $module . '_update_' . $update;
                    }
                }
            }
        }
    }
    return $update_functions;
}

/**
 * Constructs a graph which encodes the dependencies between module updates.
 *
 * This function returns an associative array which contains a "directed graph"
 * representation of the dependencies between a provided list of update
 * functions, as well as any outside update functions that they directly depend
 * on but that were not in the provided list. The vertices of the graph
 * represent the update functions themselves, and each edge represents a
 * requirement that the first update function needs to run before the second.
 * For example, consider this graph:
 *
 * system_update_8001 ---> system_update_8002 ---> system_update_8003
 *
 * Visually, this indicates that system_update_8001() must run before
 * system_update_8002(), which in turn must run before system_update_8003().
 *
 * The function takes into account standard dependencies within each module, as
 * shown above (i.e., the fact that each module's updates must run in numerical
 * order), but also finds any cross-module dependencies that are defined by
 * modules which implement hook_update_dependencies(), and builds them into the
 * graph as well.
 *
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list().
 *
 * @return array
 *   A multidimensional array representing the dependency graph, suitable for
 *   passing in to Drupal\Component\Graph\Graph::searchAndSort(), but with extra
 *   information about each update function also included. Each array key
 *   contains the name of an update function, including all update functions
 *   from the provided list as well as any outside update functions which they
 *   directly depend on. Each value is an associative array containing the
 *   following keys:
 *   - 'edges': A representation of any other update functions that immediately
 *     depend on this one. See Drupal\Component\Graph\Graph::searchAndSort() for
 *     more details on the format.
 *   - 'module': The name of the module that this update function belongs to.
 *   - 'number': The number of this update function within that module.
 *
 * @see \Drupal\Component\Graph\Graph::searchAndSort()
 * @see update_resolve_dependencies()
 */
function update_build_dependency_graph($update_functions) {
    // Initialize an array that will define a directed graph representing the
    // dependencies between update functions.
    $graph = [];
    // Go through each update function and build an initial list of dependencies.
    foreach ($update_functions as $module => $functions) {
        $previous_function = NULL;
        foreach ($functions as $number => $function) {
            // Add an edge to the directed graph representing the fact that each
            // update function in a given module must run after the update that
            // numerically precedes it.
            if ($previous_function) {
                $graph[$previous_function]['edges'][$function] = TRUE;
            }
            $previous_function = $function;
            // Define the module and update number associated with this function.
            $graph[$function]['module'] = $module;
            $graph[$function]['number'] = $number;
        }
    }
    // Now add any explicit update dependencies declared by modules.
    $update_dependencies = update_retrieve_dependencies();
    foreach ($graph as $function => $data) {
        if (!empty($update_dependencies[$data['module']][$data['number']])) {
            foreach ($update_dependencies[$data['module']][$data['number']] as $module => $number) {
                $dependency = $module . '_update_' . $number;
                $graph[$dependency]['edges'][$function] = TRUE;
                $graph[$dependency]['module'] = $module;
                $graph[$dependency]['number'] = $number;
            }
        }
    }
    return $graph;
}

/**
 * Determines if a module update is missing or unavailable.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 * @param $update_functions
 *   An organized array of update functions, in the format returned by
 *   update_get_update_function_list(). This should represent all module
 *   updates that are requested to run at the time this function is called.
 *
 * @return bool
 *   TRUE if the provided module update is not installed or is not in the
 *   provided list of updates to run; FALSE otherwise.
 */
function update_is_missing($module, $number, $update_functions) {
    return !isset($update_functions[$module][$number]) || !function_exists($update_functions[$module][$number]);
}

/**
 * Determines if a module update has already been performed.
 *
 * @param $module
 *   The name of the module.
 * @param $number
 *   The number of the update within that module.
 *
 * @return bool
 *   TRUE if the database schema indicates that the update has already been
 *   performed; FALSE otherwise.
 */
function update_already_performed($module, $number) {
    return $number <= \Drupal::service('update.update_hook_registry')->getInstalledVersion($module);
}

/**
 * Invokes hook_update_dependencies() in all installed modules.
 *
 * This function is similar to \Drupal::moduleHandler()->invokeAll(), with the
 * main difference that it does not require that a module be enabled to invoke
 * its hook, only that it be installed. This allows the update system to
 * properly perform updates even on modules that are currently disabled.
 *
 * @return array
 *   An array of return values obtained by merging the results of the
 *   hook_update_dependencies() implementations in all installed modules.
 *
 * @see \Drupal\Core\Extension\ModuleHandlerInterface::invokeAll()
 * @see hook_update_dependencies()
 */
function update_retrieve_dependencies() {
    $return = [];
    
    /** @var \Drupal\Core\Extension\ModuleExtensionList */
    $extension_list = \Drupal::service('extension.list.module');
    
    /** @var \Drupal\Core\Update\UpdateHookRegistry $update_registry */
    $update_registry = \Drupal::service('update.update_hook_registry');
    // Get a list of installed modules, arranged so that we invoke their hooks in
    // the same order that \Drupal::moduleHandler()->invokeAll() does.
    foreach ($update_registry->getAllInstalledVersions() as $module => $schema) {
        // Skip modules that are entirely missing from the filesystem here, since
        // loading .install file will call trigger_error() if invoked on a module
        // that doesn't exist. There's no way to catch() that, so avoid it entirely.
        // This can happen when there are orphaned entries in the system.schema k/v
        // store for modules that have been removed from a site without first being
        // cleanly uninstalled. We don't care here if the module has been installed
        // or not, since we'll filter those out in update_get_update_list().
        if ($schema == $update_registry::SCHEMA_UNINSTALLED || !$extension_list->exists($module)) {
            // Nothing to upgrade.
            continue;
        }
        $function = $module . '_update_dependencies';
        // Ensure install file is loaded.
        \Drupal::moduleHandler()->loadInclude($module, 'install');
        if (function_exists($function)) {
            $updated_dependencies = $function();
            // Each implementation of hook_update_dependencies() returns a
            // multidimensional, associative array containing some keys that
            // represent module names (which are strings) and other keys that
            // represent update function numbers (which are integers). We cannot use
            // array_merge_recursive() to properly merge these results, since it
            // treats strings and integers differently. Therefore, we have to
            // explicitly loop through the expected array structure here and perform
            // the merge manually.
            if (isset($updated_dependencies) && is_array($updated_dependencies)) {
                foreach ($updated_dependencies as $module_name => $module_data) {
                    foreach ($module_data as $update_version => $update_data) {
                        foreach ($update_data as $module_dependency => $update_dependency) {
                            // If there are redundant dependencies declared for the same
                            // update function (so that it is declared to depend on more than
                            // one update from a particular module), record the dependency on
                            // the highest numbered update here, since that automatically
                            // implies the previous ones. For example, if one module's
                            // implementation of hook_update_dependencies() required this
                            // ordering:
                            //
                            // system_update_8002 ---> user_update_8001
                            //
                            // but another module's implementation of the hook required this
                            // one:
                            //
                            // system_update_8003 ---> user_update_8001
                            //
                            // we record the second one, since system_update_8002() is always
                            // guaranteed to run before system_update_8003() anyway (within
                            // an individual module, updates are always run in numerical
                            // order).
                            if (!isset($return[$module_name][$update_version][$module_dependency]) || $update_dependency > $return[$module_name][$update_version][$module_dependency]) {
                                $return[$module_name][$update_version][$module_dependency] = $update_dependency;
                            }
                        }
                    }
                }
            }
        }
    }
    return $return;
}