wikimedia/mediawiki-core

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includes/api/ApiPageSet.php

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<?php
/**
 * Copyright © 2006, 2013 Yuri Astrakhan "<Firstname><Lastname>@gmail.com"
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

use MediaWiki\Api\Validator\SubmoduleDef;
use MediaWiki\Cache\GenderCache;
use MediaWiki\Cache\LinkBatch;
use MediaWiki\Cache\LinkBatchFactory;
use MediaWiki\Cache\LinkCache;
use MediaWiki\Linker\LinkTarget;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\PageIdentity;
use MediaWiki\Page\PageReference;
use MediaWiki\Request\FauxRequest;
use MediaWiki\SpecialPage\RedirectSpecialArticle;
use MediaWiki\SpecialPage\SpecialPageFactory;
use MediaWiki\Title\MalformedTitleException;
use MediaWiki\Title\NamespaceInfo;
use MediaWiki\Title\Title;
use MediaWiki\Title\TitleFactory;
use Wikimedia\ParamValidator\ParamValidator;
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\IResultWrapper;

/**
 * This class contains a list of pages that the client has requested.
 * Initially, when the client passes in titles=, pageids=, or revisions=
 * parameter, an instance of the ApiPageSet class will normalize titles,
 * determine if the pages/revisions exist, and prefetch any additional page
 * data requested.
 *
 * When a generator is used, the result of the generator will become the input
 * for the second instance of this class, and all subsequent actions will use
 * the second instance for all their work.
 *
 * @ingroup API
 * @since 1.21 derives from ApiBase instead of ApiQueryBase
 */
class ApiPageSet extends ApiBase {
    /**
     * Constructor flag: The new instance of ApiPageSet will ignore the 'generator=' parameter
     * @since 1.21
     */
    private const DISABLE_GENERATORS = 1;

    /** @var ApiBase used for getDb() call */
    private $mDbSource;

    /** @var array */
    private $mParams;

    /** @var bool */
    private $mResolveRedirects;

    /** @var bool */
    private $mConvertTitles;

    /** @var bool */
    private $mAllowGenerator;

    /** @var int[][] [ns][dbkey] => page_id or negative when missing */
    private $mAllPages = [];

    /** @var Title[] */
    private $mTitles = [];

    /** @var int[][] [ns][dbkey] => page_id or negative when missing */
    private $mGoodAndMissingPages = [];

    /** @var int[][] [ns][dbkey] => page_id */
    private $mGoodPages = [];

    /** @var array<int,Title> */
    private $mGoodTitles = [];

    /** @var int[][] [ns][dbkey] => fake page_id */
    private $mMissingPages = [];

    /** @var Title[] */
    private $mMissingTitles = [];

    /** @var array[] [fake_page_id] => [ 'title' => $title, 'invalidreason' => $reason ] */
    private $mInvalidTitles = [];

    /** @var int[] */
    private $mMissingPageIDs = [];

    /** @var Title[] */
    private $mRedirectTitles = [];

    /** @var Title[] */
    private $mSpecialTitles = [];

    /** @var int[][] separate from mAllPages to avoid breaking getAllTitlesByNamespace() */
    private $mAllSpecials = [];

    /** @var string[] */
    private $mNormalizedTitles = [];

    /** @var string[] */
    private $mInterwikiTitles = [];

    /** @var Title[] */
    private $mPendingRedirectIDs = [];

    /** @var Title[][] [dbkey] => [ Title $from, Title $to ] */
    private $mPendingRedirectSpecialPages = [];

    /** @var Title[] */
    private $mResolvedRedirectTitles = [];

    /** @var string[] */
    private $mConvertedTitles = [];

    /** @var int[] Array of revID (int) => pageID (int) */
    private $mGoodRevIDs = [];

    /** @var int[] Array of revID (int) => pageID (int) */
    private $mLiveRevIDs = [];

    /** @var int[] Array of revID (int) => pageID (int) */
    private $mDeletedRevIDs = [];

    /** @var int[] */
    private $mMissingRevIDs = [];

    /** @var array[][] [ns][dbkey] => data array */
    private $mGeneratorData = [];

    /** @var int */
    private $mFakePageId = -1;

    /** @var string */
    private $mCacheMode = 'public';

    /** @var array */
    private $mRequestedPageFields = [];

    /** @var int */
    private $mDefaultNamespace;

    /** @var callable|null */
    private $mRedirectMergePolicy;

    /** @var string[]|null see getGenerators() */
    private static $generators = null;

    private Language $contentLanguage;
    private LinkCache $linkCache;
    private NamespaceInfo $namespaceInfo;
    private GenderCache $genderCache;
    private LinkBatchFactory $linkBatchFactory;
    private TitleFactory $titleFactory;
    private ILanguageConverter $languageConverter;
    private SpecialPageFactory $specialPageFactory;

    /**
     * Add all items from $values into the result
     * @param array &$result Output
     * @param array $values Values to add
     * @param string[] $flags The names of boolean flags to mark this element
     * @param string|null $name If given, name of the value
     */
    private static function addValues( array &$result, $values, $flags = [], $name = null ) {
        foreach ( $values as $val ) {
            if ( $val instanceof Title ) {
                $v = [];
                ApiQueryBase::addTitleInfo( $v, $val );
            } elseif ( $name !== null ) {
                $v = [ $name => $val ];
            } else {
                $v = $val;
            }
            foreach ( $flags as $flag ) {
                $v[$flag] = true;
            }
            $result[] = $v;
        }
    }

    /**
     * @param ApiBase $dbSource Module implementing getDB().
     *        Allows PageSet to reuse existing db connection from the shared state like ApiQuery.
     * @param int $flags Zero or more flags like DISABLE_GENERATORS
     * @param int $defaultNamespace The namespace to use if none is specified by a prefix.
     * @since 1.21 accepts $flags instead of two boolean values
     */
    public function __construct( ApiBase $dbSource, $flags = 0, $defaultNamespace = NS_MAIN ) {
        parent::__construct( $dbSource->getMain(), $dbSource->getModuleName() );
        $this->mDbSource = $dbSource;
        $this->mAllowGenerator = ( $flags & self::DISABLE_GENERATORS ) == 0;
        $this->mDefaultNamespace = $defaultNamespace;

        $this->mParams = $this->extractRequestParams();
        $this->mResolveRedirects = $this->mParams['redirects'];
        $this->mConvertTitles = $this->mParams['converttitles'];

        // Needs service injection - T283314
        $services = MediaWikiServices::getInstance();
        $this->contentLanguage = $services->getContentLanguage();
        $this->linkCache = $services->getLinkCache();
        $this->namespaceInfo = $services->getNamespaceInfo();
        $this->genderCache = $services->getGenderCache();
        $this->linkBatchFactory = $services->getLinkBatchFactory();
        $this->titleFactory = $services->getTitleFactory();
        $this->languageConverter = $services->getLanguageConverterFactory()
            ->getLanguageConverter( $this->contentLanguage );
        $this->specialPageFactory = $services->getSpecialPageFactory();
    }

    /**
     * In case execute() is not called, call this method to mark all relevant parameters as used
     * This prevents unused parameters from being reported as warnings
     */
    public function executeDryRun() {
        $this->executeInternal( true );
    }

    /**
     * Populate the PageSet from the request parameters.
     */
    public function execute() {
        $this->executeInternal( false );
    }

    /**
     * Populate the PageSet from the request parameters.
     * @param bool $isDryRun If true, instantiates generator, but only to mark
     *    relevant parameters as used
     */
    private function executeInternal( $isDryRun ) {
        $generatorName = $this->mAllowGenerator ? $this->mParams['generator'] : null;
        if ( isset( $generatorName ) ) {
            $dbSource = $this->mDbSource;
            if ( !$dbSource instanceof ApiQuery ) {
                // If the parent container of this pageset is not ApiQuery, we must create it to run generator
                $dbSource = $this->getMain()->getModuleManager()->getModule( 'query' );
            }
            $generator = $dbSource->getModuleManager()->getModule( $generatorName, null, true );
            if ( $generator === null ) {
                $this->dieWithError( [ 'apierror-badgenerator-unknown', $generatorName ], 'badgenerator' );
            }
            if ( !$generator instanceof ApiQueryGeneratorBase ) {
                $this->dieWithError( [ 'apierror-badgenerator-notgenerator', $generatorName ], 'badgenerator' );
            }
            // Create a temporary pageset to store generator's output,
            // add any additional fields generator may need, and execute pageset to populate titles/pageids
            // @phan-suppress-next-line PhanTypeMismatchArgumentNullable T240141
            $tmpPageSet = new ApiPageSet( $dbSource, self::DISABLE_GENERATORS );
            $generator->setGeneratorMode( $tmpPageSet );
            $this->mCacheMode = $generator->getCacheMode( $generator->extractRequestParams() );

            if ( !$isDryRun ) {
                $generator->requestExtraData( $tmpPageSet );
            }
            $tmpPageSet->executeInternal( $isDryRun );

            // populate this pageset with the generator output
            if ( !$isDryRun ) {
                $generator->executeGenerator( $this );

                // @phan-suppress-next-line PhanTypeMismatchArgumentNullable T240141
                $this->getHookRunner()->onAPIQueryGeneratorAfterExecute( $generator, $this );
            } else {
                // Prevent warnings from being reported on these parameters
                $main = $this->getMain();
                foreach ( $generator->extractRequestParams() as $paramName => $param ) {
                    $main->markParamsUsed( $generator->encodeParamName( $paramName ) );
                }
            }

            if ( !$isDryRun ) {
                $this->resolvePendingRedirects();
            }
        } else {
            // Only one of the titles/pageids/revids is allowed at the same time
            $dataSource = null;
            if ( isset( $this->mParams['titles'] ) ) {
                $dataSource = 'titles';
            }
            if ( isset( $this->mParams['pageids'] ) ) {
                if ( isset( $dataSource ) ) {
                    $this->dieWithError(
                        [
                            'apierror-invalidparammix-cannotusewith',
                            $this->encodeParamName( 'pageids' ),
                            $this->encodeParamName( $dataSource )
                        ],
                        'multisource'
                    );
                }
                $dataSource = 'pageids';
            }
            if ( isset( $this->mParams['revids'] ) ) {
                if ( isset( $dataSource ) ) {
                    $this->dieWithError(
                        [
                            'apierror-invalidparammix-cannotusewith',
                            $this->encodeParamName( 'revids' ),
                            $this->encodeParamName( $dataSource )
                        ],
                        'multisource'
                    );
                }
                $dataSource = 'revids';
            }

            if ( !$isDryRun ) {
                // Populate page information with the original user input
                switch ( $dataSource ) {
                    case 'titles':
                        $this->initFromTitles( $this->mParams['titles'] );
                        break;
                    case 'pageids':
                        $this->initFromPageIds( $this->mParams['pageids'] );
                        break;
                    case 'revids':
                        if ( $this->mResolveRedirects ) {
                            $this->addWarning( 'apiwarn-redirectsandrevids' );
                        }
                        $this->mResolveRedirects = false;
                        $this->initFromRevIDs( $this->mParams['revids'] );
                        break;
                    default:
                        // Do nothing - some queries do not need any of the data sources.
                        break;
                }
            }
        }
    }

    /**
     * Check whether this PageSet is resolving redirects
     * @return bool
     */
    public function isResolvingRedirects() {
        return $this->mResolveRedirects;
    }

    /**
     * Return the parameter name that is the source of data for this PageSet
     *
     * If multiple source parameters are specified (e.g. titles and pageids),
     * one will be named arbitrarily.
     *
     * @return string|null
     */
    public function getDataSource() {
        if ( $this->mAllowGenerator && isset( $this->mParams['generator'] ) ) {
            return 'generator';
        }
        if ( isset( $this->mParams['titles'] ) ) {
            return 'titles';
        }
        if ( isset( $this->mParams['pageids'] ) ) {
            return 'pageids';
        }
        if ( isset( $this->mParams['revids'] ) ) {
            return 'revids';
        }

        return null;
    }

    /**
     * Request an additional field from the page table.
     * Must be called before execute()
     * @param string $fieldName
     */
    public function requestField( $fieldName ) {
        $this->mRequestedPageFields[$fieldName] = null;
    }

    /**
     * Get the value of a custom field previously requested through
     * requestField()
     * @param string $fieldName
     * @return mixed Field value
     */
    public function getCustomField( $fieldName ) {
        return $this->mRequestedPageFields[$fieldName];
    }

    /**
     * Get the fields that have to be queried from the page table:
     * the ones requested through requestField() and a few basic ones
     * we always need
     * @return string[] Array of field names
     */
    public function getPageTableFields() {
        // Ensure we get minimum required fields
        // DON'T change this order
        $pageFlds = [
            'page_namespace' => null,
            'page_title' => null,
            'page_id' => null,
        ];

        if ( $this->mResolveRedirects ) {
            $pageFlds['page_is_redirect'] = null;
        }

        $pageFlds['page_content_model'] = null;

        if ( $this->getConfig()->get( MainConfigNames::PageLanguageUseDB ) ) {
            $pageFlds['page_lang'] = null;
        }

        foreach ( LinkCache::getSelectFields() as $field ) {
            $pageFlds[$field] = null;
        }

        $pageFlds = array_merge( $pageFlds, $this->mRequestedPageFields );

        return array_keys( $pageFlds );
    }

    /**
     * Returns an array [ns][dbkey] => page_id for all requested titles.
     * page_id is a unique negative number in case title was not found.
     * Invalid titles will also have negative page IDs and will be in namespace 0
     * @return array
     */
    public function getAllTitlesByNamespace() {
        return $this->mAllPages;
    }

    /**
     * All existing and missing pages including redirects.
     * Does not include special pages, interwiki links, and invalid titles.
     * If redirects are resolved, both the redirect and the target will be included here.
     *
     * @deprecated since 1.37, use getPages() instead.
     * @return Title[]
     */
    public function getTitles() {
        return $this->mTitles;
    }

    /**
     * All existing and missing pages including redirects.
     * Does not include special pages, interwiki links, and invalid titles.
     * If redirects are resolved, both the redirect and the target will be included here.
     *
     * @since 1.37
     * @return PageIdentity[]
     */
    public function getPages(): array {
        return $this->mTitles;
    }

    /**
     * Returns the number of unique pages (not revisions) in the set.
     * @return int
     */
    public function getTitleCount() {
        return count( $this->mTitles );
    }

    /**
     * Returns an array [ns][dbkey] => page_id for all good titles.
     * @return array
     */
    public function getGoodTitlesByNamespace() {
        return $this->mGoodPages;
    }

    /**
     * Title objects that were found in the database, including redirects.
     * If redirects are resolved, this will include existing redirect targets.
     * @deprecated since 1.37, use getGoodPages() instead.
     * @return array<int,Title> Array page_id (int) => Title (obj)
     */
    public function getGoodTitles() {
        return $this->mGoodTitles;
    }

    /**
     * Pages that were found in the database, including redirects.
     * If redirects are resolved, this will include existing redirect targets.
     * @since 1.37
     * @return array<int,PageIdentity> Array page_id (int) => PageIdentity (obj)
     */
    public function getGoodPages(): array {
        return $this->mGoodTitles;
    }

    /**
     * Returns the number of found unique pages (not revisions) in the set.
     * @return int
     */
    public function getGoodTitleCount() {
        return count( $this->mGoodTitles );
    }

    /**
     * Returns an array [ns][dbkey] => fake_page_id for all missing titles.
     * fake_page_id is a unique negative number.
     * @return array
     */
    public function getMissingTitlesByNamespace() {
        return $this->mMissingPages;
    }

    /**
     * Title objects that were NOT found in the database.
     * The array's index will be negative for each item.
     * If redirects are resolved, this will include missing redirect targets.
     * @deprecated since 1.37, use getMissingPages instead.
     * @return Title[]
     */
    public function getMissingTitles() {
        return $this->mMissingTitles;
    }

    /**
     * Pages that were NOT found in the database.
     * The array's index will be negative for each item.
     * If redirects are resolved, this will include missing redirect targets.
     * @since 1.37
     * @return PageIdentity[]
     */
    public function getMissingPages(): array {
        return $this->mMissingTitles;
    }

    /**
     * Returns an array [ns][dbkey] => page_id for all good and missing titles.
     * @return array
     */
    public function getGoodAndMissingTitlesByNamespace() {
        return $this->mGoodAndMissingPages;
    }

    /**
     * Title objects for good and missing titles.
     * @deprecated since 1.37, use getGoodAndMissingPages() instead.
     * @return Title[]
     */
    public function getGoodAndMissingTitles() {
        return $this->mGoodTitles + $this->mMissingTitles;
    }

    /**
     * Pages for good and missing titles.
     * @since 1.37
     * @return PageIdentity[]
     */
    public function getGoodAndMissingPages(): array {
        return $this->mGoodTitles + $this->mMissingTitles;
    }

    /**
     * Titles that were deemed invalid by Title::newFromText()
     * The array's index will be unique and negative for each item
     * @return array[] Array of arrays with 'title' and 'invalidreason' properties
     */
    public function getInvalidTitlesAndReasons() {
        return $this->mInvalidTitles;
    }

    /**
     * Page IDs that were not found in the database
     * @return int[] Array of page IDs
     */
    public function getMissingPageIDs() {
        return $this->mMissingPageIDs;
    }

    /**
     * Get a list of redirect resolutions - maps a title to its redirect
     * target.
     * @deprecated since 1.37, use getRedirectTargets instead.
     * @return Title[]
     */
    public function getRedirectTitles() {
        return $this->mRedirectTitles;
    }

    /**
     * Get a list of redirect resolutions - maps a title to its redirect
     * target.
     * @since 1.37
     * @return LinkTarget[]
     */
    public function getRedirectTargets(): array {
        return $this->mRedirectTitles;
    }

    /**
     * Get a list of redirect resolutions - maps a title to its redirect
     * target. Includes generator data for redirect source when available.
     * @param ApiResult|null $result
     * @return string[][]
     * @since 1.21
     */
    public function getRedirectTitlesAsResult( $result = null ) {
        $values = [];
        foreach ( $this->getRedirectTitles() as $titleStrFrom => $titleTo ) {
            $r = [
                'from' => strval( $titleStrFrom ),
                'to' => $titleTo->getPrefixedText(),
            ];
            if ( $titleTo->hasFragment() ) {
                $r['tofragment'] = $titleTo->getFragment();
            }
            if ( $titleTo->isExternal() ) {
                $r['tointerwiki'] = $titleTo->getInterwiki();
            }
            if ( isset( $this->mResolvedRedirectTitles[$titleStrFrom] ) ) {
                $titleFrom = $this->mResolvedRedirectTitles[$titleStrFrom];
                $ns = $titleFrom->getNamespace();
                $dbkey = $titleFrom->getDBkey();
                if ( isset( $this->mGeneratorData[$ns][$dbkey] ) ) {
                    $r = array_merge( $this->mGeneratorData[$ns][$dbkey], $r );
                }
            }

            $values[] = $r;
        }
        if ( $values && $result ) {
            ApiResult::setIndexedTagName( $values, 'r' );
        }

        return $values;
    }

    /**
     * Get a list of title normalizations - maps a title to its normalized
     * version.
     * @return string[] Array of raw_prefixed_title (string) => prefixed_title (string)
     */
    public function getNormalizedTitles() {
        return $this->mNormalizedTitles;
    }

    /**
     * Get a list of title normalizations - maps a title to its normalized
     * version in the form of result array.
     * @param ApiResult|null $result
     * @return string[][]
     * @since 1.21
     */
    public function getNormalizedTitlesAsResult( $result = null ) {
        $values = [];
        foreach ( $this->getNormalizedTitles() as $rawTitleStr => $titleStr ) {
            $encode = $this->contentLanguage->normalize( $rawTitleStr ) !== $rawTitleStr;
            $values[] = [
                'fromencoded' => $encode,
                'from' => $encode ? rawurlencode( $rawTitleStr ) : $rawTitleStr,
                'to' => $titleStr
            ];
        }
        if ( $values && $result ) {
            ApiResult::setIndexedTagName( $values, 'n' );
        }

        return $values;
    }

    /**
     * Get a list of title conversions - maps a title to its converted
     * version.
     * @return string[] Array of raw_prefixed_title (string) => prefixed_title (string)
     */
    public function getConvertedTitles() {
        return $this->mConvertedTitles;
    }

    /**
     * Get a list of title conversions - maps a title to its converted
     * version as a result array.
     * @param ApiResult|null $result
     * @return string[][] Array of (from, to) strings
     * @since 1.21
     */
    public function getConvertedTitlesAsResult( $result = null ) {
        $values = [];
        foreach ( $this->getConvertedTitles() as $rawTitleStr => $titleStr ) {
            $values[] = [
                'from' => $rawTitleStr,
                'to' => $titleStr
            ];
        }
        if ( $values && $result ) {
            ApiResult::setIndexedTagName( $values, 'c' );
        }

        return $values;
    }

    /**
     * Get a list of interwiki titles - maps a title to its interwiki
     * prefix.
     * @return string[] Array of raw_prefixed_title (string) => interwiki_prefix (string)
     */
    public function getInterwikiTitles() {
        return $this->mInterwikiTitles;
    }

    /**
     * Get a list of interwiki titles - maps a title to its interwiki
     * prefix as result.
     * @param ApiResult|null $result
     * @param bool $iwUrl
     * @return string[][]
     * @since 1.21
     */
    public function getInterwikiTitlesAsResult( $result = null, $iwUrl = false ) {
        $values = [];
        foreach ( $this->getInterwikiTitles() as $rawTitleStr => $interwikiStr ) {
            $item = [
                'title' => $rawTitleStr,
                'iw' => $interwikiStr,
            ];
            if ( $iwUrl ) {
                $title = $this->titleFactory->newFromText( $rawTitleStr );
                $item['url'] = $title->getFullURL( '', false, PROTO_CURRENT );
            }
            $values[] = $item;
        }
        if ( $values && $result ) {
            ApiResult::setIndexedTagName( $values, 'i' );
        }

        return $values;
    }

    /**
     * Get an array of invalid/special/missing titles.
     *
     * @param string[] $invalidChecks List of types of invalid titles to include.
     *   Recognized values are:
     *   - invalidTitles: Titles and reasons from $this->getInvalidTitlesAndReasons()
     *   - special: Titles from $this->getSpecialTitles()
     *   - missingIds: ids from $this->getMissingPageIDs()
     *   - missingRevIds: ids from $this->getMissingRevisionIDs()
     *   - missingTitles: Titles from $this->getMissingTitles()
     *   - interwikiTitles: Titles from $this->getInterwikiTitlesAsResult()
     * @return array Array suitable for inclusion in the response
     * @since 1.23
     */
    public function getInvalidTitlesAndRevisions( $invalidChecks = [ 'invalidTitles',
        'special', 'missingIds', 'missingRevIds', 'missingTitles', 'interwikiTitles' ]
    ) {
        $result = [];
        if ( in_array( 'invalidTitles', $invalidChecks ) ) {
            self::addValues( $result, $this->getInvalidTitlesAndReasons(), [ 'invalid' ] );
        }
        if ( in_array( 'special', $invalidChecks ) ) {
            $known = [];
            $unknown = [];
            foreach ( $this->getSpecialTitles() as $title ) {
                if ( $title->isKnown() ) {
                    $known[] = $title;
                } else {
                    $unknown[] = $title;
                }
            }
            self::addValues( $result, $unknown, [ 'special', 'missing' ] );
            self::addValues( $result, $known, [ 'special' ] );
        }
        if ( in_array( 'missingIds', $invalidChecks ) ) {
            self::addValues( $result, $this->getMissingPageIDs(), [ 'missing' ], 'pageid' );
        }
        if ( in_array( 'missingRevIds', $invalidChecks ) ) {
            self::addValues( $result, $this->getMissingRevisionIDs(), [ 'missing' ], 'revid' );
        }
        if ( in_array( 'missingTitles', $invalidChecks ) ) {
            $known = [];
            $unknown = [];
            foreach ( $this->getMissingTitles() as $title ) {
                if ( $title->isKnown() ) {
                    $known[] = $title;
                } else {
                    $unknown[] = $title;
                }
            }
            self::addValues( $result, $unknown, [ 'missing' ] );
            self::addValues( $result, $known, [ 'missing', 'known' ] );
        }
        if ( in_array( 'interwikiTitles', $invalidChecks ) ) {
            self::addValues( $result, $this->getInterwikiTitlesAsResult() );
        }

        return $result;
    }

    /**
     * Get the list of valid revision IDs (requested with the revids= parameter)
     * @return int[] Array of revID (int) => pageID (int)
     */
    public function getRevisionIDs() {
        return $this->mGoodRevIDs;
    }

    /**
     * Get the list of non-deleted revision IDs (requested with the revids= parameter)
     * @return int[] Array of revID (int) => pageID (int)
     */
    public function getLiveRevisionIDs() {
        return $this->mLiveRevIDs;
    }

    /**
     * Get the list of revision IDs that were associated with deleted titles.
     * @return int[] Array of revID (int) => pageID (int)
     */
    public function getDeletedRevisionIDs() {
        return $this->mDeletedRevIDs;
    }

    /**
     * Revision IDs that were not found in the database
     * @return int[] Array of revision IDs
     */
    public function getMissingRevisionIDs() {
        return $this->mMissingRevIDs;
    }

    /**
     * Revision IDs that were not found in the database as result array.
     * @param ApiResult|null $result
     * @return int[][]
     * @since 1.21
     */
    public function getMissingRevisionIDsAsResult( $result = null ) {
        $values = [];
        foreach ( $this->getMissingRevisionIDs() as $revid ) {
            $values[$revid] = [
                'revid' => $revid,
                'missing' => true,
            ];
        }
        if ( $values && $result ) {
            ApiResult::setIndexedTagName( $values, 'rev' );
        }

        return $values;
    }

    /**
     * Get the list of titles with negative namespace
     * @deprecated since 1.37, use getSpecialPages() instead.
     * @return Title[]
     */
    public function getSpecialTitles() {
        return $this->mSpecialTitles;
    }

    /**
     * Get the list of pages with negative namespace
     * @since 1.37
     * @return PageReference[]
     */
    public function getSpecialPages(): array {
        return $this->mSpecialTitles;
    }

    /**
     * Returns the number of revisions (requested with revids= parameter).
     * @return int Number of revisions.
     */
    public function getRevisionCount() {
        return count( $this->getRevisionIDs() );
    }

    /**
     * Populate this PageSet
     * @param string[]|LinkTarget[]|PageReference[] $titles
     */
    public function populateFromTitles( $titles ) {
        $this->initFromTitles( $titles );
    }

    /**
     * Populate this PageSet from a list of page IDs
     * @param int[] $pageIDs
     */
    public function populateFromPageIDs( $pageIDs ) {
        $this->initFromPageIds( $pageIDs );
    }

    /**
     * Populate this PageSet from a rowset returned from the database
     *
     * Note that the query result must include the columns returned by
     * $this->getPageTableFields().
     *
     * @param IDatabase $db
     * @param IResultWrapper $queryResult
     */
    public function populateFromQueryResult( $db, $queryResult ) {
        $this->initFromQueryResult( $queryResult );
    }

    /**
     * Populate this PageSet from a list of revision IDs
     * @param int[] $revIDs Array of revision IDs
     */
    public function populateFromRevisionIDs( $revIDs ) {
        $this->initFromRevIDs( $revIDs );
    }

    /**
     * Extract all requested fields from the row received from the database
     * @param stdClass $row Result row
     */
    public function processDbRow( $row ) {
        // Store Title object in various data structures
        $title = $this->titleFactory->newFromRow( $row );

        $this->linkCache->addGoodLinkObjFromRow( $title, $row );

        $pageId = (int)$row->page_id;
        $this->mAllPages[$row->page_namespace][$row->page_title] = $pageId;
        $this->mTitles[] = $title;

        if ( $this->mResolveRedirects && $row->page_is_redirect == '1' ) {
            $this->mPendingRedirectIDs[$pageId] = $title;
        } else {
            $this->mGoodPages[$row->page_namespace][$row->page_title] = $pageId;
            $this->mGoodAndMissingPages[$row->page_namespace][$row->page_title] = $pageId;
            $this->mGoodTitles[$pageId] = $title;
        }

        foreach ( $this->mRequestedPageFields as $fieldName => &$fieldValues ) {
            $fieldValues[$pageId] = $row->$fieldName;
        }
    }

    /**
     * This method populates internal variables with page information
     * based on the given array of title strings.
     *
     * Steps:
     * #1 For each title, get data from `page` table
     * #2 If page was not found in the DB, store it as missing
     *
     * Additionally, when resolving redirects:
     * #3 If no more redirects left, stop.
     * #4 For each redirect, get its target from the `redirect` table.
     * #5 Substitute the original LinkBatch object with the new list
     * #6 Repeat from step #1
     *
     * @param string[]|LinkTarget[]|PageReference[] $titles
     */
    private function initFromTitles( $titles ) {
        // Get validated and normalized title objects
        $linkBatch = $this->processTitlesArray( $titles );
        if ( $linkBatch->isEmpty() ) {
            // There might be special-page redirects
            $this->resolvePendingRedirects();
            return;
        }

        $db = $this->getDB();

        // Get pageIDs data from the `page` table
        $res = $db->newSelectQueryBuilder()
            ->select( $this->getPageTableFields() )
            ->from( 'page' )
            ->where( $linkBatch->constructSet( 'page', $db ) )
            ->caller( __METHOD__ )
            ->fetchResultSet();

        // Hack: get the ns:titles stored in [ ns => [ titles ] ] format
        $this->initFromQueryResult( $res, $linkBatch->data, true ); // process Titles

        // Resolve any found redirects
        $this->resolvePendingRedirects();
    }

    /**
     * Does the same as initFromTitles(), but is based on page IDs instead
     * @param int[] $pageids
     * @param bool $filterIds Whether the IDs need filtering
     */
    private function initFromPageIds( $pageids, $filterIds = true ) {
        if ( !$pageids ) {
            return;
        }

        $pageids = array_map( 'intval', $pageids ); // paranoia
        $remaining = array_fill_keys( $pageids, true );

        if ( $filterIds ) {
            $pageids = $this->filterIDs( [ [ 'page', 'page_id' ] ], $pageids );
        }

        $res = null;
        if ( $pageids ) {
            $db = $this->getDB();

            // Get pageIDs data from the `page` table
            $res = $db->newSelectQueryBuilder()
                ->select( $this->getPageTableFields() )
                ->from( 'page' )
                ->where( [ 'page_id' => $pageids ] )
                ->caller( __METHOD__ )
                ->fetchResultSet();
        }

        $this->initFromQueryResult( $res, $remaining, false ); // process PageIDs

        // Resolve any found redirects
        $this->resolvePendingRedirects();
    }

    /**
     * Iterate through the result of the query on 'page' table,
     * and for each row create and store title object and save any extra fields requested.
     * @param IResultWrapper|null $res DB Query result
     * @param array|null &$remaining Array of either pageID or ns/title elements (optional).
     *        If given, any missing items will go to $mMissingPageIDs and $mMissingTitles
     * @param bool|null $processTitles Must be provided together with $remaining.
     *        If true, treat $remaining as an array of [ns][title]
     *        If false, treat it as an array of [pageIDs]
     */
    private function initFromQueryResult( $res, &$remaining = null, $processTitles = null ) {
        if ( $remaining !== null && $processTitles === null ) {
            ApiBase::dieDebug( __METHOD__, 'Missing $processTitles parameter when $remaining is provided' );
        }

        $usernames = [];
        if ( $res ) {
            foreach ( $res as $row ) {
                $pageId = (int)$row->page_id;

                // Remove found page from the list of remaining items
                if ( $remaining ) {
                    if ( $processTitles ) {
                        unset( $remaining[$row->page_namespace][$row->page_title] );
                    } else {
                        unset( $remaining[$pageId] );
                    }
                }

                // Store any extra fields requested by modules
                $this->processDbRow( $row );

                // Need gender information
                if ( $this->namespaceInfo->hasGenderDistinction( $row->page_namespace ) ) {
                    $usernames[] = $row->page_title;
                }
            }
        }

        if ( $remaining ) {
            // Any items left in the $remaining list are added as missing
            if ( $processTitles ) {
                // The remaining titles in $remaining are non-existent pages
                foreach ( $remaining as $ns => $dbkeys ) {
                    foreach ( $dbkeys as $dbkey => $_ ) {
                        $title = $this->titleFactory->makeTitle( $ns, $dbkey );
                        $this->linkCache->addBadLinkObj( $title );
                        $this->mAllPages[$ns][$dbkey] = $this->mFakePageId;
                        $this->mMissingPages[$ns][$dbkey] = $this->mFakePageId;
                        $this->mGoodAndMissingPages[$ns][$dbkey] = $this->mFakePageId;
                        $this->mMissingTitles[$this->mFakePageId] = $title;
                        $this->mFakePageId--;
                        $this->mTitles[] = $title;

                        // need gender information
                        if ( $this->namespaceInfo->hasGenderDistinction( $ns ) ) {
                            $usernames[] = $dbkey;
                        }
                    }
                }
            } else {
                // The remaining pageids do not exist
                if ( !$this->mMissingPageIDs ) {
                    $this->mMissingPageIDs = array_keys( $remaining );
                } else {
                    $this->mMissingPageIDs = array_merge( $this->mMissingPageIDs, array_keys( $remaining ) );
                }
            }
        }

        // Get gender information
        $this->genderCache->doQuery( $usernames, __METHOD__ );
    }

    /**
     * Does the same as initFromTitles(), but is based on revision IDs
     * instead
     * @param int[] $revids Array of revision IDs
     */
    private function initFromRevIDs( $revids ) {
        if ( !$revids ) {
            return;
        }

        $revids = array_map( 'intval', $revids ); // paranoia
        $db = $this->getDB();
        $pageids = [];
        $remaining = array_fill_keys( $revids, true );

        $revids = $this->filterIDs( [ [ 'revision', 'rev_id' ], [ 'archive', 'ar_rev_id' ] ], $revids );
        $goodRemaining = array_fill_keys( $revids, true );

        if ( $revids ) {
            $fields = [ 'rev_id', 'rev_page' ];

            // Get pageIDs data from the `page` table
            $res = $db->newSelectQueryBuilder()
                ->select( $fields )
                ->from( 'page' )
                ->where( [ 'rev_id' => $revids ] )
                ->join( 'revision', null, [ 'rev_page = page_id' ] )
                ->caller( __METHOD__ )
                ->fetchResultSet();
            foreach ( $res as $row ) {
                $revid = (int)$row->rev_id;
                $pageid = (int)$row->rev_page;
                $this->mGoodRevIDs[$revid] = $pageid;
                $this->mLiveRevIDs[$revid] = $pageid;
                $pageids[$pageid] = '';
                unset( $remaining[$revid] );
                unset( $goodRemaining[$revid] );
            }
        }

        // Populate all the page information
        $this->initFromPageIds( array_keys( $pageids ), false );

        // If the user can see deleted revisions, pull out the corresponding
        // titles from the archive table and include them too. We ignore
        // ar_page_id because deleted revisions are tied by title, not page_id.
        if ( $goodRemaining &&
            $this->getAuthority()->isAllowed( 'deletedhistory' ) ) {

            $res = $db->newSelectQueryBuilder()
                ->select( [ 'ar_rev_id', 'ar_namespace', 'ar_title' ] )
                ->from( 'archive' )
                ->where( [ 'ar_rev_id' => array_keys( $goodRemaining ) ] )
                ->caller( __METHOD__ )
                ->fetchResultSet();

            $titles = [];
            foreach ( $res as $row ) {
                $revid = (int)$row->ar_rev_id;
                $titles[$revid] = $this->titleFactory->makeTitle( $row->ar_namespace, $row->ar_title );
                unset( $remaining[$revid] );
            }

            $this->initFromTitles( $titles );

            foreach ( $titles as $revid => $title ) {
                $ns = $title->getNamespace();
                $dbkey = $title->getDBkey();

                // Handle converted titles
                if ( !isset( $this->mAllPages[$ns][$dbkey] ) &&
                    isset( $this->mConvertedTitles[$title->getPrefixedText()] )
                ) {
                    $title = $this->titleFactory->newFromText( $this->mConvertedTitles[$title->getPrefixedText()] );
                    $ns = $title->getNamespace();
                    $dbkey = $title->getDBkey();
                }

                if ( isset( $this->mAllPages[$ns][$dbkey] ) ) {
                    $this->mGoodRevIDs[$revid] = $this->mAllPages[$ns][$dbkey];
                    $this->mDeletedRevIDs[$revid] = $this->mAllPages[$ns][$dbkey];
                } else {
                    $remaining[$revid] = true;
                }
            }
        }

        $this->mMissingRevIDs = array_keys( $remaining );
    }

    /**
     * Resolve any redirects in the result if redirect resolution was
     * requested. This function is called repeatedly until all redirects
     * have been resolved.
     */
    private function resolvePendingRedirects() {
        if ( $this->mResolveRedirects ) {
            $db = $this->getDB();

            // Repeat until all redirects have been resolved
            // The infinite loop is prevented by keeping all known pages in $this->mAllPages
            while ( $this->mPendingRedirectIDs || $this->mPendingRedirectSpecialPages ) {
                // Resolve redirects by querying the pagelinks table, and repeat the process
                // Create a new linkBatch object for the next pass
                $linkBatch = $this->loadRedirectTargets();

                if ( $linkBatch->isEmpty() ) {
                    break;
                }

                $set = $linkBatch->constructSet( 'page', $db );
                if ( $set === false ) {
                    break;
                }

                // Get pageIDs data from the `page` table
                $res = $db->newSelectQueryBuilder()
                    ->select( $this->getPageTableFields() )
                    ->from( 'page' )
                    ->where( $set )
                    ->caller( __METHOD__ )
                    ->fetchResultSet();

                // Hack: get the ns:titles stored in [ns => array(titles)] format
                $this->initFromQueryResult( $res, $linkBatch->data, true );
            }
        }
    }

    /**
     * Get the targets of the pending redirects from the database
     *
     * Also creates entries in the redirect table for redirects that don't
     * have one.
     * @return LinkBatch
     */
    private function loadRedirectTargets() {
        $titlesToResolve = [];
        $db = $this->getDB();

        if ( $this->mPendingRedirectIDs ) {
            $res = $db->newSelectQueryBuilder()
                ->select( [
                    'rd_from',
                    'rd_namespace',
                    'rd_fragment',
                    'rd_interwiki',
                    'rd_title'
                ] )
                ->from( 'redirect' )
                ->where( [ 'rd_from' => array_keys( $this->mPendingRedirectIDs ) ] )
                ->caller( __METHOD__ )
                ->fetchResultSet();

            foreach ( $res as $row ) {
                $rdfrom = (int)$row->rd_from;
                $from = $this->mPendingRedirectIDs[$rdfrom]->getPrefixedText();
                $to = $this->titleFactory->makeTitle(
                    $row->rd_namespace,
                    $row->rd_title,
                    $row->rd_fragment,
                    $row->rd_interwiki
                );
                $this->mResolvedRedirectTitles[$from] = $this->mPendingRedirectIDs[$rdfrom];
                unset( $this->mPendingRedirectIDs[$rdfrom] );
                if ( $to->isExternal() ) {
                    $this->mInterwikiTitles[$to->getPrefixedText()] = $to->getInterwiki();
                } elseif ( !isset( $this->mAllPages[$to->getNamespace()][$to->getDBkey()] )
                    && !( $this->mConvertTitles && isset( $this->mConvertedTitles[$to->getPrefixedText()] ) )
                ) {
                    $titlesToResolve[] = $to;
                }
                $this->mRedirectTitles[$from] = $to;
            }
        }

        if ( $this->mPendingRedirectSpecialPages ) {
            foreach ( $this->mPendingRedirectSpecialPages as [ $from, $to ] ) {
                /** @var Title $from */
                $fromKey = $from->getPrefixedText();
                $this->mResolvedRedirectTitles[$fromKey] = $from;
                $this->mRedirectTitles[$fromKey] = $to;
                if ( $to->isExternal() ) {
                    $this->mInterwikiTitles[$to->getPrefixedText()] = $to->getInterwiki();
                } elseif ( !isset( $this->mAllPages[$to->getNamespace()][$to->getDBkey()] ) ) {
                    $titlesToResolve[] = $to;
                }
            }
            $this->mPendingRedirectSpecialPages = [];

            // Set private caching since we don't know what criteria the
            // special pages used to decide on these redirects.
            $this->mCacheMode = 'private';
        }

        return $this->processTitlesArray( $titlesToResolve );
    }

    /**
     * Get the cache mode for the data generated by this module.
     * All PageSet users should take into account whether this returns a more-restrictive
     * cache mode than the using module itself. For possible return values and other
     * details about cache modes, see ApiMain::setCacheMode()
     *
     * Public caching will only be allowed if *all* the modules that supply
     * data for a given request return a cache mode of public.
     *
     * @param array|null $params
     * @return string
     * @since 1.21
     */
    public function getCacheMode( $params = null ) {
        return $this->mCacheMode;
    }

    /**
     * Given an array of title strings, convert them into Title objects.
     * Alternatively, an array of Title objects may be given.
     * This method validates access rights for the title,
     * and appends normalization values to the output.
     *
     * @param string[]|LinkTarget[]|PageReference[] $titles
     * @return LinkBatch
     */
    private function processTitlesArray( $titles ) {
        $linkBatch = $this->linkBatchFactory->newLinkBatch();

        /** @var Title[] $titleObjects */
        $titleObjects = [];
        foreach ( $titles as $index => $title ) {
            if ( is_string( $title ) ) {
                try {
                    /** @var Title $titleObj */
                    $titleObj = $this->titleFactory->newFromTextThrow( $title, $this->mDefaultNamespace );
                } catch ( MalformedTitleException $ex ) {
                    // Handle invalid titles gracefully
                    if ( !isset( $this->mAllPages[0][$title] ) ) {
                        $this->mAllPages[0][$title] = $this->mFakePageId;
                        $this->mInvalidTitles[$this->mFakePageId] = [
                            'title' => $title,
                            'invalidreason' => $this->getErrorFormatter()->formatException( $ex, [ 'bc' => true ] ),
                        ];
                        $this->mFakePageId--;
                    }
                    continue; // There's nothing else we can do
                }
            } elseif ( $title instanceof LinkTarget ) {
                $titleObj = $this->titleFactory->newFromLinkTarget( $title );
            } else {
                $titleObj = $this->titleFactory->newFromPageReference( $title );
            }

            $titleObjects[$index] = $titleObj;
        }

        // Get gender information
        $this->genderCache->doTitlesArray( $titleObjects, __METHOD__ );

        foreach ( $titleObjects as $index => $titleObj ) {
            $title = is_string( $titles[$index] ) ? $titles[$index] : false;
            $unconvertedTitle = $titleObj->getPrefixedText();
            $titleWasConverted = false;
            if ( $titleObj->isExternal() ) {
                // This title is an interwiki link.
                $this->mInterwikiTitles[$unconvertedTitle] = $titleObj->getInterwiki();
            } else {
                // Variants checking
                if (
                    $this->mConvertTitles
                    && $this->languageConverter->hasVariants()
                    && !$titleObj->exists()
                ) {
                    // ILanguageConverter::findVariantLink will modify titleText and
                    // titleObj into the canonical variant if possible
                    $titleText = $title !== false ? $title : $titleObj->getPrefixedText();
                    $this->languageConverter->findVariantLink( $titleText, $titleObj );
                    $titleWasConverted = $unconvertedTitle !== $titleObj->getPrefixedText();
                }

                if ( $titleObj->getNamespace() < 0 ) {
                    // Handle Special and Media pages
                    $titleObj = $titleObj->fixSpecialName();
                    $ns = $titleObj->getNamespace();
                    $dbkey = $titleObj->getDBkey();
                    if ( !isset( $this->mAllSpecials[$ns][$dbkey] ) ) {
                        $this->mAllSpecials[$ns][$dbkey] = $this->mFakePageId;
                        $target = null;
                        if ( $ns === NS_SPECIAL && $this->mResolveRedirects ) {
                            $special = $this->specialPageFactory->getPage( $dbkey );
                            if ( $special instanceof RedirectSpecialArticle ) {
                                // Only RedirectSpecialArticle is intended to redirect to an article, other kinds of
                                // RedirectSpecialPage are probably applying weird URL parameters we don't want to
                                // handle.
                                $context = new DerivativeContext( $this );
                                $context->setTitle( $titleObj );
                                $context->setRequest( new FauxRequest );
                                $special->setContext( $context );
                                [ /* $alias */, $subpage ] = $this->specialPageFactory->resolveAlias( $dbkey );
                                $target = $special->getRedirect( $subpage );
                            }
                        }
                        if ( $target ) {
                            $this->mPendingRedirectSpecialPages[$dbkey] = [ $titleObj, $target ];
                        } else {
                            $this->mSpecialTitles[$this->mFakePageId] = $titleObj;
                            $this->mFakePageId--;
                        }
                    }
                } else {
                    // Regular page
                    $linkBatch->addObj( $titleObj );
                }
            }

            // Make sure we remember the original title that was
            // given to us. This way the caller can correlate new
            // titles with the originally requested when e.g. the
            // namespace is localized or the capitalization is
            // different
            if ( $titleWasConverted ) {
                $this->mConvertedTitles[$unconvertedTitle] = $titleObj->getPrefixedText();
                // In this case the page can't be Special.
                if ( $title !== false && $title !== $unconvertedTitle ) {
                    $this->mNormalizedTitles[$title] = $unconvertedTitle;
                }
            } elseif ( $title !== false && $title !== $titleObj->getPrefixedText() ) {
                $this->mNormalizedTitles[$title] = $titleObj->getPrefixedText();
            }
        }

        return $linkBatch;
    }

    /**
     * Set data for a title.
     *
     * This data may be extracted into an ApiResult using
     * self::populateGeneratorData. This should generally be limited to
     * data that is likely to be particularly useful to end users rather than
     * just being a dump of everything returned in non-generator mode.
     *
     * Redirects here will *not* be followed, even if 'redirects' was
     * specified, since in the case of multiple redirects we can't know which
     * source's data to use on the target.
     *
     * @param PageReference|LinkTarget $title
     * @param array $data
     */
    public function setGeneratorData( $title, array $data ) {
        $ns = $title->getNamespace();
        $dbkey = $title->getDBkey();
        $this->mGeneratorData[$ns][$dbkey] = $data;
    }

    /**
     * Controls how generator data about a redirect source is merged into
     * the generator data for the redirect target. When not set no data
     * is merged. Note that if multiple titles redirect to the same target
     * the order of operations is undefined.
     *
     * Example to include generated data from redirect in target, prefering
     * the data generated for the destination when there is a collision:
     * @code
     *   $pageSet->setRedirectMergePolicy( function( array $current, array $new ) {
     *       return $current + $new;
     *   } );
     * @endcode
     *
     * @param callable|null $callable Recieves two array arguments, first the
     *  generator data for the redirect target and second the generator data
     *  for the redirect source. Returns the resulting generator data to use
     *  for the redirect target.
     */
    public function setRedirectMergePolicy( $callable ) {
        $this->mRedirectMergePolicy = $callable;
    }

    /**
     * Resolve the title a redirect points to.
     *
     * Will follow sequential redirects to find the final page. In
     * the case of a redirect cycle the original page will be returned.
     * self::resolvePendingRedirects must be executed before calling
     * this method.
     *
     * @param Title $titleFrom A title from $this->mResolvedRedirectTitles
     * @return Title
     */
    private function resolveRedirectTitleDest( Title $titleFrom ): Title {
        $seen = [];
        $dest = $titleFrom;
        while ( isset( $this->mRedirectTitles[$dest->getPrefixedText()] ) ) {
            $dest = $this->mRedirectTitles[$dest->getPrefixedText()];
            if ( isset( $seen[$dest->getPrefixedText()] ) ) {
                return $titleFrom;
            }
            $seen[$dest->getPrefixedText()] = true;
        }
        return $dest;
    }

    /**
     * Populate the generator data for all titles in the result
     *
     * The page data may be inserted into an ApiResult object or into an
     * associative array. The $path parameter specifies the path within the
     * ApiResult or array to find the "pages" node.
     *
     * The "pages" node itself must be an associative array mapping the page ID
     * or fake page ID values returned by this pageset (see
     * self::getAllTitlesByNamespace() and self::getSpecialTitles()) to
     * associative arrays of page data. Each of those subarrays will have the
     * data from self::setGeneratorData() merged in.
     *
     * Data that was set by self::setGeneratorData() for pages not in the
     * "pages" node will be ignored.
     *
     * @param ApiResult|array &$result
     * @param array $path
     * @return bool Whether the data fit
     */
    public function populateGeneratorData( &$result, array $path = [] ) {
        if ( $result instanceof ApiResult ) {
            $data = $result->getResultData( $path );
            if ( $data === null ) {
                return true;
            }
        } else {
            $data = &$result;
            foreach ( $path as $key ) {
                if ( !isset( $data[$key] ) ) {
                    // Path isn't in $result, so nothing to add, so everything
                    // "fits"
                    return true;
                }
                $data = &$data[$key];
            }
        }
        foreach ( $this->mGeneratorData as $ns => $dbkeys ) {
            if ( $ns === NS_SPECIAL ) {
                $pages = [];
                foreach ( $this->mSpecialTitles as $id => $title ) {
                    $pages[$title->getDBkey()] = $id;
                }
            } else {
                if ( !isset( $this->mAllPages[$ns] ) ) {
                    // No known titles in the whole namespace. Skip it.
                    continue;
                }
                $pages = $this->mAllPages[$ns];
            }
            foreach ( $dbkeys as $dbkey => $genData ) {
                if ( !isset( $pages[$dbkey] ) ) {
                    // Unknown title. Forget it.
                    continue;
                }
                $pageId = $pages[$dbkey];
                if ( !isset( $data[$pageId] ) ) {
                    // $pageId didn't make it into the result. Ignore it.
                    continue;
                }

                if ( $result instanceof ApiResult ) {
                    $path2 = array_merge( $path, [ $pageId ] );
                    foreach ( $genData as $key => $value ) {
                        if ( !$result->addValue( $path2, $key, $value ) ) {
                            return false;
                        }
                    }
                } else {
                    $data[$pageId] = array_merge( $data[$pageId], $genData );
                }
            }
        }

        // Merge data generated about redirect titles into the redirect destination
        if ( $this->mRedirectMergePolicy ) {
            foreach ( $this->mResolvedRedirectTitles as $titleFrom ) {
                $dest = $this->resolveRedirectTitleDest( $titleFrom );
                $fromNs = $titleFrom->getNamespace();
                $fromDBkey = $titleFrom->getDBkey();
                $toPageId = $dest->getArticleID();
                if ( isset( $data[$toPageId] ) &&
                    isset( $this->mGeneratorData[$fromNs][$fromDBkey] )
                ) {
                    // It is necessary to set both $data and add to $result, if an ApiResult,
                    // to ensure multiple redirects to the same destination are all merged.
                    $data[$toPageId] = call_user_func(
                        $this->mRedirectMergePolicy,
                        $data[$toPageId],
                        $this->mGeneratorData[$fromNs][$fromDBkey]
                    );
                    if ( $result instanceof ApiResult &&
                        !$result->addValue( $path, $toPageId, $data[$toPageId], ApiResult::OVERRIDE )
                    ) {
                        return false;
                    }
                }
            }
        }

        return true;
    }

    /**
     * Get the database connection (read-only)
     * @return \Wikimedia\Rdbms\IReadableDatabase
     */
    protected function getDB() {
        return $this->mDbSource->getDB();
    }

    public function getAllowedParams( $flags = 0 ) {
        $result = [
            'titles' => [
                ParamValidator::PARAM_ISMULTI => true,
                ApiBase::PARAM_HELP_MSG => 'api-pageset-param-titles',
            ],
            'pageids' => [
                ParamValidator::PARAM_TYPE => 'integer',
                ParamValidator::PARAM_ISMULTI => true,
                ApiBase::PARAM_HELP_MSG => 'api-pageset-param-pageids',
            ],
            'revids' => [
                ParamValidator::PARAM_TYPE => 'integer',
                ParamValidator::PARAM_ISMULTI => true,
                ApiBase::PARAM_HELP_MSG => 'api-pageset-param-revids',
            ],
            'generator' => [
                ParamValidator::PARAM_TYPE => null,
                ApiBase::PARAM_HELP_MSG => 'api-pageset-param-generator',
                SubmoduleDef::PARAM_SUBMODULE_PARAM_PREFIX => 'g',
            ],
            'redirects' => [
                ParamValidator::PARAM_DEFAULT => false,
                ApiBase::PARAM_HELP_MSG => $this->mAllowGenerator
                    ? 'api-pageset-param-redirects-generator'
                    : 'api-pageset-param-redirects-nogenerator',
            ],
            'converttitles' => [
                ParamValidator::PARAM_DEFAULT => false,
                ApiBase::PARAM_HELP_MSG => [
                    'api-pageset-param-converttitles',
                    [ Message::listParam( LanguageConverter::$languagesWithVariants, 'text' ) ],
                ],
            ],
        ];

        if ( !$this->mAllowGenerator ) {
            unset( $result['generator'] );
        } elseif ( $flags & ApiBase::GET_VALUES_FOR_HELP ) {
            $result['generator'][ParamValidator::PARAM_TYPE] = 'submodule';
            $result['generator'][SubmoduleDef::PARAM_SUBMODULE_MAP] = $this->getGenerators();
        }

        return $result;
    }

    public function handleParamNormalization( $paramName, $value, $rawValue ) {
        parent::handleParamNormalization( $paramName, $value, $rawValue );

        if ( $paramName === 'titles' ) {
            // For the 'titles' parameter, we want to split it like ApiBase would
            // and add any changed titles to $this->mNormalizedTitles
            $value = ParamValidator::explodeMultiValue( $value, self::LIMIT_SML2 + 1 );
            $l = count( $value );
            $rawValue = ParamValidator::explodeMultiValue( $rawValue, $l );
            for ( $i = 0; $i < $l; $i++ ) {
                if ( $value[$i] !== $rawValue[$i] ) {
                    $this->mNormalizedTitles[$rawValue[$i]] = $value[$i];
                }
            }
        }
    }

    /**
     * Get an array of all available generators
     * @return string[]
     */
    private function getGenerators() {
        if ( self::$generators === null ) {
            $query = $this->mDbSource;
            if ( !( $query instanceof ApiQuery ) ) {
                // If the parent container of this pageset is not ApiQuery,
                // we must create it to get module manager
                $query = $this->getMain()->getModuleManager()->getModule( 'query' );
            }
            $gens = [];
            $prefix = $query->getModulePath() . '+';
            $mgr = $query->getModuleManager();
            foreach ( $mgr->getNamesWithClasses() as $name => $class ) {
                if ( is_subclass_of( $class, ApiQueryGeneratorBase::class ) ) {
                    $gens[$name] = $prefix . $name;
                }
            }
            ksort( $gens );
            self::$generators = $gens;
        }

        return self::$generators;
    }
}