ApiComparePages.php

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<?php
use MediaWiki\MediaWikiServices;
use MediaWiki\Revision\MutableRevisionRecord;
use MediaWiki\Revision\RevisionRecord;
use MediaWiki\Revision\RevisionArchiveRecord;
use MediaWiki\Revision\RevisionStore;
use MediaWiki\Revision\SlotRecord;
 
class ApiComparePages extends ApiBase {
 
    private $revisionStore;
 
    private $slotRoleRegistry;
 
    private $guessedTitle = false, $props;
 
    public function __construct( ApiMain $mainModule, $moduleName, $modulePrefix = '' ) {
        parent::__construct( $mainModule, $moduleName, $modulePrefix );
        $this->revisionStore = MediaWikiServices::getInstance()->getRevisionStore();
        $this->slotRoleRegistry = MediaWikiServices::getInstance()->getSlotRoleRegistry();
    }
 
    public function execute() {
        $params = $this->extractRequestParams();
 
        // Parameter validation
        $this->requireAtLeastOneParameter(
            $params, 'fromtitle', 'fromid', 'fromrev', 'fromtext', 'fromslots'
        );
        $this->requireAtLeastOneParameter(
            $params, 'totitle', 'toid', 'torev', 'totext', 'torelative', 'toslots'
        );
 
        $this->props = array_flip( $params['prop'] );
 
        // Cache responses publicly by default. This may be overridden later.
        $this->getMain()->setCacheMode( 'public' );
 
        // Get the 'from' RevisionRecord
        list( $fromRev, $fromRelRev, $fromValsRev ) = $this->getDiffRevision( 'from', $params );
 
        // Get the 'to' RevisionRecord
        if ( $params['torelative'] !== null ) {
            if ( !$fromRelRev ) {
                $this->dieWithError( 'apierror-compare-relative-to-nothing' );
            }
            if ( $params['torelative'] !== 'cur' && $fromRelRev instanceof RevisionArchiveRecord ) {
                // RevisionStore's getPreviousRevision/getNextRevision blow up
                // when passed an RevisionArchiveRecord for a deleted page
                $this->dieWithError( [ 'apierror-compare-relative-to-deleted', $params['torelative'] ] );
            }
            switch ( $params['torelative'] ) {
                case 'prev':
                    // Swap 'from' and 'to'
                    list( $toRev, $toRelRev, $toValsRev ) = [ $fromRev, $fromRelRev, $fromValsRev ];
                    $fromRev = $this->revisionStore->getPreviousRevision( $toRelRev );
                    $fromRelRev = $fromRev;
                    $fromValsRev = $fromRev;
                    if ( !$fromRev ) {
                        $title = Title::newFromLinkTarget( $toRelRev->getPageAsLinkTarget() );
                        $this->addWarning( [
                            'apiwarn-compare-no-prev',
                            wfEscapeWikiText( $title->getPrefixedText() ),
                            $toRelRev->getId()
                        ] );
 
                        // (T203433) Create an empty dummy revision as the "previous".
                        // The main slot has to exist, the rest will be handled by DifferenceEngine.
                        $fromRev = $this->revisionStore->newMutableRevisionFromArray( [
                            'title' => $title ?: Title::makeTitle( NS_SPECIAL, 'Badtitle/' . __METHOD__ )
                        ] );
                        $fromRev->setContent(
                            SlotRecord::MAIN,
                            $toRelRev->getContent( SlotRecord::MAIN, RevisionRecord::RAW )
                                ->getContentHandler()
                                ->makeEmptyContent()
                        );
                    }
                    break;
 
                case 'next':
                    $toRev = $this->revisionStore->getNextRevision( $fromRelRev );
                    $toRelRev = $toRev;
                    $toValsRev = $toRev;
                    if ( !$toRev ) {
                        $title = Title::newFromLinkTarget( $fromRelRev->getPageAsLinkTarget() );
                        $this->addWarning( [
                            'apiwarn-compare-no-next',
                            wfEscapeWikiText( $title->getPrefixedText() ),
                            $fromRelRev->getId()
                        ] );
 
                        // (T203433) The web UI treats "next" as "cur" in this case.
                        // Avoid repeating metadata by making a MutableRevisionRecord with no changes.
                        $toRev = MutableRevisionRecord::newFromParentRevision( $fromRelRev );
                    }
                    break;
 
                case 'cur':
                    $title = $fromRelRev->getPageAsLinkTarget();
                    $toRev = $this->revisionStore->getRevisionByTitle( $title );
                    if ( !$toRev ) {
                        $title = Title::newFromLinkTarget( $title );
                        $this->dieWithError(
                            [ 'apierror-missingrev-title', wfEscapeWikiText( $title->getPrefixedText() ) ], 'nosuchrevid'
                        );
                    }
                    $toRelRev = $toRev;
                    $toValsRev = $toRev;
                    break;
            }
        } else {
            list( $toRev, $toRelRev, $toValsRev ) = $this->getDiffRevision( 'to', $params );
        }
 
        // Handle missing from or to revisions (should never happen)
        // @codeCoverageIgnoreStart
        if ( !$fromRev || !$toRev ) {
            $this->dieWithError( 'apierror-baddiff' );
        }
        // @codeCoverageIgnoreEnd
 
        // Handle revdel
        if ( !$fromRev->audienceCan(
            RevisionRecord::DELETED_TEXT, RevisionRecord::FOR_THIS_USER, $this->getUser()
        ) ) {
            $this->dieWithError( [ 'apierror-missingcontent-revid', $fromRev->getId() ], 'missingcontent' );
        }
        if ( !$toRev->audienceCan(
            RevisionRecord::DELETED_TEXT, RevisionRecord::FOR_THIS_USER, $this->getUser()
        ) ) {
            $this->dieWithError( [ 'apierror-missingcontent-revid', $toRev->getId() ], 'missingcontent' );
        }
 
        // Get the diff
        $context = new DerivativeContext( $this->getContext() );
        if ( $fromRelRev && $fromRelRev->getPageAsLinkTarget() ) {
            $context->setTitle( Title::newFromLinkTarget( $fromRelRev->getPageAsLinkTarget() ) );
        } elseif ( $toRelRev && $toRelRev->getPageAsLinkTarget() ) {
            $context->setTitle( Title::newFromLinkTarget( $toRelRev->getPageAsLinkTarget() ) );
        } else {
            $guessedTitle = $this->guessTitle();
            if ( $guessedTitle ) {
                $context->setTitle( $guessedTitle );
            }
        }
        $de = new DifferenceEngine( $context );
        $de->setRevisions( $fromRev, $toRev );
        if ( $params['slots'] === null ) {
            $difftext = $de->getDiffBody();
            if ( $difftext === false ) {
                $this->dieWithError( 'apierror-baddiff' );
            }
        } else {
            $difftext = [];
            foreach ( $params['slots'] as $role ) {
                $difftext[$role] = $de->getDiffBodyForRole( $role );
            }
        }
 
        // Fill in the response
        $vals = [];
        $this->setVals( $vals, 'from', $fromValsRev );
        $this->setVals( $vals, 'to', $toValsRev );
 
        if ( isset( $this->props['rel'] ) ) {
            if ( !$fromRev instanceof MutableRevisionRecord ) {
                $rev = $this->revisionStore->getPreviousRevision( $fromRev );
                if ( $rev ) {
                    $vals['prev'] = $rev->getId();
                }
            }
            if ( !$toRev instanceof MutableRevisionRecord ) {
                $rev = $this->revisionStore->getNextRevision( $toRev );
                if ( $rev ) {
                    $vals['next'] = $rev->getId();
                }
            }
        }
 
        if ( isset( $this->props['diffsize'] ) ) {
            $vals['diffsize'] = 0;
            foreach ( (array)$difftext as $text ) {
                $vals['diffsize'] += strlen( $text );
            }
        }
        if ( isset( $this->props['diff'] ) ) {
            if ( is_array( $difftext ) ) {
                ApiResult::setArrayType( $difftext, 'kvp', 'diff' );
                $vals['bodies'] = $difftext;
            } else {
                ApiResult::setContentValue( $vals, 'body', $difftext );
            }
        }
 
        // Diffs can be really big and there's little point in having
        // ApiResult truncate it to an empty response since the diff is the
        // whole reason this module exists. So pass NO_SIZE_CHECK here.
        $this->getResult()->addValue( null, $this->getModuleName(), $vals, ApiResult::NO_SIZE_CHECK );
    }
 
    private function getRevisionById( $id ) {
        $rev = $this->revisionStore->getRevisionById( $id );
        if ( !$rev && $this->getUser()->isAllowedAny( 'deletedtext', 'undelete' ) ) {
            // Try the 'archive' table
            $arQuery = $this->revisionStore->getArchiveQueryInfo();
            $row = $this->getDB()->selectRow(
                $arQuery['tables'],
                array_merge(
                    $arQuery['fields'],
                    [ 'ar_namespace', 'ar_title' ]
                ),
                [ 'ar_rev_id' => $id ],
                __METHOD__,
                [],
                $arQuery['joins']
            );
            if ( $row ) {
                $rev = $this->revisionStore->newRevisionFromArchiveRow( $row );
                $rev->isArchive = true;
            }
        }
        return $rev;
    }
 
    private function guessTitle() {
        if ( $this->guessedTitle !== false ) {
            return $this->guessedTitle;
        }
 
        $this->guessedTitle = null;
        $params = $this->extractRequestParams();
 
        foreach ( [ 'from', 'to' ] as $prefix ) {
            if ( $params["{$prefix}rev"] !== null ) {
                $rev = $this->getRevisionById( $params["{$prefix}rev"] );
                if ( $rev ) {
                    $this->guessedTitle = Title::newFromLinkTarget( $rev->getPageAsLinkTarget() );
                    break;
                }
            }
 
            if ( $params["{$prefix}title"] !== null ) {
                $title = Title::newFromText( $params["{$prefix}title"] );
                if ( $title && !$title->isExternal() ) {
                    $this->guessedTitle = $title;
                    break;
                }
            }
 
            if ( $params["{$prefix}id"] !== null ) {
                $title = Title::newFromID( $params["{$prefix}id"] );
                if ( $title ) {
                    $this->guessedTitle = $title;
                    break;
                }
            }
        }
 
        return $this->guessedTitle;
    }
 
    private function guessModel( $role ) {
        $params = $this->extractRequestParams();
 
        $title = null;
        foreach ( [ 'from', 'to' ] as $prefix ) {
            if ( $params["{$prefix}rev"] !== null ) {
                $rev = $this->getRevisionById( $params["{$prefix}rev"] );
                if ( $rev && $rev->hasSlot( $role ) ) {
                    return $rev->getSlot( $role, RevisionRecord::RAW )->getModel();
                }
            }
        }
 
        $guessedTitle = $this->guessTitle();
        if ( $guessedTitle ) {
            return $this->slotRoleRegistry->getRoleHandler( $role )->getDefaultModel( $guessedTitle );
        }
 
        if ( isset( $params["fromcontentmodel-$role"] ) ) {
            return $params["fromcontentmodel-$role"];
        }
        if ( isset( $params["tocontentmodel-$role"] ) ) {
            return $params["tocontentmodel-$role"];
        }
 
        if ( $role === SlotRecord::MAIN ) {
            if ( isset( $params['fromcontentmodel'] ) ) {
                return $params['fromcontentmodel'];
            }
            if ( isset( $params['tocontentmodel'] ) ) {
                return $params['tocontentmodel'];
            }
        }
 
        return null;
    }
 
    private function getDiffRevision( $prefix, array $params ) {
        // Back compat params
        $this->requireMaxOneParameter( $params, "{$prefix}text", "{$prefix}slots" );
        $this->requireMaxOneParameter( $params, "{$prefix}section", "{$prefix}slots" );
        if ( $params["{$prefix}text"] !== null ) {
            $params["{$prefix}slots"] = [ SlotRecord::MAIN ];
            $params["{$prefix}text-main"] = $params["{$prefix}text"];
            $params["{$prefix}section-main"] = null;
            $params["{$prefix}contentmodel-main"] = $params["{$prefix}contentmodel"];
            $params["{$prefix}contentformat-main"] = $params["{$prefix}contentformat"];
        }
 
        $title = null;
        $rev = null;
        $suppliedContent = $params["{$prefix}slots"] !== null;
 
        // Get the revision and title, if applicable
        $revId = null;
        if ( $params["{$prefix}rev"] !== null ) {
            $revId = $params["{$prefix}rev"];
        } elseif ( $params["{$prefix}title"] !== null || $params["{$prefix}id"] !== null ) {
            if ( $params["{$prefix}title"] !== null ) {
                $title = Title::newFromText( $params["{$prefix}title"] );
                if ( !$title || $title->isExternal() ) {
                    $this->dieWithError(
                        [ 'apierror-invalidtitle', wfEscapeWikiText( $params["{$prefix}title"] ) ]
                    );
                }
            } else {
                $title = Title::newFromID( $params["{$prefix}id"] );
                if ( !$title ) {
                    $this->dieWithError( [ 'apierror-nosuchpageid', $params["{$prefix}id"] ] );
                }
            }
            $revId = $title->getLatestRevID();
            if ( !$revId ) {
                $revId = null;
                // Only die here if we're not using supplied text
                if ( !$suppliedContent ) {
                    if ( $title->exists() ) {
                        $this->dieWithError(
                            [ 'apierror-missingrev-title', wfEscapeWikiText( $title->getPrefixedText() ) ], 'nosuchrevid'
                        );
                    } else {
                        $this->dieWithError(
                            [ 'apierror-missingtitle-byname', wfEscapeWikiText( $title->getPrefixedText() ) ],
                            'missingtitle'
                        );
                    }
                }
            }
        }
        if ( $revId !== null ) {
            $rev = $this->getRevisionById( $revId );
            if ( !$rev ) {
                $this->dieWithError( [ 'apierror-nosuchrevid', $revId ] );
            }
            $title = Title::newFromLinkTarget( $rev->getPageAsLinkTarget() );
 
            // If we don't have supplied content, return here. Otherwise,
            // continue on below with the supplied content.
            if ( !$suppliedContent ) {
                $newRev = $rev;
 
                // Deprecated 'fromsection'/'tosection'
                if ( isset( $params["{$prefix}section"] ) ) {
                    $section = $params["{$prefix}section"];
                    $newRev = MutableRevisionRecord::newFromParentRevision( $rev );
                    $content = $rev->getContent( SlotRecord::MAIN, RevisionRecord::FOR_THIS_USER,
                        $this->getUser() );
                    if ( !$content ) {
                        $this->dieWithError(
                            [ 'apierror-missingcontent-revid-role', $rev->getId(), SlotRecord::MAIN ], 'missingcontent'
                        );
                    }
                    $content = $content ? $content->getSection( $section ) : null;
                    if ( !$content ) {
                        $this->dieWithError(
                            [ "apierror-compare-nosuch{$prefix}section", wfEscapeWikiText( $section ) ],
                            "nosuch{$prefix}section"
                        );
                    }
                    $newRev->setContent( SlotRecord::MAIN, $content );
                }
 
                return [ $newRev, $rev, $rev ];
            }
        }
 
        // Override $content based on supplied text
        if ( !$title ) {
            $title = $this->guessTitle();
        }
        if ( $rev ) {
            $newRev = MutableRevisionRecord::newFromParentRevision( $rev );
        } else {
            $newRev = $this->revisionStore->newMutableRevisionFromArray( [
                'title' => $title ?: Title::makeTitle( NS_SPECIAL, 'Badtitle/' . __METHOD__ )
            ] );
        }
        foreach ( $params["{$prefix}slots"] as $role ) {
            $text = $params["{$prefix}text-{$role}"];
            if ( $text === null ) {
                // The SlotRecord::MAIN role can't be deleted
                if ( $role === SlotRecord::MAIN ) {
                    $this->dieWithError( [ 'apierror-compare-maintextrequired', $prefix ] );
                }
 
                // These parameters make no sense without text. Reject them to avoid
                // confusion.
                foreach ( [ 'section', 'contentmodel', 'contentformat' ] as $param ) {
                    if ( isset( $params["{$prefix}{$param}-{$role}"] ) ) {
                        $this->dieWithError( [
                            'apierror-compare-notext',
                            wfEscapeWikiText( "{$prefix}{$param}-{$role}" ),
                            wfEscapeWikiText( "{$prefix}text-{$role}" ),
                        ] );
                    }
                }
 
                $newRev->removeSlot( $role );
                continue;
            }
 
            $model = $params["{$prefix}contentmodel-{$role}"];
            $format = $params["{$prefix}contentformat-{$role}"];
 
            if ( !$model && $rev && $rev->hasSlot( $role ) ) {
                $model = $rev->getSlot( $role, RevisionRecord::RAW )->getModel();
            }
            if ( !$model && $title && $role === SlotRecord::MAIN ) {
                // @todo: Use SlotRoleRegistry and do this for all slots
                $model = $title->getContentModel();
            }
            if ( !$model ) {
                $model = $this->guessModel( $role );
            }
            if ( !$model ) {
                $model = CONTENT_MODEL_WIKITEXT;
                $this->addWarning( [ 'apiwarn-compare-nocontentmodel', $model ] );
            }
 
            try {
                $content = ContentHandler::makeContent( $text, $title, $model, $format );
            } catch ( MWContentSerializationException $ex ) {
                $this->dieWithException( $ex, [
                    'wrap' => ApiMessage::create( 'apierror-contentserializationexception', 'parseerror' )
                ] );
            }
 
            if ( $params["{$prefix}pst"] ) {
                if ( !$title ) {
                    $this->dieWithError( 'apierror-compare-no-title' );
                }
                $popts = ParserOptions::newFromContext( $this->getContext() );
                $content = $content->preSaveTransform( $title, $this->getUser(), $popts );
            }
 
            $section = $params["{$prefix}section-{$role}"];
            if ( $section !== null && $section !== '' ) {
                if ( !$rev ) {
                    $this->dieWithError( "apierror-compare-no{$prefix}revision" );
                }
                $oldContent = $rev->getContent( $role, RevisionRecord::FOR_THIS_USER, $this->getUser() );
                if ( !$oldContent ) {
                    $this->dieWithError(
                        [ 'apierror-missingcontent-revid-role', $rev->getId(), wfEscapeWikiText( $role ) ],
                        'missingcontent'
                    );
                }
                if ( !$oldContent->getContentHandler()->supportsSections() ) {
                    $this->dieWithError( [ 'apierror-sectionsnotsupported', $content->getModel() ] );
                }
                try {
                    $content = $oldContent->replaceSection( $section, $content, '' );
                } catch ( Exception $ex ) {
                    // Probably a content model mismatch.
                    $content = null;
                }
                if ( !$content ) {
                    $this->dieWithError( [ 'apierror-sectionreplacefailed' ] );
                }
            }
 
            // Deprecated 'fromsection'/'tosection'
            if ( $role === SlotRecord::MAIN && isset( $params["{$prefix}section"] ) ) {
                $section = $params["{$prefix}section"];
                $content = $content->getSection( $section );
                if ( !$content ) {
                    $this->dieWithError(
                        [ "apierror-compare-nosuch{$prefix}section", wfEscapeWikiText( $section ) ],
                        "nosuch{$prefix}section"
                    );
                }
            }
 
            $newRev->setContent( $role, $content );
        }
        return [ $newRev, $rev, null ];
    }
 
    private function setVals( &$vals, $prefix, $rev ) {
        if ( $rev ) {
            $title = $rev->getPageAsLinkTarget();
            if ( isset( $this->props['ids'] ) ) {
                $vals["{$prefix}id"] = $title->getArticleID();
                $vals["{$prefix}revid"] = $rev->getId();
            }
            if ( isset( $this->props['title'] ) ) {
                ApiQueryBase::addTitleInfo( $vals, $title, $prefix );
            }
            if ( isset( $this->props['size'] ) ) {
                $vals["{$prefix}size"] = $rev->getSize();
            }
 
            $anyHidden = false;
            if ( $rev->isDeleted( RevisionRecord::DELETED_TEXT ) ) {
                $vals["{$prefix}texthidden"] = true;
                $anyHidden = true;
            }
 
            if ( $rev->isDeleted( RevisionRecord::DELETED_USER ) ) {
                $vals["{$prefix}userhidden"] = true;
                $anyHidden = true;
            }
            if ( isset( $this->props['user'] ) ) {
                $user = $rev->getUser( RevisionRecord::FOR_THIS_USER, $this->getUser() );
                if ( $user ) {
                    $vals["{$prefix}user"] = $user->getName();
                    $vals["{$prefix}userid"] = $user->getId();
                }
            }
 
            if ( $rev->isDeleted( RevisionRecord::DELETED_COMMENT ) ) {
                $vals["{$prefix}commenthidden"] = true;
                $anyHidden = true;
            }
            if ( isset( $this->props['comment'] ) || isset( $this->props['parsedcomment'] ) ) {
                $comment = $rev->getComment( RevisionRecord::FOR_THIS_USER, $this->getUser() );
                if ( $comment !== null ) {
                    if ( isset( $this->props['comment'] ) ) {
                        $vals["{$prefix}comment"] = $comment->text;
                    }
                    $vals["{$prefix}parsedcomment"] = Linker::formatComment(
                        $comment->text, Title::newFromLinkTarget( $title )
                    );
                }
            }
 
            if ( $anyHidden ) {
                $this->getMain()->setCacheMode( 'private' );
                if ( $rev->isDeleted( RevisionRecord::DELETED_RESTRICTED ) ) {
                    $vals["{$prefix}suppressed"] = true;
                }
            }
 
            if ( !empty( $rev->isArchive ) ) {
                $this->getMain()->setCacheMode( 'private' );
                $vals["{$prefix}archive"] = true;
            }
        }
    }
 
    public function getAllowedParams() {
        $slotRoles = $this->slotRoleRegistry->getKnownRoles();
        sort( $slotRoles, SORT_STRING );
 
        // Parameters for the 'from' and 'to' content
        $fromToParams = [
            'title' => null,
            'id' => [
                ApiBase::PARAM_TYPE => 'integer'
            ],
            'rev' => [
                ApiBase::PARAM_TYPE => 'integer'
            ],
 
            'slots' => [
                ApiBase::PARAM_TYPE => $slotRoles,
                ApiBase::PARAM_ISMULTI => true,
            ],
            'text-{slot}' => [
                ApiBase::PARAM_TEMPLATE_VARS => [ 'slot' => 'slots' ], // fixed below
                ApiBase::PARAM_TYPE => 'text',
            ],
            'section-{slot}' => [
                ApiBase::PARAM_TEMPLATE_VARS => [ 'slot' => 'slots' ], // fixed below
                ApiBase::PARAM_TYPE => 'string',
            ],
            'contentformat-{slot}' => [
                ApiBase::PARAM_TEMPLATE_VARS => [ 'slot' => 'slots' ], // fixed below
                ApiBase::PARAM_TYPE => ContentHandler::getAllContentFormats(),
            ],
            'contentmodel-{slot}' => [
                ApiBase::PARAM_TEMPLATE_VARS => [ 'slot' => 'slots' ], // fixed below
                ApiBase::PARAM_TYPE => ContentHandler::getContentModels(),
            ],
            'pst' => false,
 
            'text' => [
                ApiBase::PARAM_TYPE => 'text',
                ApiBase::PARAM_DEPRECATED => true,
            ],
            'contentformat' => [
                ApiBase::PARAM_TYPE => ContentHandler::getAllContentFormats(),
                ApiBase::PARAM_DEPRECATED => true,
            ],
            'contentmodel' => [
                ApiBase::PARAM_TYPE => ContentHandler::getContentModels(),
                ApiBase::PARAM_DEPRECATED => true,
            ],
            'section' => [
                ApiBase::PARAM_DFLT => null,
                ApiBase::PARAM_DEPRECATED => true,
            ],
        ];
 
        $ret = [];
        foreach ( $fromToParams as $k => $v ) {
            if ( isset( $v[ApiBase::PARAM_TEMPLATE_VARS]['slot'] ) ) {
                $v[ApiBase::PARAM_TEMPLATE_VARS]['slot'] = 'fromslots';
            }
            $ret["from$k"] = $v;
        }
        foreach ( $fromToParams as $k => $v ) {
            if ( isset( $v[ApiBase::PARAM_TEMPLATE_VARS]['slot'] ) ) {
                $v[ApiBase::PARAM_TEMPLATE_VARS]['slot'] = 'toslots';
            }
            $ret["to$k"] = $v;
        }
 
        $ret = wfArrayInsertAfter(
            $ret,
            [ 'torelative' => [ ApiBase::PARAM_TYPE => [ 'prev', 'next', 'cur' ], ] ],
            'torev'
        );
 
        $ret['prop'] = [
            ApiBase::PARAM_DFLT => 'diff|ids|title',
            ApiBase::PARAM_TYPE => [
                'diff',
                'diffsize',
                'rel',
                'ids',
                'title',
                'user',
                'comment',
                'parsedcomment',
                'size',
            ],
            ApiBase::PARAM_ISMULTI => true,
            ApiBase::PARAM_HELP_MSG_PER_VALUE => [],
        ];
 
        $ret['slots'] = [
            ApiBase::PARAM_TYPE => $slotRoles,
            ApiBase::PARAM_ISMULTI => true,
            ApiBase::PARAM_ALL => true,
        ];
 
        return $ret;
    }
 
    protected function getExamplesMessages() {
        return [
            'action=compare&fromrev=1&torev=2'
                => 'apihelp-compare-example-1',
        ];
    }
}