HistoryAction.php

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<?php
use MediaWiki\MediaWikiServices;
use Wikimedia\Rdbms\ResultWrapper;
use Wikimedia\Rdbms\FakeResultWrapper;

class HistoryAction extends FormlessAction {
    const DIR_PREV = 0;
    const DIR_NEXT = 1;

    public $message;

    public function getName() {
        return 'history';
    }

    public function requiresWrite() {
        return false;
    }

    public function requiresUnblock() {
        return false;
    }

    protected function getPageTitle() {
        return $this->msg( 'history-title', $this->getTitle()->getPrefixedText() )->text();
    }

    protected function getDescription() {
        // Creation of a subtitle link pointing to [[Special:Log]]
        $linkRenderer = MediaWikiServices::getInstance()->getLinkRenderer();
        $subtitle = $linkRenderer->makeKnownLink(
            SpecialPage::getTitleFor( 'Log' ),
            $this->msg( 'viewpagelogs' )->text(),
            [],
            [ 'page' => $this->getTitle()->getPrefixedText() ]
        );

        $links = [];
        // Allow extensions to add more links
        Hooks::run( 'HistoryPageToolLinks', [ $this->getContext(), $linkRenderer, &$links ] );
        if ( $links ) {
            $subtitle .= ''
                . $this->msg( 'word-separator' )->escaped()
                . $this->msg( 'parentheses' )
                    ->rawParams( $this->getLanguage()->pipeList( $links ) )
                    ->escaped();
        }
        return $subtitle;
    }

    public function getArticle() {
        return $this->page;
    }

    private function preCacheMessages() {
        // Precache various messages
        if ( !isset( $this->message ) ) {
            $msgs = [ 'cur', 'last', 'pipe-separator' ];
            foreach ( $msgs as $msg ) {
                $this->message[$msg] = $this->msg( $msg )->escaped();
            }
        }
    }

    function onView() {
        $out = $this->getOutput();
        $request = $this->getRequest();

        if ( $out->checkLastModified( $this->page->getTouched() ) ) {
            return; // Client cache fresh and headers sent, nothing more to do.
        }

        $this->preCacheMessages();
        $config = $this->context->getConfig();

        # Fill in the file cache if not set already
        if ( HTMLFileCache::useFileCache( $this->getContext() ) ) {
            $cache = new HTMLFileCache( $this->getTitle(), 'history' );
            if ( !$cache->isCacheGood( /* Assume up to date */ ) ) {
                ob_start( [ &$cache, 'saveToFileCache' ] );
            }
        }

        // Setup page variables.
        $out->setFeedAppendQuery( 'action=history' );
        $out->addModules( 'mediawiki.action.history' );
        $out->addModuleStyles( [
            'mediawiki.action.history.styles',
            'mediawiki.special.changeslist',
        ] );
        if ( $config->get( 'UseMediaWikiUIEverywhere' ) ) {
            $out = $this->getOutput();
            $out->addModuleStyles( [
                'mediawiki.ui.input',
                'mediawiki.ui.checkbox',
            ] );
        }

        // Handle atom/RSS feeds.
        $feedType = $request->getVal( 'feed' );
        if ( $feedType ) {
            $this->feed( $feedType );

            return;
        }

        $this->addHelpLink( '//meta.wikimedia.org/wiki/Special:MyLanguage/Help:Page_history', true );

        // Fail nicely if article doesn't exist.
        if ( !$this->page->exists() ) {
            global $wgSend404Code;
            if ( $wgSend404Code ) {
                $out->setStatusCode( 404 );
            }
            $out->addWikiMsg( 'nohistory' );

            $dbr = wfGetDB( DB_REPLICA );

            # show deletion/move log if there is an entry
            LogEventsList::showLogExtract(
                $out,
                [ 'delete', 'move', 'protect' ],
                $this->getTitle(),
                '',
                [ 'lim' => 10,
                    'conds' => [ 'log_action != ' . $dbr->addQuotes( 'revision' ) ],
                    'showIfEmpty' => false,
                    'msgKey' => [ 'moveddeleted-notice' ]
                ]
            );

            return;
        }

        $year = $request->getInt( 'year' );
        $month = $request->getInt( 'month' );
        $tagFilter = $request->getVal( 'tagfilter' );
        $tagSelector = ChangeTags::buildTagFilterSelector( $tagFilter, false, $this->getContext() );

        if ( $request->getBool( 'deleted' ) ) {
            $conds = [ 'rev_deleted != 0' ];
        } else {
            $conds = [];
        }
        if ( $this->getUser()->isAllowed( 'deletedhistory' ) ) {
            $checkDeleted = Xml::checkLabel( $this->msg( 'history-show-deleted' )->text(),
                'deleted', 'mw-show-deleted-only', $request->getBool( 'deleted' ) ) . "\n";
        } else {
            $checkDeleted = '';
        }

        // Add the general form
        $action = htmlspecialchars( wfScript() );
        $content = Html::hidden( 'title', $this->getTitle()->getPrefixedDBkey() ) . "\n";
        $content .= Html::hidden( 'action', 'history' ) . "\n";
        $content .= Xml::dateMenu(
            ( $year == null ? MWTimestamp::getLocalInstance()->format( 'Y' ) : $year ),
            $month
        ) . "\u{00A0}";
        $content .= $tagSelector ? ( implode( "\u{00A0}", $tagSelector ) . "\u{00A0}" ) : '';
        $content .= $checkDeleted . Html::submitButton(
            $this->msg( 'historyaction-submit' )->text(),
            [],
            [ 'mw-ui-progressive' ]
        );
        $out->addHTML(
            "<form action=\"$action\" method=\"get\" id=\"mw-history-searchform\">" .
            Xml::fieldset(
                $this->msg( 'history-fieldset-title' )->text(),
                $content,
                [ 'id' => 'mw-history-search' ]
            ) .
            '</form>'
        );

        Hooks::run( 'PageHistoryBeforeList', [ &$this->page, $this->getContext() ] );

        // Create and output the list.
        $pager = new HistoryPager( $this, $year, $month, $tagFilter, $conds );
        $out->addHTML(
            $pager->getNavigationBar() .
            $pager->getBody() .
            $pager->getNavigationBar()
        );
        $out->preventClickjacking( $pager->getPreventClickjacking() );
    }

    function fetchRevisions( $limit, $offset, $direction ) {
        // Fail if article doesn't exist.
        if ( !$this->getTitle()->exists() ) {
            return new FakeResultWrapper( [] );
        }

        $dbr = wfGetDB( DB_REPLICA );

        if ( $direction === self::DIR_PREV ) {
            list( $dirs, $oper ) = [ "ASC", ">=" ];
        } else { /* $direction === self::DIR_NEXT */
            list( $dirs, $oper ) = [ "DESC", "<=" ];
        }

        if ( $offset ) {
            $offsets = [ "rev_timestamp $oper " . $dbr->addQuotes( $dbr->timestamp( $offset ) ) ];
        } else {
            $offsets = [];
        }

        $page_id = $this->page->getId();

        $revQuery = Revision::getQueryInfo();
        return $dbr->select(
            $revQuery['tables'],
            $revQuery['fields'],
            array_merge( [ 'rev_page' => $page_id ], $offsets ),
            __METHOD__,
            [
                'ORDER BY' => "rev_timestamp $dirs",
                'USE INDEX' => [ 'revision' => 'page_timestamp' ],
                'LIMIT' => $limit
            ],
            $revQuery['joins']
        );
    }

    function feed( $type ) {
        if ( !FeedUtils::checkFeedOutput( $type ) ) {
            return;
        }
        $request = $this->getRequest();

        $feedClasses = $this->context->getConfig()->get( 'FeedClasses' );
        $feed = new $feedClasses[$type](
            $this->getTitle()->getPrefixedText() . ' - ' .
            $this->msg( 'history-feed-title' )->inContentLanguage()->text(),
            $this->msg( 'history-feed-description' )->inContentLanguage()->text(),
            $this->getTitle()->getFullURL( 'action=history' )
        );

        // Get a limit on number of feed entries. Provide a sane default
        // of 10 if none is defined (but limit to $wgFeedLimit max)
        $limit = $request->getInt( 'limit', 10 );
        $limit = min(
            max( $limit, 1 ),
            $this->context->getConfig()->get( 'FeedLimit' )
        );

        $items = $this->fetchRevisions( $limit, 0, self::DIR_NEXT );

        // Generate feed elements enclosed between header and footer.
        $feed->outHeader();
        if ( $items->numRows() ) {
            foreach ( $items as $row ) {
                $feed->outItem( $this->feedItem( $row ) );
            }
        } else {
            $feed->outItem( $this->feedEmpty() );
        }
        $feed->outFooter();
    }

    function feedEmpty() {
        return new FeedItem(
            $this->msg( 'nohistory' )->inContentLanguage()->text(),
            $this->msg( 'history-feed-empty' )->inContentLanguage()->parseAsBlock(),
            $this->getTitle()->getFullURL(),
            wfTimestamp( TS_MW ),
            '',
            $this->getTitle()->getTalkPage()->getFullURL()
        );
    }

    function feedItem( $row ) {
        $rev = new Revision( $row, 0, $this->getTitle() );

        $text = FeedUtils::formatDiffRow(
            $this->getTitle(),
            $this->getTitle()->getPreviousRevisionID( $rev->getId() ),
            $rev->getId(),
            $rev->getTimestamp(),
            $rev->getComment()
        );
        if ( $rev->getComment() == '' ) {
            $contLang = MediaWikiServices::getInstance()->getContentLanguage();
            $title = $this->msg( 'history-feed-item-nocomment',
                $rev->getUserText(),
                $contLang->timeanddate( $rev->getTimestamp() ),
                $contLang->date( $rev->getTimestamp() ),
                $contLang->time( $rev->getTimestamp() )
            )->inContentLanguage()->text();
        } else {
            $title = $rev->getUserText() .
                $this->msg( 'colon-separator' )->inContentLanguage()->text() .
                FeedItem::stripComment( $rev->getComment() );
        }

        return new FeedItem(
            $title,
            $text,
            $this->getTitle()->getFullURL( 'diff=' . $rev->getId() . '&oldid=prev' ),
            $rev->getTimestamp(),
            $rev->getUserText(),
            $this->getTitle()->getTalkPage()->getFullURL()
        );
    }
}

class HistoryPager extends ReverseChronologicalPager {
    public $lastRow = false;

    public $counter, $historyPage, $buttons, $conds;

    protected $oldIdChecked;

    protected $preventClickjacking = false;
    protected $parentLens;

    protected $showTagEditUI;

    private $tagFilter;

    function __construct( $historyPage, $year = '', $month = '', $tagFilter = '', $conds = [] ) {
        parent::__construct( $historyPage->getContext() );
        $this->historyPage = $historyPage;
        $this->tagFilter = $tagFilter;
        $this->getDateCond( $year, $month );
        $this->conds = $conds;
        $this->showTagEditUI = ChangeTags::showTagEditingUI( $this->getUser() );
    }

    // For hook compatibility...
    function getArticle() {
        return $this->historyPage->getArticle();
    }

    function getSqlComment() {
        if ( $this->conds ) {
            return 'history page filtered'; // potentially slow, see CR r58153
        } else {
            return 'history page unfiltered';
        }
    }

    function getQueryInfo() {
        $revQuery = Revision::getQueryInfo( [ 'user' ] );
        $queryInfo = [
            'tables' => $revQuery['tables'],
            'fields' => $revQuery['fields'],
            'conds' => array_merge(
                [ 'rev_page' => $this->getWikiPage()->getId() ],
                $this->conds ),
            'options' => [ 'USE INDEX' => [ 'revision' => 'page_timestamp' ] ],
            'join_conds' => $revQuery['joins'],
        ];
        ChangeTags::modifyDisplayQuery(
            $queryInfo['tables'],
            $queryInfo['fields'],
            $queryInfo['conds'],
            $queryInfo['join_conds'],
            $queryInfo['options'],
            $this->tagFilter
        );

        // Avoid PHP 7.1 warning of passing $this by reference
        $historyPager = $this;
        Hooks::run( 'PageHistoryPager::getQueryInfo', [ &$historyPager, &$queryInfo ] );

        return $queryInfo;
    }

    function getIndexField() {
        return 'rev_timestamp';
    }

    function formatRow( $row ) {
        if ( $this->lastRow ) {
            $latest = ( $this->counter == 1 && $this->mIsFirst );
            $firstInList = $this->counter == 1;
            $this->counter++;

            $notifTimestamp = $this->getConfig()->get( 'ShowUpdatedMarker' )
                ? $this->getTitle()->getNotificationTimestamp( $this->getUser() )
                : false;

            $s = $this->historyLine(
                $this->lastRow, $row, $notifTimestamp, $latest, $firstInList );
        } else {
            $s = '';
        }
        $this->lastRow = $row;

        return $s;
    }

    function doBatchLookups() {
        if ( !Hooks::run( 'PageHistoryPager::doBatchLookups', [ $this, $this->mResult ] ) ) {
            return;
        }

        # Do a link batch query
        $this->mResult->seek( 0 );
        $batch = new LinkBatch();
        $revIds = [];
        foreach ( $this->mResult as $row ) {
            if ( $row->rev_parent_id ) {
                $revIds[] = $row->rev_parent_id;
            }
            if ( !is_null( $row->user_name ) ) {
                $batch->add( NS_USER, $row->user_name );
                $batch->add( NS_USER_TALK, $row->user_name );
            } else { # for anons or usernames of imported revisions
                $batch->add( NS_USER, $row->rev_user_text );
                $batch->add( NS_USER_TALK, $row->rev_user_text );
            }
        }
        $this->parentLens = Revision::getParentLengths( $this->mDb, $revIds );
        $batch->execute();
        $this->mResult->seek( 0 );
    }

    function getStartBody() {
        $this->lastRow = false;
        $this->counter = 1;
        $this->oldIdChecked = 0;

        $this->getOutput()->wrapWikiMsg( "<div class='mw-history-legend'>\n$1\n</div>", 'histlegend' );
        $s = Html::openElement( 'form', [ 'action' => wfScript(),
            'id' => 'mw-history-compare' ] ) . "\n";
        $s .= Html::hidden( 'title', $this->getTitle()->getPrefixedDBkey() ) . "\n";
        $s .= Html::hidden( 'action', 'historysubmit' ) . "\n";
        $s .= Html::hidden( 'type', 'revision' ) . "\n";

        // Button container stored in $this->buttons for re-use in getEndBody()
        $this->buttons = '<div>';
        $className = 'historysubmit mw-history-compareselectedversions-button';
        $attrs = [ 'class' => $className ]
            + Linker::tooltipAndAccesskeyAttribs( 'compareselectedversions' );
        $this->buttons .= $this->submitButton( $this->msg( 'compareselectedversions' )->text(),
            $attrs
        ) . "\n";

        $user = $this->getUser();
        $actionButtons = '';
        if ( $user->isAllowed( 'deleterevision' ) ) {
            $actionButtons .= $this->getRevisionButton( 'revisiondelete', 'showhideselectedversions' );
        }
        if ( $this->showTagEditUI ) {
            $actionButtons .= $this->getRevisionButton( 'editchangetags', 'history-edit-tags' );
        }
        if ( $actionButtons ) {
            $this->buttons .= Xml::tags( 'div', [ 'class' =>
                'mw-history-revisionactions' ], $actionButtons );
        }

        if ( $user->isAllowed( 'deleterevision' ) || $this->showTagEditUI ) {
            $this->buttons .= ( new ListToggle( $this->getOutput() ) )->getHTML();
        }

        $this->buttons .= '</div>';

        $s .= $this->buttons;
        $s .= '<ul id="pagehistory">' . "\n";

        return $s;
    }

    private function getRevisionButton( $name, $msg ) {
        $this->preventClickjacking();
        # Note bug #20966, <button> is non-standard in IE<8
        $element = Html::element(
            'button',
            [
                'type' => 'submit',
                'name' => $name,
                'value' => '1',
                'class' => "historysubmit mw-history-$name-button",
            ],
            $this->msg( $msg )->text()
        ) . "\n";
        return $element;
    }

    function getEndBody() {
        if ( $this->lastRow ) {
            $latest = $this->counter == 1 && $this->mIsFirst;
            $firstInList = $this->counter == 1;
            if ( $this->mIsBackwards ) {
                # Next row is unknown, but for UI reasons, probably exists if an offset has been specified
                if ( $this->mOffset == '' ) {
                    $next = null;
                } else {
                    $next = 'unknown';
                }
            } else {
                # The next row is the past-the-end row
                $next = $this->mPastTheEndRow;
            }
            $this->counter++;

            $notifTimestamp = $this->getConfig()->get( 'ShowUpdatedMarker' )
                ? $this->getTitle()->getNotificationTimestamp( $this->getUser() )
                : false;

            $s = $this->historyLine(
                $this->lastRow, $next, $notifTimestamp, $latest, $firstInList );
        } else {
            $s = '';
        }
        $s .= "</ul>\n";
        # Add second buttons only if there is more than one rev
        if ( $this->getNumRows() > 2 ) {
            $s .= $this->buttons;
        }
        $s .= '</form>';

        return $s;
    }

    function submitButton( $message, $attributes = [] ) {
        # Disable submit button if history has 1 revision only
        if ( $this->getNumRows() > 1 ) {
            return Html::submitButton( $message, $attributes );
        } else {
            return '';
        }
    }

    function historyLine( $row, $next, $notificationtimestamp = false,
        $latest = false, $firstInList = false ) {
        $rev = new Revision( $row, 0, $this->getTitle() );

        if ( is_object( $next ) ) {
            $prevRev = new Revision( $next, 0, $this->getTitle() );
        } else {
            $prevRev = null;
        }

        $curlink = $this->curLink( $rev, $latest );
        $lastlink = $this->lastLink( $rev, $next );
        $curLastlinks = $curlink . $this->historyPage->message['pipe-separator'] . $lastlink;
        $histLinks = Html::rawElement(
            'span',
            [ 'class' => 'mw-history-histlinks' ],
            $this->msg( 'parentheses' )->rawParams( $curLastlinks )->escaped()
        );

        $diffButtons = $this->diffButtons( $rev, $firstInList );
        $s = $histLinks . $diffButtons;

        $link = $this->revLink( $rev );
        $classes = [];

        $del = '';
        $user = $this->getUser();
        $canRevDelete = $user->isAllowed( 'deleterevision' );
        // Show checkboxes for each revision, to allow for revision deletion and
        // change tags
        if ( $canRevDelete || $this->showTagEditUI ) {
            $this->preventClickjacking();
            // If revision was hidden from sysops and we don't need the checkbox
            // for anything else, disable it
            if ( !$this->showTagEditUI && !$rev->userCan( Revision::DELETED_RESTRICTED, $user ) ) {
                $del = Xml::check( 'deleterevisions', false, [ 'disabled' => 'disabled' ] );
            // Otherwise, enable the checkbox...
            } else {
                $del = Xml::check( 'showhiderevisions', false,
                    [ 'name' => 'ids[' . $rev->getId() . ']' ] );
            }
        // User can only view deleted revisions...
        } elseif ( $rev->getVisibility() && $user->isAllowed( 'deletedhistory' ) ) {
            // If revision was hidden from sysops, disable the link
            if ( !$rev->userCan( Revision::DELETED_RESTRICTED, $user ) ) {
                $del = Linker::revDeleteLinkDisabled( false );
            // Otherwise, show the link...
            } else {
                $query = [ 'type' => 'revision',
                    'target' => $this->getTitle()->getPrefixedDBkey(), 'ids' => $rev->getId() ];
                $del .= Linker::revDeleteLink( $query,
                    $rev->isDeleted( Revision::DELETED_RESTRICTED ), false );
            }
        }
        if ( $del ) {
            $s .= " $del ";
        }

        $lang = $this->getLanguage();
        $dirmark = $lang->getDirMark();

        $s .= " $link";
        $s .= $dirmark;
        $s .= " <span class='history-user'>" .
            Linker::revUserTools( $rev, true ) . "</span>";
        $s .= $dirmark;

        if ( $rev->isMinor() ) {
            $s .= ' ' . ChangesList::flag( 'minor', $this->getContext() );
        }

        # Sometimes rev_len isn't populated
        if ( $rev->getSize() !== null ) {
            # Size is always public data
            $prevSize = $this->parentLens[$row->rev_parent_id] ?? 0;
            $sDiff = ChangesList::showCharacterDifference( $prevSize, $rev->getSize() );
            $fSize = Linker::formatRevisionSize( $rev->getSize() );
            $s .= ' <span class="mw-changeslist-separator">. .</span> ' . "$fSize $sDiff";
        }

        # Text following the character difference is added just before running hooks
        $s2 = Linker::revComment( $rev, false, true );

        if ( $notificationtimestamp && ( $row->rev_timestamp >= $notificationtimestamp ) ) {
            $s2 .= ' <span class="updatedmarker">' . $this->msg( 'updatedmarker' )->escaped() . '</span>';
            $classes[] = 'mw-history-line-updated';
        }

        $tools = [];

        # Rollback and undo links
        if ( $prevRev && $this->getTitle()->quickUserCan( 'edit', $user ) ) {
            if ( $latest && $this->getTitle()->quickUserCan( 'rollback', $user ) ) {
                // Get a rollback link without the brackets
                $rollbackLink = Linker::generateRollback(
                    $rev,
                    $this->getContext(),
                    [ 'verify', 'noBrackets' ]
                );
                if ( $rollbackLink ) {
                    $this->preventClickjacking();
                    $tools[] = $rollbackLink;
                }
            }

            if ( !$rev->isDeleted( Revision::DELETED_TEXT )
                && !$prevRev->isDeleted( Revision::DELETED_TEXT )
            ) {
                # Create undo tooltip for the first (=latest) line only
                $undoTooltip = $latest
                    ? [ 'title' => $this->msg( 'tooltip-undo' )->text() ]
                    : [];
                $undolink = MediaWikiServices::getInstance()->getLinkRenderer()->makeKnownLink(
                    $this->getTitle(),
                    $this->msg( 'editundo' )->text(),
                    $undoTooltip,
                    [
                        'action' => 'edit',
                        'undoafter' => $prevRev->getId(),
                        'undo' => $rev->getId()
                    ]
                );
                $tools[] = "<span class=\"mw-history-undo\">{$undolink}</span>";
            }
        }
        // Allow extension to add their own links here
        Hooks::run( 'HistoryRevisionTools', [ $rev, &$tools, $prevRev, $user ] );

        if ( $tools ) {
            $s2 .= ' ' . $this->msg( 'parentheses' )->rawParams( $lang->pipeList( $tools ) )->escaped();
        }

        # Tags
        list( $tagSummary, $newClasses ) = ChangeTags::formatSummaryRow(
            $row->ts_tags,
            'history',
            $this->getContext()
        );
        $classes = array_merge( $classes, $newClasses );
        if ( $tagSummary !== '' ) {
            $s2 .= " $tagSummary";
        }

        # Include separator between character difference and following text
        if ( $s2 !== '' ) {
            $s .= ' <span class="mw-changeslist-separator">. .</span> ' . $s2;
        }

        $attribs = [ 'data-mw-revid' => $rev->getId() ];

        Hooks::run( 'PageHistoryLineEnding', [ $this, &$row, &$s, &$classes, &$attribs ] );
        $attribs = array_filter( $attribs,
            [ Sanitizer::class, 'isReservedDataAttribute' ],
            ARRAY_FILTER_USE_KEY
        );

        if ( $classes ) {
            $attribs['class'] = implode( ' ', $classes );
        }

        return Xml::tags( 'li', $attribs, $s ) . "\n";
    }

    function revLink( $rev ) {
        $date = $this->getLanguage()->userTimeAndDate( $rev->getTimestamp(), $this->getUser() );
        if ( $rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
            $link = MediaWikiServices::getInstance()->getLinkRenderer()->makeKnownLink(
                $this->getTitle(),
                $date,
                [ 'class' => 'mw-changeslist-date' ],
                [ 'oldid' => $rev->getId() ]
            );
        } else {
            $link = htmlspecialchars( $date );
        }
        if ( $rev->isDeleted( Revision::DELETED_TEXT ) ) {
            $link = "<span class=\"history-deleted\">$link</span>";
        }

        return $link;
    }

    function curLink( $rev, $latest ) {
        $cur = $this->historyPage->message['cur'];
        if ( $latest || !$rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
            return $cur;
        } else {
            return MediaWikiServices::getInstance()->getLinkRenderer()->makeKnownLink(
                $this->getTitle(),
                new HtmlArmor( $cur ),
                [],
                [
                    'diff' => $this->getWikiPage()->getLatest(),
                    'oldid' => $rev->getId()
                ]
            );
        }
    }

    function lastLink( $prevRev, $next ) {
        $last = $this->historyPage->message['last'];

        if ( $next === null ) {
            # Probably no next row
            return $last;
        }

        $linkRenderer = MediaWikiServices::getInstance()->getLinkRenderer();
        if ( $next === 'unknown' ) {
            # Next row probably exists but is unknown, use an oldid=prev link
            return $linkRenderer->makeKnownLink(
                $this->getTitle(),
                new HtmlArmor( $last ),
                [],
                [
                    'diff' => $prevRev->getId(),
                    'oldid' => 'prev'
                ]
            );
        }

        $nextRev = new Revision( $next );

        if ( !$prevRev->userCan( Revision::DELETED_TEXT, $this->getUser() )
            || !$nextRev->userCan( Revision::DELETED_TEXT, $this->getUser() )
        ) {
            return $last;
        }

        return $linkRenderer->makeKnownLink(
            $this->getTitle(),
            new HtmlArmor( $last ),
            [],
            [
                'diff' => $prevRev->getId(),
                'oldid' => $next->rev_id
            ]
        );
    }

    function diffButtons( $rev, $firstInList ) {
        if ( $this->getNumRows() > 1 ) {
            $id = $rev->getId();
            $radio = [ 'type' => 'radio', 'value' => $id ];
            if ( $firstInList ) {
                $first = Xml::element( 'input',
                    array_merge( $radio, [
                        'style' => 'visibility:hidden',
                        'name' => 'oldid',
                        'id' => 'mw-oldid-null' ] )
                );
                $checkmark = [ 'checked' => 'checked' ];
            } else {
                # Check visibility of old revisions
                if ( !$rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
                    $radio['disabled'] = 'disabled';
                    $checkmark = []; // We will check the next possible one
                } elseif ( !$this->oldIdChecked ) {
                    $checkmark = [ 'checked' => 'checked' ];
                    $this->oldIdChecked = $id;
                } else {
                    $checkmark = [];
                }
                $first = Xml::element( 'input',
                    array_merge( $radio, $checkmark, [
                        'name' => 'oldid',
                        'id' => "mw-oldid-$id" ] ) );
                $checkmark = [];
            }
            $second = Xml::element( 'input',
                array_merge( $radio, $checkmark, [
                    'name' => 'diff',
                    'id' => "mw-diff-$id" ] ) );

            return $first . $second;
        } else {
            return '';
        }
    }

    function preventClickjacking( $enable = true ) {
        $this->preventClickjacking = $enable;
    }

    function getPreventClickjacking() {
        return $this->preventClickjacking;
    }

}