objectcache: avoid using process cache in nested callbacks

[mediawiki.git] / includes / actions / HistoryAction.php

<?php
/**
 * Page history
 *
 * Split off from Article.php and Skin.php, 2003-12-22
 *
 * 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
 * @ingroup Actions
 */

/**
 * This class handles printing the history page for an article. In order to
 * be efficient, it uses timestamps rather than offsets for paging, to avoid
 * costly LIMIT,offset queries.
 *
 * Construct it by passing in an Article, and call $h->history() to print the
 * history.
 *
 * @ingroup Actions
 */
class HistoryAction extends FormlessAction {
        const DIR_PREV = 0;
        const DIR_NEXT = 1;

        /** @var array Array of message keys and strings */
        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]]
                return Linker::linkKnown(
                        SpecialPage::getTitleFor( 'Log' ),
                        $this->msg( 'viewpagelogs' )->escaped(),
                        [],
                        [ 'page' => $this->getTitle()->getPrefixedText() ]
                );
        }

        /**
         * @return WikiPage|Article|ImagePage|CategoryPage|Page The Article object we are working on.
         */
        public function getArticle() {
                return $this->page;
        }

        /**
         * As we use the same small set of messages in various methods and that
         * they are called often, we call them once and save them in $this->message
         */
        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();
                        }
                }
        }

        /**
         * Print the history page for an article.
         */
        function onView() {
                $out = $this->getOutput();
                $request = $this->getRequest();

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

                        return;
                }

                /**
                 * Add date selector to quickly get to a certain time
                 */
                $year = $request->getInt( 'year' );
                $month = $request->getInt( 'month' );
                $tagFilter = $request->getVal( 'tagfilter' );
                $tagSelector = ChangeTags::buildTagFilterSelector( $tagFilter );

                /**
                 * Option to show only revisions that have been (partially) hidden via RevisionDelete
                 */
                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() );
                $out->addHTML(
                        "<form action=\"$action\" method=\"get\" id=\"mw-history-searchform\">" .
                        Xml::fieldset(
                                $this->msg( 'history-fieldset-title' )->text(),
                                false,
                                [ 'id' => 'mw-history-search' ]
                        ) .
                        Html::hidden( 'title', $this->getTitle()->getPrefixedDBkey() ) . "\n" .
                        Html::hidden( 'action', 'history' ) . "\n" .
                        Xml::dateMenu(
                                ( $year == null ? MWTimestamp::getLocalInstance()->format( 'Y' ) : $year ),
                                $month
                        ) . '&#160;' .
                        ( $tagSelector ? ( implode( '&#160;', $tagSelector ) . '&#160;' ) : '' ) .
                        $checkDeleted .
                        Html::submitButton(
                                $this->msg( 'historyaction-submit' )->text(),
                                [],
                                [ 'mw-ui-progressive' ]
                        ) . "\n" .
                        '</fieldset></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() );

        }

        /**
         * Fetch an array of revisions, specified by a given limit, offset and
         * direction. This is now only used by the feeds. It was previously
         * used by the main UI but that's now handled by the pager.
         *
         * @param int $limit The limit number of revisions to get
         * @param int $offset
         * @param int $direction Either self::DIR_PREV or self::DIR_NEXT
         * @return ResultWrapper
         */
        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();

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

        /**
         * Output a subscription feed listing recent edits to this page.
         *
         * @param string $type Feed type
         */
        function feed( $type ) {
                if ( !FeedUtils::checkFeedOutput( $type ) ) {
                        return;
                }
                $request = $this->getRequest();

                $feedClasses = $this->context->getConfig()->get( 'FeedClasses' );
                /** @var RSSFeed|AtomFeed $feed */
                $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()
                );
        }

        /**
         * Generate a FeedItem object from a given revision table row
         * Borrows Recent Changes' feed generation functions for formatting;
         * includes a diff to the previous revision (if any).
         *
         * @param stdClass|array $row Database row
         * @return FeedItem
         */
        function feedItem( $row ) {
                $rev = new Revision( $row );
                $rev->setTitle( $this->getTitle() );
                $text = FeedUtils::formatDiffRow(
                        $this->getTitle(),
                        $this->getTitle()->getPreviousRevisionID( $rev->getId() ),
                        $rev->getId(),
                        $rev->getTimestamp(),
                        $rev->getComment()
                );
                if ( $rev->getComment() == '' ) {
                        global $wgContLang;
                        $title = $this->msg( 'history-feed-item-nocomment',
                                $rev->getUserText(),
                                $wgContLang->timeanddate( $rev->getTimestamp() ),
                                $wgContLang->date( $rev->getTimestamp() ),
                                $wgContLang->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()
                );
        }
}

/**
 * @ingroup Pager
 * @ingroup Actions
 */
class HistoryPager extends ReverseChronologicalPager {
        /**
         * @var bool|stdClass
         */
        public $lastRow = false;

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

        protected $oldIdChecked;

        protected $preventClickjacking = false;
        /**
         * @var array
         */
        protected $parentLens;

        /** @var bool Whether to show the tag editing UI */
        protected $showTagEditUI;

        /**
         * @param HistoryAction $historyPage
         * @param string $year
         * @param string $month
         * @param string $tagFilter
         * @param array $conds
         */
        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() {
                $queryInfo = [
                        'tables' => [ 'revision', 'user' ],
                        'fields' => array_merge( Revision::selectFields(), Revision::selectUserFields() ),
                        'conds' => array_merge(
                                [ 'rev_page' => $this->getWikiPage()->getId() ],
                                $this->conds ),
                        'options' => [ 'USE INDEX' => [ 'revision' => 'page_timestamp' ] ],
                        'join_conds' => [ 'user' => Revision::userJoinCond() ],
                ];
                ChangeTags::modifyDisplayQuery(
                        $queryInfo['tables'],
                        $queryInfo['fields'],
                        $queryInfo['conds'],
                        $queryInfo['join_conds'],
                        $queryInfo['options'],
                        $this->tagFilter
                );
                Hooks::run( 'PageHistoryPager::getQueryInfo', [ &$this, &$queryInfo ] );

                return $queryInfo;
        }

        function getIndexField() {
                return 'rev_timestamp';
        }

        /**
         * @param stdClass $row
         * @return string
         */
        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 );
        }

        /**
         * Creates begin of history list with a submit button
         *
         * @return string HTML output
         */
        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;
        }

        /**
         * Creates a submit button
         *
         * @param string $message Text of the submit button, will be escaped
         * @param array $attributes Attributes
         * @return string HTML output for the submit button
         */
        function submitButton( $message, $attributes = [] ) {
                # Disable submit button if history has 1 revision only
                if ( $this->getNumRows() > 1 ) {
                        return Html::submitButton( $message, $attributes );
                } else {
                        return '';
                }
        }

        /**
         * Returns a row from the history printout.
         *
         * @todo document some more, and maybe clean up the code (some params redundant?)
         *
         * @param stdClass $row The database row corresponding to the previous line.
         * @param mixed $next The database row corresponding to the next line
         *   (chronologically previous)
         * @param bool|string $notificationtimestamp
         * @param bool $latest Whether this row corresponds to the page's latest revision.
         * @param bool $firstInList Whether this row corresponds to the first
         *   displayed on this history page.
         * @return string HTML output for the row
         */
        function historyLine( $row, $next, $notificationtimestamp = false,
                $latest = false, $firstInList = false ) {
                $rev = new Revision( $row );
                $rev->setTitle( $this->getTitle() );

                if ( is_object( $next ) ) {
                        $prevRev = new Revision( $next );
                        $prevRev->setTitle( $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 = isset( $this->parentLens[$row->rev_parent_id] )
                                ? $this->parentLens[$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 = Linker::linkKnown(
                                        $this->getTitle(),
                                        $this->msg( 'editundo' )->escaped(),
                                        $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;
                }

                Hooks::run( 'PageHistoryLineEnding', [ $this, &$row, &$s, &$classes ] );

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

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

        /**
         * Create a link to view this revision of the page
         *
         * @param Revision $rev
         * @return string
         */
        function revLink( $rev ) {
                $date = $this->getLanguage()->userTimeAndDate( $rev->getTimestamp(), $this->getUser() );
                $date = htmlspecialchars( $date );
                if ( $rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
                        $link = Linker::linkKnown(
                                $this->getTitle(),
                                $date,
                                [ 'class' => 'mw-changeslist-date' ],
                                [ 'oldid' => $rev->getId() ]
                        );
                } else {
                        $link = $date;
                }
                if ( $rev->isDeleted( Revision::DELETED_TEXT ) ) {
                        $link = "<span class=\"history-deleted\">$link</span>";
                }

                return $link;
        }

        /**
         * Create a diff-to-current link for this revision for this page
         *
         * @param Revision $rev
         * @param bool $latest This is the latest revision of the page?
         * @return string
         */
        function curLink( $rev, $latest ) {
                $cur = $this->historyPage->message['cur'];
                if ( $latest || !$rev->userCan( Revision::DELETED_TEXT, $this->getUser() ) ) {
                        return $cur;
                } else {
                        return Linker::linkKnown(
                                $this->getTitle(),
                                $cur,
                                [],
                                [
                                        'diff' => $this->getWikiPage()->getLatest(),
                                        'oldid' => $rev->getId()
                                ]
                        );
                }
        }

        /**
         * Create a diff-to-previous link for this revision for this page.
         *
         * @param Revision $prevRev The revision being displayed
         * @param stdClass|string|null $next The next revision in list (that is
         *        the previous one in chronological order).
         *        May either be a row, "unknown" or null.
         * @return string
         */
        function lastLink( $prevRev, $next ) {
                $last = $this->historyPage->message['last'];

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

                if ( $next === 'unknown' ) {
                        # Next row probably exists but is unknown, use an oldid=prev link
                        return Linker::linkKnown(
                                $this->getTitle(),
                                $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 Linker::linkKnown(
                        $this->getTitle(),
                        $last,
                        [],
                        [
                                'diff' => $prevRev->getId(),
                                'oldid' => $next->rev_id
                        ]
                );
        }

        /**
         * Create radio buttons for page history
         *
         * @param Revision $rev
         * @param bool $firstInList Is this version the first one?
         *
         * @return string HTML output for the radio buttons
         */
        function diffButtons( $rev, $firstInList ) {
                if ( $this->getNumRows() > 1 ) {
                        $id = $rev->getId();
                        $radio = [ 'type' => 'radio', 'value' => $id ];
                        /** @todo Move title texts to javascript */
                        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 '';
                }
        }

        /**
         * This is called if a write operation is possible from the generated HTML
         * @param bool $enable
         */
        function preventClickjacking( $enable = true ) {
                $this->preventClickjacking = $enable;
        }

        /**
         * Get the "prevent clickjacking" flag
         * @return bool
         */
        function getPreventClickjacking() {
                return $this->preventClickjacking;
        }

}