includes/diff/DifferenceEngine.php

   1 <?php
   2 /**
   3  * User interface for the difference engine.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup DifferenceEngine
  22  */
  23
  24 use MediaWiki\Storage\RevisionRecord;
  25
  26 /**
  27  * DifferenceEngine is responsible for rendering the difference between two revisions as HTML.
  28  * This includes interpreting URL parameters, retrieving revision data, checking access permissions,
  29  * selecting and invoking the diff generator class for the individual slots, doing post-processing
  30  * on the generated diff, adding the rest of the HTML (such as headers) and writing the whole thing
  31  * to OutputPage.
  32  *
  33  * DifferenceEngine can be subclassed by extensions, by customizing
  34  * ContentHandler::createDifferenceEngine; the content handler will be selected based on the
  35  * content model of the main slot (of the new revision, when the two are different).
  36  * That might change after PageTypeHandler gets introduced.
  37  *
  38  * In the past, the class was also used for slot-level diff generation, and extensions might still
  39  * subclass it and add such functionality. When that is the case (sepcifically, when a
  40  * ContentHandler returns a standard SlotDiffRenderer but a nonstandard DifferenceEngine)
  41  * DifferenceEngineSlotDiffRenderer will be used to convert the old behavior into the new one.
  42  *
  43  * @ingroup DifferenceEngine
  44  *
  45  * @todo This class is huge and poorly defined. It should be split into a controller responsible
  46  * for interpreting query parameters, retrieving data and checking permissions; and a HTML renderer.
  47  */
  48 class DifferenceEngine extends ContextSource {
  49
  50         use DeprecationHelper;
  51
  52         /**
  53          * Constant to indicate diff cache compatibility.
  54          * Bump this when changing the diff formatting in a way that
  55          * fixes important bugs or such to force cached diff views to
  56          * clear.
  57          */
  58         const DIFF_VERSION = '1.12';
  59
  60         /**
  61          * Revision ID for the old revision. 0 for the revision previous to $mNewid, false
  62          * if the diff does not have an old revision (e.g. 'oldid=<first revision of page>&diff=prev'),
  63          * or the revision does not exist, null if the revision is unsaved.
  64          * @var int|false|null
  65          */
  66         protected $mOldid;
  67
  68         /**
  69          * Revision ID for the new revision. 0 for the last revision of the current page
  70          * (as defined by the request context), false if the revision does not exist, null
  71          * if it is unsaved, or an alias such as 'next'.
  72          * @var int|string|false|null
  73          */
  74         protected $mNewid;
  75
  76         /**
  77          * Old revision (left pane).
  78          * Allowed to be an unsaved revision, unlikely that's ever needed though.
  79          * False when the old revision does not exist; this can happen when using
  80          * diff=prev on the first revision. Null when the revision should exist but
  81          * doesn't (e.g. load failure); loadRevisionData() will return false in that
  82          * case. Also null until lazy-loaded. Ignored completely when isContentOverridden
  83          * is set.
  84          * Since 1.32 public access is deprecated.
  85          * @var Revision|null|false
  86          */
  87         protected $mOldRev;
  88
  89         /**
  90          * New revision (right pane).
  91          * Note that this might be an unsaved revision (e.g. for edit preview).
  92          * Null in case of load failure; diff methods will just return an error message in that case,
  93          * and loadRevisionData() will return false. Also null until lazy-loaded. Ignored completely
  94          * when isContentOverridden is set.
  95          * Since 1.32 public access is deprecated.
  96          * @var Revision|null
  97          */
  98         protected $mNewRev;
  99
 100         /**
 101          * Title of $mOldRev or null if the old revision does not exist or does not belong to a page.
 102          * Since 1.32 public access is deprecated and the property can be null.
 103          * @var Title|null
 104          */
 105         protected $mOldPage;
 106
 107         /**
 108          * Title of $mNewRev or null if the new revision does not exist or does not belong to a page.
 109          * Since 1.32 public access is deprecated and the property can be null.
 110          * @var Title|null
 111          */
 112         protected $mNewPage;
 113
 114         /**
 115          * Change tags of $mOldRev or null if it does not exist / is not saved.
 116          * @var string[]|null
 117          */
 118         private $mOldTags;
 119
 120         /**
 121          * Change tags of $mNewRev or null if it does not exist / is not saved.
 122          * @var string[]|null
 123          */
 124         private $mNewTags;
 125
 126         /**
 127          * @var Content|null
 128          * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
 129          *   This property is set to the content of the main slot, but not actually used for the main diff.
 130          */
 131         private $mOldContent;
 132
 133         /**
 134          * @var Content|null
 135          * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
 136          *   This property is set to the content of the main slot, but not actually used for the main diff.
 137          */
 138         private $mNewContent;
 139
 140         /** @var Language */
 141         protected $mDiffLang;
 142
 143         /** @var bool Have the revisions IDs been loaded */
 144         private $mRevisionsIdsLoaded = false;
 145
 146         /** @var bool Have the revisions been loaded */
 147         protected $mRevisionsLoaded = false;
 148
 149         /** @var int How many text blobs have been loaded, 0, 1 or 2? */
 150         protected $mTextLoaded = 0;
 151
 152         /**
 153          * Was the content overridden via setContent()?
 154          * If the content was overridden, most internal state (e.g. mOldid or mOldRev) should be ignored
 155          * and only mOldContent and mNewContent is reliable.
 156          * (Note that setRevisions() does not set this flag as in that case all properties are
 157          * overriden and remain consistent with each other, so no special handling is needed.)
 158          * @var bool
 159          */
 160         protected $isContentOverridden = false;
 161
 162         /** @var bool Was the diff fetched from cache? */
 163         protected $mCacheHit = false;
 164
 165         /**
 166          * Set this to true to add debug info to the HTML output.
 167          * Warning: this may cause RSS readers to spuriously mark articles as "new"
 168          * (T22601)
 169          */
 170         public $enableDebugComment = false;
 171
 172         /** @var bool If true, line X is not displayed when X is 1, for example
 173          *    to increase readability and conserve space with many small diffs.
 174          */
 175         protected $mReducedLineNumbers = false;
 176
 177         /** @var string Link to action=markpatrolled */
 178         protected $mMarkPatrolledLink = null;
 179
 180         /** @var bool Show rev_deleted content if allowed */
 181         protected $unhide = false;
 182
 183         /** @var bool Refresh the diff cache */
 184         protected $mRefreshCache = false;
 185
 186         /** @var SlotDiffRenderer[] DifferenceEngine classes for the slots, keyed by role name. */
 187         protected $slotDiffRenderers = null;
 188
 189         /**
 190          * Temporary hack for B/C while slot diff related methods of DifferenceEngine are being
 191          * deprecated. When true, we are inside a DifferenceEngineSlotDiffRenderer and
 192          * $slotDiffRenderers should not be used.
 193          * @var bool
 194          */
 195         protected $isSlotDiffRenderer = false;
 196
 197         /**#@-*/
 198
 199         /**
 200          * @param IContextSource|null $context Context to use, anything else will be ignored
 201          * @param int $old Old ID we want to show and diff with.
 202          * @param string|int $new Either revision ID or 'prev' or 'next'. Default: 0.
 203          * @param int $rcid Deprecated, no longer used!
 204          * @param bool $refreshCache If set, refreshes the diff cache
 205          * @param bool $unhide If set, allow viewing deleted revs
 206          */
 207         public function __construct( $context = null, $old = 0, $new = 0, $rcid = 0,
 208                 $refreshCache = false, $unhide = false
 209         ) {
 210                 $this->deprecatePublicProperty( 'mOldid', '1.32', __CLASS__ );
 211                 $this->deprecatePublicProperty( 'mNewid', '1.32', __CLASS__ );
 212                 $this->deprecatePublicProperty( 'mOldRev', '1.32', __CLASS__ );
 213                 $this->deprecatePublicProperty( 'mNewRev', '1.32', __CLASS__ );
 214                 $this->deprecatePublicProperty( 'mOldPage', '1.32', __CLASS__ );
 215                 $this->deprecatePublicProperty( 'mNewPage', '1.32', __CLASS__ );
 216                 $this->deprecatePublicProperty( 'mOldContent', '1.32', __CLASS__ );
 217                 $this->deprecatePublicProperty( 'mNewContent', '1.32', __CLASS__ );
 218                 $this->deprecatePublicProperty( 'mRevisionsLoaded', '1.32', __CLASS__ );
 219                 $this->deprecatePublicProperty( 'mTextLoaded', '1.32', __CLASS__ );
 220                 $this->deprecatePublicProperty( 'mCacheHit', '1.32', __CLASS__ );
 221
 222                 if ( $context instanceof IContextSource ) {
 223                         $this->setContext( $context );
 224                 }
 225
 226                 wfDebug( "DifferenceEngine old '$old' new '$new' rcid '$rcid'\n" );
 227
 228                 $this->mOldid = $old;
 229                 $this->mNewid = $new;
 230                 $this->mRefreshCache = $refreshCache;
 231                 $this->unhide = $unhide;
 232         }
 233
 234         /**
 235          * @return SlotDiffRenderer[] Diff renderers for each slot, keyed by role name.
 236          *   Includes slots only present in one of the revisions.
 237          */
 238         protected function getSlotDiffRenderers() {
 239                 if ( $this->isSlotDiffRenderer ) {
 240                         throw new LogicException( __METHOD__ . ' called in slot diff renderer mode' );
 241                 }
 242
 243                 if ( $this->slotDiffRenderers === null ) {
 244                         if ( !$this->loadRevisionData() ) {
 245                                 return [];
 246                         }
 247
 248                         $slotContents = $this->getSlotContents();
 249                         $this->slotDiffRenderers = array_map( function ( $contents ) {
 250                                 /** @var $content Content */
 251                                 $content = $contents['new'] ?: $contents['old'];
 252                                 return $content->getContentHandler()->getSlotDiffRenderer( $this->getContext() );
 253                         }, $slotContents );
 254                 }
 255                 return $this->slotDiffRenderers;
 256         }
 257
 258         /**
 259          * Mark this DifferenceEngine as a slot renderer (as opposed to a page renderer).
 260          * This is used in legacy mode when the DifferenceEngine is wrapped in a
 261          * DifferenceEngineSlotDiffRenderer.
 262          * @internal For use by DifferenceEngineSlotDiffRenderer only.
 263          */
 264         public function markAsSlotDiffRenderer() {
 265                 $this->isSlotDiffRenderer = true;
 266         }
 267
 268         /**
 269          * Get the old and new content objects for all slots.
 270          * This method does not do any permission checks.
 271          * @return array [ role => [ 'old' => SlotRecord|null, 'new' => SlotRecord|null ], ... ]
 272          */
 273         protected function getSlotContents() {
 274                 if ( $this->isContentOverridden ) {
 275                         return [
 276                                 'main' => [
 277                                         'old' => $this->mOldContent,
 278                                         'new' => $this->mNewContent,
 279                                 ]
 280                         ];
 281                 } elseif ( !$this->loadRevisionData() ) {
 282                         return [];
 283                 }
 284
 285                 $newSlots = $this->mNewRev->getRevisionRecord()->getSlots()->getSlots();
 286                 if ( $this->mOldRev ) {
 287                         $oldSlots = $this->mOldRev->getRevisionRecord()->getSlots()->getSlots();
 288                 } else {
 289                         $oldSlots = [];
 290                 }
 291                 // The order here will determine the visual order of the diff. The current logic is
 292                 // slots of the new revision first in natural order, then deleted ones. This is ad hoc
 293                 // and should not be relied on - in the future we may want the ordering to depend
 294                 // on the page type.
 295                 $roles = array_merge( array_keys( $newSlots ), array_keys( $oldSlots ) );
 296
 297                 $slots = [];
 298                 foreach ( $roles as $role ) {
 299                         $slots[$role] = [
 300                                 'old' => isset( $oldSlots[$role] ) ? $oldSlots[$role]->getContent() : null,
 301                                 'new' => isset( $newSlots[$role] ) ? $newSlots[$role]->getContent() : null,
 302                         ];
 303                 }
 304                 // move main slot to front
 305                 if ( isset( $slots['main'] ) ) {
 306                         $slots = [ 'main' => $slots['main'] ] + $slots;
 307                 }
 308                 return $slots;
 309         }
 310
 311         public function getTitle() {
 312                 // T202454 avoid errors when there is no title
 313                 return parent::getTitle() ?: Title::makeTitle( NS_SPECIAL, 'BadTitle/DifferenceEngine' );
 314         }
 315
 316         /**
 317          * Set reduced line numbers mode.
 318          * When set, line X is not displayed when X is 1, for example to increase readability and
 319          * conserve space with many small diffs.
 320          * @param bool $value
 321          */
 322         public function setReducedLineNumbers( $value = true ) {
 323                 $this->mReducedLineNumbers = $value;
 324         }
 325
 326         /**
 327          * Get the language of the difference engine, defaults to page content language
 328          *
 329          * @return Language
 330          */
 331         public function getDiffLang() {
 332                 if ( $this->mDiffLang === null ) {
 333                         # Default language in which the diff text is written.
 334                         $this->mDiffLang = $this->getTitle()->getPageLanguage();
 335                 }
 336
 337                 return $this->mDiffLang;
 338         }
 339
 340         /**
 341          * @return bool
 342          */
 343         public function wasCacheHit() {
 344                 return $this->mCacheHit;
 345         }
 346
 347         /**
 348          * Get the ID of old revision (left pane) of the diff. 0 for the revision
 349          * previous to getNewid(), false if the old revision does not exist, null
 350          * if it's unsaved.
 351          * To get a real revision ID instead of 0, call loadRevisionData() first.
 352          * @return int|false|null
 353          */
 354         public function getOldid() {
 355                 $this->loadRevisionIds();
 356
 357                 return $this->mOldid;
 358         }
 359
 360         /**
 361          * Get the ID of new revision (right pane) of the diff. 0 for the current revision,
 362          * false if the new revision does not exist, null if it's unsaved.
 363          * To get a real revision ID instead of 0, call loadRevisionData() first.
 364          * @return int|false|null
 365          */
 366         public function getNewid() {
 367                 $this->loadRevisionIds();
 368
 369                 return $this->mNewid;
 370         }
 371
 372         /**
 373          * Get the left side of the diff.
 374          * Could be null when the first revision of the page is diffed to 'prev' (or in the case of
 375          * load failure).
 376          * @return RevisionRecord|null
 377          */
 378         public function getOldRevision() {
 379                 return $this->mOldRev ? $this->mOldRev->getRevisionRecord() : null;
 380         }
 381
 382         /**
 383          * Get the right side of the diff.
 384          * Should not be null but can still happen in the case of load failure.
 385          * @return RevisionRecord|null
 386          */
 387         public function getNewRevision() {
 388                 return $this->mNewRev ? $this->mNewRev->getRevisionRecord() : null;
 389         }
 390
 391         /**
 392          * Look up a special:Undelete link to the given deleted revision id,
 393          * as a workaround for being unable to load deleted diffs in currently.
 394          *
 395          * @param int $id Revision ID
 396          *
 397          * @return string|bool Link HTML or false
 398          */
 399         public function deletedLink( $id ) {
 400                 if ( $this->getUser()->isAllowed( 'deletedhistory' ) ) {
 401                         $dbr = wfGetDB( DB_REPLICA );
 402                         $arQuery = Revision::getArchiveQueryInfo();
 403                         $row = $dbr->selectRow(
 404                                 $arQuery['tables'],
 405                                 array_merge( $arQuery['fields'], [ 'ar_namespace', 'ar_title' ] ),
 406                                 [ 'ar_rev_id' => $id ],
 407                                 __METHOD__,
 408                                 [],
 409                                 $arQuery['joins']
 410                         );
 411                         if ( $row ) {
 412                                 $rev = Revision::newFromArchiveRow( $row );
 413                                 $title = Title::makeTitleSafe( $row->ar_namespace, $row->ar_title );
 414
 415                                 return SpecialPage::getTitleFor( 'Undelete' )->getFullURL( [
 416                                         'target' => $title->getPrefixedText(),
 417                                         'timestamp' => $rev->getTimestamp()
 418                                 ] );
 419                         }
 420                 }
 421
 422                 return false;
 423         }
 424
 425         /**
 426          * Build a wikitext link toward a deleted revision, if viewable.
 427          *
 428          * @param int $id Revision ID
 429          *
 430          * @return string Wikitext fragment
 431          */
 432         public function deletedIdMarker( $id ) {
 433                 $link = $this->deletedLink( $id );
 434                 if ( $link ) {
 435                         return "[$link $id]";
 436                 } else {
 437                         return (string)$id;
 438                 }
 439         }
 440
 441         private function showMissingRevision() {
 442                 $out = $this->getOutput();
 443
 444                 $missing = [];
 445                 if ( $this->mOldRev === null ||
 446                         ( $this->mOldRev && $this->mOldContent === null )
 447                 ) {
 448                         $missing[] = $this->deletedIdMarker( $this->mOldid );
 449                 }
 450                 if ( $this->mNewRev === null ||
 451                         ( $this->mNewRev && $this->mNewContent === null )
 452                 ) {
 453                         $missing[] = $this->deletedIdMarker( $this->mNewid );
 454                 }
 455
 456                 $out->setPageTitle( $this->msg( 'errorpagetitle' ) );
 457                 $msg = $this->msg( 'difference-missing-revision' )
 458                         ->params( $this->getLanguage()->listToText( $missing ) )
 459                         ->numParams( count( $missing ) )
 460                         ->parseAsBlock();
 461                 $out->addHTML( $msg );
 462         }
 463
 464         public function showDiffPage( $diffOnly = false ) {
 465                 # Allow frames except in certain special cases
 466                 $out = $this->getOutput();
 467                 $out->allowClickjacking();
 468                 $out->setRobotPolicy( 'noindex,nofollow' );
 469
 470                 // Allow extensions to add any extra output here
 471                 Hooks::run( 'DifferenceEngineShowDiffPage', [ $out ] );
 472
 473                 if ( !$this->loadRevisionData() ) {
 474                         if ( Hooks::run( 'DifferenceEngineShowDiffPageMaybeShowMissingRevision', [ $this ] ) ) {
 475                                 $this->showMissingRevision();
 476                         }
 477                         return;
 478                 }
 479
 480                 $user = $this->getUser();
 481                 $permErrors = [];
 482                 if ( $this->mNewPage ) {
 483                         $permErrors = $this->mNewPage->getUserPermissionsErrors( 'read', $user );
 484                 }
 485                 if ( $this->mOldPage ) {
 486                         $permErrors = wfMergeErrorArrays( $permErrors,
 487                                 $this->mOldPage->getUserPermissionsErrors( 'read', $user ) );
 488                 }
 489                 if ( count( $permErrors ) ) {
 490                         throw new PermissionsError( 'read', $permErrors );
 491                 }
 492
 493                 $rollback = '';
 494
 495                 $query = [];
 496                 # Carry over 'diffonly' param via navigation links
 497                 if ( $diffOnly != $user->getBoolOption( 'diffonly' ) ) {
 498                         $query['diffonly'] = $diffOnly;
 499                 }
 500                 # Cascade unhide param in links for easy deletion browsing
 501                 if ( $this->unhide ) {
 502                         $query['unhide'] = 1;
 503                 }
 504
 505                 # Check if one of the revisions is deleted/suppressed
 506                 $deleted = $suppressed = false;
 507                 $allowed = $this->mNewRev->userCan( Revision::DELETED_TEXT, $user );
 508
 509                 $revisionTools = [];
 510
 511                 # mOldRev is false if the difference engine is called with a "vague" query for
 512                 # a diff between a version V and its previous version V' AND the version V
 513                 # is the first version of that article. In that case, V' does not exist.
 514                 if ( $this->mOldRev === false ) {
 515                         if ( $this->mNewPage ) {
 516                                 $out->setPageTitle( $this->msg( 'difference-title', $this->mNewPage->getPrefixedText() ) );
 517                         }
 518                         $samePage = true;
 519                         $oldHeader = '';
 520                         // Allow extensions to change the $oldHeader variable
 521                         Hooks::run( 'DifferenceEngineOldHeaderNoOldRev', [ &$oldHeader ] );
 522                 } else {
 523                         Hooks::run( 'DiffViewHeader', [ $this, $this->mOldRev, $this->mNewRev ] );
 524
 525                         if ( !$this->mOldPage || !$this->mNewPage ) {
 526                                 // XXX say something to the user?
 527                                 $samePage = false;
 528                         } elseif ( $this->mNewPage->equals( $this->mOldPage ) ) {
 529                                 $out->setPageTitle( $this->msg( 'difference-title', $this->mNewPage->getPrefixedText() ) );
 530                                 $samePage = true;
 531                         } else {
 532                                 $out->setPageTitle( $this->msg( 'difference-title-multipage',
 533                                         $this->mOldPage->getPrefixedText(), $this->mNewPage->getPrefixedText() ) );
 534                                 $out->addSubtitle( $this->msg( 'difference-multipage' ) );
 535                                 $samePage = false;
 536                         }
 537
 538                         if ( $samePage && $this->mNewPage && $this->mNewPage->quickUserCan( 'edit', $user ) ) {
 539                                 if ( $this->mNewRev->isCurrent() && $this->mNewPage->userCan( 'rollback', $user ) ) {
 540                                         $rollbackLink = Linker::generateRollback( $this->mNewRev, $this->getContext() );
 541                                         if ( $rollbackLink ) {
 542                                                 $out->preventClickjacking();
 543                                                 $rollback = "\u{00A0}\u{00A0}\u{00A0}" . $rollbackLink;
 544                                         }
 545                                 }
 546
 547                                 if ( !$this->mOldRev->isDeleted( Revision::DELETED_TEXT ) &&
 548                                         !$this->mNewRev->isDeleted( Revision::DELETED_TEXT )
 549                                 ) {
 550                                         $undoLink = Html::element( 'a', [
 551                                                         'href' => $this->mNewPage->getLocalURL( [
 552                                                                 'action' => 'edit',
 553                                                                 'undoafter' => $this->mOldid,
 554                                                                 'undo' => $this->mNewid
 555                                                         ] ),
 556                                                         'title' => Linker::titleAttrib( 'undo' ),
 557                                                 ],
 558                                                 $this->msg( 'editundo' )->text()
 559                                         );
 560                                         $revisionTools['mw-diff-undo'] = $undoLink;
 561                                 }
 562                         }
 563
 564                         # Make "previous revision link"
 565                         if ( $samePage && $this->mOldPage && $this->mOldRev->getPrevious() ) {
 566                                 $prevlink = Linker::linkKnown(
 567                                         $this->mOldPage,
 568                                         $this->msg( 'previousdiff' )->escaped(),
 569                                         [ 'id' => 'differences-prevlink' ],
 570                                         [ 'diff' => 'prev', 'oldid' => $this->mOldid ] + $query
 571                                 );
 572                         } else {
 573                                 $prevlink = "\u{00A0}";
 574                         }
 575
 576                         if ( $this->mOldRev->isMinor() ) {
 577                                 $oldminor = ChangesList::flag( 'minor' );
 578                         } else {
 579                                 $oldminor = '';
 580                         }
 581
 582                         $ldel = $this->revisionDeleteLink( $this->mOldRev );
 583                         $oldRevisionHeader = $this->getRevisionHeader( $this->mOldRev, 'complete' );
 584                         $oldChangeTags = ChangeTags::formatSummaryRow( $this->mOldTags, 'diff', $this->getContext() );
 585
 586                         $oldHeader = '<div id="mw-diff-otitle1"><strong>' . $oldRevisionHeader . '</strong></div>' .
 587                                 '<div id="mw-diff-otitle2">' .
 588                                 Linker::revUserTools( $this->mOldRev, !$this->unhide ) . '</div>' .
 589                                 '<div id="mw-diff-otitle3">' . $oldminor .
 590                                 Linker::revComment( $this->mOldRev, !$diffOnly, !$this->unhide ) . $ldel . '</div>' .
 591                                 '<div id="mw-diff-otitle5">' . $oldChangeTags[0] . '</div>' .
 592                                 '<div id="mw-diff-otitle4">' . $prevlink . '</div>';
 593
 594                         // Allow extensions to change the $oldHeader variable
 595                         Hooks::run( 'DifferenceEngineOldHeader', [ $this, &$oldHeader, $prevlink, $oldminor,
 596                                 $diffOnly, $ldel, $this->unhide ] );
 597
 598                         if ( $this->mOldRev->isDeleted( Revision::DELETED_TEXT ) ) {
 599                                 $deleted = true; // old revisions text is hidden
 600                                 if ( $this->mOldRev->isDeleted( Revision::DELETED_RESTRICTED ) ) {
 601                                         $suppressed = true; // also suppressed
 602                                 }
 603                         }
 604
 605                         # Check if this user can see the revisions
 606                         if ( !$this->mOldRev->userCan( Revision::DELETED_TEXT, $user ) ) {
 607                                 $allowed = false;
 608                         }
 609                 }
 610
 611                 $out->addJsConfigVars( [
 612                         'wgDiffOldId' => $this->mOldid,
 613                         'wgDiffNewId' => $this->mNewid,
 614                 ] );
 615
 616                 # Make "next revision link"
 617                 # Skip next link on the top revision
 618                 if ( $samePage && $this->mNewPage && !$this->mNewRev->isCurrent() ) {
 619                         $nextlink = Linker::linkKnown(
 620                                 $this->mNewPage,
 621                                 $this->msg( 'nextdiff' )->escaped(),
 622                                 [ 'id' => 'differences-nextlink' ],
 623                                 [ 'diff' => 'next', 'oldid' => $this->mNewid ] + $query
 624                         );
 625                 } else {
 626                         $nextlink = "\u{00A0}";
 627                 }
 628
 629                 if ( $this->mNewRev->isMinor() ) {
 630                         $newminor = ChangesList::flag( 'minor' );
 631                 } else {
 632                         $newminor = '';
 633                 }
 634
 635                 # Handle RevisionDelete links...
 636                 $rdel = $this->revisionDeleteLink( $this->mNewRev );
 637
 638                 # Allow extensions to define their own revision tools
 639                 Hooks::run( 'DiffRevisionTools',
 640                         [ $this->mNewRev, &$revisionTools, $this->mOldRev, $user ] );
 641                 $formattedRevisionTools = [];
 642                 // Put each one in parentheses (poor man's button)
 643                 foreach ( $revisionTools as $key => $tool ) {
 644                         $toolClass = is_string( $key ) ? $key : 'mw-diff-tool';
 645                         $element = Html::rawElement(
 646                                 'span',
 647                                 [ 'class' => $toolClass ],
 648                                 $this->msg( 'parentheses' )->rawParams( $tool )->escaped()
 649                         );
 650                         $formattedRevisionTools[] = $element;
 651                 }
 652                 $newRevisionHeader = $this->getRevisionHeader( $this->mNewRev, 'complete' ) .
 653                         ' ' . implode( ' ', $formattedRevisionTools );
 654                 $newChangeTags = ChangeTags::formatSummaryRow( $this->mNewTags, 'diff', $this->getContext() );
 655
 656                 $newHeader = '<div id="mw-diff-ntitle1"><strong>' . $newRevisionHeader . '</strong></div>' .
 657                         '<div id="mw-diff-ntitle2">' . Linker::revUserTools( $this->mNewRev, !$this->unhide ) .
 658                         " $rollback</div>" .
 659                         '<div id="mw-diff-ntitle3">' . $newminor .
 660                         Linker::revComment( $this->mNewRev, !$diffOnly, !$this->unhide ) . $rdel . '</div>' .
 661                         '<div id="mw-diff-ntitle5">' . $newChangeTags[0] . '</div>' .
 662                         '<div id="mw-diff-ntitle4">' . $nextlink . $this->markPatrolledLink() . '</div>';
 663
 664                 // Allow extensions to change the $newHeader variable
 665                 Hooks::run( 'DifferenceEngineNewHeader', [ $this, &$newHeader, $formattedRevisionTools,
 666                         $nextlink, $rollback, $newminor, $diffOnly, $rdel, $this->unhide ] );
 667
 668                 if ( $this->mNewRev->isDeleted( Revision::DELETED_TEXT ) ) {
 669                         $deleted = true; // new revisions text is hidden
 670                         if ( $this->mNewRev->isDeleted( Revision::DELETED_RESTRICTED ) ) {
 671                                 $suppressed = true; // also suppressed
 672                         }
 673                 }
 674
 675                 # If the diff cannot be shown due to a deleted revision, then output
 676                 # the diff header and links to unhide (if available)...
 677                 if ( $deleted && ( !$this->unhide || !$allowed ) ) {
 678                         $this->showDiffStyle();
 679                         $multi = $this->getMultiNotice();
 680                         $out->addHTML( $this->addHeader( '', $oldHeader, $newHeader, $multi ) );
 681                         if ( !$allowed ) {
 682                                 $msg = $suppressed ? 'rev-suppressed-no-diff' : 'rev-deleted-no-diff';
 683                                 # Give explanation for why revision is not visible
 684                                 $out->wrapWikiMsg( "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n",
 685                                         [ $msg ] );
 686                         } else {
 687                                 # Give explanation and add a link to view the diff...
 688                                 $query = $this->getRequest()->appendQueryValue( 'unhide', '1' );
 689                                 $link = $this->getTitle()->getFullURL( $query );
 690                                 $msg = $suppressed ? 'rev-suppressed-unhide-diff' : 'rev-deleted-unhide-diff';
 691                                 $out->wrapWikiMsg(
 692                                         "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n",
 693                                         [ $msg, $link ]
 694                                 );
 695                         }
 696                 # Otherwise, output a regular diff...
 697                 } else {
 698                         # Add deletion notice if the user is viewing deleted content
 699                         $notice = '';
 700                         if ( $deleted ) {
 701                                 $msg = $suppressed ? 'rev-suppressed-diff-view' : 'rev-deleted-diff-view';
 702                                 $notice = "<div id='mw-$msg' class='mw-warning plainlinks'>\n" .
 703                                         $this->msg( $msg )->parse() .
 704                                         "</div>\n";
 705                         }
 706                         $this->showDiff( $oldHeader, $newHeader, $notice );
 707                         if ( !$diffOnly ) {
 708                                 $this->renderNewRevision();
 709                         }
 710                 }
 711         }
 712
 713         /**
 714          * Build a link to mark a change as patrolled.
 715          *
 716          * Returns empty string if there's either no revision to patrol or the user is not allowed to.
 717          * Side effect: When the patrol link is build, this method will call
 718          * OutputPage::preventClickjacking() and load mediawiki.page.patrol.ajax.
 719          *
 720          * @return string HTML or empty string
 721          */
 722         public function markPatrolledLink() {
 723                 if ( $this->mMarkPatrolledLink === null ) {
 724                         $linkInfo = $this->getMarkPatrolledLinkInfo();
 725                         // If false, there is no patrol link needed/allowed
 726                         if ( !$linkInfo || !$this->mNewPage ) {
 727                                 $this->mMarkPatrolledLink = '';
 728                         } else {
 729                                 $this->mMarkPatrolledLink = ' <span class="patrollink" data-mw="interface">[' .
 730                                         Linker::linkKnown(
 731                                                 $this->mNewPage,
 732                                                 $this->msg( 'markaspatrolleddiff' )->escaped(),
 733                                                 [],
 734                                                 [
 735                                                         'action' => 'markpatrolled',
 736                                                         'rcid' => $linkInfo['rcid'],
 737                                                 ]
 738                                         ) . ']</span>';
 739                                 // Allow extensions to change the markpatrolled link
 740                                 Hooks::run( 'DifferenceEngineMarkPatrolledLink', [ $this,
 741                                         &$this->mMarkPatrolledLink, $linkInfo['rcid'] ] );
 742                         }
 743                 }
 744                 return $this->mMarkPatrolledLink;
 745         }
 746
 747         /**
 748          * Returns an array of meta data needed to build a "mark as patrolled" link and
 749          * adds the mediawiki.page.patrol.ajax to the output.
 750          *
 751          * @return array|false An array of meta data for a patrol link (rcid only)
 752          *  or false if no link is needed
 753          */
 754         protected function getMarkPatrolledLinkInfo() {
 755                 global $wgUseRCPatrol;
 756
 757                 $user = $this->getUser();
 758
 759                 // Prepare a change patrol link, if applicable
 760                 if (
 761                         // Is patrolling enabled and the user allowed to?
 762                         $wgUseRCPatrol && $this->mNewPage && $this->mNewPage->quickUserCan( 'patrol', $user ) &&
 763                         // Only do this if the revision isn't more than 6 hours older
 764                         // than the Max RC age (6h because the RC might not be cleaned out regularly)
 765                         RecentChange::isInRCLifespan( $this->mNewRev->getTimestamp(), 21600 )
 766                 ) {
 767                         // Look for an unpatrolled change corresponding to this diff
 768                         $db = wfGetDB( DB_REPLICA );
 769                         $change = RecentChange::newFromConds(
 770                                 [
 771                                         'rc_timestamp' => $db->timestamp( $this->mNewRev->getTimestamp() ),
 772                                         'rc_this_oldid' => $this->mNewid,
 773                                         'rc_patrolled' => RecentChange::PRC_UNPATROLLED
 774                                 ],
 775                                 __METHOD__
 776                         );
 777
 778                         if ( $change && !$change->getPerformer()->equals( $user ) ) {
 779                                 $rcid = $change->getAttribute( 'rc_id' );
 780                         } else {
 781                                 // None found or the page has been created by the current user.
 782                                 // If the user could patrol this it already would be patrolled
 783                                 $rcid = 0;
 784                         }
 785
 786                         // Allow extensions to possibly change the rcid here
 787                         // For example the rcid might be set to zero due to the user
 788                         // being the same as the performer of the change but an extension
 789                         // might still want to show it under certain conditions
 790                         Hooks::run( 'DifferenceEngineMarkPatrolledRCID', [ &$rcid, $this, $change, $user ] );
 791
 792                         // Build the link
 793                         if ( $rcid ) {
 794                                 $this->getOutput()->preventClickjacking();
 795                                 if ( $user->isAllowed( 'writeapi' ) ) {
 796                                         $this->getOutput()->addModules( 'mediawiki.page.patrol.ajax' );
 797                                 }
 798
 799                                 return [
 800                                         'rcid' => $rcid,
 801                                 ];
 802                         }
 803                 }
 804
 805                 // No mark as patrolled link applicable
 806                 return false;
 807         }
 808
 809         /**
 810          * @param Revision $rev
 811          *
 812          * @return string
 813          */
 814         protected function revisionDeleteLink( $rev ) {
 815                 $link = Linker::getRevDeleteLink( $this->getUser(), $rev, $rev->getTitle() );
 816                 if ( $link !== '' ) {
 817                         $link = "\u{00A0}\u{00A0}\u{00A0}" . $link . ' ';
 818                 }
 819
 820                 return $link;
 821         }
 822
 823         /**
 824          * Show the new revision of the page.
 825          */
 826         public function renderNewRevision() {
 827                 $out = $this->getOutput();
 828                 $revHeader = $this->getRevisionHeader( $this->mNewRev );
 829                 # Add "current version as of X" title
 830                 $out->addHTML( "<hr class='diff-hr' id='mw-oldid' />
 831                 <h2 class='diff-currentversion-title'>{$revHeader}</h2>\n" );
 832                 # Page content may be handled by a hooked call instead...
 833                 if ( Hooks::run( 'ArticleContentOnDiff', [ $this, $out ] ) ) {
 834                         $this->loadNewText();
 835                         if ( !$this->mNewPage ) {
 836                                 // New revision is unsaved; bail out.
 837                                 // TODO in theory rendering the new revision is a meaningful thing to do
 838                                 // even if it's unsaved, but a lot of untangling is required to do it safely.
 839                         }
 840
 841                         $out->setRevisionId( $this->mNewid );
 842                         $out->setRevisionTimestamp( $this->mNewRev->getTimestamp() );
 843                         $out->setArticleFlag( true );
 844
 845                         if ( !Hooks::run( 'ArticleContentViewCustom',
 846                                 [ $this->mNewContent, $this->mNewPage, $out ] )
 847                         ) {
 848                                 // Handled by extension
 849                         } else {
 850                                 // Normal page
 851                                 if ( $this->getTitle()->equals( $this->mNewPage ) ) {
 852                                         // If the Title stored in the context is the same as the one
 853                                         // of the new revision, we can use its associated WikiPage
 854                                         // object.
 855                                         $wikiPage = $this->getWikiPage();
 856                                 } else {
 857                                         // Otherwise we need to create our own WikiPage object
 858                                         $wikiPage = WikiPage::factory( $this->mNewPage );
 859                                 }
 860
 861                                 $parserOutput = $this->getParserOutput( $wikiPage, $this->mNewRev );
 862
 863                                 # WikiPage::getParserOutput() should not return false, but just in case
 864                                 if ( $parserOutput ) {
 865                                         // Allow extensions to change parser output here
 866                                         if ( Hooks::run( 'DifferenceEngineRenderRevisionAddParserOutput',
 867                                                 [ $this, $out, $parserOutput, $wikiPage ] )
 868                                         ) {
 869                                                 $out->addParserOutput( $parserOutput, [
 870                                                         'enableSectionEditLinks' => $this->mNewRev->isCurrent()
 871                                                                 && $this->mNewRev->getTitle()->quickUserCan( 'edit', $this->getUser() ),
 872                                                 ] );
 873                                         }
 874                                 }
 875                         }
 876                 }
 877
 878                 // Allow extensions to optionally not show the final patrolled link
 879                 if ( Hooks::run( 'DifferenceEngineRenderRevisionShowFinalPatrolLink' ) ) {
 880                         # Add redundant patrol link on bottom...
 881                         $out->addHTML( $this->markPatrolledLink() );
 882                 }
 883         }
 884
 885         /**
 886          * @param WikiPage $page
 887          * @param Revision $rev
 888          *
 889          * @return ParserOutput|bool False if the revision was not found
 890          */
 891         protected function getParserOutput( WikiPage $page, Revision $rev ) {
 892                 $parserOptions = $page->makeParserOptions( $this->getContext() );
 893                 $parserOutput = $page->getParserOutput( $parserOptions, $rev->getId() );
 894
 895                 return $parserOutput;
 896         }
 897
 898         /**
 899          * Get the diff text, send it to the OutputPage object
 900          * Returns false if the diff could not be generated, otherwise returns true
 901          *
 902          * @param string|bool $otitle Header for old text or false
 903          * @param string|bool $ntitle Header for new text or false
 904          * @param string $notice HTML between diff header and body
 905          *
 906          * @return bool
 907          */
 908         public function showDiff( $otitle, $ntitle, $notice = '' ) {
 909                 // Allow extensions to affect the output here
 910                 Hooks::run( 'DifferenceEngineShowDiff', [ $this ] );
 911
 912                 $diff = $this->getDiff( $otitle, $ntitle, $notice );
 913                 if ( $diff === false ) {
 914                         $this->showMissingRevision();
 915
 916                         return false;
 917                 } else {
 918                         $this->showDiffStyle();
 919                         $this->getOutput()->addHTML( $diff );
 920
 921                         return true;
 922                 }
 923         }
 924
 925         /**
 926          * Add style sheets for diff display.
 927          */
 928         public function showDiffStyle() {
 929                 if ( !$this->isSlotDiffRenderer ) {
 930                         $this->getOutput()->addModuleStyles( 'mediawiki.diff.styles' );
 931                         foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
 932                                 $slotDiffRenderer->addModules( $this->getOutput() );
 933                         }
 934                 }
 935         }
 936
 937         /**
 938          * Get complete diff table, including header
 939          *
 940          * @param string|bool $otitle Header for old text or false
 941          * @param string|bool $ntitle Header for new text or false
 942          * @param string $notice HTML between diff header and body
 943          *
 944          * @return mixed
 945          */
 946         public function getDiff( $otitle, $ntitle, $notice = '' ) {
 947                 $body = $this->getDiffBody();
 948                 if ( $body === false ) {
 949                         return false;
 950                 }
 951
 952                 $multi = $this->getMultiNotice();
 953                 // Display a message when the diff is empty
 954                 if ( $body === '' ) {
 955                         $notice .= '<div class="mw-diff-empty">' .
 956                                 $this->msg( 'diff-empty' )->parse() .
 957                                 "</div>\n";
 958                 }
 959
 960                 return $this->addHeader( $body, $otitle, $ntitle, $multi, $notice );
 961         }
 962
 963         /**
 964          * Get the diff table body, without header
 965          *
 966          * @return mixed (string/false)
 967          */
 968         public function getDiffBody() {
 969                 $this->mCacheHit = true;
 970                 // Check if the diff should be hidden from this user
 971                 if ( !$this->isContentOverridden ) {
 972                         if ( !$this->loadRevisionData() ) {
 973                                 return false;
 974                         } elseif ( $this->mOldRev &&
 975                                 !$this->mOldRev->userCan( Revision::DELETED_TEXT, $this->getUser() )
 976                         ) {
 977                                 return false;
 978                         } elseif ( $this->mNewRev &&
 979                                 !$this->mNewRev->userCan( Revision::DELETED_TEXT, $this->getUser() )
 980                         ) {
 981                                 return false;
 982                         }
 983                         // Short-circuit
 984                         if ( $this->mOldRev === false || ( $this->mOldRev && $this->mNewRev &&
 985                                 $this->mOldRev->getId() && $this->mOldRev->getId() == $this->mNewRev->getId() )
 986                         ) {
 987                                 if ( Hooks::run( 'DifferenceEngineShowEmptyOldContent', [ $this ] ) ) {
 988                                         return '';
 989                                 }
 990                         }
 991                 }
 992
 993                 // Cacheable?
 994                 $key = false;
 995                 $cache = ObjectCache::getMainWANInstance();
 996                 if ( $this->mOldid && $this->mNewid ) {
 997                         // Check if subclass is still using the old way
 998                         // for backwards-compatibility
 999                         $key = $this->getDiffBodyCacheKey();
1000                         if ( $key === null ) {
1001                                 $key = $cache->makeKey( ...$this->getDiffBodyCacheKeyParams() );
1002                         }
1003
1004                         // Try cache
1005                         if ( !$this->mRefreshCache ) {
1006                                 $difftext = $cache->get( $key );
1007                                 if ( $difftext ) {
1008                                         wfIncrStats( 'diff_cache.hit' );
1009                                         $difftext = $this->localiseDiff( $difftext );
1010                                         $difftext .= "\n<!-- diff cache key $key -->\n";
1011
1012                                         return $difftext;
1013                                 }
1014                         } // don't try to load but save the result
1015                 }
1016                 $this->mCacheHit = false;
1017
1018                 // Loadtext is permission safe, this just clears out the diff
1019                 if ( !$this->loadText() ) {
1020                         return false;
1021                 }
1022
1023                 $difftext = '';
1024                 // We've checked for revdelete at the beginning of this method; it's OK to ignore
1025                 // read permissions here.
1026                 $slotContents = $this->getSlotContents();
1027                 foreach ( $this->getSlotDiffRenderers() as $role => $slotDiffRenderer ) {
1028                         $slotDiff = $slotDiffRenderer->getDiff( $slotContents[$role]['old'],
1029                                 $slotContents[$role]['new'] );
1030                         if ( $slotDiff && $role !== 'main' ) {
1031                                 // TODO use human-readable role name at least
1032                                 $slotTitle = $role;
1033                                 $difftext .= $this->getSlotHeader( $slotTitle );
1034                         }
1035                         $difftext .= $slotDiff;
1036                 }
1037
1038                 // Avoid PHP 7.1 warning from passing $this by reference
1039                 $diffEngine = $this;
1040
1041                 // Save to cache for 7 days
1042                 if ( !Hooks::run( 'AbortDiffCache', [ &$diffEngine ] ) ) {
1043                         wfIncrStats( 'diff_cache.uncacheable' );
1044                 } elseif ( $key !== false && $difftext !== false ) {
1045                         wfIncrStats( 'diff_cache.miss' );
1046                         $cache->set( $key, $difftext, 7 * 86400 );
1047                 } else {
1048                         wfIncrStats( 'diff_cache.uncacheable' );
1049                 }
1050                 // localise line numbers and title attribute text
1051                 if ( $difftext !== false ) {
1052                         $difftext = $this->localiseDiff( $difftext );
1053                 }
1054
1055                 return $difftext;
1056         }
1057
1058         /**
1059          * Get the diff table body for one slot, without header
1060          *
1061          * @param string $role
1062          * @return string|false
1063          */
1064         public function getDiffBodyForRole( $role ) {
1065                 $diffRenderers = $this->getSlotDiffRenderers();
1066                 if ( !isset( $diffRenderers[$role] ) ) {
1067                         return false;
1068                 }
1069
1070                 $slotContents = $this->getSlotContents();
1071                 $slotDiff = $diffRenderers[$role]->getDiff( $slotContents[$role]['old'],
1072                         $slotContents[$role]['new'] );
1073                 if ( !$slotDiff ) {
1074                         return false;
1075                 }
1076
1077                 if ( $role !== 'main' ) {
1078                         // TODO use human-readable role name at least
1079                         $slotTitle = $role;
1080                         $slotDiff = $this->getSlotHeader( $slotTitle ) . $slotDiff;
1081                 }
1082
1083                 return $this->localiseDiff( $slotDiff );
1084         }
1085
1086         /**
1087          * Get a slot header for inclusion in a diff body (as a table row).
1088          *
1089          * @param string $headerText The text of the header
1090          * @return string
1091          *
1092          */
1093         protected function getSlotHeader( $headerText ) {
1094                 // The old revision is missing on oldid=<first>&diff=prev; only 2 columns in that case.
1095                 $columnCount = $this->mOldRev ? 4 : 2;
1096                 $userLang = $this->getLanguage()->getHtmlCode();
1097                 return Html::rawElement( 'tr', [ 'class' => 'mw-diff-slot-header', 'lang' => $userLang ],
1098                         Html::element( 'th', [ 'colspan' => $columnCount ], $headerText ) );
1099         }
1100
1101         /**
1102          * Returns the cache key for diff body text or content.
1103          *
1104          * @deprecated since 1.31, use getDiffBodyCacheKeyParams() instead
1105          * @since 1.23
1106          *
1107          * @throws MWException
1108          * @return string|null
1109          */
1110         protected function getDiffBodyCacheKey() {
1111                 return null;
1112         }
1113
1114         /**
1115          * Get the cache key parameters
1116          *
1117          * Subclasses can replace the first element in the array to something
1118          * more specific to the type of diff (e.g. "inline-diff"), or append
1119          * if the cache should vary on more things. Overriding entirely should
1120          * be avoided.
1121          *
1122          * @since 1.31
1123          *
1124          * @return array
1125          * @throws MWException
1126          */
1127         protected function getDiffBodyCacheKeyParams() {
1128                 if ( !$this->mOldid || !$this->mNewid ) {
1129                         throw new MWException( 'mOldid and mNewid must be set to get diff cache key.' );
1130                 }
1131
1132                 $engine = $this->getEngine();
1133                 $params = [
1134                         'diff',
1135                         $engine,
1136                         self::DIFF_VERSION,
1137                         "old-{$this->mOldid}",
1138                         "rev-{$this->mNewid}"
1139                 ];
1140
1141                 if ( $engine === 'wikidiff2' ) {
1142                         $params[] = phpversion( 'wikidiff2' );
1143                         $params[] = $this->getConfig()->get( 'WikiDiff2MovedParagraphDetectionCutoff' );
1144                 }
1145
1146                 if ( !$this->isSlotDiffRenderer ) {
1147                         foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
1148                                 $params = array_merge( $params, $slotDiffRenderer->getExtraCacheKeys() );
1149                         }
1150                 }
1151
1152                 return $params;
1153         }
1154
1155         /**
1156          * Implements DifferenceEngineSlotDiffRenderer::getExtraCacheKeys(). Only used when
1157          * DifferenceEngine is wrapped in DifferenceEngineSlotDiffRenderer.
1158          * @return array
1159          * @internal for use by DifferenceEngineSlotDiffRenderer only
1160          * @deprecated
1161          */
1162         public function getExtraCacheKeys() {
1163                 // This method is called when the DifferenceEngine is used for a slot diff. We only care
1164                 // about special things, not the revision IDs, which are added to the cache key by the
1165                 // page-level DifferenceEngine, and which might not have a valid value for this object.
1166                 $this->mOldid = 123456789;
1167                 $this->mNewid = 987654321;
1168
1169                 // This will repeat a bunch of unnecessary key fields for each slot. Not nice but harmless.
1170                 $cacheString = $this->getDiffBodyCacheKey();
1171                 if ( $cacheString ) {
1172                         return [ $cacheString ];
1173                 }
1174
1175                 $params = $this->getDiffBodyCacheKeyParams();
1176
1177                 // Try to get rid of the standard keys to keep the cache key human-readable:
1178                 // call the getDiffBodyCacheKeyParams implementation of the base class, and if
1179                 // the child class includes the same keys, drop them.
1180                 // Uses an obscure PHP feature where static calls to non-static methods are allowed
1181                 // as long as we are already in a non-static method of the same class, and the call context
1182                 // ($this) will be inherited.
1183                 // phpcs:ignore Squiz.Classes.SelfMemberReference.NotUsed
1184                 $standardParams = DifferenceEngine::getDiffBodyCacheKeyParams();
1185                 if ( array_slice( $params, 0, count( $standardParams ) ) === $standardParams ) {
1186                         $params = array_slice( $params, count( $standardParams ) );
1187                 }
1188
1189                 return $params;
1190         }
1191
1192         /**
1193          * Generate a diff, no caching.
1194          *
1195          * @since 1.21
1196          *
1197          * @param Content $old Old content
1198          * @param Content $new New content
1199          *
1200          * @throws Exception If old or new content is not an instance of TextContent.
1201          * @return bool|string
1202          *
1203          * @deprecated since 1.32, use a SlotDiffRenderer instead.
1204          */
1205         public function generateContentDiffBody( Content $old, Content $new ) {
1206                 $slotDiffRenderer = $new->getContentHandler()->getSlotDiffRenderer( $this->getContext() );
1207                 if (
1208                         $slotDiffRenderer instanceof DifferenceEngineSlotDiffRenderer
1209                         && $this->isSlotDiffRenderer
1210                 ) {
1211                         // Oops, we are just about to enter an infinite loop (the slot-level DifferenceEngine
1212                         // called a DifferenceEngineSlotDiffRenderer that wraps the same DifferenceEngine class).
1213                         // This will happen when a content model has no custom slot diff renderer, it does have
1214                         // a custom difference engine, but that does not override this method.
1215                         throw new Exception( get_class( $this ) . ': could not maintain backwards compatibility. '
1216                                 . 'Please use a SlotDiffRenderer.' );
1217                 }
1218                 return $slotDiffRenderer->getDiff( $old, $new ) . $this->getDebugString();
1219         }
1220
1221         /**
1222          * Generate a diff, no caching
1223          *
1224          * @param string $otext Old text, must be already segmented
1225          * @param string $ntext New text, must be already segmented
1226          *
1227          * @throws Exception If content handling for text content is configured in a way
1228          *   that makes maintaining B/C hard.
1229          * @return bool|string
1230          *
1231          * @deprecated since 1.32, use a TextSlotDiffRenderer instead.
1232          */
1233         public function generateTextDiffBody( $otext, $ntext ) {
1234                 $slotDiffRenderer = ContentHandler::getForModelID( CONTENT_MODEL_TEXT )
1235                         ->getSlotDiffRenderer( $this->getContext() );
1236                 if ( !( $slotDiffRenderer instanceof TextSlotDiffRenderer ) ) {
1237                         // Someone used the GetSlotDiffRenderer hook to replace the renderer.
1238                         // This is too unlikely to happen to bother handling properly.
1239                         throw new Exception( 'The slot diff renderer for text content should be a '
1240                                 . 'TextSlotDiffRenderer subclass' );
1241                 }
1242                 return $slotDiffRenderer->getTextDiff( $otext, $ntext ) . $this->getDebugString();
1243         }
1244
1245         /**
1246          * Process $wgExternalDiffEngine and get a sane, usable engine
1247          *
1248          * @return bool|string 'wikidiff2', path to an executable, or false
1249          * @internal For use by this class and TextSlotDiffRenderer only.
1250          */
1251         public static function getEngine() {
1252                 global $wgExternalDiffEngine;
1253                 // We use the global here instead of Config because we write to the value,
1254                 // and Config is not mutable.
1255                 if ( $wgExternalDiffEngine == 'wikidiff' || $wgExternalDiffEngine == 'wikidiff3' ) {
1256                         wfDeprecated( "\$wgExternalDiffEngine = '{$wgExternalDiffEngine}'", '1.27' );
1257                         $wgExternalDiffEngine = false;
1258                 } elseif ( $wgExternalDiffEngine == 'wikidiff2' ) {
1259                         wfDeprecated( "\$wgExternalDiffEngine = '{$wgExternalDiffEngine}'", '1.32' );
1260                         $wgExternalDiffEngine = false;
1261                 } elseif ( !is_string( $wgExternalDiffEngine ) && $wgExternalDiffEngine !== false ) {
1262                         // And prevent people from shooting themselves in the foot...
1263                         wfWarn( '$wgExternalDiffEngine is set to a non-string value, forcing it to false' );
1264                         $wgExternalDiffEngine = false;
1265                 }
1266
1267                 if ( is_string( $wgExternalDiffEngine ) && is_executable( $wgExternalDiffEngine ) ) {
1268                         return $wgExternalDiffEngine;
1269                 } elseif ( $wgExternalDiffEngine === false && function_exists( 'wikidiff2_do_diff' ) ) {
1270                         return 'wikidiff2';
1271                 } else {
1272                         // Native PHP
1273                         return false;
1274                 }
1275         }
1276
1277         /**
1278          * Generates diff, to be wrapped internally in a logging/instrumentation
1279          *
1280          * @param string $otext Old text, must be already segmented
1281          * @param string $ntext New text, must be already segmented
1282          *
1283          * @throws Exception If content handling for text content is configured in a way
1284          *   that makes maintaining B/C hard.
1285          * @return bool|string
1286          *
1287          * @deprecated since 1.32, use a TextSlotDiffRenderer instead.
1288          */
1289         protected function textDiff( $otext, $ntext ) {
1290                 $slotDiffRenderer = ContentHandler::getForModelID( CONTENT_MODEL_TEXT )
1291                         ->getSlotDiffRenderer( $this->getContext() );
1292                 if ( !( $slotDiffRenderer instanceof TextSlotDiffRenderer ) ) {
1293                         // Someone used the GetSlotDiffRenderer hook to replace the renderer.
1294                         // This is too unlikely to happen to bother handling properly.
1295                         throw new Exception( 'The slot diff renderer for text content should be a '
1296                                 . 'TextSlotDiffRenderer subclass' );
1297                 }
1298                 return $slotDiffRenderer->getTextDiff( $otext, $ntext ) . $this->getDebugString();
1299         }
1300
1301         /**
1302          * Generate a debug comment indicating diff generating time,
1303          * server node, and generator backend.
1304          *
1305          * @param string $generator : What diff engine was used
1306          *
1307          * @return string
1308          */
1309         protected function debug( $generator = "internal" ) {
1310                 global $wgShowHostnames;
1311                 if ( !$this->enableDebugComment ) {
1312                         return '';
1313                 }
1314                 $data = [ $generator ];
1315                 if ( $wgShowHostnames ) {
1316                         $data[] = wfHostname();
1317                 }
1318                 $data[] = wfTimestamp( TS_DB );
1319
1320                 return "<!-- diff generator: " .
1321                         implode( " ", array_map( "htmlspecialchars", $data ) ) .
1322                         " -->\n";
1323         }
1324
1325         private function getDebugString() {
1326                 $engine = self::getEngine();
1327                 if ( $engine === 'wikidiff2' ) {
1328                         return $this->debug( 'wikidiff2' );
1329                 } elseif ( $engine === false ) {
1330                         return $this->debug( 'native PHP' );
1331                 } else {
1332                         return $this->debug( "external $engine" );
1333                 }
1334         }
1335
1336         /**
1337          * Localise diff output
1338          *
1339          * @param string $text
1340          * @return string
1341          */
1342         private function localiseDiff( $text ) {
1343                 $text = $this->localiseLineNumbers( $text );
1344                 if ( $this->getEngine() === 'wikidiff2' &&
1345                         version_compare( phpversion( 'wikidiff2' ), '1.5.1', '>=' )
1346                 ) {
1347                         $text = $this->addLocalisedTitleTooltips( $text );
1348                 }
1349                 return $text;
1350         }
1351
1352         /**
1353          * Replace line numbers with the text in the user's language
1354          *
1355          * @param string $text
1356          *
1357          * @return mixed
1358          */
1359         public function localiseLineNumbers( $text ) {
1360                 return preg_replace_callback(
1361                         '/<!--LINE (\d+)-->/',
1362                         [ $this, 'localiseLineNumbersCb' ],
1363                         $text
1364                 );
1365         }
1366
1367         public function localiseLineNumbersCb( $matches ) {
1368                 if ( $matches[1] === '1' && $this->mReducedLineNumbers ) {
1369                         return '';
1370                 }
1371
1372                 return $this->msg( 'lineno' )->numParams( $matches[1] )->escaped();
1373         }
1374
1375         /**
1376          * Add title attributes for tooltips on moved paragraph indicators
1377          *
1378          * @param string $text
1379          * @return string
1380          */
1381         private function addLocalisedTitleTooltips( $text ) {
1382                 return preg_replace_callback(
1383                         '/class="mw-diff-movedpara-(left|right)"/',
1384                         [ $this, 'addLocalisedTitleTooltipsCb' ],
1385                         $text
1386                 );
1387         }
1388
1389         /**
1390          * @param array $matches
1391          * @return string
1392          */
1393         private function addLocalisedTitleTooltipsCb( array $matches ) {
1394                 $key = $matches[1] === 'right' ?
1395                         'diff-paragraph-moved-toold' :
1396                         'diff-paragraph-moved-tonew';
1397                 return $matches[0] . ' title="' . $this->msg( $key )->escaped() . '"';
1398         }
1399
1400         /**
1401          * If there are revisions between the ones being compared, return a note saying so.
1402          *
1403          * @return string
1404          */
1405         public function getMultiNotice() {
1406                 // The notice only make sense if we are diffing two saved revisions of the same page.
1407                 if (
1408                         !$this->mOldRev || !$this->mNewRev
1409                         || !$this->mOldPage || !$this->mNewPage
1410                         || !$this->mOldPage->equals( $this->mNewPage )
1411                 ) {
1412                         return '';
1413                 }
1414
1415                 if ( $this->mOldRev->getTimestamp() > $this->mNewRev->getTimestamp() ) {
1416                         $oldRev = $this->mNewRev; // flip
1417                         $newRev = $this->mOldRev; // flip
1418                 } else { // normal case
1419                         $oldRev = $this->mOldRev;
1420                         $newRev = $this->mNewRev;
1421                 }
1422
1423                 // Sanity: don't show the notice if too many rows must be scanned
1424                 // @todo show some special message for that case
1425                 $nEdits = $this->mNewPage->countRevisionsBetween( $oldRev, $newRev, 1000 );
1426                 if ( $nEdits > 0 && $nEdits <= 1000 ) {
1427                         $limit = 100; // use diff-multi-manyusers if too many users
1428                         $users = $this->mNewPage->getAuthorsBetween( $oldRev, $newRev, $limit );
1429                         $numUsers = count( $users );
1430
1431                         if ( $numUsers == 1 && $users[0] == $newRev->getUserText( Revision::RAW ) ) {
1432                                 $numUsers = 0; // special case to say "by the same user" instead of "by one other user"
1433                         }
1434
1435                         return self::intermediateEditsMsg( $nEdits, $numUsers, $limit );
1436                 }
1437
1438                 return ''; // nothing
1439         }
1440
1441         /**
1442          * Get a notice about how many intermediate edits and users there are
1443          *
1444          * @param int $numEdits
1445          * @param int $numUsers
1446          * @param int $limit
1447          *
1448          * @return string
1449          */
1450         public static function intermediateEditsMsg( $numEdits, $numUsers, $limit ) {
1451                 if ( $numUsers === 0 ) {
1452                         $msg = 'diff-multi-sameuser';
1453                 } elseif ( $numUsers > $limit ) {
1454                         $msg = 'diff-multi-manyusers';
1455                         $numUsers = $limit;
1456                 } else {
1457                         $msg = 'diff-multi-otherusers';
1458                 }
1459
1460                 return wfMessage( $msg )->numParams( $numEdits, $numUsers )->parse();
1461         }
1462
1463         /**
1464          * Get a header for a specified revision.
1465          *
1466          * @param Revision $rev
1467          * @param string $complete 'complete' to get the header wrapped depending
1468          *        the visibility of the revision and a link to edit the page.
1469          *
1470          * @return string HTML fragment
1471          */
1472         public function getRevisionHeader( Revision $rev, $complete = '' ) {
1473                 $lang = $this->getLanguage();
1474                 $user = $this->getUser();
1475                 $revtimestamp = $rev->getTimestamp();
1476                 $timestamp = $lang->userTimeAndDate( $revtimestamp, $user );
1477                 $dateofrev = $lang->userDate( $revtimestamp, $user );
1478                 $timeofrev = $lang->userTime( $revtimestamp, $user );
1479
1480                 $header = $this->msg(
1481                         $rev->isCurrent() ? 'currentrev-asof' : 'revisionasof',
1482                         $timestamp,
1483                         $dateofrev,
1484                         $timeofrev
1485                 )->escaped();
1486
1487                 if ( $complete !== 'complete' ) {
1488                         return $header;
1489                 }
1490
1491                 $title = $rev->getTitle();
1492
1493                 $header = Linker::linkKnown( $title, $header, [],
1494                         [ 'oldid' => $rev->getId() ] );
1495
1496                 if ( $rev->userCan( Revision::DELETED_TEXT, $user ) ) {
1497                         $editQuery = [ 'action' => 'edit' ];
1498                         if ( !$rev->isCurrent() ) {
1499                                 $editQuery['oldid'] = $rev->getId();
1500                         }
1501
1502                         $key = $title->quickUserCan( 'edit', $user ) ? 'editold' : 'viewsourceold';
1503                         $msg = $this->msg( $key )->escaped();
1504                         $editLink = $this->msg( 'parentheses' )->rawParams(
1505                                 Linker::linkKnown( $title, $msg, [], $editQuery ) )->escaped();
1506                         $header .= ' ' . Html::rawElement(
1507                                 'span',
1508                                 [ 'class' => 'mw-diff-edit' ],
1509                                 $editLink
1510                         );
1511                         if ( $rev->isDeleted( Revision::DELETED_TEXT ) ) {
1512                                 $header = Html::rawElement(
1513                                         'span',
1514                                         [ 'class' => 'history-deleted' ],
1515                                         $header
1516                                 );
1517                         }
1518                 } else {
1519                         $header = Html::rawElement( 'span', [ 'class' => 'history-deleted' ], $header );
1520                 }
1521
1522                 return $header;
1523         }
1524
1525         /**
1526          * Add the header to a diff body
1527          *
1528          * @param string $diff Diff body
1529          * @param string $otitle Old revision header
1530          * @param string $ntitle New revision header
1531          * @param string $multi Notice telling user that there are intermediate
1532          *   revisions between the ones being compared
1533          * @param string $notice Other notices, e.g. that user is viewing deleted content
1534          *
1535          * @return string
1536          */
1537         public function addHeader( $diff, $otitle, $ntitle, $multi = '', $notice = '' ) {
1538                 // shared.css sets diff in interface language/dir, but the actual content
1539                 // is often in a different language, mostly the page content language/dir
1540                 $header = Html::openElement( 'table', [
1541                         'class' => [ 'diff', 'diff-contentalign-' . $this->getDiffLang()->alignStart() ],
1542                         'data-mw' => 'interface',
1543                 ] );
1544                 $userLang = htmlspecialchars( $this->getLanguage()->getHtmlCode() );
1545
1546                 if ( !$diff && !$otitle ) {
1547                         $header .= "
1548                         <tr class=\"diff-title\" lang=\"{$userLang}\">
1549                         <td class=\"diff-ntitle\">{$ntitle}</td>
1550                         </tr>";
1551                         $multiColspan = 1;
1552                 } else {
1553                         if ( $diff ) { // Safari/Chrome show broken output if cols not used
1554                                 $header .= "
1555                                 <col class=\"diff-marker\" />
1556                                 <col class=\"diff-content\" />
1557                                 <col class=\"diff-marker\" />
1558                                 <col class=\"diff-content\" />";
1559                                 $colspan = 2;
1560                                 $multiColspan = 4;
1561                         } else {
1562                                 $colspan = 1;
1563                                 $multiColspan = 2;
1564                         }
1565                         if ( $otitle || $ntitle ) {
1566                                 $header .= "
1567                                 <tr class=\"diff-title\" lang=\"{$userLang}\">
1568                                 <td colspan=\"$colspan\" class=\"diff-otitle\">{$otitle}</td>
1569                                 <td colspan=\"$colspan\" class=\"diff-ntitle\">{$ntitle}</td>
1570                                 </tr>";
1571                         }
1572                 }
1573
1574                 if ( $multi != '' ) {
1575                         $header .= "<tr><td colspan=\"{$multiColspan}\" " .
1576                                 "class=\"diff-multi\" lang=\"{$userLang}\">{$multi}</td></tr>";
1577                 }
1578                 if ( $notice != '' ) {
1579                         $header .= "<tr><td colspan=\"{$multiColspan}\" " .
1580                                 "class=\"diff-notice\" lang=\"{$userLang}\">{$notice}</td></tr>";
1581                 }
1582
1583                 return $header . $diff . "</table>";
1584         }
1585
1586         /**
1587          * Use specified text instead of loading from the database
1588          * @param Content $oldContent
1589          * @param Content $newContent
1590          * @since 1.21
1591          * @deprecated since 1.32, use setRevisions or ContentHandler::getSlotDiffRenderer.
1592          */
1593         public function setContent( Content $oldContent, Content $newContent ) {
1594                 $this->mOldContent = $oldContent;
1595                 $this->mNewContent = $newContent;
1596
1597                 $this->mTextLoaded = 2;
1598                 $this->mRevisionsLoaded = true;
1599                 $this->isContentOverridden = true;
1600                 $this->slotDiffRenderers = null;
1601         }
1602
1603         /**
1604          * Use specified text instead of loading from the database.
1605          * @param RevisionRecord|null $oldRevision
1606          * @param RevisionRecord $newRevision
1607          */
1608         public function setRevisions(
1609                 RevisionRecord $oldRevision = null, RevisionRecord $newRevision
1610         ) {
1611                 if ( $oldRevision ) {
1612                         $this->mOldRev = new Revision( $oldRevision );
1613                         $this->mOldid = $oldRevision->getId();
1614                         $this->mOldPage = Title::newFromLinkTarget( $oldRevision->getPageAsLinkTarget() );
1615                         // This method is meant for edit diffs and such so there is no reason to provide a
1616                         // revision that's not readable to the user, but check it just in case.
1617                         $this->mOldContent = $oldRevision ? $oldRevision->getContent( 'main',
1618                                 RevisionRecord::FOR_THIS_USER, $this->getUser() ) : null;
1619                 } else {
1620                         $this->mOldPage = null;
1621                         $this->mOldRev = $this->mOldid = false;
1622                 }
1623                 $this->mNewRev = new Revision( $newRevision );
1624                 $this->mNewid = $newRevision->getId();
1625                 $this->mNewPage = Title::newFromLinkTarget( $newRevision->getPageAsLinkTarget() );
1626                 $this->mNewContent = $newRevision->getContent( 'main',
1627                         RevisionRecord::FOR_THIS_USER, $this->getUser() );
1628
1629                 $this->mRevisionsIdsLoaded = $this->mRevisionsLoaded = true;
1630                 $this->mTextLoaded = !!$oldRevision + 1;
1631                 $this->isContentOverridden = false;
1632                 $this->slotDiffRenderers = null;
1633         }
1634
1635         /**
1636          * Set the language in which the diff text is written
1637          *
1638          * @param Language $lang
1639          * @since 1.19
1640          */
1641         public function setTextLanguage( $lang ) {
1642                 if ( !$lang instanceof Language ) {
1643                         wfDeprecated( __METHOD__ . ' with other type than Language for $lang', '1.32' );
1644                 }
1645                 $this->mDiffLang = wfGetLangObj( $lang );
1646         }
1647
1648         /**
1649          * Maps a revision pair definition as accepted by DifferenceEngine constructor
1650          * to a pair of actual integers representing revision ids.
1651          *
1652          * @param int $old Revision id, e.g. from URL parameter 'oldid'
1653          * @param int|string $new Revision id or strings 'next' or 'prev', e.g. from URL parameter 'diff'
1654          *
1655          * @return array List of two revision ids, older first, later second.
1656          *     Zero signifies invalid argument passed.
1657          *     false signifies that there is no previous/next revision ($old is the oldest/newest one).
1658          */
1659         public function mapDiffPrevNext( $old, $new ) {
1660                 if ( $new === 'prev' ) {
1661                         // Show diff between revision $old and the previous one. Get previous one from DB.
1662                         $newid = intval( $old );
1663                         $oldid = $this->getTitle()->getPreviousRevisionID( $newid );
1664                 } elseif ( $new === 'next' ) {
1665                         // Show diff between revision $old and the next one. Get next one from DB.
1666                         $oldid = intval( $old );
1667                         $newid = $this->getTitle()->getNextRevisionID( $oldid );
1668                 } else {
1669                         $oldid = intval( $old );
1670                         $newid = intval( $new );
1671                 }
1672
1673                 return [ $oldid, $newid ];
1674         }
1675
1676         /**
1677          * Load revision IDs
1678          */
1679         private function loadRevisionIds() {
1680                 if ( $this->mRevisionsIdsLoaded ) {
1681                         return;
1682                 }
1683
1684                 $this->mRevisionsIdsLoaded = true;
1685
1686                 $old = $this->mOldid;
1687                 $new = $this->mNewid;
1688
1689                 list( $this->mOldid, $this->mNewid ) = self::mapDiffPrevNext( $old, $new );
1690                 if ( $new === 'next' && $this->mNewid === false ) {
1691                         # if no result, NewId points to the newest old revision. The only newer
1692                         # revision is cur, which is "0".
1693                         $this->mNewid = 0;
1694                 }
1695
1696                 Hooks::run(
1697                         'NewDifferenceEngine',
1698                         [ $this->getTitle(), &$this->mOldid, &$this->mNewid, $old, $new ]
1699                 );
1700         }
1701
1702         /**
1703          * Load revision metadata for the specified revisions. If newid is 0, then compare
1704          * the old revision in oldid to the current revision of the current page (as defined
1705          * by the request context); if oldid is 0, then compare the revision in newid to the
1706          * immediately previous one.
1707          *
1708          * If oldid is false, leave the corresponding revision object set
1709          * to false. This can happen with 'diff=prev' pointing to a non-existent revision,
1710          * and is also used directly by the API.
1711          *
1712          * @return bool Whether both revisions were loaded successfully. Setting mOldRev
1713          *   to false counts as successful loading.
1714          */
1715         public function loadRevisionData() {
1716                 if ( $this->mRevisionsLoaded ) {
1717                         return $this->isContentOverridden || $this->mNewRev && !is_null( $this->mOldRev );
1718                 }
1719
1720                 // Whether it succeeds or fails, we don't want to try again
1721                 $this->mRevisionsLoaded = true;
1722
1723                 $this->loadRevisionIds();
1724
1725                 // Load the new revision object
1726                 if ( $this->mNewid ) {
1727                         $this->mNewRev = Revision::newFromId( $this->mNewid );
1728                 } else {
1729                         $this->mNewRev = Revision::newFromTitle(
1730                                 $this->getTitle(),
1731                                 false,
1732                                 Revision::READ_NORMAL
1733                         );
1734                 }
1735
1736                 if ( !$this->mNewRev instanceof Revision ) {
1737                         return false;
1738                 }
1739
1740                 // Update the new revision ID in case it was 0 (makes life easier doing UI stuff)
1741                 $this->mNewid = $this->mNewRev->getId();
1742                 if ( $this->mNewid ) {
1743                         $this->mNewPage = $this->mNewRev->getTitle();
1744                 } else {
1745                         $this->mNewPage = null;
1746                 }
1747
1748                 // Load the old revision object
1749                 $this->mOldRev = false;
1750                 if ( $this->mOldid ) {
1751                         $this->mOldRev = Revision::newFromId( $this->mOldid );
1752                 } elseif ( $this->mOldid === 0 ) {
1753                         $rev = $this->mNewRev->getPrevious();
1754                         if ( $rev ) {
1755                                 $this->mOldid = $rev->getId();
1756                                 $this->mOldRev = $rev;
1757                         } else {
1758                                 // No previous revision; mark to show as first-version only.
1759                                 $this->mOldid = false;
1760                                 $this->mOldRev = false;
1761                         }
1762                 } /* elseif ( $this->mOldid === false ) leave mOldRev false; */
1763
1764                 if ( is_null( $this->mOldRev ) ) {
1765                         return false;
1766                 }
1767
1768                 if ( $this->mOldRev && $this->mOldRev->getId() ) {
1769                         $this->mOldPage = $this->mOldRev->getTitle();
1770                 } else {
1771                         $this->mOldPage = null;
1772                 }
1773
1774                 // Load tags information for both revisions
1775                 $dbr = wfGetDB( DB_REPLICA );
1776                 if ( $this->mOldid !== false ) {
1777                         $this->mOldTags = $dbr->selectField(
1778                                 'tag_summary',
1779                                 'ts_tags',
1780                                 [ 'ts_rev_id' => $this->mOldid ],
1781                                 __METHOD__
1782                         );
1783                 } else {
1784                         $this->mOldTags = false;
1785                 }
1786                 $this->mNewTags = $dbr->selectField(
1787                         'tag_summary',
1788                         'ts_tags',
1789                         [ 'ts_rev_id' => $this->mNewid ],
1790                         __METHOD__
1791                 );
1792
1793                 return true;
1794         }
1795
1796         /**
1797          * Load the text of the revisions, as well as revision data.
1798          * When the old revision is missing (mOldRev is false), loading mOldContent is not attempted.
1799          *
1800          * @return bool Whether the content of both revisions could be loaded successfully.
1801          *   (When mOldRev is false, that still counts as a success.)
1802          *
1803          */
1804         public function loadText() {
1805                 if ( $this->mTextLoaded == 2 ) {
1806                         return $this->loadRevisionData() && ( $this->mOldRev === false || $this->mOldContent )
1807                                 && $this->mNewContent;
1808                 }
1809
1810                 // Whether it succeeds or fails, we don't want to try again
1811                 $this->mTextLoaded = 2;
1812
1813                 if ( !$this->loadRevisionData() ) {
1814                         return false;
1815                 }
1816
1817                 if ( $this->mOldRev ) {
1818                         $this->mOldContent = $this->mOldRev->getContent( Revision::FOR_THIS_USER, $this->getUser() );
1819                         if ( $this->mOldContent === null ) {
1820                                 return false;
1821                         }
1822                 }
1823
1824                 $this->mNewContent = $this->mNewRev->getContent( Revision::FOR_THIS_USER, $this->getUser() );
1825                 Hooks::run( 'DifferenceEngineLoadTextAfterNewContentIsLoaded', [ $this ] );
1826                 if ( $this->mNewContent === null ) {
1827                         return false;
1828                 }
1829
1830                 return true;
1831         }
1832
1833         /**
1834          * Load the text of the new revision, not the old one
1835          *
1836          * @return bool Whether the content of the new revision could be loaded successfully.
1837          */
1838         public function loadNewText() {
1839                 if ( $this->mTextLoaded >= 1 ) {
1840                         return $this->loadRevisionData();
1841                 }
1842
1843                 $this->mTextLoaded = 1;
1844
1845                 if ( !$this->loadRevisionData() ) {
1846                         return false;
1847                 }
1848
1849                 $this->mNewContent = $this->mNewRev->getContent( Revision::FOR_THIS_USER, $this->getUser() );
1850
1851                 Hooks::run( 'DifferenceEngineAfterLoadNewText', [ $this ] );
1852
1853                 return true;
1854         }
1855
1856 }