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\MediaWikiServices;
  25 use MediaWiki\Revision\RevisionRecord;
  26 use MediaWiki\Revision\SlotRecord;
  27 use MediaWiki\Storage\NameTableAccessException;
  28
  29 /**
  30  * DifferenceEngine is responsible for rendering the difference between two revisions as HTML.
  31  * This includes interpreting URL parameters, retrieving revision data, checking access permissions,
  32  * selecting and invoking the diff generator class for the individual slots, doing post-processing
  33  * on the generated diff, adding the rest of the HTML (such as headers) and writing the whole thing
  34  * to OutputPage.
  35  *
  36  * DifferenceEngine can be subclassed by extensions, by customizing
  37  * ContentHandler::createDifferenceEngine; the content handler will be selected based on the
  38  * content model of the main slot (of the new revision, when the two are different).
  39  * That might change after PageTypeHandler gets introduced.
  40  *
  41  * In the past, the class was also used for slot-level diff generation, and extensions might still
  42  * subclass it and add such functionality. When that is the case (sepcifically, when a
  43  * ContentHandler returns a standard SlotDiffRenderer but a nonstandard DifferenceEngine)
  44  * DifferenceEngineSlotDiffRenderer will be used to convert the old behavior into the new one.
  45  *
  46  * @ingroup DifferenceEngine
  47  *
  48  * @todo This class is huge and poorly defined. It should be split into a controller responsible
  49  * for interpreting query parameters, retrieving data and checking permissions; and a HTML renderer.
  50  */
  51 class DifferenceEngine extends ContextSource {
  52
  53         use DeprecationHelper;
  54
  55         /**
  56          * Constant to indicate diff cache compatibility.
  57          * Bump this when changing the diff formatting in a way that
  58          * fixes important bugs or such to force cached diff views to
  59          * clear.
  60          */
  61         const DIFF_VERSION = '1.12';
  62
  63         /**
  64          * Revision ID for the old revision. 0 for the revision previous to $mNewid, false
  65          * if the diff does not have an old revision (e.g. 'oldid=<first revision of page>&diff=prev'),
  66          * or the revision does not exist, null if the revision is unsaved.
  67          * @var int|false|null
  68          */
  69         protected $mOldid;
  70
  71         /**
  72          * Revision ID for the new revision. 0 for the last revision of the current page
  73          * (as defined by the request context), false if the revision does not exist, null
  74          * if it is unsaved, or an alias such as 'next'.
  75          * @var int|string|false|null
  76          */
  77         protected $mNewid;
  78
  79         /**
  80          * Old revision (left pane).
  81          * Allowed to be an unsaved revision, unlikely that's ever needed though.
  82          * False when the old revision does not exist; this can happen when using
  83          * diff=prev on the first revision. Null when the revision should exist but
  84          * doesn't (e.g. load failure); loadRevisionData() will return false in that
  85          * case. Also null until lazy-loaded. Ignored completely when isContentOverridden
  86          * is set.
  87          * Since 1.32 public access is deprecated.
  88          * @var Revision|null|false
  89          */
  90         protected $mOldRev;
  91
  92         /**
  93          * New revision (right pane).
  94          * Note that this might be an unsaved revision (e.g. for edit preview).
  95          * Null in case of load failure; diff methods will just return an error message in that case,
  96          * and loadRevisionData() will return false. Also null until lazy-loaded. Ignored completely
  97          * when isContentOverridden is set.
  98          * Since 1.32 public access is deprecated.
  99          * @var Revision|null
 100          */
 101         protected $mNewRev;
 102
 103         /**
 104          * Title of $mOldRev or null if the old revision does not exist or does not belong to a page.
 105          * Since 1.32 public access is deprecated and the property can be null.
 106          * @var Title|null
 107          */
 108         protected $mOldPage;
 109
 110         /**
 111          * Title of $mNewRev or null if the new revision does not exist or does not belong to a page.
 112          * Since 1.32 public access is deprecated and the property can be null.
 113          * @var Title|null
 114          */
 115         protected $mNewPage;
 116
 117         /**
 118          * Change tags of $mOldRev or null if it does not exist / is not saved.
 119          * @var string[]|null
 120          */
 121         private $mOldTags;
 122
 123         /**
 124          * Change tags of $mNewRev or null if it does not exist / is not saved.
 125          * @var string[]|null
 126          */
 127         private $mNewTags;
 128
 129         /**
 130          * @var Content|null
 131          * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
 132          *   This property is set to the content of the main slot, but not actually used for the main diff.
 133          */
 134         private $mOldContent;
 135
 136         /**
 137          * @var Content|null
 138          * @deprecated since 1.32, content slots are now handled by the corresponding SlotDiffRenderer.
 139          *   This property is set to the content of the main slot, but not actually used for the main diff.
 140          */
 141         private $mNewContent;
 142
 143         /** @var Language */
 144         protected $mDiffLang;
 145
 146         /** @var bool Have the revisions IDs been loaded */
 147         private $mRevisionsIdsLoaded = false;
 148
 149         /** @var bool Have the revisions been loaded */
 150         protected $mRevisionsLoaded = false;
 151
 152         /** @var int How many text blobs have been loaded, 0, 1 or 2? */
 153         protected $mTextLoaded = 0;
 154
 155         /**
 156          * Was the content overridden via setContent()?
 157          * If the content was overridden, most internal state (e.g. mOldid or mOldRev) should be ignored
 158          * and only mOldContent and mNewContent is reliable.
 159          * (Note that setRevisions() does not set this flag as in that case all properties are
 160          * overriden and remain consistent with each other, so no special handling is needed.)
 161          * @var bool
 162          */
 163         protected $isContentOverridden = false;
 164
 165         /** @var bool Was the diff fetched from cache? */
 166         protected $mCacheHit = false;
 167
 168         /**
 169          * Set this to true to add debug info to the HTML output.
 170          * Warning: this may cause RSS readers to spuriously mark articles as "new"
 171          * (T22601)
 172          */
 173         public $enableDebugComment = false;
 174
 175         /** @var bool If true, line X is not displayed when X is 1, for example
 176          *    to increase readability and conserve space with many small diffs.
 177          */
 178         protected $mReducedLineNumbers = false;
 179
 180         /** @var string Link to action=markpatrolled */
 181         protected $mMarkPatrolledLink = null;
 182
 183         /** @var bool Show rev_deleted content if allowed */
 184         protected $unhide = false;
 185
 186         /** @var bool Refresh the diff cache */
 187         protected $mRefreshCache = false;
 188
 189         /** @var SlotDiffRenderer[] DifferenceEngine classes for the slots, keyed by role name. */
 190         protected $slotDiffRenderers = null;
 191
 192         /**
 193          * Temporary hack for B/C while slot diff related methods of DifferenceEngine are being
 194          * deprecated. When true, we are inside a DifferenceEngineSlotDiffRenderer and
 195          * $slotDiffRenderers should not be used.
 196          * @var bool
 197          */
 198         protected $isSlotDiffRenderer = false;
 199
 200         /** #@- */
 201
 202         /**
 203          * @param IContextSource|null $context Context to use, anything else will be ignored
 204          * @param int $old Old ID we want to show and diff with.
 205          * @param string|int $new Either revision ID or 'prev' or 'next'. Default: 0.
 206          * @param int $rcid Deprecated, no longer used!
 207          * @param bool $refreshCache If set, refreshes the diff cache
 208          * @param bool $unhide If set, allow viewing deleted revs
 209          */
 210         public function __construct( $context = null, $old = 0, $new = 0, $rcid = 0,
 211                 $refreshCache = false, $unhide = false
 212         ) {
 213                 $this->deprecatePublicProperty( 'mOldid', '1.32', __CLASS__ );
 214                 $this->deprecatePublicProperty( 'mNewid', '1.32', __CLASS__ );
 215                 $this->deprecatePublicProperty( 'mOldRev', '1.32', __CLASS__ );
 216                 $this->deprecatePublicProperty( 'mNewRev', '1.32', __CLASS__ );
 217                 $this->deprecatePublicProperty( 'mOldPage', '1.32', __CLASS__ );
 218                 $this->deprecatePublicProperty( 'mNewPage', '1.32', __CLASS__ );
 219                 $this->deprecatePublicProperty( 'mOldContent', '1.32', __CLASS__ );
 220                 $this->deprecatePublicProperty( 'mNewContent', '1.32', __CLASS__ );
 221                 $this->deprecatePublicProperty( 'mRevisionsLoaded', '1.32', __CLASS__ );
 222                 $this->deprecatePublicProperty( 'mTextLoaded', '1.32', __CLASS__ );
 223                 $this->deprecatePublicProperty( 'mCacheHit', '1.32', __CLASS__ );
 224
 225                 if ( $context instanceof IContextSource ) {
 226                         $this->setContext( $context );
 227                 }
 228
 229                 wfDebug( "DifferenceEngine old '$old' new '$new' rcid '$rcid'\n" );
 230
 231                 $this->mOldid = $old;
 232                 $this->mNewid = $new;
 233                 $this->mRefreshCache = $refreshCache;
 234                 $this->unhide = $unhide;
 235         }
 236
 237         /**
 238          * @return SlotDiffRenderer[] Diff renderers for each slot, keyed by role name.
 239          *   Includes slots only present in one of the revisions.
 240          */
 241         protected function getSlotDiffRenderers() {
 242                 if ( $this->isSlotDiffRenderer ) {
 243                         throw new LogicException( __METHOD__ . ' called in slot diff renderer mode' );
 244                 }
 245
 246                 if ( $this->slotDiffRenderers === null ) {
 247                         if ( !$this->loadRevisionData() ) {
 248                                 return [];
 249                         }
 250
 251                         $slotContents = $this->getSlotContents();
 252                         $this->slotDiffRenderers = array_map( function ( $contents ) {
 253                                 /** @var Content $content */
 254                                 $content = $contents['new'] ?: $contents['old'];
 255                                 return $content->getContentHandler()->getSlotDiffRenderer( $this->getContext() );
 256                         }, $slotContents );
 257                 }
 258                 return $this->slotDiffRenderers;
 259         }
 260
 261         /**
 262          * Mark this DifferenceEngine as a slot renderer (as opposed to a page renderer).
 263          * This is used in legacy mode when the DifferenceEngine is wrapped in a
 264          * DifferenceEngineSlotDiffRenderer.
 265          * @internal For use by DifferenceEngineSlotDiffRenderer only.
 266          */
 267         public function markAsSlotDiffRenderer() {
 268                 $this->isSlotDiffRenderer = true;
 269         }
 270
 271         /**
 272          * Get the old and new content objects for all slots.
 273          * This method does not do any permission checks.
 274          * @return array [ role => [ 'old' => SlotRecord|null, 'new' => SlotRecord|null ], ... ]
 275          */
 276         protected function getSlotContents() {
 277                 if ( $this->isContentOverridden ) {
 278                         return [
 279                                 SlotRecord::MAIN => [
 280                                         'old' => $this->mOldContent,
 281                                         'new' => $this->mNewContent,
 282                                 ]
 283                         ];
 284                 } elseif ( !$this->loadRevisionData() ) {
 285                         return [];
 286                 }
 287
 288                 $newSlots = $this->mNewRev->getRevisionRecord()->getSlots()->getSlots();
 289                 if ( $this->mOldRev ) {
 290                         $oldSlots = $this->mOldRev->getRevisionRecord()->getSlots()->getSlots();
 291                 } else {
 292                         $oldSlots = [];
 293                 }
 294                 // The order here will determine the visual order of the diff. The current logic is
 295                 // slots of the new revision first in natural order, then deleted ones. This is ad hoc
 296                 // and should not be relied on - in the future we may want the ordering to depend
 297                 // on the page type.
 298                 $roles = array_merge( array_keys( $newSlots ), array_keys( $oldSlots ) );
 299
 300                 $slots = [];
 301                 foreach ( $roles as $role ) {
 302                         $slots[$role] = [
 303                                 'old' => isset( $oldSlots[$role] ) ? $oldSlots[$role]->getContent() : null,
 304                                 'new' => isset( $newSlots[$role] ) ? $newSlots[$role]->getContent() : null,
 305                         ];
 306                 }
 307                 // move main slot to front
 308                 if ( isset( $slots[SlotRecord::MAIN] ) ) {
 309                         $slots = [ SlotRecord::MAIN => $slots[SlotRecord::MAIN] ] + $slots;
 310                 }
 311                 return $slots;
 312         }
 313
 314         public function getTitle() {
 315                 // T202454 avoid errors when there is no title
 316                 return parent::getTitle() ?: Title::makeTitle( NS_SPECIAL, 'BadTitle/DifferenceEngine' );
 317         }
 318
 319         /**
 320          * Set reduced line numbers mode.
 321          * When set, line X is not displayed when X is 1, for example to increase readability and
 322          * conserve space with many small diffs.
 323          * @param bool $value
 324          */
 325         public function setReducedLineNumbers( $value = true ) {
 326                 $this->mReducedLineNumbers = $value;
 327         }
 328
 329         /**
 330          * Get the language of the difference engine, defaults to page content language
 331          *
 332          * @return Language
 333          */
 334         public function getDiffLang() {
 335                 if ( $this->mDiffLang === null ) {
 336                         # Default language in which the diff text is written.
 337                         $this->mDiffLang = $this->getTitle()->getPageLanguage();
 338                 }
 339
 340                 return $this->mDiffLang;
 341         }
 342
 343         /**
 344          * @return bool
 345          */
 346         public function wasCacheHit() {
 347                 return $this->mCacheHit;
 348         }
 349
 350         /**
 351          * Get the ID of old revision (left pane) of the diff. 0 for the revision
 352          * previous to getNewid(), false if the old revision does not exist, null
 353          * if it's unsaved.
 354          * To get a real revision ID instead of 0, call loadRevisionData() first.
 355          * @return int|false|null
 356          */
 357         public function getOldid() {
 358                 $this->loadRevisionIds();
 359
 360                 return $this->mOldid;
 361         }
 362
 363         /**
 364          * Get the ID of new revision (right pane) of the diff. 0 for the current revision,
 365          * false if the new revision does not exist, null if it's unsaved.
 366          * To get a real revision ID instead of 0, call loadRevisionData() first.
 367          * @return int|false|null
 368          */
 369         public function getNewid() {
 370                 $this->loadRevisionIds();
 371
 372                 return $this->mNewid;
 373         }
 374
 375         /**
 376          * Get the left side of the diff.
 377          * Could be null when the first revision of the page is diffed to 'prev' (or in the case of
 378          * load failure).
 379          * @return RevisionRecord|null
 380          */
 381         public function getOldRevision() {
 382                 return $this->mOldRev ? $this->mOldRev->getRevisionRecord() : null;
 383         }
 384
 385         /**
 386          * Get the right side of the diff.
 387          * Should not be null but can still happen in the case of load failure.
 388          * @return RevisionRecord|null
 389          */
 390         public function getNewRevision() {
 391                 return $this->mNewRev ? $this->mNewRev->getRevisionRecord() : null;
 392         }
 393
 394         /**
 395          * Look up a special:Undelete link to the given deleted revision id,
 396          * as a workaround for being unable to load deleted diffs in currently.
 397          *
 398          * @param int $id Revision ID
 399          *
 400          * @return string|bool Link HTML or false
 401          */
 402         public function deletedLink( $id ) {
 403                 $permissionManager = MediaWikiServices::getInstance()->getPermissionManager();
 404                 if ( $permissionManager->userHasRight( $this->getUser(), 'deletedhistory' ) ) {
 405                         $dbr = wfGetDB( DB_REPLICA );
 406                         $arQuery = Revision::getArchiveQueryInfo();
 407                         $row = $dbr->selectRow(
 408                                 $arQuery['tables'],
 409                                 array_merge( $arQuery['fields'], [ 'ar_namespace', 'ar_title' ] ),
 410                                 [ 'ar_rev_id' => $id ],
 411                                 __METHOD__,
 412                                 [],
 413                                 $arQuery['joins']
 414                         );
 415                         if ( $row ) {
 416                                 $rev = Revision::newFromArchiveRow( $row );
 417                                 $title = Title::makeTitleSafe( $row->ar_namespace, $row->ar_title );
 418
 419                                 return SpecialPage::getTitleFor( 'Undelete' )->getFullURL( [
 420                                         'target' => $title->getPrefixedText(),
 421                                         'timestamp' => $rev->getTimestamp()
 422                                 ] );
 423                         }
 424                 }
 425
 426                 return false;
 427         }
 428
 429         /**
 430          * Build a wikitext link toward a deleted revision, if viewable.
 431          *
 432          * @param int $id Revision ID
 433          *
 434          * @return string Wikitext fragment
 435          */
 436         public function deletedIdMarker( $id ) {
 437                 $link = $this->deletedLink( $id );
 438                 if ( $link ) {
 439                         return "[$link $id]";
 440                 } else {
 441                         return (string)$id;
 442                 }
 443         }
 444
 445         private function showMissingRevision() {
 446                 $out = $this->getOutput();
 447
 448                 $missing = [];
 449                 if ( $this->mOldRev === null ||
 450                         ( $this->mOldRev && $this->mOldContent === null )
 451                 ) {
 452                         $missing[] = $this->deletedIdMarker( $this->mOldid );
 453                 }
 454                 if ( $this->mNewRev === null ||
 455                         ( $this->mNewRev && $this->mNewContent === null )
 456                 ) {
 457                         $missing[] = $this->deletedIdMarker( $this->mNewid );
 458                 }
 459
 460                 $out->setPageTitle( $this->msg( 'errorpagetitle' ) );
 461                 $msg = $this->msg( 'difference-missing-revision' )
 462                         ->params( $this->getLanguage()->listToText( $missing ) )
 463                         ->numParams( count( $missing ) )
 464                         ->parseAsBlock();
 465                 $out->addHTML( $msg );
 466         }
 467
 468         public function showDiffPage( $diffOnly = false ) {
 469                 # Allow frames except in certain special cases
 470                 $out = $this->getOutput();
 471                 $out->allowClickjacking();
 472                 $out->setRobotPolicy( 'noindex,nofollow' );
 473
 474                 // Allow extensions to add any extra output here
 475                 Hooks::run( 'DifferenceEngineShowDiffPage', [ $out ] );
 476
 477                 if ( !$this->loadRevisionData() ) {
 478                         if ( Hooks::run( 'DifferenceEngineShowDiffPageMaybeShowMissingRevision', [ $this ] ) ) {
 479                                 $this->showMissingRevision();
 480                         }
 481                         return;
 482                 }
 483
 484                 $user = $this->getUser();
 485                 $permErrors = [];
 486                 if ( $this->mNewPage ) {
 487                         $permErrors = $this->mNewPage->getUserPermissionsErrors( 'read', $user );
 488                 }
 489                 if ( $this->mOldPage ) {
 490                         $permErrors = wfMergeErrorArrays( $permErrors,
 491                                 $this->mOldPage->getUserPermissionsErrors( 'read', $user ) );
 492                 }
 493                 if ( count( $permErrors ) ) {
 494                         throw new PermissionsError( 'read', $permErrors );
 495                 }
 496
 497                 $rollback = '';
 498
 499                 $query = [];
 500                 # Carry over 'diffonly' param via navigation links
 501                 if ( $diffOnly != $user->getBoolOption( 'diffonly' ) ) {
 502                         $query['diffonly'] = $diffOnly;
 503                 }
 504                 # Cascade unhide param in links for easy deletion browsing
 505                 if ( $this->unhide ) {
 506                         $query['unhide'] = 1;
 507                 }
 508
 509                 # Check if one of the revisions is deleted/suppressed
 510                 $deleted = $suppressed = false;
 511                 $allowed = $this->mNewRev->userCan( RevisionRecord::DELETED_TEXT, $user );
 512
 513                 $revisionTools = [];
 514
 515                 # mOldRev is false if the difference engine is called with a "vague" query for
 516                 # a diff between a version V and its previous version V' AND the version V
 517                 # is the first version of that article. In that case, V' does not exist.
 518                 if ( $this->mOldRev === false ) {
 519                         if ( $this->mNewPage ) {
 520                                 $out->setPageTitle( $this->msg( 'difference-title', $this->mNewPage->getPrefixedText() ) );
 521                         }
 522                         $samePage = true;
 523                         $oldHeader = '';
 524                         // Allow extensions to change the $oldHeader variable
 525                         Hooks::run( 'DifferenceEngineOldHeaderNoOldRev', [ &$oldHeader ] );
 526                 } else {
 527                         Hooks::run( 'DiffViewHeader', [ $this, $this->mOldRev, $this->mNewRev ] );
 528
 529                         if ( !$this->mOldPage || !$this->mNewPage ) {
 530                                 // XXX say something to the user?
 531                                 $samePage = false;
 532                         } elseif ( $this->mNewPage->equals( $this->mOldPage ) ) {
 533                                 $out->setPageTitle( $this->msg( 'difference-title', $this->mNewPage->getPrefixedText() ) );
 534                                 $samePage = true;
 535                         } else {
 536                                 $out->setPageTitle( $this->msg( 'difference-title-multipage',
 537                                         $this->mOldPage->getPrefixedText(), $this->mNewPage->getPrefixedText() ) );
 538                                 $out->addSubtitle( $this->msg( 'difference-multipage' ) );
 539                                 $samePage = false;
 540                         }
 541
 542                         $permissionManager = MediaWikiServices::getInstance()->getPermissionManager();
 543
 544                         if ( $samePage && $this->mNewPage && $permissionManager->quickUserCan(
 545                                 'edit', $user, $this->mNewPage
 546                         ) ) {
 547                                 if ( $this->mNewRev->isCurrent() && $permissionManager->quickUserCan(
 548                                         'rollback', $user, $this->mNewPage
 549                                 ) ) {
 550                                         $rollbackLink = Linker::generateRollback( $this->mNewRev, $this->getContext(),
 551                                                 [ 'noBrackets' ] );
 552                                         if ( $rollbackLink ) {
 553                                                 $out->preventClickjacking();
 554                                                 $rollback = "\u{00A0}\u{00A0}\u{00A0}" . $rollbackLink;
 555                                         }
 556                                 }
 557
 558                                 if ( $this->userCanEdit( $this->mOldRev ) &&
 559                                         $this->userCanEdit( $this->mNewRev )
 560                                 ) {
 561                                         $undoLink = Html::element( 'a', [
 562                                                         'href' => $this->mNewPage->getLocalURL( [
 563                                                                 'action' => 'edit',
 564                                                                 'undoafter' => $this->mOldid,
 565                                                                 'undo' => $this->mNewid
 566                                                         ] ),
 567                                                         'title' => Linker::titleAttrib( 'undo' ),
 568                                                 ],
 569                                                 $this->msg( 'editundo' )->text()
 570                                         );
 571                                         $revisionTools['mw-diff-undo'] = $undoLink;
 572                                 }
 573                         }
 574
 575                         # Make "previous revision link"
 576                         if ( $samePage && $this->mOldPage && $this->mOldRev->getPrevious() ) {
 577                                 $prevlink = Linker::linkKnown(
 578                                         $this->mOldPage,
 579                                         $this->msg( 'previousdiff' )->escaped(),
 580                                         [ 'id' => 'differences-prevlink' ],
 581                                         [ 'diff' => 'prev', 'oldid' => $this->mOldid ] + $query
 582                                 );
 583                         } else {
 584                                 $prevlink = "\u{00A0}";
 585                         }
 586
 587                         if ( $this->mOldRev->isMinor() ) {
 588                                 $oldminor = ChangesList::flag( 'minor' );
 589                         } else {
 590                                 $oldminor = '';
 591                         }
 592
 593                         $ldel = $this->revisionDeleteLink( $this->mOldRev );
 594                         $oldRevisionHeader = $this->getRevisionHeader( $this->mOldRev, 'complete' );
 595                         $oldChangeTags = ChangeTags::formatSummaryRow( $this->mOldTags, 'diff', $this->getContext() );
 596
 597                         $oldHeader = '<div id="mw-diff-otitle1"><strong>' . $oldRevisionHeader . '</strong></div>' .
 598                                 '<div id="mw-diff-otitle2">' .
 599                                 Linker::revUserTools( $this->mOldRev, !$this->unhide ) . '</div>' .
 600                                 '<div id="mw-diff-otitle3">' . $oldminor .
 601                                 Linker::revComment( $this->mOldRev, !$diffOnly, !$this->unhide ) . $ldel . '</div>' .
 602                                 '<div id="mw-diff-otitle5">' . $oldChangeTags[0] . '</div>' .
 603                                 '<div id="mw-diff-otitle4">' . $prevlink . '</div>';
 604
 605                         // Allow extensions to change the $oldHeader variable
 606                         Hooks::run( 'DifferenceEngineOldHeader', [ $this, &$oldHeader, $prevlink, $oldminor,
 607                                 $diffOnly, $ldel, $this->unhide ] );
 608
 609                         if ( $this->mOldRev->isDeleted( RevisionRecord::DELETED_TEXT ) ) {
 610                                 $deleted = true; // old revisions text is hidden
 611                                 if ( $this->mOldRev->isDeleted( RevisionRecord::DELETED_RESTRICTED ) ) {
 612                                         $suppressed = true; // also suppressed
 613                                 }
 614                         }
 615
 616                         # Check if this user can see the revisions
 617                         if ( !$this->mOldRev->userCan( RevisionRecord::DELETED_TEXT, $user ) ) {
 618                                 $allowed = false;
 619                         }
 620                 }
 621
 622                 $out->addJsConfigVars( [
 623                         'wgDiffOldId' => $this->mOldid,
 624                         'wgDiffNewId' => $this->mNewid,
 625                 ] );
 626
 627                 # Make "next revision link"
 628                 # Skip next link on the top revision
 629                 if ( $samePage && $this->mNewPage && !$this->mNewRev->isCurrent() ) {
 630                         $nextlink = Linker::linkKnown(
 631                                 $this->mNewPage,
 632                                 $this->msg( 'nextdiff' )->escaped(),
 633                                 [ 'id' => 'differences-nextlink' ],
 634                                 [ 'diff' => 'next', 'oldid' => $this->mNewid ] + $query
 635                         );
 636                 } else {
 637                         $nextlink = "\u{00A0}";
 638                 }
 639
 640                 if ( $this->mNewRev->isMinor() ) {
 641                         $newminor = ChangesList::flag( 'minor' );
 642                 } else {
 643                         $newminor = '';
 644                 }
 645
 646                 # Handle RevisionDelete links...
 647                 $rdel = $this->revisionDeleteLink( $this->mNewRev );
 648
 649                 # Allow extensions to define their own revision tools
 650                 Hooks::run( 'DiffRevisionTools',
 651                         [ $this->mNewRev, &$revisionTools, $this->mOldRev, $user ] );
 652                 $formattedRevisionTools = [];
 653                 // Put each one in parentheses (poor man's button)
 654                 foreach ( $revisionTools as $key => $tool ) {
 655                         $toolClass = is_string( $key ) ? $key : 'mw-diff-tool';
 656                         $element = Html::rawElement(
 657                                 'span',
 658                                 [ 'class' => $toolClass ],
 659                                 $this->msg( 'parentheses' )->rawParams( $tool )->escaped()
 660                         );
 661                         $formattedRevisionTools[] = $element;
 662                 }
 663                 $newRevisionHeader = $this->getRevisionHeader( $this->mNewRev, 'complete' ) .
 664                         ' ' . implode( ' ', $formattedRevisionTools );
 665                 $newChangeTags = ChangeTags::formatSummaryRow( $this->mNewTags, 'diff', $this->getContext() );
 666
 667                 $newHeader = '<div id="mw-diff-ntitle1"><strong>' . $newRevisionHeader . '</strong></div>' .
 668                         '<div id="mw-diff-ntitle2">' . Linker::revUserTools( $this->mNewRev, !$this->unhide ) .
 669                         " $rollback</div>" .
 670                         '<div id="mw-diff-ntitle3">' . $newminor .
 671                         Linker::revComment( $this->mNewRev, !$diffOnly, !$this->unhide ) . $rdel . '</div>' .
 672                         '<div id="mw-diff-ntitle5">' . $newChangeTags[0] . '</div>' .
 673                         '<div id="mw-diff-ntitle4">' . $nextlink . $this->markPatrolledLink() . '</div>';
 674
 675                 // Allow extensions to change the $newHeader variable
 676                 Hooks::run( 'DifferenceEngineNewHeader', [ $this, &$newHeader, $formattedRevisionTools,
 677                         $nextlink, $rollback, $newminor, $diffOnly, $rdel, $this->unhide ] );
 678
 679                 if ( $this->mNewRev->isDeleted( RevisionRecord::DELETED_TEXT ) ) {
 680                         $deleted = true; // new revisions text is hidden
 681                         if ( $this->mNewRev->isDeleted( RevisionRecord::DELETED_RESTRICTED ) ) {
 682                                 $suppressed = true; // also suppressed
 683                         }
 684                 }
 685
 686                 # If the diff cannot be shown due to a deleted revision, then output
 687                 # the diff header and links to unhide (if available)...
 688                 if ( $deleted && ( !$this->unhide || !$allowed ) ) {
 689                         $this->showDiffStyle();
 690                         $multi = $this->getMultiNotice();
 691                         $out->addHTML( $this->addHeader( '', $oldHeader, $newHeader, $multi ) );
 692                         if ( !$allowed ) {
 693                                 $msg = $suppressed ? 'rev-suppressed-no-diff' : 'rev-deleted-no-diff';
 694                                 # Give explanation for why revision is not visible
 695                                 $out->wrapWikiMsg( "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n",
 696                                         [ $msg ] );
 697                         } else {
 698                                 # Give explanation and add a link to view the diff...
 699                                 $query = $this->getRequest()->appendQueryValue( 'unhide', '1' );
 700                                 $link = $this->getTitle()->getFullURL( $query );
 701                                 $msg = $suppressed ? 'rev-suppressed-unhide-diff' : 'rev-deleted-unhide-diff';
 702                                 $out->wrapWikiMsg(
 703                                         "<div id='mw-$msg' class='mw-warning plainlinks'>\n$1\n</div>\n",
 704                                         [ $msg, $link ]
 705                                 );
 706                         }
 707                 # Otherwise, output a regular diff...
 708                 } else {
 709                         # Add deletion notice if the user is viewing deleted content
 710                         $notice = '';
 711                         if ( $deleted ) {
 712                                 $msg = $suppressed ? 'rev-suppressed-diff-view' : 'rev-deleted-diff-view';
 713                                 $notice = "<div id='mw-$msg' class='mw-warning plainlinks'>\n" .
 714                                         $this->msg( $msg )->parse() .
 715                                         "</div>\n";
 716                         }
 717                         $this->showDiff( $oldHeader, $newHeader, $notice );
 718                         if ( !$diffOnly ) {
 719                                 $this->renderNewRevision();
 720                         }
 721                 }
 722         }
 723
 724         /**
 725          * Build a link to mark a change as patrolled.
 726          *
 727          * Returns empty string if there's either no revision to patrol or the user is not allowed to.
 728          * Side effect: When the patrol link is build, this method will call
 729          * OutputPage::preventClickjacking() and load mediawiki.page.patrol.ajax.
 730          *
 731          * @return string HTML or empty string
 732          */
 733         public function markPatrolledLink() {
 734                 if ( $this->mMarkPatrolledLink === null ) {
 735                         $linkInfo = $this->getMarkPatrolledLinkInfo();
 736                         // If false, there is no patrol link needed/allowed
 737                         if ( !$linkInfo || !$this->mNewPage ) {
 738                                 $this->mMarkPatrolledLink = '';
 739                         } else {
 740                                 $this->mMarkPatrolledLink = ' <span class="patrollink" data-mw="interface">[' .
 741                                         Linker::linkKnown(
 742                                                 $this->mNewPage,
 743                                                 $this->msg( 'markaspatrolleddiff' )->escaped(),
 744                                                 [],
 745                                                 [
 746                                                         'action' => 'markpatrolled',
 747                                                         'rcid' => $linkInfo['rcid'],
 748                                                 ]
 749                                         ) . ']</span>';
 750                                 // Allow extensions to change the markpatrolled link
 751                                 Hooks::run( 'DifferenceEngineMarkPatrolledLink', [ $this,
 752                                         &$this->mMarkPatrolledLink, $linkInfo['rcid'] ] );
 753                         }
 754                 }
 755                 return $this->mMarkPatrolledLink;
 756         }
 757
 758         /**
 759          * Returns an array of meta data needed to build a "mark as patrolled" link and
 760          * adds the mediawiki.page.patrol.ajax to the output.
 761          *
 762          * @return array|false An array of meta data for a patrol link (rcid only)
 763          *  or false if no link is needed
 764          */
 765         protected function getMarkPatrolledLinkInfo() {
 766                 $user = $this->getUser();
 767                 $config = $this->getConfig();
 768                 $permissionManager = MediaWikiServices::getInstance()->getPermissionManager();
 769
 770                 // Prepare a change patrol link, if applicable
 771                 if (
 772                         // Is patrolling enabled and the user allowed to?
 773                         $config->get( 'UseRCPatrol' ) &&
 774                         $this->mNewPage &&
 775                         $permissionManager->quickUserCan( 'patrol', $user, $this->mNewPage ) &&
 776                         // Only do this if the revision isn't more than 6 hours older
 777                         // than the Max RC age (6h because the RC might not be cleaned out regularly)
 778                         RecentChange::isInRCLifespan( $this->mNewRev->getTimestamp(), 21600 )
 779                 ) {
 780                         // Look for an unpatrolled change corresponding to this diff
 781                         $db = wfGetDB( DB_REPLICA );
 782                         $change = RecentChange::newFromConds(
 783                                 [
 784                                         'rc_timestamp' => $db->timestamp( $this->mNewRev->getTimestamp() ),
 785                                         'rc_this_oldid' => $this->mNewid,
 786                                         'rc_patrolled' => RecentChange::PRC_UNPATROLLED
 787                                 ],
 788                                 __METHOD__
 789                         );
 790
 791                         if ( $change && !$change->getPerformer()->equals( $user ) ) {
 792                                 $rcid = $change->getAttribute( 'rc_id' );
 793                         } else {
 794                                 // None found or the page has been created by the current user.
 795                                 // If the user could patrol this it already would be patrolled
 796                                 $rcid = 0;
 797                         }
 798
 799                         // Allow extensions to possibly change the rcid here
 800                         // For example the rcid might be set to zero due to the user
 801                         // being the same as the performer of the change but an extension
 802                         // might still want to show it under certain conditions
 803                         Hooks::run( 'DifferenceEngineMarkPatrolledRCID', [ &$rcid, $this, $change, $user ] );
 804
 805                         // Build the link
 806                         if ( $rcid ) {
 807                                 $this->getOutput()->preventClickjacking();
 808                                 if ( $permissionManager->userHasRight( $user, 'writeapi' ) ) {
 809                                         $this->getOutput()->addModules( 'mediawiki.page.patrol.ajax' );
 810                                 }
 811
 812                                 return [
 813                                         'rcid' => $rcid,
 814                                 ];
 815                         }
 816                 }
 817
 818                 // No mark as patrolled link applicable
 819                 return false;
 820         }
 821
 822         /**
 823          * @param Revision $rev
 824          *
 825          * @return string
 826          */
 827         protected function revisionDeleteLink( $rev ) {
 828                 $link = Linker::getRevDeleteLink( $this->getUser(), $rev, $rev->getTitle() );
 829                 if ( $link !== '' ) {
 830                         $link = "\u{00A0}\u{00A0}\u{00A0}" . $link . ' ';
 831                 }
 832
 833                 return $link;
 834         }
 835
 836         /**
 837          * Show the new revision of the page.
 838          *
 839          * @note Not supported after calling setContent().
 840          */
 841         public function renderNewRevision() {
 842                 if ( $this->isContentOverridden ) {
 843                         // The code below only works with a Revision object. We could construct a fake revision
 844                         // (here or in setContent), but since this does not seem needed at the moment,
 845                         // we'll just fail for now.
 846                         throw new LogicException(
 847                                 __METHOD__
 848                                 . ' is not supported after calling setContent(). Use setRevisions() instead.'
 849                         );
 850                 }
 851
 852                 $out = $this->getOutput();
 853                 $revHeader = $this->getRevisionHeader( $this->mNewRev );
 854                 # Add "current version as of X" title
 855                 $out->addHTML( "<hr class='diff-hr' id='mw-oldid' />
 856                 <h2 class='diff-currentversion-title'>{$revHeader}</h2>\n" );
 857                 # Page content may be handled by a hooked call instead...
 858                 if ( Hooks::run( 'ArticleContentOnDiff', [ $this, $out ] ) ) {
 859                         $this->loadNewText();
 860                         if ( !$this->mNewPage ) {
 861                                 // New revision is unsaved; bail out.
 862                                 // TODO in theory rendering the new revision is a meaningful thing to do
 863                                 // even if it's unsaved, but a lot of untangling is required to do it safely.
 864                                 return;
 865                         }
 866
 867                         $out->setRevisionId( $this->mNewid );
 868                         $out->setRevisionTimestamp( $this->mNewRev->getTimestamp() );
 869                         $out->setArticleFlag( true );
 870
 871                         if ( !Hooks::run( 'ArticleRevisionViewCustom',
 872                                 [ $this->mNewRev->getRevisionRecord(), $this->mNewPage, $out ] )
 873                         ) {
 874                                 // Handled by extension
 875                                 // NOTE: sync with hooks called in Article::view()
 876                         } elseif ( !Hooks::run( 'ArticleContentViewCustom',
 877                                 [ $this->mNewContent, $this->mNewPage, $out ], '1.32' )
 878                         ) {
 879                                 // Handled by extension
 880                                 // NOTE: sync with hooks called in Article::view()
 881                         } else {
 882                                 // Normal page
 883                                 if ( $this->getTitle()->equals( $this->mNewPage ) ) {
 884                                         // If the Title stored in the context is the same as the one
 885                                         // of the new revision, we can use its associated WikiPage
 886                                         // object.
 887                                         $wikiPage = $this->getWikiPage();
 888                                 } else {
 889                                         // Otherwise we need to create our own WikiPage object
 890                                         $wikiPage = WikiPage::factory( $this->mNewPage );
 891                                 }
 892
 893                                 $parserOutput = $this->getParserOutput( $wikiPage, $this->mNewRev );
 894
 895                                 # WikiPage::getParserOutput() should not return false, but just in case
 896                                 if ( $parserOutput ) {
 897                                         // Allow extensions to change parser output here
 898                                         if ( Hooks::run( 'DifferenceEngineRenderRevisionAddParserOutput',
 899                                                 [ $this, $out, $parserOutput, $wikiPage ] )
 900                                         ) {
 901                                                 $out->addParserOutput( $parserOutput, [
 902                                                         'enableSectionEditLinks' => $this->mNewRev->isCurrent()
 903                                                                 && MediaWikiServices::getInstance()->getPermissionManager()->quickUserCan(
 904                                                                         'edit',
 905                                                                         $this->getUser(),
 906                                                                         $this->mNewRev->getTitle()
 907                                                                 )
 908                                                 ] );
 909                                         }
 910                                 }
 911                         }
 912                 }
 913
 914                 // Allow extensions to optionally not show the final patrolled link
 915                 if ( Hooks::run( 'DifferenceEngineRenderRevisionShowFinalPatrolLink' ) ) {
 916                         # Add redundant patrol link on bottom...
 917                         $out->addHTML( $this->markPatrolledLink() );
 918                 }
 919         }
 920
 921         /**
 922          * @param WikiPage $page
 923          * @param Revision $rev
 924          *
 925          * @return ParserOutput|bool False if the revision was not found
 926          */
 927         protected function getParserOutput( WikiPage $page, Revision $rev ) {
 928                 if ( !$rev->getId() ) {
 929                         // WikiPage::getParserOutput wants a revision ID. Passing 0 will incorrectly show
 930                         // the current revision, so fail instead. If need be, WikiPage::getParserOutput
 931                         // could be made to accept a Revision or RevisionRecord instead of the id.
 932                         return false;
 933                 }
 934
 935                 $parserOptions = $page->makeParserOptions( $this->getContext() );
 936                 $parserOutput = $page->getParserOutput( $parserOptions, $rev->getId() );
 937
 938                 return $parserOutput;
 939         }
 940
 941         /**
 942          * Get the diff text, send it to the OutputPage object
 943          * Returns false if the diff could not be generated, otherwise returns true
 944          *
 945          * @param string|bool $otitle Header for old text or false
 946          * @param string|bool $ntitle Header for new text or false
 947          * @param string $notice HTML between diff header and body
 948          *
 949          * @return bool
 950          */
 951         public function showDiff( $otitle, $ntitle, $notice = '' ) {
 952                 // Allow extensions to affect the output here
 953                 Hooks::run( 'DifferenceEngineShowDiff', [ $this ] );
 954
 955                 $diff = $this->getDiff( $otitle, $ntitle, $notice );
 956                 if ( $diff === false ) {
 957                         $this->showMissingRevision();
 958
 959                         return false;
 960                 } else {
 961                         $this->showDiffStyle();
 962                         $this->getOutput()->addHTML( $diff );
 963
 964                         return true;
 965                 }
 966         }
 967
 968         /**
 969          * Add style sheets for diff display.
 970          */
 971         public function showDiffStyle() {
 972                 if ( !$this->isSlotDiffRenderer ) {
 973                         $this->getOutput()->addModuleStyles( [
 974                                 'mediawiki.interface.helpers.styles',
 975                                 'mediawiki.diff.styles'
 976                         ] );
 977                         foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
 978                                 $slotDiffRenderer->addModules( $this->getOutput() );
 979                         }
 980                 }
 981         }
 982
 983         /**
 984          * Get complete diff table, including header
 985          *
 986          * @param string|bool $otitle Header for old text or false
 987          * @param string|bool $ntitle Header for new text or false
 988          * @param string $notice HTML between diff header and body
 989          *
 990          * @return mixed
 991          */
 992         public function getDiff( $otitle, $ntitle, $notice = '' ) {
 993                 $body = $this->getDiffBody();
 994                 if ( $body === false ) {
 995                         return false;
 996                 }
 997
 998                 $multi = $this->getMultiNotice();
 999                 // Display a message when the diff is empty
1000                 if ( $body === '' ) {
1001                         $notice .= '<div class="mw-diff-empty">' .
1002                                 $this->msg( 'diff-empty' )->parse() .
1003                                 "</div>\n";
1004                 }
1005
1006                 return $this->addHeader( $body, $otitle, $ntitle, $multi, $notice );
1007         }
1008
1009         /**
1010          * Get the diff table body, without header
1011          *
1012          * @return mixed (string/false)
1013          */
1014         public function getDiffBody() {
1015                 $this->mCacheHit = true;
1016                 // Check if the diff should be hidden from this user
1017                 if ( !$this->isContentOverridden ) {
1018                         if ( !$this->loadRevisionData() ) {
1019                                 return false;
1020                         } elseif ( $this->mOldRev &&
1021                                 !$this->mOldRev->userCan( RevisionRecord::DELETED_TEXT, $this->getUser() )
1022                         ) {
1023                                 return false;
1024                         } elseif ( $this->mNewRev &&
1025                                 !$this->mNewRev->userCan( RevisionRecord::DELETED_TEXT, $this->getUser() )
1026                         ) {
1027                                 return false;
1028                         }
1029                         // Short-circuit
1030                         if ( $this->mOldRev === false || ( $this->mOldRev && $this->mNewRev &&
1031                                 $this->mOldRev->getId() && $this->mOldRev->getId() == $this->mNewRev->getId() )
1032                         ) {
1033                                 if ( Hooks::run( 'DifferenceEngineShowEmptyOldContent', [ $this ] ) ) {
1034                                         return '';
1035                                 }
1036                         }
1037                 }
1038
1039                 // Cacheable?
1040                 $key = false;
1041                 $cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
1042                 if ( $this->mOldid && $this->mNewid ) {
1043                         // Check if subclass is still using the old way
1044                         // for backwards-compatibility
1045                         $key = $this->getDiffBodyCacheKey();
1046                         if ( $key === null ) {
1047                                 $key = $cache->makeKey( ...$this->getDiffBodyCacheKeyParams() );
1048                         }
1049
1050                         // Try cache
1051                         if ( !$this->mRefreshCache ) {
1052                                 $difftext = $cache->get( $key );
1053                                 if ( is_string( $difftext ) ) {
1054                                         wfIncrStats( 'diff_cache.hit' );
1055                                         $difftext = $this->localiseDiff( $difftext );
1056                                         $difftext .= "\n<!-- diff cache key $key -->\n";
1057
1058                                         return $difftext;
1059                                 }
1060                         } // don't try to load but save the result
1061                 }
1062                 $this->mCacheHit = false;
1063
1064                 // Loadtext is permission safe, this just clears out the diff
1065                 if ( !$this->loadText() ) {
1066                         return false;
1067                 }
1068
1069                 $difftext = '';
1070                 // We've checked for revdelete at the beginning of this method; it's OK to ignore
1071                 // read permissions here.
1072                 $slotContents = $this->getSlotContents();
1073                 foreach ( $this->getSlotDiffRenderers() as $role => $slotDiffRenderer ) {
1074                         $slotDiff = $slotDiffRenderer->getDiff( $slotContents[$role]['old'],
1075                                 $slotContents[$role]['new'] );
1076                         if ( $slotDiff && $role !== SlotRecord::MAIN ) {
1077                                 // FIXME: ask SlotRoleHandler::getSlotNameMessage
1078                                 $slotTitle = $role;
1079                                 $difftext .= $this->getSlotHeader( $slotTitle );
1080                         }
1081                         $difftext .= $slotDiff;
1082                 }
1083
1084                 // Avoid PHP 7.1 warning from passing $this by reference
1085                 $diffEngine = $this;
1086
1087                 // Save to cache for 7 days
1088                 if ( !Hooks::run( 'AbortDiffCache', [ &$diffEngine ] ) ) {
1089                         wfIncrStats( 'diff_cache.uncacheable' );
1090                 } elseif ( $key !== false && $difftext !== false ) {
1091                         wfIncrStats( 'diff_cache.miss' );
1092                         $cache->set( $key, $difftext, 7 * 86400 );
1093                 } else {
1094                         wfIncrStats( 'diff_cache.uncacheable' );
1095                 }
1096                 // localise line numbers and title attribute text
1097                 if ( $difftext !== false ) {
1098                         $difftext = $this->localiseDiff( $difftext );
1099                 }
1100
1101                 return $difftext;
1102         }
1103
1104         /**
1105          * Get the diff table body for one slot, without header
1106          *
1107          * @param string $role
1108          * @return string|false
1109          */
1110         public function getDiffBodyForRole( $role ) {
1111                 $diffRenderers = $this->getSlotDiffRenderers();
1112                 if ( !isset( $diffRenderers[$role] ) ) {
1113                         return false;
1114                 }
1115
1116                 $slotContents = $this->getSlotContents();
1117                 $slotDiff = $diffRenderers[$role]->getDiff( $slotContents[$role]['old'],
1118                         $slotContents[$role]['new'] );
1119                 if ( !$slotDiff ) {
1120                         return false;
1121                 }
1122
1123                 if ( $role !== SlotRecord::MAIN ) {
1124                         // TODO use human-readable role name at least
1125                         $slotTitle = $role;
1126                         $slotDiff = $this->getSlotHeader( $slotTitle ) . $slotDiff;
1127                 }
1128
1129                 return $this->localiseDiff( $slotDiff );
1130         }
1131
1132         /**
1133          * Get a slot header for inclusion in a diff body (as a table row).
1134          *
1135          * @param string $headerText The text of the header
1136          * @return string
1137          *
1138          */
1139         protected function getSlotHeader( $headerText ) {
1140                 // The old revision is missing on oldid=<first>&diff=prev; only 2 columns in that case.
1141                 $columnCount = $this->mOldRev ? 4 : 2;
1142                 $userLang = $this->getLanguage()->getHtmlCode();
1143                 return Html::rawElement( 'tr', [ 'class' => 'mw-diff-slot-header', 'lang' => $userLang ],
1144                         Html::element( 'th', [ 'colspan' => $columnCount ], $headerText ) );
1145         }
1146
1147         /**
1148          * Returns the cache key for diff body text or content.
1149          *
1150          * @deprecated since 1.31, use getDiffBodyCacheKeyParams() instead
1151          * @since 1.23
1152          *
1153          * @throws MWException
1154          * @return string|null
1155          */
1156         protected function getDiffBodyCacheKey() {
1157                 return null;
1158         }
1159
1160         /**
1161          * Get the cache key parameters
1162          *
1163          * Subclasses can replace the first element in the array to something
1164          * more specific to the type of diff (e.g. "inline-diff"), or append
1165          * if the cache should vary on more things. Overriding entirely should
1166          * be avoided.
1167          *
1168          * @since 1.31
1169          *
1170          * @return array
1171          * @throws MWException
1172          */
1173         protected function getDiffBodyCacheKeyParams() {
1174                 if ( !$this->mOldid || !$this->mNewid ) {
1175                         throw new MWException( 'mOldid and mNewid must be set to get diff cache key.' );
1176                 }
1177
1178                 $engine = $this->getEngine();
1179                 $params = [
1180                         'diff',
1181                         $engine,
1182                         self::DIFF_VERSION,
1183                         "old-{$this->mOldid}",
1184                         "rev-{$this->mNewid}"
1185                 ];
1186
1187                 if ( $engine === 'wikidiff2' ) {
1188                         $params[] = phpversion( 'wikidiff2' );
1189                 }
1190
1191                 if ( !$this->isSlotDiffRenderer ) {
1192                         foreach ( $this->getSlotDiffRenderers() as $slotDiffRenderer ) {
1193                                 $params = array_merge( $params, $slotDiffRenderer->getExtraCacheKeys() );
1194                         }
1195                 }
1196
1197                 return $params;
1198         }
1199
1200         /**
1201          * Implements DifferenceEngineSlotDiffRenderer::getExtraCacheKeys(). Only used when
1202          * DifferenceEngine is wrapped in DifferenceEngineSlotDiffRenderer.
1203          * @return array
1204          * @internal for use by DifferenceEngineSlotDiffRenderer only
1205          * @deprecated
1206          */
1207         public function getExtraCacheKeys() {
1208                 // This method is called when the DifferenceEngine is used for a slot diff. We only care
1209                 // about special things, not the revision IDs, which are added to the cache key by the
1210                 // page-level DifferenceEngine, and which might not have a valid value for this object.
1211                 $this->mOldid = 123456789;
1212                 $this->mNewid = 987654321;
1213
1214                 // This will repeat a bunch of unnecessary key fields for each slot. Not nice but harmless.
1215                 $cacheString = $this->getDiffBodyCacheKey();
1216                 if ( $cacheString ) {
1217                         return [ $cacheString ];
1218                 }
1219
1220                 $params = $this->getDiffBodyCacheKeyParams();
1221
1222                 // Try to get rid of the standard keys to keep the cache key human-readable:
1223                 // call the getDiffBodyCacheKeyParams implementation of the base class, and if
1224                 // the child class includes the same keys, drop them.
1225                 // Uses an obscure PHP feature where static calls to non-static methods are allowed
1226                 // as long as we are already in a non-static method of the same class, and the call context
1227                 // ($this) will be inherited.
1228                 // phpcs:ignore Squiz.Classes.SelfMemberReference.NotUsed
1229                 $standardParams = DifferenceEngine::getDiffBodyCacheKeyParams();
1230                 if ( array_slice( $params, 0, count( $standardParams ) ) === $standardParams ) {
1231                         $params = array_slice( $params, count( $standardParams ) );
1232                 }
1233
1234                 return $params;
1235         }
1236
1237         /**
1238          * Generate a diff, no caching.
1239          *
1240          * @since 1.21
1241          *
1242          * @param Content $old Old content
1243          * @param Content $new New content
1244          *
1245          * @throws Exception If old or new content is not an instance of TextContent.
1246          * @return bool|string
1247          *
1248          * @deprecated since 1.32, use a SlotDiffRenderer instead.
1249          */
1250         public function generateContentDiffBody( Content $old, Content $new ) {
1251                 $slotDiffRenderer = $new->getContentHandler()->getSlotDiffRenderer( $this->getContext() );
1252                 if (
1253                         $slotDiffRenderer instanceof DifferenceEngineSlotDiffRenderer
1254                         && $this->isSlotDiffRenderer
1255                 ) {
1256                         // Oops, we are just about to enter an infinite loop (the slot-level DifferenceEngine
1257                         // called a DifferenceEngineSlotDiffRenderer that wraps the same DifferenceEngine class).
1258                         // This will happen when a content model has no custom slot diff renderer, it does have
1259                         // a custom difference engine, but that does not override this method.
1260                         throw new Exception( get_class( $this ) . ': could not maintain backwards compatibility. '
1261                                 . 'Please use a SlotDiffRenderer.' );
1262                 }
1263                 return $slotDiffRenderer->getDiff( $old, $new ) . $this->getDebugString();
1264         }
1265
1266         /**
1267          * Generate a diff, no caching
1268          *
1269          * @param string $otext Old text, must be already segmented
1270          * @param string $ntext New text, must be already segmented
1271          *
1272          * @throws Exception If content handling for text content is configured in a way
1273          *   that makes maintaining B/C hard.
1274          * @return bool|string
1275          *
1276          * @deprecated since 1.32, use a TextSlotDiffRenderer instead.
1277          */
1278         public function generateTextDiffBody( $otext, $ntext ) {
1279                 $slotDiffRenderer = ContentHandler::getForModelID( CONTENT_MODEL_TEXT )
1280                         ->getSlotDiffRenderer( $this->getContext() );
1281                 if ( !( $slotDiffRenderer instanceof TextSlotDiffRenderer ) ) {
1282                         // Someone used the GetSlotDiffRenderer hook to replace the renderer.
1283                         // This is too unlikely to happen to bother handling properly.
1284                         throw new Exception( 'The slot diff renderer for text content should be a '
1285                                 . 'TextSlotDiffRenderer subclass' );
1286                 }
1287                 return $slotDiffRenderer->getTextDiff( $otext, $ntext ) . $this->getDebugString();
1288         }
1289
1290         /**
1291          * Process ExternalDiffEngine config and get a sane, usable engine
1292          *
1293          * @return bool|string 'wikidiff2', path to an executable, or false
1294          * @internal For use by this class and TextSlotDiffRenderer only.
1295          */
1296         public static function getEngine() {
1297                 $externalDiffEngine = MediaWikiServices::getInstance()->getMainConfig()
1298                         ->get( 'ExternalDiffEngine' );
1299
1300                 if ( $externalDiffEngine ) {
1301                         if ( is_string( $externalDiffEngine ) ) {
1302                                 if ( is_executable( $externalDiffEngine ) ) {
1303                                         return $externalDiffEngine;
1304                                 }
1305                                 wfDebug( 'ExternalDiffEngine config points to a non-executable, ignoring' );
1306                         } else {
1307                                 wfWarn( 'ExternalDiffEngine config is set to a non-string value, ignoring' );
1308                         }
1309                 }
1310
1311                 if ( function_exists( 'wikidiff2_do_diff' ) ) {
1312                         return 'wikidiff2';
1313                 }
1314
1315                 // Native PHP
1316                 return false;
1317         }
1318
1319         /**
1320          * Generates diff, to be wrapped internally in a logging/instrumentation
1321          *
1322          * @param string $otext Old text, must be already segmented
1323          * @param string $ntext New text, must be already segmented
1324          *
1325          * @throws Exception If content handling for text content is configured in a way
1326          *   that makes maintaining B/C hard.
1327          * @return bool|string
1328          *
1329          * @deprecated since 1.32, use a TextSlotDiffRenderer instead.
1330          */
1331         protected function textDiff( $otext, $ntext ) {
1332                 $slotDiffRenderer = ContentHandler::getForModelID( CONTENT_MODEL_TEXT )
1333                         ->getSlotDiffRenderer( $this->getContext() );
1334                 if ( !( $slotDiffRenderer instanceof TextSlotDiffRenderer ) ) {
1335                         // Someone used the GetSlotDiffRenderer hook to replace the renderer.
1336                         // This is too unlikely to happen to bother handling properly.
1337                         throw new Exception( 'The slot diff renderer for text content should be a '
1338                                 . 'TextSlotDiffRenderer subclass' );
1339                 }
1340                 return $slotDiffRenderer->getTextDiff( $otext, $ntext ) . $this->getDebugString();
1341         }
1342
1343         /**
1344          * Generate a debug comment indicating diff generating time,
1345          * server node, and generator backend.
1346          *
1347          * @param string $generator : What diff engine was used
1348          *
1349          * @return string
1350          */
1351         protected function debug( $generator = "internal" ) {
1352                 if ( !$this->enableDebugComment ) {
1353                         return '';
1354                 }
1355                 $data = [ $generator ];
1356                 if ( $this->getConfig()->get( 'ShowHostnames' ) ) {
1357                         $data[] = wfHostname();
1358                 }
1359                 $data[] = wfTimestamp( TS_DB );
1360
1361                 return "<!-- diff generator: " .
1362                         implode( " ", array_map( "htmlspecialchars", $data ) ) .
1363                         " -->\n";
1364         }
1365
1366         private function getDebugString() {
1367                 $engine = self::getEngine();
1368                 if ( $engine === 'wikidiff2' ) {
1369                         return $this->debug( 'wikidiff2' );
1370                 } elseif ( $engine === false ) {
1371                         return $this->debug( 'native PHP' );
1372                 } else {
1373                         return $this->debug( "external $engine" );
1374                 }
1375         }
1376
1377         /**
1378          * Localise diff output
1379          *
1380          * @param string $text
1381          * @return string
1382          */
1383         private function localiseDiff( $text ) {
1384                 $text = $this->localiseLineNumbers( $text );
1385                 if ( $this->getEngine() === 'wikidiff2' &&
1386                         version_compare( phpversion( 'wikidiff2' ), '1.5.1', '>=' )
1387                 ) {
1388                         $text = $this->addLocalisedTitleTooltips( $text );
1389                 }
1390                 return $text;
1391         }
1392
1393         /**
1394          * Replace line numbers with the text in the user's language
1395          *
1396          * @param string $text
1397          *
1398          * @return mixed
1399          */
1400         public function localiseLineNumbers( $text ) {
1401                 return preg_replace_callback(
1402                         '/<!--LINE (\d+)-->/',
1403                         [ $this, 'localiseLineNumbersCb' ],
1404                         $text
1405                 );
1406         }
1407
1408         public function localiseLineNumbersCb( $matches ) {
1409                 if ( $matches[1] === '1' && $this->mReducedLineNumbers ) {
1410                         return '';
1411                 }
1412
1413                 return $this->msg( 'lineno' )->numParams( $matches[1] )->escaped();
1414         }
1415
1416         /**
1417          * Add title attributes for tooltips on moved paragraph indicators
1418          *
1419          * @param string $text
1420          * @return string
1421          */
1422         private function addLocalisedTitleTooltips( $text ) {
1423                 return preg_replace_callback(
1424                         '/class="mw-diff-movedpara-(left|right)"/',
1425                         [ $this, 'addLocalisedTitleTooltipsCb' ],
1426                         $text
1427                 );
1428         }
1429
1430         /**
1431          * @param array $matches
1432          * @return string
1433          */
1434         private function addLocalisedTitleTooltipsCb( array $matches ) {
1435                 $key = $matches[1] === 'right' ?
1436                         'diff-paragraph-moved-toold' :
1437                         'diff-paragraph-moved-tonew';
1438                 return $matches[0] . ' title="' . $this->msg( $key )->escaped() . '"';
1439         }
1440
1441         /**
1442          * If there are revisions between the ones being compared, return a note saying so.
1443          *
1444          * @return string
1445          */
1446         public function getMultiNotice() {
1447                 // The notice only make sense if we are diffing two saved revisions of the same page.
1448                 if (
1449                         !$this->mOldRev || !$this->mNewRev
1450                         || !$this->mOldPage || !$this->mNewPage
1451                         || !$this->mOldPage->equals( $this->mNewPage )
1452                 ) {
1453                         return '';
1454                 }
1455
1456                 if ( $this->mOldRev->getTimestamp() > $this->mNewRev->getTimestamp() ) {
1457                         $oldRev = $this->mNewRev; // flip
1458                         $newRev = $this->mOldRev; // flip
1459                 } else { // normal case
1460                         $oldRev = $this->mOldRev;
1461                         $newRev = $this->mNewRev;
1462                 }
1463
1464                 // Sanity: don't show the notice if too many rows must be scanned
1465                 // @todo show some special message for that case
1466                 $nEdits = $this->mNewPage->countRevisionsBetween( $oldRev, $newRev, 1000 );
1467                 if ( $nEdits > 0 && $nEdits <= 1000 ) {
1468                         $limit = 100; // use diff-multi-manyusers if too many users
1469                         $users = $this->mNewPage->getAuthorsBetween( $oldRev, $newRev, $limit );
1470                         $numUsers = count( $users );
1471
1472                         if ( $numUsers == 1 && $users[0] == $newRev->getUserText( RevisionRecord::RAW ) ) {
1473                                 $numUsers = 0; // special case to say "by the same user" instead of "by one other user"
1474                         }
1475
1476                         return self::intermediateEditsMsg( $nEdits, $numUsers, $limit );
1477                 }
1478
1479                 return '';
1480         }
1481
1482         /**
1483          * Get a notice about how many intermediate edits and users there are
1484          *
1485          * @param int $numEdits
1486          * @param int $numUsers
1487          * @param int $limit
1488          *
1489          * @return string
1490          */
1491         public static function intermediateEditsMsg( $numEdits, $numUsers, $limit ) {
1492                 if ( $numUsers === 0 ) {
1493                         $msg = 'diff-multi-sameuser';
1494                 } elseif ( $numUsers > $limit ) {
1495                         $msg = 'diff-multi-manyusers';
1496                         $numUsers = $limit;
1497                 } else {
1498                         $msg = 'diff-multi-otherusers';
1499                 }
1500
1501                 return wfMessage( $msg )->numParams( $numEdits, $numUsers )->parse();
1502         }
1503
1504         /**
1505          * @param Revision $rev
1506          * @return bool whether the user can see and edit the revision.
1507          */
1508         private function userCanEdit( Revision $rev ) {
1509                 $user = $this->getUser();
1510
1511                 if ( !$rev->userCan( RevisionRecord::DELETED_TEXT, $user ) ) {
1512                         return false;
1513                 }
1514
1515                 return true;
1516         }
1517
1518         /**
1519          * Get a header for a specified revision.
1520          *
1521          * @param Revision $rev
1522          * @param string $complete 'complete' to get the header wrapped depending
1523          *        the visibility of the revision and a link to edit the page.
1524          *
1525          * @return string HTML fragment
1526          */
1527         public function getRevisionHeader( Revision $rev, $complete = '' ) {
1528                 $lang = $this->getLanguage();
1529                 $user = $this->getUser();
1530                 $revtimestamp = $rev->getTimestamp();
1531                 $timestamp = $lang->userTimeAndDate( $revtimestamp, $user );
1532                 $dateofrev = $lang->userDate( $revtimestamp, $user );
1533                 $timeofrev = $lang->userTime( $revtimestamp, $user );
1534
1535                 $header = $this->msg(
1536                         $rev->isCurrent() ? 'currentrev-asof' : 'revisionasof',
1537                         $timestamp,
1538                         $dateofrev,
1539                         $timeofrev
1540                 )->escaped();
1541
1542                 if ( $complete !== 'complete' ) {
1543                         return $header;
1544                 }
1545
1546                 $title = $rev->getTitle();
1547
1548                 $header = Linker::linkKnown( $title, $header, [],
1549                         [ 'oldid' => $rev->getId() ] );
1550
1551                 if ( $this->userCanEdit( $rev ) ) {
1552                         $editQuery = [ 'action' => 'edit' ];
1553                         if ( !$rev->isCurrent() ) {
1554                                 $editQuery['oldid'] = $rev->getId();
1555                         }
1556
1557                         $key = MediaWikiServices::getInstance()->getPermissionManager()
1558                                 ->quickUserCan( 'edit', $user, $title ) ? 'editold' : 'viewsourceold';
1559                         $msg = $this->msg( $key )->escaped();
1560                         $editLink = $this->msg( 'parentheses' )->rawParams(
1561                                 Linker::linkKnown( $title, $msg, [], $editQuery ) )->escaped();
1562                         $header .= ' ' . Html::rawElement(
1563                                 'span',
1564                                 [ 'class' => 'mw-diff-edit' ],
1565                                 $editLink
1566                         );
1567                         if ( $rev->isDeleted( RevisionRecord::DELETED_TEXT ) ) {
1568                                 $header = Html::rawElement(
1569                                         'span',
1570                                         [ 'class' => 'history-deleted' ],
1571                                         $header
1572                                 );
1573                         }
1574                 } else {
1575                         $header = Html::rawElement( 'span', [ 'class' => 'history-deleted' ], $header );
1576                 }
1577
1578                 return $header;
1579         }
1580
1581         /**
1582          * Add the header to a diff body
1583          *
1584          * @param string $diff Diff body
1585          * @param string $otitle Old revision header
1586          * @param string $ntitle New revision header
1587          * @param string $multi Notice telling user that there are intermediate
1588          *   revisions between the ones being compared
1589          * @param string $notice Other notices, e.g. that user is viewing deleted content
1590          *
1591          * @return string
1592          */
1593         public function addHeader( $diff, $otitle, $ntitle, $multi = '', $notice = '' ) {
1594                 // shared.css sets diff in interface language/dir, but the actual content
1595                 // is often in a different language, mostly the page content language/dir
1596                 $header = Html::openElement( 'table', [
1597                         'class' => [ 'diff', 'diff-contentalign-' . $this->getDiffLang()->alignStart() ],
1598                         'data-mw' => 'interface',
1599                 ] );
1600                 $userLang = htmlspecialchars( $this->getLanguage()->getHtmlCode() );
1601
1602                 if ( !$diff && !$otitle ) {
1603                         $header .= "
1604                         <tr class=\"diff-title\" lang=\"{$userLang}\">
1605                         <td class=\"diff-ntitle\">{$ntitle}</td>
1606                         </tr>";
1607                         $multiColspan = 1;
1608                 } else {
1609                         if ( $diff ) { // Safari/Chrome show broken output if cols not used
1610                                 $header .= "
1611                                 <col class=\"diff-marker\" />
1612                                 <col class=\"diff-content\" />
1613                                 <col class=\"diff-marker\" />
1614                                 <col class=\"diff-content\" />";
1615                                 $colspan = 2;
1616                                 $multiColspan = 4;
1617                         } else {
1618                                 $colspan = 1;
1619                                 $multiColspan = 2;
1620                         }
1621                         if ( $otitle || $ntitle ) {
1622                                 $header .= "
1623                                 <tr class=\"diff-title\" lang=\"{$userLang}\">
1624                                 <td colspan=\"$colspan\" class=\"diff-otitle\">{$otitle}</td>
1625                                 <td colspan=\"$colspan\" class=\"diff-ntitle\">{$ntitle}</td>
1626                                 </tr>";
1627                         }
1628                 }
1629
1630                 if ( $multi != '' ) {
1631                         $header .= "<tr><td colspan=\"{$multiColspan}\" " .
1632                                 "class=\"diff-multi\" lang=\"{$userLang}\">{$multi}</td></tr>";
1633                 }
1634                 if ( $notice != '' ) {
1635                         $header .= "<tr><td colspan=\"{$multiColspan}\" " .
1636                                 "class=\"diff-notice\" lang=\"{$userLang}\">{$notice}</td></tr>";
1637                 }
1638
1639                 return $header . $diff . "</table>";
1640         }
1641
1642         /**
1643          * Use specified text instead of loading from the database
1644          * @param Content $oldContent
1645          * @param Content $newContent
1646          * @since 1.21
1647          * @deprecated since 1.32, use setRevisions or ContentHandler::getSlotDiffRenderer.
1648          */
1649         public function setContent( Content $oldContent, Content $newContent ) {
1650                 $this->mOldContent = $oldContent;
1651                 $this->mNewContent = $newContent;
1652
1653                 $this->mTextLoaded = 2;
1654                 $this->mRevisionsLoaded = true;
1655                 $this->isContentOverridden = true;
1656                 $this->slotDiffRenderers = null;
1657         }
1658
1659         /**
1660          * Use specified text instead of loading from the database.
1661          * @param RevisionRecord|null $oldRevision
1662          * @param RevisionRecord $newRevision
1663          */
1664         public function setRevisions(
1665                 RevisionRecord $oldRevision = null, RevisionRecord $newRevision
1666         ) {
1667                 if ( $oldRevision ) {
1668                         $this->mOldRev = new Revision( $oldRevision );
1669                         $this->mOldid = $oldRevision->getId();
1670                         $this->mOldPage = Title::newFromLinkTarget( $oldRevision->getPageAsLinkTarget() );
1671                         // This method is meant for edit diffs and such so there is no reason to provide a
1672                         // revision that's not readable to the user, but check it just in case.
1673                         $this->mOldContent = $oldRevision->getContent( SlotRecord::MAIN,
1674                                 RevisionRecord::FOR_THIS_USER, $this->getUser() );
1675                 } else {
1676                         $this->mOldPage = null;
1677                         $this->mOldRev = $this->mOldid = false;
1678                 }
1679                 $this->mNewRev = new Revision( $newRevision );
1680                 $this->mNewid = $newRevision->getId();
1681                 $this->mNewPage = Title::newFromLinkTarget( $newRevision->getPageAsLinkTarget() );
1682                 $this->mNewContent = $newRevision->getContent( SlotRecord::MAIN,
1683                         RevisionRecord::FOR_THIS_USER, $this->getUser() );
1684
1685                 $this->mRevisionsIdsLoaded = $this->mRevisionsLoaded = true;
1686                 $this->mTextLoaded = $oldRevision ? 2 : 1;
1687                 $this->isContentOverridden = false;
1688                 $this->slotDiffRenderers = null;
1689         }
1690
1691         /**
1692          * Set the language in which the diff text is written
1693          *
1694          * @param Language $lang
1695          * @since 1.19
1696          */
1697         public function setTextLanguage( Language $lang ) {
1698                 $this->mDiffLang = $lang;
1699         }
1700
1701         /**
1702          * Maps a revision pair definition as accepted by DifferenceEngine constructor
1703          * to a pair of actual integers representing revision ids.
1704          *
1705          * @param int $old Revision id, e.g. from URL parameter 'oldid'
1706          * @param int|string $new Revision id or strings 'next' or 'prev', e.g. from URL parameter 'diff'
1707          *
1708          * @return array List of two revision ids, older first, later second.
1709          *     Zero signifies invalid argument passed.
1710          *     false signifies that there is no previous/next revision ($old is the oldest/newest one).
1711          */
1712         public function mapDiffPrevNext( $old, $new ) {
1713                 $rl = MediaWikiServices::getInstance()->getRevisionLookup();
1714                 if ( $new === 'prev' ) {
1715                         // Show diff between revision $old and the previous one. Get previous one from DB.
1716                         $newid = intval( $old );
1717                         $oldid = false;
1718                         $newRev = $rl->getRevisionById( $newid );
1719                         if ( $newRev ) {
1720                                 $oldRev = $rl->getPreviousRevision( $newRev );
1721                                 if ( $oldRev ) {
1722                                         $oldid = $oldRev->getId();
1723                                 }
1724                         }
1725                 } elseif ( $new === 'next' ) {
1726                         // Show diff between revision $old and the next one. Get next one from DB.
1727                         $oldid = intval( $old );
1728                         $newid = false;
1729                         $oldRev = $rl->getRevisionById( $oldid );
1730                         if ( $oldRev ) {
1731                                 $newRev = $rl->getNextRevision( $oldRev );
1732                                 if ( $newRev ) {
1733                                         $newid = $newRev->getId();
1734                                 }
1735                         }
1736                 } else {
1737                         $oldid = intval( $old );
1738                         $newid = intval( $new );
1739                 }
1740
1741                 return [ $oldid, $newid ];
1742         }
1743
1744         /**
1745          * Load revision IDs
1746          */
1747         private function loadRevisionIds() {
1748                 if ( $this->mRevisionsIdsLoaded ) {
1749                         return;
1750                 }
1751
1752                 $this->mRevisionsIdsLoaded = true;
1753
1754                 $old = $this->mOldid;
1755                 $new = $this->mNewid;
1756
1757                 list( $this->mOldid, $this->mNewid ) = self::mapDiffPrevNext( $old, $new );
1758                 if ( $new === 'next' && $this->mNewid === false ) {
1759                         # if no result, NewId points to the newest old revision. The only newer
1760                         # revision is cur, which is "0".
1761                         $this->mNewid = 0;
1762                 }
1763
1764                 Hooks::run(
1765                         'NewDifferenceEngine',
1766                         [ $this->getTitle(), &$this->mOldid, &$this->mNewid, $old, $new ]
1767                 );
1768         }
1769
1770         /**
1771          * Load revision metadata for the specified revisions. If newid is 0, then compare
1772          * the old revision in oldid to the current revision of the current page (as defined
1773          * by the request context); if oldid is 0, then compare the revision in newid to the
1774          * immediately previous one.
1775          *
1776          * If oldid is false, leave the corresponding revision object set to false. This can
1777          * happen with 'diff=prev' pointing to a non-existent revision, and is also used directly
1778          * by the API.
1779          *
1780          * @return bool Whether both revisions were loaded successfully. Setting mOldRev
1781          *   to false counts as successful loading.
1782          */
1783         public function loadRevisionData() {
1784                 if ( $this->mRevisionsLoaded ) {
1785                         return $this->isContentOverridden || ( $this->mOldRev !== null && $this->mNewRev !== null );
1786                 }
1787
1788                 // Whether it succeeds or fails, we don't want to try again
1789                 $this->mRevisionsLoaded = true;
1790
1791                 $this->loadRevisionIds();
1792
1793                 // Load the new revision object
1794                 if ( $this->mNewid ) {
1795                         $this->mNewRev = Revision::newFromId( $this->mNewid );
1796                 } else {
1797                         $this->mNewRev = Revision::newFromTitle(
1798                                 $this->getTitle(),
1799                                 false,
1800                                 Revision::READ_NORMAL
1801                         );
1802                 }
1803
1804                 if ( !$this->mNewRev instanceof Revision ) {
1805                         return false;
1806                 }
1807
1808                 // Update the new revision ID in case it was 0 (makes life easier doing UI stuff)
1809                 $this->mNewid = $this->mNewRev->getId();
1810                 if ( $this->mNewid ) {
1811                         $this->mNewPage = $this->mNewRev->getTitle();
1812                 } else {
1813                         $this->mNewPage = null;
1814                 }
1815
1816                 // Load the old revision object
1817                 $this->mOldRev = false;
1818                 if ( $this->mOldid ) {
1819                         $this->mOldRev = Revision::newFromId( $this->mOldid );
1820                 } elseif ( $this->mOldid === 0 ) {
1821                         $rev = $this->mNewRev->getPrevious();
1822                         if ( $rev ) {
1823                                 $this->mOldid = $rev->getId();
1824                                 $this->mOldRev = $rev;
1825                         } else {
1826                                 // No previous revision; mark to show as first-version only.
1827                                 $this->mOldid = false;
1828                                 $this->mOldRev = false;
1829                         }
1830                 } /* elseif ( $this->mOldid === false ) leave mOldRev false; */
1831
1832                 if ( is_null( $this->mOldRev ) ) {
1833                         return false;
1834                 }
1835
1836                 if ( $this->mOldRev && $this->mOldRev->getId() ) {
1837                         $this->mOldPage = $this->mOldRev->getTitle();
1838                 } else {
1839                         $this->mOldPage = null;
1840                 }
1841
1842                 // Load tags information for both revisions
1843                 $dbr = wfGetDB( DB_REPLICA );
1844                 $changeTagDefStore = MediaWikiServices::getInstance()->getChangeTagDefStore();
1845                 if ( $this->mOldid !== false ) {
1846                         $tagIds = $dbr->selectFieldValues(
1847                                 'change_tag',
1848                                 'ct_tag_id',
1849                                 [ 'ct_rev_id' => $this->mOldid ],
1850                                 __METHOD__
1851                         );
1852                         $tags = [];
1853                         foreach ( $tagIds as $tagId ) {
1854                                 try {
1855                                         $tags[] = $changeTagDefStore->getName( (int)$tagId );
1856                                 } catch ( NameTableAccessException $exception ) {
1857                                         continue;
1858                                 }
1859                         }
1860                         $this->mOldTags = implode( ',', $tags );
1861                 } else {
1862                         $this->mOldTags = false;
1863                 }
1864
1865                 $tagIds = $dbr->selectFieldValues(
1866                         'change_tag',
1867                         'ct_tag_id',
1868                         [ 'ct_rev_id' => $this->mNewid ],
1869                         __METHOD__
1870                 );
1871                 $tags = [];
1872                 foreach ( $tagIds as $tagId ) {
1873                         try {
1874                                 $tags[] = $changeTagDefStore->getName( (int)$tagId );
1875                         } catch ( NameTableAccessException $exception ) {
1876                                 continue;
1877                         }
1878                 }
1879                 $this->mNewTags = implode( ',', $tags );
1880
1881                 return true;
1882         }
1883
1884         /**
1885          * Load the text of the revisions, as well as revision data.
1886          * When the old revision is missing (mOldRev is false), loading mOldContent is not attempted.
1887          *
1888          * @return bool Whether the content of both revisions could be loaded successfully.
1889          *   (When mOldRev is false, that still counts as a success.)
1890          *
1891          */
1892         public function loadText() {
1893                 if ( $this->mTextLoaded == 2 ) {
1894                         return $this->loadRevisionData() && ( $this->mOldRev === false || $this->mOldContent )
1895                                 && $this->mNewContent;
1896                 }
1897
1898                 // Whether it succeeds or fails, we don't want to try again
1899                 $this->mTextLoaded = 2;
1900
1901                 if ( !$this->loadRevisionData() ) {
1902                         return false;
1903                 }
1904
1905                 if ( $this->mOldRev ) {
1906                         $this->mOldContent = $this->mOldRev->getContent(
1907                                 RevisionRecord::FOR_THIS_USER, $this->getUser()
1908                         );
1909                         if ( $this->mOldContent === null ) {
1910                                 return false;
1911                         }
1912                 }
1913
1914                 $this->mNewContent = $this->mNewRev->getContent(
1915                         RevisionRecord::FOR_THIS_USER, $this->getUser()
1916                 );
1917                 Hooks::run( 'DifferenceEngineLoadTextAfterNewContentIsLoaded', [ $this ] );
1918                 if ( $this->mNewContent === null ) {
1919                         return false;
1920                 }
1921
1922                 return true;
1923         }
1924
1925         /**
1926          * Load the text of the new revision, not the old one
1927          *
1928          * @return bool Whether the content of the new revision could be loaded successfully.
1929          */
1930         public function loadNewText() {
1931                 if ( $this->mTextLoaded >= 1 ) {
1932                         return $this->loadRevisionData();
1933                 }
1934
1935                 $this->mTextLoaded = 1;
1936
1937                 if ( !$this->loadRevisionData() ) {
1938                         return false;
1939                 }
1940
1941                 $this->mNewContent = $this->mNewRev->getContent(
1942                         RevisionRecord::FOR_THIS_USER, $this->getUser()
1943                 );
1944
1945                 Hooks::run( 'DifferenceEngineAfterLoadNewText', [ $this ] );
1946
1947                 return true;
1948         }
1949
1950 }