includes/changetags/ChangeTags.php

   1 <?php
   2 /**
   3  * Recent changes tagging.
   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 Change tagging
  22  */
  23
  24 class ChangeTags {
  25         /**
  26          * Can't delete tags with more than this many uses. Similar in intent to
  27          * the bigdelete user right
  28          * @todo Use the job queue for tag deletion to avoid this restriction
  29          */
  30         const MAX_DELETE_USES = 5000;
  31
  32         /**
  33          * Creates HTML for the given tags
  34          *
  35          * @param string $tags Comma-separated list of tags
  36          * @param string $page A label for the type of action which is being displayed,
  37          *   for example: 'history', 'contributions' or 'newpages'
  38          * @return array Array with two items: (html, classes)
  39          *   - html: String: HTML for displaying the tags (empty string when param $tags is empty)
  40          *   - classes: Array of strings: CSS classes used in the generated html, one class for each tag
  41          */
  42         public static function formatSummaryRow( $tags, $page ) {
  43                 global $wgLang;
  44
  45                 if ( !$tags ) {
  46                         return array( '', array() );
  47                 }
  48
  49                 $classes = array();
  50
  51                 $tags = explode( ',', $tags );
  52                 $displayTags = array();
  53                 foreach ( $tags as $tag ) {
  54                         if ( !$tag ) {
  55                                 continue;
  56                         }
  57                         $description = self::tagDescription( $tag );
  58                         if ( $description === false ) {
  59                                 continue;
  60                         }
  61                         $displayTags[] = Xml::tags(
  62                                 'span',
  63                                 array( 'class' => 'mw-tag-marker ' .
  64                                                                 Sanitizer::escapeClass( "mw-tag-marker-$tag" ) ),
  65                                 $description
  66                         );
  67                         $classes[] = Sanitizer::escapeClass( "mw-tag-$tag" );
  68                 }
  69
  70                 if ( !$displayTags ) {
  71                         return array( '', array() );
  72                 }
  73
  74                 $markers = wfMessage( 'tag-list-wrapper' )
  75                         ->numParams( count( $displayTags ) )
  76                         ->rawParams( $wgLang->commaList( $displayTags ) )
  77                         ->parse();
  78                 $markers = Xml::tags( 'span', array( 'class' => 'mw-tag-markers' ), $markers );
  79
  80                 return array( $markers, $classes );
  81         }
  82
  83         /**
  84          * Get a short description for a tag.
  85          *
  86          * Checks if message key "mediawiki:tag-$tag" exists. If it does not,
  87          * returns the HTML-escaped tag name. Uses the message if the message
  88          * exists, provided it is not disabled. If the message is disabled,
  89          * we consider the tag hidden, and return false.
  90          *
  91          * @param string $tag Tag
  92          * @return string|bool Tag description or false if tag is to be hidden.
  93          * @since 1.25 Returns false if tag is to be hidden.
  94          */
  95         public static function tagDescription( $tag ) {
  96                 $msg = wfMessage( "tag-$tag" );
  97                 if ( !$msg->exists() ) {
  98                         // No such message, so return the HTML-escaped tag name.
  99                         return htmlspecialchars( $tag );
 100                 }
 101                 if ( $msg->isDisabled() ) {
 102                         // The message exists but is disabled, hide the tag.
 103                         return false;
 104                 }
 105
 106                 // Message exists and isn't disabled, use it.
 107                 return $msg->parse();
 108         }
 109
 110         /**
 111          * Add tags to a change given its rc_id, rev_id and/or log_id
 112          *
 113          * @param string|array $tags Tags to add to the change
 114          * @param int|null $rc_id The rc_id of the change to add the tags to
 115          * @param int|null $rev_id The rev_id of the change to add the tags to
 116          * @param int|null $log_id The log_id of the change to add the tags to
 117          * @param string $params Params to put in the ct_params field of table 'change_tag'
 118          *
 119          * @throws MWException
 120          * @return bool False if no changes are made, otherwise true
 121          */
 122         public static function addTags( $tags, $rc_id = null, $rev_id = null,
 123                 $log_id = null, $params = null
 124         ) {
 125                 $result = self::updateTags( $tags, null, $rc_id, $rev_id, $log_id, $params );
 126                 return (bool)$result[0];
 127         }
 128
 129         /**
 130          * Add and remove tags to/from a change given its rc_id, rev_id and/or log_id,
 131          * without verifying that the tags exist or are valid. If a tag is present in
 132          * both $tagsToAdd and $tagsToRemove, it will be removed.
 133          *
 134          * This function should only be used by extensions to manipulate tags they
 135          * have registered using the ListDefinedTags hook. When dealing with user
 136          * input, call updateTagsWithChecks() instead.
 137          *
 138          * @param string|array|null $tagsToAdd Tags to add to the change
 139          * @param string|array|null $tagsToRemove Tags to remove from the change
 140          * @param int|null &$rc_id The rc_id of the change to add the tags to.
 141          * Pass a variable whose value is null if the rc_id is not relevant or unknown.
 142          * @param int|null &$rev_id The rev_id of the change to add the tags to.
 143          * Pass a variable whose value is null if the rev_id is not relevant or unknown.
 144          * @param int|null &$log_id The log_id of the change to add the tags to.
 145          * Pass a variable whose value is null if the log_id is not relevant or unknown.
 146          * @param string $params Params to put in the ct_params field of table
 147          * 'change_tag' when adding tags
 148          *
 149          * @throws MWException When $rc_id, $rev_id and $log_id are all null
 150          * @return array Index 0 is an array of tags actually added, index 1 is an
 151          * array of tags actually removed, index 2 is an array of tags present on the
 152          * revision or log entry before any changes were made
 153          *
 154          * @since 1.25
 155          */
 156         public static function updateTags( $tagsToAdd, $tagsToRemove, &$rc_id = null,
 157                 &$rev_id = null, &$log_id = null, $params = null ) {
 158
 159                 $tagsToAdd = array_filter( (array)$tagsToAdd ); // Make sure we're submitting all tags...
 160                 $tagsToRemove = array_filter( (array)$tagsToRemove );
 161
 162                 if ( !$rc_id && !$rev_id && !$log_id ) {
 163                         throw new MWException( 'At least one of: RCID, revision ID, and log ID MUST be ' .
 164                                 'specified when adding or removing a tag from a change!' );
 165                 }
 166
 167                 $dbw = wfGetDB( DB_MASTER );
 168
 169                 // Might as well look for rcids and so on.
 170                 if ( !$rc_id ) {
 171                         // Info might be out of date, somewhat fractionally, on slave.
 172                         if ( $log_id ) {
 173                                 $rc_id = $dbw->selectField(
 174                                         'recentchanges',
 175                                         'rc_id',
 176                                         array( 'rc_logid' => $log_id ),
 177                                         __METHOD__
 178                                 );
 179                         } elseif ( $rev_id ) {
 180                                 $rc_id = $dbw->selectField(
 181                                         'recentchanges',
 182                                         'rc_id',
 183                                         array( 'rc_this_oldid' => $rev_id ),
 184                                         __METHOD__
 185                                 );
 186                         }
 187                 } elseif ( !$log_id && !$rev_id ) {
 188                         // Info might be out of date, somewhat fractionally, on slave.
 189                         $log_id = $dbw->selectField(
 190                                 'recentchanges',
 191                                 'rc_logid',
 192                                 array( 'rc_id' => $rc_id ),
 193                                 __METHOD__
 194                         );
 195                         $rev_id = $dbw->selectField(
 196                                 'recentchanges',
 197                                 'rc_this_oldid',
 198                                 array( 'rc_id' => $rc_id ),
 199                                 __METHOD__
 200                         );
 201                 }
 202
 203                 // update the tag_summary row
 204                 $prevTags = array();
 205                 if ( !self::updateTagSummaryRow( $tagsToAdd, $tagsToRemove, $rc_id, $rev_id,
 206                         $log_id, $prevTags ) ) {
 207
 208                         // nothing to do
 209                         return array( array(), array(), $prevTags );
 210                 }
 211
 212                 // insert a row into change_tag for each new tag
 213                 if ( count( $tagsToAdd ) ) {
 214                         $tagsRows = array();
 215                         foreach ( $tagsToAdd as $tag ) {
 216                                 // Filter so we don't insert NULLs as zero accidentally.
 217                                 // Keep in mind that $rc_id === null means "I don't care/know about the
 218                                 // rc_id, just delete $tag on this revision/log entry". It doesn't
 219                                 // mean "only delete tags on this revision/log WHERE rc_id IS NULL".
 220                                 $tagsRows[] = array_filter(
 221                                         array(
 222                                                 'ct_tag' => $tag,
 223                                                 'ct_rc_id' => $rc_id,
 224                                                 'ct_log_id' => $log_id,
 225                                                 'ct_rev_id' => $rev_id,
 226                                                 'ct_params' => $params
 227                                         )
 228                                 );
 229                         }
 230
 231                         $dbw->insert( 'change_tag', $tagsRows, __METHOD__, array( 'IGNORE' ) );
 232                 }
 233
 234                 // delete from change_tag
 235                 if ( count( $tagsToRemove ) ) {
 236                         foreach ( $tagsToRemove as $tag ) {
 237                                 $conds = array_filter(
 238                                         array(
 239                                                 'ct_tag' => $tag,
 240                                                 'ct_rc_id' => $rc_id,
 241                                                 'ct_log_id' => $log_id,
 242                                                 'ct_rev_id' => $rev_id
 243                                         )
 244                                 );
 245                                 $dbw->delete( 'change_tag', $conds, __METHOD__ );
 246                         }
 247                 }
 248
 249                 self::purgeTagUsageCache();
 250                 return array( $tagsToAdd, $tagsToRemove, $prevTags );
 251         }
 252
 253         /**
 254          * Adds or removes a given set of tags to/from the relevant row of the
 255          * tag_summary table. Modifies the tagsToAdd and tagsToRemove arrays to
 256          * reflect the tags that were actually added and/or removed.
 257          *
 258          * @param array &$tagsToAdd
 259          * @param array &$tagsToRemove If a tag is present in both $tagsToAdd and
 260          * $tagsToRemove, it will be removed
 261          * @param int|null $rc_id Null if not known or not applicable
 262          * @param int|null $rev_id Null if not known or not applicable
 263          * @param int|null $log_id Null if not known or not applicable
 264          * @param array &$prevTags Optionally outputs a list of the tags that were
 265          * in the tag_summary row to begin with
 266          * @return bool True if any modifications were made, otherwise false
 267          * @since 1.25
 268          */
 269         protected static function updateTagSummaryRow( &$tagsToAdd, &$tagsToRemove,
 270                 $rc_id, $rev_id, $log_id, &$prevTags = array() ) {
 271
 272                 $dbw = wfGetDB( DB_MASTER );
 273
 274                 $tsConds = array_filter( array(
 275                         'ts_rc_id' => $rc_id,
 276                         'ts_rev_id' => $rev_id,
 277                         'ts_log_id' => $log_id
 278                 ) );
 279
 280                 // Can't both add and remove a tag at the same time...
 281                 $tagsToAdd = array_diff( $tagsToAdd, $tagsToRemove );
 282
 283                 // Update the summary row.
 284                 // $prevTags can be out of date on slaves, especially when addTags is called consecutively,
 285                 // causing loss of tags added recently in tag_summary table.
 286                 $prevTags = $dbw->selectField( 'tag_summary', 'ts_tags', $tsConds, __METHOD__ );
 287                 $prevTags = $prevTags ? $prevTags : '';
 288                 $prevTags = array_filter( explode( ',', $prevTags ) );
 289
 290                 // add tags
 291                 $tagsToAdd = array_values( array_diff( $tagsToAdd, $prevTags ) );
 292                 $newTags = array_unique( array_merge( $prevTags, $tagsToAdd ) );
 293
 294                 // remove tags
 295                 $tagsToRemove = array_values( array_intersect( $tagsToRemove, $newTags ) );
 296                 $newTags = array_values( array_diff( $newTags, $tagsToRemove ) );
 297
 298                 sort( $prevTags );
 299                 sort( $newTags );
 300                 if ( $prevTags == $newTags ) {
 301                         // No change.
 302                         return false;
 303                 }
 304
 305                 if ( !$newTags ) {
 306                         // no tags left, so delete the row altogether
 307                         $dbw->delete( 'tag_summary', $tsConds, __METHOD__ );
 308                 } else {
 309                         $dbw->replace( 'tag_summary',
 310                                 array( 'ts_rev_id', 'ts_rc_id', 'ts_log_id' ),
 311                                 array_filter( array_merge( $tsConds, array( 'ts_tags' => implode( ',', $newTags ) ) ) ),
 312                                 __METHOD__
 313                         );
 314                 }
 315
 316                 return true;
 317         }
 318
 319         /**
 320          * Helper function to generate a fatal status with a 'not-allowed' type error.
 321          *
 322          * @param string $msgOne Message key to use in the case of one tag
 323          * @param string $msgMulti Message key to use in the case of more than one tag
 324          * @param array $tags Restricted tags (passed as $1 into the message, count of
 325          * $tags passed as $2)
 326          * @return Status
 327          * @since 1.25
 328          */
 329         protected static function restrictedTagError( $msgOne, $msgMulti, $tags ) {
 330                 $lang = RequestContext::getMain()->getLanguage();
 331                 $count = count( $tags );
 332                 return Status::newFatal( ( $count > 1 ) ? $msgMulti : $msgOne,
 333                         $lang->commaList( $tags ), $count );
 334         }
 335
 336         /**
 337          * Is it OK to allow the user to apply all the specified tags at the same time
 338          * as they edit/make the change?
 339          *
 340          * @param array $tags Tags that you are interested in applying
 341          * @param User|null $user User whose permission you wish to check, or null if
 342          * you don't care (e.g. maintenance scripts)
 343          * @return Status
 344          * @since 1.25
 345          */
 346         public static function canAddTagsAccompanyingChange( array $tags,
 347                 User $user = null ) {
 348
 349                 if ( !is_null( $user ) && !$user->isAllowed( 'applychangetags' ) ) {
 350                         return Status::newFatal( 'tags-apply-no-permission' );
 351                 }
 352
 353                 // to be applied, a tag has to be explicitly defined
 354                 // @todo Allow extensions to define tags that can be applied by users...
 355                 $allowedTags = self::listExplicitlyDefinedTags();
 356                 $disallowedTags = array_diff( $tags, $allowedTags );
 357                 if ( $disallowedTags ) {
 358                         return self::restrictedTagError( 'tags-apply-not-allowed-one',
 359                                 'tags-apply-not-allowed-multi', $disallowedTags );
 360                 }
 361
 362                 return Status::newGood();
 363         }
 364
 365         /**
 366          * Adds tags to a given change, checking whether it is allowed first, but
 367          * without adding a log entry. Useful for cases where the tag is being added
 368          * along with the action that generated the change (e.g. tagging an edit as
 369          * it is being made).
 370          *
 371          * Extensions should not use this function, unless directly handling a user
 372          * request to add a particular tag. Normally, extensions should call
 373          * ChangeTags::updateTags() instead.
 374          *
 375          * @param array $tags Tags to apply
 376          * @param int|null $rc_id The rc_id of the change to add the tags to
 377          * @param int|null $rev_id The rev_id of the change to add the tags to
 378          * @param int|null $log_id The log_id of the change to add the tags to
 379          * @param string $params Params to put in the ct_params field of table
 380          * 'change_tag' when adding tags
 381          * @param User $user Who to give credit for the action
 382          * @return Status
 383          * @since 1.25
 384          */
 385         public static function addTagsAccompanyingChangeWithChecks(
 386                 array $tags, $rc_id, $rev_id, $log_id, $params, User $user
 387         ) {
 388
 389                 // are we allowed to do this?
 390                 $result = self::canAddTagsAccompanyingChange( $tags, $user );
 391                 if ( !$result->isOK() ) {
 392                         $result->value = null;
 393                         return $result;
 394                 }
 395
 396                 // do it!
 397                 self::addTags( $tags, $rc_id, $rev_id, $log_id, $params );
 398
 399                 return Status::newGood( true );
 400         }
 401
 402         /**
 403          * Is it OK to allow the user to adds and remove the given tags tags to/from a
 404          * change?
 405          *
 406          * @param array $tagsToAdd Tags that you are interested in adding
 407          * @param array $tagsToRemove Tags that you are interested in removing
 408          * @param User|null $user User whose permission you wish to check, or null if
 409          * you don't care (e.g. maintenance scripts)
 410          * @return Status
 411          * @since 1.25
 412          */
 413         public static function canUpdateTags( array $tagsToAdd, array $tagsToRemove,
 414                 User $user = null ) {
 415
 416                 if ( !is_null( $user ) && !$user->isAllowed( 'changetags' ) ) {
 417                         return Status::newFatal( 'tags-update-no-permission' );
 418                 }
 419
 420                 // to be added, a tag has to be explicitly defined
 421                 // @todo Allow extensions to define tags that can be applied by users...
 422                 $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
 423                 $diff = array_diff( $tagsToAdd, $explicitlyDefinedTags );
 424                 if ( $diff ) {
 425                         return self::restrictedTagError( 'tags-update-add-not-allowed-one',
 426                                 'tags-update-add-not-allowed-multi', $diff );
 427                 }
 428
 429                 // to be removed, a tag has to be either explicitly defined or not defined
 430                 // at all
 431                 $definedTags = self::listDefinedTags();
 432                 $diff = array_diff( $tagsToRemove, $explicitlyDefinedTags );
 433                 if ( $diff ) {
 434                         $intersect = array_intersect( $diff, $definedTags );
 435                         if ( $intersect ) {
 436                                 return self::restrictedTagError( 'tags-update-remove-not-allowed-one',
 437                                         'tags-update-remove-not-allowed-multi', $intersect );
 438                         }
 439                 }
 440
 441                 return Status::newGood();
 442         }
 443
 444         /**
 445          * Adds and/or removes tags to/from a given change, checking whether it is
 446          * allowed first, and adding a log entry afterwards.
 447          *
 448          * Includes a call to ChangeTag::canUpdateTags(), so your code doesn't need
 449          * to do that. However, it doesn't check whether the *_id parameters are a
 450          * valid combination. That is up to you to enforce. See ApiTag::execute() for
 451          * an example.
 452          *
 453          * @param array|null $tagsToAdd If none, pass array() or null
 454          * @param array|null $tagsToRemove If none, pass array() or null
 455          * @param int|null $rc_id The rc_id of the change to add the tags to
 456          * @param int|null $rev_id The rev_id of the change to add the tags to
 457          * @param int|null $log_id The log_id of the change to add the tags to
 458          * @param string $params Params to put in the ct_params field of table
 459          * 'change_tag' when adding tags
 460          * @param string $reason Comment for the log
 461          * @param User $user Who to give credit for the action
 462          * @return Status If successful, the value of this Status object will be an
 463          * object (stdClass) with the following fields:
 464          *  - logId: the ID of the added log entry, or null if no log entry was added
 465          *    (i.e. no operation was performed)
 466          *  - addedTags: an array containing the tags that were actually added
 467          *  - removedTags: an array containing the tags that were actually removed
 468          * @since 1.25
 469          */
 470         public static function updateTagsWithChecks( $tagsToAdd, $tagsToRemove,
 471                 $rc_id, $rev_id, $log_id, $params, $reason, User $user ) {
 472
 473                 if ( is_null( $tagsToAdd ) ) {
 474                         $tagsToAdd = array();
 475                 }
 476                 if ( is_null( $tagsToRemove ) ) {
 477                         $tagsToRemove = array();
 478                 }
 479                 if ( !$tagsToAdd && !$tagsToRemove ) {
 480                         // no-op, don't bother
 481                         return Status::newGood( (object)array(
 482                                 'logId' => null,
 483                                 'addedTags' => array(),
 484                                 'removedTags' => array(),
 485                         ) );
 486                 }
 487
 488                 // are we allowed to do this?
 489                 $result = self::canUpdateTags( $tagsToAdd, $tagsToRemove, $user );
 490                 if ( !$result->isOK() ) {
 491                         $result->value = null;
 492                         return $result;
 493                 }
 494
 495                 // basic rate limiting
 496                 if ( $user->pingLimiter( 'changetag' ) ) {
 497                         return Status::newFatal( 'actionthrottledtext' );
 498                 }
 499
 500                 // do it!
 501                 list( $tagsAdded, $tagsRemoved, $initialTags ) = self::updateTags( $tagsToAdd,
 502                         $tagsToRemove, $rc_id, $rev_id, $log_id, $params );
 503                 if ( !$tagsAdded && !$tagsRemoved ) {
 504                         // no-op, don't log it
 505                         return Status::newGood( (object)array(
 506                                 'logId' => null,
 507                                 'addedTags' => array(),
 508                                 'removedTags' => array(),
 509                         ) );
 510                 }
 511
 512                 // log it
 513                 $logEntry = new ManualLogEntry( 'tag', 'update' );
 514                 $logEntry->setPerformer( $user );
 515                 $logEntry->setComment( $reason );
 516
 517                 // find the appropriate target page
 518                 if ( $rev_id ) {
 519                         $rev = Revision::newFromId( $rev_id );
 520                         if ( $rev ) {
 521                                 $logEntry->setTarget( $rev->getTitle() );
 522                         }
 523                 } elseif ( $log_id ) {
 524                         // This function is from revision deletion logic and has nothing to do with
 525                         // change tags, but it appears to be the only other place in core where we
 526                         // perform logged actions on log items.
 527                         $logEntry->setTarget( RevDelLogList::suggestTarget( 0, array( $log_id ) ) );
 528                 }
 529
 530                 if ( !$logEntry->getTarget() ) {
 531                         // target is required, so we have to set something
 532                         $logEntry->setTarget( SpecialPage::getTitleFor( 'Tags' ) );
 533                 }
 534
 535                 $logParams = array(
 536                         '4::revid' => $rev_id,
 537                         '5::logid' => $log_id,
 538                         '6:list:tagsAdded' => $tagsAdded,
 539                         '7:number:tagsAddedCount' => count( $tagsAdded ),
 540                         '8:list:tagsRemoved' => $tagsRemoved,
 541                         '9:number:tagsRemovedCount' => count( $tagsRemoved ),
 542                         'initialTags' => $initialTags,
 543                 );
 544                 $logEntry->setParameters( $logParams );
 545                 $logEntry->setRelations( array( 'Tag' => array_merge( $tagsAdded, $tagsRemoved ) ) );
 546
 547                 $dbw = wfGetDB( DB_MASTER );
 548                 $logId = $logEntry->insert( $dbw );
 549                 // Only send this to UDP, not RC, similar to patrol events
 550                 $logEntry->publish( $logId, 'udp' );
 551
 552                 return Status::newGood( (object)array(
 553                         'logId' => $logId,
 554                         'addedTags' => $tagsAdded,
 555                         'removedTags' => $tagsRemoved,
 556                 ) );
 557         }
 558
 559         /**
 560          * Applies all tags-related changes to a query.
 561          * Handles selecting tags, and filtering.
 562          * Needs $tables to be set up properly, so we can figure out which join conditions to use.
 563          *
 564          * @param string|array $tables Table names, see DatabaseBase::select
 565          * @param string|array $fields Fields used in query, see DatabaseBase::select
 566          * @param string|array $conds Conditions used in query, see DatabaseBase::select
 567          * @param array $join_conds Join conditions, see DatabaseBase::select
 568          * @param array $options Options, see Database::select
 569          * @param bool|string $filter_tag Tag to select on
 570          *
 571          * @throws MWException When unable to determine appropriate JOIN condition for tagging
 572          */
 573         public static function modifyDisplayQuery( &$tables, &$fields, &$conds,
 574                                                                                 &$join_conds, &$options, $filter_tag = false ) {
 575                 global $wgRequest, $wgUseTagFilter;
 576
 577                 if ( $filter_tag === false ) {
 578                         $filter_tag = $wgRequest->getVal( 'tagfilter' );
 579                 }
 580
 581                 // Figure out which conditions can be done.
 582                 if ( in_array( 'recentchanges', $tables ) ) {
 583                         $join_cond = 'ct_rc_id=rc_id';
 584                 } elseif ( in_array( 'logging', $tables ) ) {
 585                         $join_cond = 'ct_log_id=log_id';
 586                 } elseif ( in_array( 'revision', $tables ) ) {
 587                         $join_cond = 'ct_rev_id=rev_id';
 588                 } elseif ( in_array( 'archive', $tables ) ) {
 589                         $join_cond = 'ct_rev_id=ar_rev_id';
 590                 } else {
 591                         throw new MWException( 'Unable to determine appropriate JOIN condition for tagging.' );
 592                 }
 593
 594                 $fields['ts_tags'] = wfGetDB( DB_SLAVE )->buildGroupConcatField(
 595                         ',', 'change_tag', 'ct_tag', $join_cond
 596                 );
 597
 598                 if ( $wgUseTagFilter && $filter_tag ) {
 599                         // Somebody wants to filter on a tag.
 600                         // Add an INNER JOIN on change_tag
 601
 602                         $tables[] = 'change_tag';
 603                         $join_conds['change_tag'] = array( 'INNER JOIN', $join_cond );
 604                         $conds['ct_tag'] = $filter_tag;
 605                 }
 606         }
 607
 608         /**
 609          * Build a text box to select a change tag
 610          *
 611          * @param string $selected Tag to select by default
 612          * @param bool $fullForm
 613          *        - if false, then it returns an array of (label, form).
 614          *        - if true, it returns an entire form around the selector.
 615          * @param Title $title Title object to send the form to.
 616          *        Used when, and only when $fullForm is true.
 617          * @return string|array
 618          *        - if $fullForm is false: Array with
 619          *        - if $fullForm is true: String, html fragment
 620          */
 621         public static function buildTagFilterSelector( $selected = '',
 622                 $fullForm = false, Title $title = null
 623         ) {
 624                 global $wgUseTagFilter;
 625
 626                 if ( !$wgUseTagFilter || !count( self::listDefinedTags() ) ) {
 627                         return $fullForm ? '' : array();
 628                 }
 629
 630                 $data = array(
 631                         Html::rawElement(
 632                                 'label',
 633                                 array( 'for' => 'tagfilter' ),
 634                                 wfMessage( 'tag-filter' )->parse()
 635                         ),
 636                         Xml::input(
 637                                 'tagfilter',
 638                                 20,
 639                                 $selected,
 640                                 array( 'class' => 'mw-tagfilter-input mw-ui-input mw-ui-input-inline', 'id' => 'tagfilter' )
 641                         )
 642                 );
 643
 644                 if ( !$fullForm ) {
 645                         return $data;
 646                 }
 647
 648                 $html = implode( '&#160;', $data );
 649                 $html .= "\n" .
 650                         Xml::element(
 651                                 'input',
 652                                 array( 'type' => 'submit', 'value' => wfMessage( 'tag-filter-submit' )->text() )
 653                         );
 654                 $html .= "\n" . Html::hidden( 'title', $title->getPrefixedText() );
 655                 $html = Xml::tags(
 656                         'form',
 657                         array( 'action' => $title->getLocalURL(), 'class' => 'mw-tagfilter-form', 'method' => 'get' ),
 658                         $html
 659                 );
 660
 661                 return $html;
 662         }
 663
 664         /**
 665          * Defines a tag in the valid_tag table, without checking that the tag name
 666          * is valid.
 667          * Extensions should NOT use this function; they can use the ListDefinedTags
 668          * hook instead.
 669          *
 670          * @param string $tag Tag to create
 671          * @since 1.25
 672          */
 673         public static function defineTag( $tag ) {
 674                 $dbw = wfGetDB( DB_MASTER );
 675                 $dbw->replace( 'valid_tag',
 676                         array( 'vt_tag' ),
 677                         array( 'vt_tag' => $tag ),
 678                         __METHOD__ );
 679
 680                 // clear the memcache of defined tags
 681                 self::purgeTagCacheAll();
 682         }
 683
 684         /**
 685          * Removes a tag from the valid_tag table. The tag may remain in use by
 686          * extensions, and may still show up as 'defined' if an extension is setting
 687          * it from the ListDefinedTags hook.
 688          *
 689          * @param string $tag Tag to remove
 690          * @since 1.25
 691          */
 692         public static function undefineTag( $tag ) {
 693                 $dbw = wfGetDB( DB_MASTER );
 694                 $dbw->delete( 'valid_tag', array( 'vt_tag' => $tag ), __METHOD__ );
 695
 696                 // clear the memcache of defined tags
 697                 self::purgeTagCacheAll();
 698         }
 699
 700         /**
 701          * Writes a tag action into the tag management log.
 702          *
 703          * @param string $action
 704          * @param string $tag
 705          * @param string $reason
 706          * @param User $user Who to attribute the action to
 707          * @param int $tagCount For deletion only, how many usages the tag had before
 708          * it was deleted.
 709          * @return int ID of the inserted log entry
 710          * @since 1.25
 711          */
 712         protected static function logTagManagementAction( $action, $tag, $reason,
 713                 User $user, $tagCount = null ) {
 714
 715                 $dbw = wfGetDB( DB_MASTER );
 716
 717                 $logEntry = new ManualLogEntry( 'managetags', $action );
 718                 $logEntry->setPerformer( $user );
 719                 // target page is not relevant, but it has to be set, so we just put in
 720                 // the title of Special:Tags
 721                 $logEntry->setTarget( Title::newFromText( 'Special:Tags' ) );
 722                 $logEntry->setComment( $reason );
 723
 724                 $params = array( '4::tag' => $tag );
 725                 if ( !is_null( $tagCount ) ) {
 726                         $params['5:number:count'] = $tagCount;
 727                 }
 728                 $logEntry->setParameters( $params );
 729                 $logEntry->setRelations( array( 'Tag' => $tag ) );
 730
 731                 $logId = $logEntry->insert( $dbw );
 732                 $logEntry->publish( $logId );
 733                 return $logId;
 734         }
 735
 736         /**
 737          * Is it OK to allow the user to activate this tag?
 738          *
 739          * @param string $tag Tag that you are interested in activating
 740          * @param User|null $user User whose permission you wish to check, or null if
 741          * you don't care (e.g. maintenance scripts)
 742          * @return Status
 743          * @since 1.25
 744          */
 745         public static function canActivateTag( $tag, User $user = null ) {
 746                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 747                         return Status::newFatal( 'tags-manage-no-permission' );
 748                 }
 749
 750                 // non-existing tags cannot be activated
 751                 $tagUsage = self::tagUsageStatistics();
 752                 if ( !isset( $tagUsage[$tag] ) ) {
 753                         return Status::newFatal( 'tags-activate-not-found', $tag );
 754                 }
 755
 756                 // defined tags cannot be activated (a defined tag is either extension-
 757                 // defined, in which case the extension chooses whether or not to active it;
 758                 // or user-defined, in which case it is considered active)
 759                 $definedTags = self::listDefinedTags();
 760                 if ( in_array( $tag, $definedTags ) ) {
 761                         return Status::newFatal( 'tags-activate-not-allowed', $tag );
 762                 }
 763
 764                 return Status::newGood();
 765         }
 766
 767         /**
 768          * Activates a tag, checking whether it is allowed first, and adding a log
 769          * entry afterwards.
 770          *
 771          * Includes a call to ChangeTag::canActivateTag(), so your code doesn't need
 772          * to do that.
 773          *
 774          * @param string $tag
 775          * @param string $reason
 776          * @param User $user Who to give credit for the action
 777          * @param bool $ignoreWarnings Can be used for API interaction, default false
 778          * @return Status If successful, the Status contains the ID of the added log
 779          * entry as its value
 780          * @since 1.25
 781          */
 782         public static function activateTagWithChecks( $tag, $reason, User $user,
 783                 $ignoreWarnings = false ) {
 784
 785                 // are we allowed to do this?
 786                 $result = self::canActivateTag( $tag, $user );
 787                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 788                         $result->value = null;
 789                         return $result;
 790                 }
 791
 792                 // do it!
 793                 self::defineTag( $tag );
 794
 795                 // log it
 796                 $logId = self::logTagManagementAction( 'activate', $tag, $reason, $user );
 797                 return Status::newGood( $logId );
 798         }
 799
 800         /**
 801          * Is it OK to allow the user to deactivate this tag?
 802          *
 803          * @param string $tag Tag that you are interested in deactivating
 804          * @param User|null $user User whose permission you wish to check, or null if
 805          * you don't care (e.g. maintenance scripts)
 806          * @return Status
 807          * @since 1.25
 808          */
 809         public static function canDeactivateTag( $tag, User $user = null ) {
 810                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 811                         return Status::newFatal( 'tags-manage-no-permission' );
 812                 }
 813
 814                 // only explicitly-defined tags can be deactivated
 815                 $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
 816                 if ( !in_array( $tag, $explicitlyDefinedTags ) ) {
 817                         return Status::newFatal( 'tags-deactivate-not-allowed', $tag );
 818                 }
 819                 return Status::newGood();
 820         }
 821
 822         /**
 823          * Deactivates a tag, checking whether it is allowed first, and adding a log
 824          * entry afterwards.
 825          *
 826          * Includes a call to ChangeTag::canDeactivateTag(), so your code doesn't need
 827          * to do that.
 828          *
 829          * @param string $tag
 830          * @param string $reason
 831          * @param User $user Who to give credit for the action
 832          * @param bool $ignoreWarnings Can be used for API interaction, default false
 833          * @return Status If successful, the Status contains the ID of the added log
 834          * entry as its value
 835          * @since 1.25
 836          */
 837         public static function deactivateTagWithChecks( $tag, $reason, User $user,
 838                 $ignoreWarnings = false ) {
 839
 840                 // are we allowed to do this?
 841                 $result = self::canDeactivateTag( $tag, $user );
 842                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 843                         $result->value = null;
 844                         return $result;
 845                 }
 846
 847                 // do it!
 848                 self::undefineTag( $tag );
 849
 850                 // log it
 851                 $logId = self::logTagManagementAction( 'deactivate', $tag, $reason, $user );
 852                 return Status::newGood( $logId );
 853         }
 854
 855         /**
 856          * Is it OK to allow the user to create this tag?
 857          *
 858          * @param string $tag Tag that you are interested in creating
 859          * @param User|null $user User whose permission you wish to check, or null if
 860          * you don't care (e.g. maintenance scripts)
 861          * @return Status
 862          * @since 1.25
 863          */
 864         public static function canCreateTag( $tag, User $user = null ) {
 865                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 866                         return Status::newFatal( 'tags-manage-no-permission' );
 867                 }
 868
 869                 // no empty tags
 870                 if ( $tag === '' ) {
 871                         return Status::newFatal( 'tags-create-no-name' );
 872                 }
 873
 874                 // tags cannot contain commas (used as a delimiter in tag_summary table) or
 875                 // slashes (would break tag description messages in MediaWiki namespace)
 876                 if ( strpos( $tag, ',' ) !== false || strpos( $tag, '/' ) !== false ) {
 877                         return Status::newFatal( 'tags-create-invalid-chars' );
 878                 }
 879
 880                 // could the MediaWiki namespace description messages be created?
 881                 $title = Title::makeTitleSafe( NS_MEDIAWIKI, "Tag-$tag-description" );
 882                 if ( is_null( $title ) ) {
 883                         return Status::newFatal( 'tags-create-invalid-title-chars' );
 884                 }
 885
 886                 // does the tag already exist?
 887                 $tagUsage = self::tagUsageStatistics();
 888                 if ( isset( $tagUsage[$tag] ) ) {
 889                         return Status::newFatal( 'tags-create-already-exists', $tag );
 890                 }
 891
 892                 // check with hooks
 893                 $canCreateResult = Status::newGood();
 894                 Hooks::run( 'ChangeTagCanCreate', array( $tag, $user, &$canCreateResult ) );
 895                 return $canCreateResult;
 896         }
 897
 898         /**
 899          * Creates a tag by adding a row to the `valid_tag` table.
 900          *
 901          * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
 902          * do that.
 903          *
 904          * @param string $tag
 905          * @param string $reason
 906          * @param User $user Who to give credit for the action
 907          * @param bool $ignoreWarnings Can be used for API interaction, default false
 908          * @return Status If successful, the Status contains the ID of the added log
 909          * entry as its value
 910          * @since 1.25
 911          */
 912         public static function createTagWithChecks( $tag, $reason, User $user,
 913                 $ignoreWarnings = false ) {
 914
 915                 // are we allowed to do this?
 916                 $result = self::canCreateTag( $tag, $user );
 917                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 918                         $result->value = null;
 919                         return $result;
 920                 }
 921
 922                 // do it!
 923                 self::defineTag( $tag );
 924
 925                 // log it
 926                 $logId = self::logTagManagementAction( 'create', $tag, $reason, $user );
 927                 return Status::newGood( $logId );
 928         }
 929
 930         /**
 931          * Permanently removes all traces of a tag from the DB. Good for removing
 932          * misspelt or temporary tags.
 933          *
 934          * This function should be directly called by maintenance scripts only, never
 935          * by user-facing code. See deleteTagWithChecks() for functionality that can
 936          * safely be exposed to users.
 937          *
 938          * @param string $tag Tag to remove
 939          * @return Status The returned status will be good unless a hook changed it
 940          * @since 1.25
 941          */
 942         public static function deleteTagEverywhere( $tag ) {
 943                 $dbw = wfGetDB( DB_MASTER );
 944                 $dbw->startAtomic( __METHOD__ );
 945
 946                 // delete from valid_tag
 947                 self::undefineTag( $tag );
 948
 949                 // find out which revisions use this tag, so we can delete from tag_summary
 950                 $result = $dbw->select( 'change_tag',
 951                         array( 'ct_rc_id', 'ct_log_id', 'ct_rev_id', 'ct_tag' ),
 952                         array( 'ct_tag' => $tag ),
 953                         __METHOD__ );
 954                 foreach ( $result as $row ) {
 955                         // remove the tag from the relevant row of tag_summary
 956                         $tagsToAdd = array();
 957                         $tagsToRemove = array( $tag );
 958                         self::updateTagSummaryRow( $tagsToAdd, $tagsToRemove, $row->ct_rc_id,
 959                                 $row->ct_rev_id, $row->ct_log_id );
 960                 }
 961
 962                 // delete from change_tag
 963                 $dbw->delete( 'change_tag', array( 'ct_tag' => $tag ), __METHOD__ );
 964
 965                 $dbw->endAtomic( __METHOD__ );
 966
 967                 // give extensions a chance
 968                 $status = Status::newGood();
 969                 Hooks::run( 'ChangeTagAfterDelete', array( $tag, &$status ) );
 970                 // let's not allow error results, as the actual tag deletion succeeded
 971                 if ( !$status->isOK() ) {
 972                         wfDebug( 'ChangeTagAfterDelete error condition downgraded to warning' );
 973                         $status->ok = true;
 974                 }
 975
 976                 // clear the memcache of defined tags
 977                 self::purgeTagCacheAll();
 978
 979                 return $status;
 980         }
 981
 982         /**
 983          * Is it OK to allow the user to delete this tag?
 984          *
 985          * @param string $tag Tag that you are interested in deleting
 986          * @param User|null $user User whose permission you wish to check, or null if
 987          * you don't care (e.g. maintenance scripts)
 988          * @return Status
 989          * @since 1.25
 990          */
 991         public static function canDeleteTag( $tag, User $user = null ) {
 992                 $tagUsage = self::tagUsageStatistics();
 993
 994                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 995                         return Status::newFatal( 'tags-manage-no-permission' );
 996                 }
 997
 998                 if ( !isset( $tagUsage[$tag] ) ) {
 999                         return Status::newFatal( 'tags-delete-not-found', $tag );
1000                 }
1001
1002                 if ( $tagUsage[$tag] > self::MAX_DELETE_USES ) {
1003                         return Status::newFatal( 'tags-delete-too-many-uses', $tag, self::MAX_DELETE_USES );
1004                 }
1005
1006                 $extensionDefined = self::listExtensionDefinedTags();
1007                 if ( in_array( $tag, $extensionDefined ) ) {
1008                         // extension-defined tags can't be deleted unless the extension
1009                         // specifically allows it
1010                         $status = Status::newFatal( 'tags-delete-not-allowed' );
1011                 } else {
1012                         // user-defined tags are deletable unless otherwise specified
1013                         $status = Status::newGood();
1014                 }
1015
1016                 Hooks::run( 'ChangeTagCanDelete', array( $tag, $user, &$status ) );
1017                 return $status;
1018         }
1019
1020         /**
1021          * Deletes a tag, checking whether it is allowed first, and adding a log entry
1022          * afterwards.
1023          *
1024          * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
1025          * do that.
1026          *
1027          * @param string $tag
1028          * @param string $reason
1029          * @param User $user Who to give credit for the action
1030          * @param bool $ignoreWarnings Can be used for API interaction, default false
1031          * @return Status If successful, the Status contains the ID of the added log
1032          * entry as its value
1033          * @since 1.25
1034          */
1035         public static function deleteTagWithChecks( $tag, $reason, User $user,
1036                 $ignoreWarnings = false ) {
1037
1038                 // are we allowed to do this?
1039                 $result = self::canDeleteTag( $tag, $user );
1040                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
1041                         $result->value = null;
1042                         return $result;
1043                 }
1044
1045                 // store the tag usage statistics
1046                 $tagUsage = self::tagUsageStatistics();
1047
1048                 // do it!
1049                 $deleteResult = self::deleteTagEverywhere( $tag );
1050                 if ( !$deleteResult->isOK() ) {
1051                         return $deleteResult;
1052                 }
1053
1054                 // log it
1055                 $logId = self::logTagManagementAction( 'delete', $tag, $reason, $user, $tagUsage[$tag] );
1056                 $deleteResult->value = $logId;
1057                 return $deleteResult;
1058         }
1059
1060         /**
1061          * Lists those tags which extensions report as being "active".
1062          *
1063          * @return array
1064          * @since 1.25
1065          */
1066         public static function listExtensionActivatedTags() {
1067                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1068                         wfMemcKey( 'active-tags' ),
1069                         function() {
1070                                 // Ask extensions which tags they consider active
1071                                 $extensionActive = array();
1072                                 Hooks::run( 'ChangeTagsListActive', array( &$extensionActive ) );
1073                                 return $extensionActive;
1074                         },
1075                         300,
1076                         array( wfMemcKey( 'active-tags' ) ),
1077                         array( 'lockTSE' => INF )
1078                 );
1079         }
1080
1081         /**
1082          * Basically lists defined tags which count even if they aren't applied to anything.
1083          * It returns a union of the results of listExplicitlyDefinedTags() and
1084          * listExtensionDefinedTags().
1085          *
1086          * @return string[] Array of strings: tags
1087          */
1088         public static function listDefinedTags() {
1089                 $tags1 = self::listExplicitlyDefinedTags();
1090                 $tags2 = self::listExtensionDefinedTags();
1091                 return array_values( array_unique( array_merge( $tags1, $tags2 ) ) );
1092         }
1093
1094         /**
1095          * Lists tags explicitly defined in the `valid_tag` table of the database.
1096          * Tags in table 'change_tag' which are not in table 'valid_tag' are not
1097          * included.
1098          *
1099          * Tries memcached first.
1100          *
1101          * @return string[] Array of strings: tags
1102          * @since 1.25
1103          */
1104         public static function listExplicitlyDefinedTags() {
1105                 $fname = __METHOD__;
1106
1107                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1108                         wfMemcKey( 'valid-tags-db' ),
1109                         function() use ( $fname ) {
1110                                 $dbr = wfGetDB( DB_SLAVE );
1111                                 $tags = $dbr->selectFieldValues(
1112                                         'valid_tag', 'vt_tag', array(), $fname );
1113
1114                                 return array_filter( array_unique( $tags ) );
1115                         },
1116                         300,
1117                         array( wfMemcKey( 'valid-tags-db' ) ),
1118                         array( 'lockTSE' => INF )
1119                 );
1120         }
1121
1122         /**
1123          * Lists tags defined by extensions using the ListDefinedTags hook.
1124          * Extensions need only define those tags they deem to be in active use.
1125          *
1126          * Tries memcached first.
1127          *
1128          * @return string[] Array of strings: tags
1129          * @since 1.25
1130          */
1131         public static function listExtensionDefinedTags() {
1132                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1133                         wfMemcKey( 'valid-tags-hook' ),
1134                         function() {
1135                                 $tags = array();
1136                                 Hooks::run( 'ListDefinedTags', array( &$tags ) );
1137                                 return array_filter( array_unique( $tags ) );
1138                         },
1139                         300,
1140                         array( wfMemcKey( 'valid-tags-hook' ) ),
1141                         array( 'lockTSE' => INF )
1142                 );
1143         }
1144
1145         /**
1146          * Invalidates the short-term cache of defined tags used by the
1147          * list*DefinedTags functions, as well as the tag statistics cache.
1148          * @since 1.25
1149          */
1150         public static function purgeTagCacheAll() {
1151                 $cache = ObjectCache::getMainWANInstance();
1152
1153                 $cache->touchCheckKey( wfMemcKey( 'active-tags' ) );
1154                 $cache->touchCheckKey( wfMemcKey( 'valid-tags-db' ) );
1155                 $cache->touchCheckKey( wfMemcKey( 'valid-tags-hook' ) );
1156
1157                 self::purgeTagUsageCache();
1158         }
1159
1160         /**
1161          * Invalidates the tag statistics cache only.
1162          * @since 1.25
1163          */
1164         public static function purgeTagUsageCache() {
1165                 $cache = ObjectCache::getMainWANInstance();
1166
1167                 $cache->touchCheckKey( wfMemcKey( 'change-tag-statistics' ) );
1168         }
1169
1170         /**
1171          * Returns a map of any tags used on the wiki to number of edits
1172          * tagged with them, ordered descending by the hitcount.
1173          *
1174          * Keeps a short-term cache in memory, so calling this multiple times in the
1175          * same request should be fine.
1176          *
1177          * @return array Array of string => int
1178          */
1179         public static function tagUsageStatistics() {
1180                 static $cachedStats = null;
1181
1182                 // Process cache to avoid I/O and repeated regens during holdoff
1183                 if ( $cachedStats !== null ) {
1184                         return $cachedStats;
1185                 }
1186
1187                 $fname = __METHOD__;
1188                 $cachedStats = ObjectCache::getMainWANInstance()->getWithSetCallback(
1189                         wfMemcKey( 'change-tag-statistics' ),
1190                         function() use ( $fname ) {
1191                                 $out = array();
1192
1193                                 $dbr = wfGetDB( DB_SLAVE, 'vslow' );
1194                                 $res = $dbr->select(
1195                                         'change_tag',
1196                                         array( 'ct_tag', 'hitcount' => 'count(*)' ),
1197                                         array(),
1198                                         $fname,
1199                                         array( 'GROUP BY' => 'ct_tag', 'ORDER BY' => 'hitcount DESC' )
1200                                 );
1201
1202                                 foreach ( $res as $row ) {
1203                                         $out[$row->ct_tag] = $row->hitcount;
1204                                 }
1205
1206                                 foreach ( ChangeTags::listDefinedTags() as $tag ) {
1207                                         if ( !isset( $out[$tag] ) ) {
1208                                                 $out[$tag] = 0;
1209                                         }
1210                                 }
1211
1212                                 return $out;
1213                         },
1214                         300,
1215                         array( wfMemcKey( 'change-tag-statistics' ) ),
1216                         array( 'lockTSE' => INF )
1217                 );
1218
1219                 return $cachedStats;
1220         }
1221
1222         /**
1223          * Indicate whether change tag editing UI is relevant
1224          *
1225          * Returns true if the user has the necessary right and there are any
1226          * editable tags defined.
1227          *
1228          * This intentionally doesn't check "any addable || any deletable", because
1229          * it seems like it would be more confusing than useful if the checkboxes
1230          * suddenly showed up because some abuse filter stopped defining a tag and
1231          * then suddenly disappeared when someone deleted all uses of that tag.
1232          *
1233          * @param User $user
1234          * @return bool
1235          */
1236         public static function showTagEditingUI( User $user ) {
1237                 return $user->isAllowed( 'changetags' ) && (bool)self::listExplicitlyDefinedTags();
1238         }
1239 }