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                 if ( $tagsToAdd ) {
 421                         // to be added, a tag has to be explicitly defined
 422                         // @todo Allow extensions to define tags that can be applied by users...
 423                         $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
 424                         $diff = array_diff( $tagsToAdd, $explicitlyDefinedTags );
 425                         if ( $diff ) {
 426                                 return self::restrictedTagError( 'tags-update-add-not-allowed-one',
 427                                         'tags-update-add-not-allowed-multi', $diff );
 428                         }
 429                 }
 430
 431                 if ( $tagsToRemove ) {
 432                         // to be removed, a tag must not be defined by an extension, or equivalently it
 433                         // has to be either explicitly defined or not defined at all
 434                         // (assuming no edge case of a tag both explicitly-defined and extension-defined)
 435                         $extensionDefinedTags = self::listExtensionDefinedTags();
 436                         $intersect = array_intersect( $tagsToRemove, $extensionDefinedTags );
 437                         if ( $intersect ) {
 438                                 return self::restrictedTagError( 'tags-update-remove-not-allowed-one',
 439                                         'tags-update-remove-not-allowed-multi', $intersect );
 440                         }
 441                 }
 442
 443                 return Status::newGood();
 444         }
 445
 446         /**
 447          * Adds and/or removes tags to/from a given change, checking whether it is
 448          * allowed first, and adding a log entry afterwards.
 449          *
 450          * Includes a call to ChangeTag::canUpdateTags(), so your code doesn't need
 451          * to do that. However, it doesn't check whether the *_id parameters are a
 452          * valid combination. That is up to you to enforce. See ApiTag::execute() for
 453          * an example.
 454          *
 455          * @param array|null $tagsToAdd If none, pass array() or null
 456          * @param array|null $tagsToRemove If none, pass array() or null
 457          * @param int|null $rc_id The rc_id of the change to add the tags to
 458          * @param int|null $rev_id The rev_id of the change to add the tags to
 459          * @param int|null $log_id The log_id of the change to add the tags to
 460          * @param string $params Params to put in the ct_params field of table
 461          * 'change_tag' when adding tags
 462          * @param string $reason Comment for the log
 463          * @param User $user Who to give credit for the action
 464          * @return Status If successful, the value of this Status object will be an
 465          * object (stdClass) with the following fields:
 466          *  - logId: the ID of the added log entry, or null if no log entry was added
 467          *    (i.e. no operation was performed)
 468          *  - addedTags: an array containing the tags that were actually added
 469          *  - removedTags: an array containing the tags that were actually removed
 470          * @since 1.25
 471          */
 472         public static function updateTagsWithChecks( $tagsToAdd, $tagsToRemove,
 473                 $rc_id, $rev_id, $log_id, $params, $reason, User $user ) {
 474
 475                 if ( is_null( $tagsToAdd ) ) {
 476                         $tagsToAdd = array();
 477                 }
 478                 if ( is_null( $tagsToRemove ) ) {
 479                         $tagsToRemove = array();
 480                 }
 481                 if ( !$tagsToAdd && !$tagsToRemove ) {
 482                         // no-op, don't bother
 483                         return Status::newGood( (object)array(
 484                                 'logId' => null,
 485                                 'addedTags' => array(),
 486                                 'removedTags' => array(),
 487                         ) );
 488                 }
 489
 490                 // are we allowed to do this?
 491                 $result = self::canUpdateTags( $tagsToAdd, $tagsToRemove, $user );
 492                 if ( !$result->isOK() ) {
 493                         $result->value = null;
 494                         return $result;
 495                 }
 496
 497                 // basic rate limiting
 498                 if ( $user->pingLimiter( 'changetag' ) ) {
 499                         return Status::newFatal( 'actionthrottledtext' );
 500                 }
 501
 502                 // do it!
 503                 list( $tagsAdded, $tagsRemoved, $initialTags ) = self::updateTags( $tagsToAdd,
 504                         $tagsToRemove, $rc_id, $rev_id, $log_id, $params );
 505                 if ( !$tagsAdded && !$tagsRemoved ) {
 506                         // no-op, don't log it
 507                         return Status::newGood( (object)array(
 508                                 'logId' => null,
 509                                 'addedTags' => array(),
 510                                 'removedTags' => array(),
 511                         ) );
 512                 }
 513
 514                 // log it
 515                 $logEntry = new ManualLogEntry( 'tag', 'update' );
 516                 $logEntry->setPerformer( $user );
 517                 $logEntry->setComment( $reason );
 518
 519                 // find the appropriate target page
 520                 if ( $rev_id ) {
 521                         $rev = Revision::newFromId( $rev_id );
 522                         if ( $rev ) {
 523                                 $logEntry->setTarget( $rev->getTitle() );
 524                         }
 525                 } elseif ( $log_id ) {
 526                         // This function is from revision deletion logic and has nothing to do with
 527                         // change tags, but it appears to be the only other place in core where we
 528                         // perform logged actions on log items.
 529                         $logEntry->setTarget( RevDelLogList::suggestTarget( 0, array( $log_id ) ) );
 530                 }
 531
 532                 if ( !$logEntry->getTarget() ) {
 533                         // target is required, so we have to set something
 534                         $logEntry->setTarget( SpecialPage::getTitleFor( 'Tags' ) );
 535                 }
 536
 537                 $logParams = array(
 538                         '4::revid' => $rev_id,
 539                         '5::logid' => $log_id,
 540                         '6:list:tagsAdded' => $tagsAdded,
 541                         '7:number:tagsAddedCount' => count( $tagsAdded ),
 542                         '8:list:tagsRemoved' => $tagsRemoved,
 543                         '9:number:tagsRemovedCount' => count( $tagsRemoved ),
 544                         'initialTags' => $initialTags,
 545                 );
 546                 $logEntry->setParameters( $logParams );
 547                 $logEntry->setRelations( array( 'Tag' => array_merge( $tagsAdded, $tagsRemoved ) ) );
 548
 549                 $dbw = wfGetDB( DB_MASTER );
 550                 $logId = $logEntry->insert( $dbw );
 551                 // Only send this to UDP, not RC, similar to patrol events
 552                 $logEntry->publish( $logId, 'udp' );
 553
 554                 return Status::newGood( (object)array(
 555                         'logId' => $logId,
 556                         'addedTags' => $tagsAdded,
 557                         'removedTags' => $tagsRemoved,
 558                 ) );
 559         }
 560
 561         /**
 562          * Applies all tags-related changes to a query.
 563          * Handles selecting tags, and filtering.
 564          * Needs $tables to be set up properly, so we can figure out which join conditions to use.
 565          *
 566          * @param string|array $tables Table names, see DatabaseBase::select
 567          * @param string|array $fields Fields used in query, see DatabaseBase::select
 568          * @param string|array $conds Conditions used in query, see DatabaseBase::select
 569          * @param array $join_conds Join conditions, see DatabaseBase::select
 570          * @param array $options Options, see Database::select
 571          * @param bool|string $filter_tag Tag to select on
 572          *
 573          * @throws MWException When unable to determine appropriate JOIN condition for tagging
 574          */
 575         public static function modifyDisplayQuery( &$tables, &$fields, &$conds,
 576                                                                                 &$join_conds, &$options, $filter_tag = false ) {
 577                 global $wgRequest, $wgUseTagFilter;
 578
 579                 if ( $filter_tag === false ) {
 580                         $filter_tag = $wgRequest->getVal( 'tagfilter' );
 581                 }
 582
 583                 // Figure out which conditions can be done.
 584                 if ( in_array( 'recentchanges', $tables ) ) {
 585                         $join_cond = 'ct_rc_id=rc_id';
 586                 } elseif ( in_array( 'logging', $tables ) ) {
 587                         $join_cond = 'ct_log_id=log_id';
 588                 } elseif ( in_array( 'revision', $tables ) ) {
 589                         $join_cond = 'ct_rev_id=rev_id';
 590                 } elseif ( in_array( 'archive', $tables ) ) {
 591                         $join_cond = 'ct_rev_id=ar_rev_id';
 592                 } else {
 593                         throw new MWException( 'Unable to determine appropriate JOIN condition for tagging.' );
 594                 }
 595
 596                 $fields['ts_tags'] = wfGetDB( DB_SLAVE )->buildGroupConcatField(
 597                         ',', 'change_tag', 'ct_tag', $join_cond
 598                 );
 599
 600                 if ( $wgUseTagFilter && $filter_tag ) {
 601                         // Somebody wants to filter on a tag.
 602                         // Add an INNER JOIN on change_tag
 603
 604                         $tables[] = 'change_tag';
 605                         $join_conds['change_tag'] = array( 'INNER JOIN', $join_cond );
 606                         $conds['ct_tag'] = $filter_tag;
 607                 }
 608         }
 609
 610         /**
 611          * Build a text box to select a change tag
 612          *
 613          * @param string $selected Tag to select by default
 614          * @param bool $fullForm
 615          *        - if false, then it returns an array of (label, form).
 616          *        - if true, it returns an entire form around the selector.
 617          * @param Title $title Title object to send the form to.
 618          *        Used when, and only when $fullForm is true.
 619          * @return string|array
 620          *        - if $fullForm is false: Array with
 621          *        - if $fullForm is true: String, html fragment
 622          */
 623         public static function buildTagFilterSelector( $selected = '',
 624                 $fullForm = false, Title $title = null
 625         ) {
 626                 global $wgUseTagFilter;
 627
 628                 if ( !$wgUseTagFilter || !count( self::listDefinedTags() ) ) {
 629                         return $fullForm ? '' : array();
 630                 }
 631
 632                 $data = array(
 633                         Html::rawElement(
 634                                 'label',
 635                                 array( 'for' => 'tagfilter' ),
 636                                 wfMessage( 'tag-filter' )->parse()
 637                         ),
 638                         Xml::input(
 639                                 'tagfilter',
 640                                 20,
 641                                 $selected,
 642                                 array( 'class' => 'mw-tagfilter-input mw-ui-input mw-ui-input-inline', 'id' => 'tagfilter' )
 643                         )
 644                 );
 645
 646                 if ( !$fullForm ) {
 647                         return $data;
 648                 }
 649
 650                 $html = implode( '&#160;', $data );
 651                 $html .= "\n" .
 652                         Xml::element(
 653                                 'input',
 654                                 array( 'type' => 'submit', 'value' => wfMessage( 'tag-filter-submit' )->text() )
 655                         );
 656                 $html .= "\n" . Html::hidden( 'title', $title->getPrefixedText() );
 657                 $html = Xml::tags(
 658                         'form',
 659                         array( 'action' => $title->getLocalURL(), 'class' => 'mw-tagfilter-form', 'method' => 'get' ),
 660                         $html
 661                 );
 662
 663                 return $html;
 664         }
 665
 666         /**
 667          * Defines a tag in the valid_tag table, without checking that the tag name
 668          * is valid.
 669          * Extensions should NOT use this function; they can use the ListDefinedTags
 670          * hook instead.
 671          *
 672          * @param string $tag Tag to create
 673          * @since 1.25
 674          */
 675         public static function defineTag( $tag ) {
 676                 $dbw = wfGetDB( DB_MASTER );
 677                 $dbw->replace( 'valid_tag',
 678                         array( 'vt_tag' ),
 679                         array( 'vt_tag' => $tag ),
 680                         __METHOD__ );
 681
 682                 // clear the memcache of defined tags
 683                 self::purgeTagCacheAll();
 684         }
 685
 686         /**
 687          * Removes a tag from the valid_tag table. The tag may remain in use by
 688          * extensions, and may still show up as 'defined' if an extension is setting
 689          * it from the ListDefinedTags hook.
 690          *
 691          * @param string $tag Tag to remove
 692          * @since 1.25
 693          */
 694         public static function undefineTag( $tag ) {
 695                 $dbw = wfGetDB( DB_MASTER );
 696                 $dbw->delete( 'valid_tag', array( 'vt_tag' => $tag ), __METHOD__ );
 697
 698                 // clear the memcache of defined tags
 699                 self::purgeTagCacheAll();
 700         }
 701
 702         /**
 703          * Writes a tag action into the tag management log.
 704          *
 705          * @param string $action
 706          * @param string $tag
 707          * @param string $reason
 708          * @param User $user Who to attribute the action to
 709          * @param int $tagCount For deletion only, how many usages the tag had before
 710          * it was deleted.
 711          * @return int ID of the inserted log entry
 712          * @since 1.25
 713          */
 714         protected static function logTagManagementAction( $action, $tag, $reason,
 715                 User $user, $tagCount = null ) {
 716
 717                 $dbw = wfGetDB( DB_MASTER );
 718
 719                 $logEntry = new ManualLogEntry( 'managetags', $action );
 720                 $logEntry->setPerformer( $user );
 721                 // target page is not relevant, but it has to be set, so we just put in
 722                 // the title of Special:Tags
 723                 $logEntry->setTarget( Title::newFromText( 'Special:Tags' ) );
 724                 $logEntry->setComment( $reason );
 725
 726                 $params = array( '4::tag' => $tag );
 727                 if ( !is_null( $tagCount ) ) {
 728                         $params['5:number:count'] = $tagCount;
 729                 }
 730                 $logEntry->setParameters( $params );
 731                 $logEntry->setRelations( array( 'Tag' => $tag ) );
 732
 733                 $logId = $logEntry->insert( $dbw );
 734                 $logEntry->publish( $logId );
 735                 return $logId;
 736         }
 737
 738         /**
 739          * Is it OK to allow the user to activate this tag?
 740          *
 741          * @param string $tag Tag that you are interested in activating
 742          * @param User|null $user User whose permission you wish to check, or null if
 743          * you don't care (e.g. maintenance scripts)
 744          * @return Status
 745          * @since 1.25
 746          */
 747         public static function canActivateTag( $tag, User $user = null ) {
 748                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 749                         return Status::newFatal( 'tags-manage-no-permission' );
 750                 }
 751
 752                 // non-existing tags cannot be activated
 753                 $tagUsage = self::tagUsageStatistics();
 754                 if ( !isset( $tagUsage[$tag] ) ) {
 755                         return Status::newFatal( 'tags-activate-not-found', $tag );
 756                 }
 757
 758                 // defined tags cannot be activated (a defined tag is either extension-
 759                 // defined, in which case the extension chooses whether or not to active it;
 760                 // or user-defined, in which case it is considered active)
 761                 $definedTags = self::listDefinedTags();
 762                 if ( in_array( $tag, $definedTags ) ) {
 763                         return Status::newFatal( 'tags-activate-not-allowed', $tag );
 764                 }
 765
 766                 return Status::newGood();
 767         }
 768
 769         /**
 770          * Activates a tag, checking whether it is allowed first, and adding a log
 771          * entry afterwards.
 772          *
 773          * Includes a call to ChangeTag::canActivateTag(), so your code doesn't need
 774          * to do that.
 775          *
 776          * @param string $tag
 777          * @param string $reason
 778          * @param User $user Who to give credit for the action
 779          * @param bool $ignoreWarnings Can be used for API interaction, default false
 780          * @return Status If successful, the Status contains the ID of the added log
 781          * entry as its value
 782          * @since 1.25
 783          */
 784         public static function activateTagWithChecks( $tag, $reason, User $user,
 785                 $ignoreWarnings = false ) {
 786
 787                 // are we allowed to do this?
 788                 $result = self::canActivateTag( $tag, $user );
 789                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 790                         $result->value = null;
 791                         return $result;
 792                 }
 793
 794                 // do it!
 795                 self::defineTag( $tag );
 796
 797                 // log it
 798                 $logId = self::logTagManagementAction( 'activate', $tag, $reason, $user );
 799                 return Status::newGood( $logId );
 800         }
 801
 802         /**
 803          * Is it OK to allow the user to deactivate this tag?
 804          *
 805          * @param string $tag Tag that you are interested in deactivating
 806          * @param User|null $user User whose permission you wish to check, or null if
 807          * you don't care (e.g. maintenance scripts)
 808          * @return Status
 809          * @since 1.25
 810          */
 811         public static function canDeactivateTag( $tag, User $user = null ) {
 812                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 813                         return Status::newFatal( 'tags-manage-no-permission' );
 814                 }
 815
 816                 // only explicitly-defined tags can be deactivated
 817                 $explicitlyDefinedTags = self::listExplicitlyDefinedTags();
 818                 if ( !in_array( $tag, $explicitlyDefinedTags ) ) {
 819                         return Status::newFatal( 'tags-deactivate-not-allowed', $tag );
 820                 }
 821                 return Status::newGood();
 822         }
 823
 824         /**
 825          * Deactivates a tag, checking whether it is allowed first, and adding a log
 826          * entry afterwards.
 827          *
 828          * Includes a call to ChangeTag::canDeactivateTag(), so your code doesn't need
 829          * to do that.
 830          *
 831          * @param string $tag
 832          * @param string $reason
 833          * @param User $user Who to give credit for the action
 834          * @param bool $ignoreWarnings Can be used for API interaction, default false
 835          * @return Status If successful, the Status contains the ID of the added log
 836          * entry as its value
 837          * @since 1.25
 838          */
 839         public static function deactivateTagWithChecks( $tag, $reason, User $user,
 840                 $ignoreWarnings = false ) {
 841
 842                 // are we allowed to do this?
 843                 $result = self::canDeactivateTag( $tag, $user );
 844                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 845                         $result->value = null;
 846                         return $result;
 847                 }
 848
 849                 // do it!
 850                 self::undefineTag( $tag );
 851
 852                 // log it
 853                 $logId = self::logTagManagementAction( 'deactivate', $tag, $reason, $user );
 854                 return Status::newGood( $logId );
 855         }
 856
 857         /**
 858          * Is it OK to allow the user to create this tag?
 859          *
 860          * @param string $tag Tag that you are interested in creating
 861          * @param User|null $user User whose permission you wish to check, or null if
 862          * you don't care (e.g. maintenance scripts)
 863          * @return Status
 864          * @since 1.25
 865          */
 866         public static function canCreateTag( $tag, User $user = null ) {
 867                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 868                         return Status::newFatal( 'tags-manage-no-permission' );
 869                 }
 870
 871                 // no empty tags
 872                 if ( $tag === '' ) {
 873                         return Status::newFatal( 'tags-create-no-name' );
 874                 }
 875
 876                 // tags cannot contain commas (used as a delimiter in tag_summary table) or
 877                 // slashes (would break tag description messages in MediaWiki namespace)
 878                 if ( strpos( $tag, ',' ) !== false || strpos( $tag, '/' ) !== false ) {
 879                         return Status::newFatal( 'tags-create-invalid-chars' );
 880                 }
 881
 882                 // could the MediaWiki namespace description messages be created?
 883                 $title = Title::makeTitleSafe( NS_MEDIAWIKI, "Tag-$tag-description" );
 884                 if ( is_null( $title ) ) {
 885                         return Status::newFatal( 'tags-create-invalid-title-chars' );
 886                 }
 887
 888                 // does the tag already exist?
 889                 $tagUsage = self::tagUsageStatistics();
 890                 if ( isset( $tagUsage[$tag] ) ) {
 891                         return Status::newFatal( 'tags-create-already-exists', $tag );
 892                 }
 893
 894                 // check with hooks
 895                 $canCreateResult = Status::newGood();
 896                 Hooks::run( 'ChangeTagCanCreate', array( $tag, $user, &$canCreateResult ) );
 897                 return $canCreateResult;
 898         }
 899
 900         /**
 901          * Creates a tag by adding a row to the `valid_tag` table.
 902          *
 903          * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
 904          * do that.
 905          *
 906          * @param string $tag
 907          * @param string $reason
 908          * @param User $user Who to give credit for the action
 909          * @param bool $ignoreWarnings Can be used for API interaction, default false
 910          * @return Status If successful, the Status contains the ID of the added log
 911          * entry as its value
 912          * @since 1.25
 913          */
 914         public static function createTagWithChecks( $tag, $reason, User $user,
 915                 $ignoreWarnings = false ) {
 916
 917                 // are we allowed to do this?
 918                 $result = self::canCreateTag( $tag, $user );
 919                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
 920                         $result->value = null;
 921                         return $result;
 922                 }
 923
 924                 // do it!
 925                 self::defineTag( $tag );
 926
 927                 // log it
 928                 $logId = self::logTagManagementAction( 'create', $tag, $reason, $user );
 929                 return Status::newGood( $logId );
 930         }
 931
 932         /**
 933          * Permanently removes all traces of a tag from the DB. Good for removing
 934          * misspelt or temporary tags.
 935          *
 936          * This function should be directly called by maintenance scripts only, never
 937          * by user-facing code. See deleteTagWithChecks() for functionality that can
 938          * safely be exposed to users.
 939          *
 940          * @param string $tag Tag to remove
 941          * @return Status The returned status will be good unless a hook changed it
 942          * @since 1.25
 943          */
 944         public static function deleteTagEverywhere( $tag ) {
 945                 $dbw = wfGetDB( DB_MASTER );
 946                 $dbw->startAtomic( __METHOD__ );
 947
 948                 // delete from valid_tag
 949                 self::undefineTag( $tag );
 950
 951                 // find out which revisions use this tag, so we can delete from tag_summary
 952                 $result = $dbw->select( 'change_tag',
 953                         array( 'ct_rc_id', 'ct_log_id', 'ct_rev_id', 'ct_tag' ),
 954                         array( 'ct_tag' => $tag ),
 955                         __METHOD__ );
 956                 foreach ( $result as $row ) {
 957                         // remove the tag from the relevant row of tag_summary
 958                         $tagsToAdd = array();
 959                         $tagsToRemove = array( $tag );
 960                         self::updateTagSummaryRow( $tagsToAdd, $tagsToRemove, $row->ct_rc_id,
 961                                 $row->ct_rev_id, $row->ct_log_id );
 962                 }
 963
 964                 // delete from change_tag
 965                 $dbw->delete( 'change_tag', array( 'ct_tag' => $tag ), __METHOD__ );
 966
 967                 $dbw->endAtomic( __METHOD__ );
 968
 969                 // give extensions a chance
 970                 $status = Status::newGood();
 971                 Hooks::run( 'ChangeTagAfterDelete', array( $tag, &$status ) );
 972                 // let's not allow error results, as the actual tag deletion succeeded
 973                 if ( !$status->isOK() ) {
 974                         wfDebug( 'ChangeTagAfterDelete error condition downgraded to warning' );
 975                         $status->ok = true;
 976                 }
 977
 978                 // clear the memcache of defined tags
 979                 self::purgeTagCacheAll();
 980
 981                 return $status;
 982         }
 983
 984         /**
 985          * Is it OK to allow the user to delete this tag?
 986          *
 987          * @param string $tag Tag that you are interested in deleting
 988          * @param User|null $user User whose permission you wish to check, or null if
 989          * you don't care (e.g. maintenance scripts)
 990          * @return Status
 991          * @since 1.25
 992          */
 993         public static function canDeleteTag( $tag, User $user = null ) {
 994                 $tagUsage = self::tagUsageStatistics();
 995
 996                 if ( !is_null( $user ) && !$user->isAllowed( 'managechangetags' ) ) {
 997                         return Status::newFatal( 'tags-manage-no-permission' );
 998                 }
 999
1000                 if ( !isset( $tagUsage[$tag] ) ) {
1001                         return Status::newFatal( 'tags-delete-not-found', $tag );
1002                 }
1003
1004                 if ( $tagUsage[$tag] > self::MAX_DELETE_USES ) {
1005                         return Status::newFatal( 'tags-delete-too-many-uses', $tag, self::MAX_DELETE_USES );
1006                 }
1007
1008                 $extensionDefined = self::listExtensionDefinedTags();
1009                 if ( in_array( $tag, $extensionDefined ) ) {
1010                         // extension-defined tags can't be deleted unless the extension
1011                         // specifically allows it
1012                         $status = Status::newFatal( 'tags-delete-not-allowed' );
1013                 } else {
1014                         // user-defined tags are deletable unless otherwise specified
1015                         $status = Status::newGood();
1016                 }
1017
1018                 Hooks::run( 'ChangeTagCanDelete', array( $tag, $user, &$status ) );
1019                 return $status;
1020         }
1021
1022         /**
1023          * Deletes a tag, checking whether it is allowed first, and adding a log entry
1024          * afterwards.
1025          *
1026          * Includes a call to ChangeTag::canDeleteTag(), so your code doesn't need to
1027          * do that.
1028          *
1029          * @param string $tag
1030          * @param string $reason
1031          * @param User $user Who to give credit for the action
1032          * @param bool $ignoreWarnings Can be used for API interaction, default false
1033          * @return Status If successful, the Status contains the ID of the added log
1034          * entry as its value
1035          * @since 1.25
1036          */
1037         public static function deleteTagWithChecks( $tag, $reason, User $user,
1038                 $ignoreWarnings = false ) {
1039
1040                 // are we allowed to do this?
1041                 $result = self::canDeleteTag( $tag, $user );
1042                 if ( $ignoreWarnings ? !$result->isOK() : !$result->isGood() ) {
1043                         $result->value = null;
1044                         return $result;
1045                 }
1046
1047                 // store the tag usage statistics
1048                 $tagUsage = self::tagUsageStatistics();
1049
1050                 // do it!
1051                 $deleteResult = self::deleteTagEverywhere( $tag );
1052                 if ( !$deleteResult->isOK() ) {
1053                         return $deleteResult;
1054                 }
1055
1056                 // log it
1057                 $logId = self::logTagManagementAction( 'delete', $tag, $reason, $user, $tagUsage[$tag] );
1058                 $deleteResult->value = $logId;
1059                 return $deleteResult;
1060         }
1061
1062         /**
1063          * Lists those tags which extensions report as being "active".
1064          *
1065          * @return array
1066          * @since 1.25
1067          */
1068         public static function listExtensionActivatedTags() {
1069                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1070                         wfMemcKey( 'active-tags' ),
1071                         function() {
1072                                 // Ask extensions which tags they consider active
1073                                 $extensionActive = array();
1074                                 Hooks::run( 'ChangeTagsListActive', array( &$extensionActive ) );
1075                                 return $extensionActive;
1076                         },
1077                         300,
1078                         array( wfMemcKey( 'active-tags' ) ),
1079                         array( 'lockTSE' => INF )
1080                 );
1081         }
1082
1083         /**
1084          * Basically lists defined tags which count even if they aren't applied to anything.
1085          * It returns a union of the results of listExplicitlyDefinedTags() and
1086          * listExtensionDefinedTags().
1087          *
1088          * @return string[] Array of strings: tags
1089          */
1090         public static function listDefinedTags() {
1091                 $tags1 = self::listExplicitlyDefinedTags();
1092                 $tags2 = self::listExtensionDefinedTags();
1093                 return array_values( array_unique( array_merge( $tags1, $tags2 ) ) );
1094         }
1095
1096         /**
1097          * Lists tags explicitly defined in the `valid_tag` table of the database.
1098          * Tags in table 'change_tag' which are not in table 'valid_tag' are not
1099          * included.
1100          *
1101          * Tries memcached first.
1102          *
1103          * @return string[] Array of strings: tags
1104          * @since 1.25
1105          */
1106         public static function listExplicitlyDefinedTags() {
1107                 $fname = __METHOD__;
1108
1109                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1110                         wfMemcKey( 'valid-tags-db' ),
1111                         function() use ( $fname ) {
1112                                 $dbr = wfGetDB( DB_SLAVE );
1113                                 $tags = $dbr->selectFieldValues(
1114                                         'valid_tag', 'vt_tag', array(), $fname );
1115
1116                                 return array_filter( array_unique( $tags ) );
1117                         },
1118                         300,
1119                         array( wfMemcKey( 'valid-tags-db' ) ),
1120                         array( 'lockTSE' => INF )
1121                 );
1122         }
1123
1124         /**
1125          * Lists tags defined by extensions using the ListDefinedTags hook.
1126          * Extensions need only define those tags they deem to be in active use.
1127          *
1128          * Tries memcached first.
1129          *
1130          * @return string[] Array of strings: tags
1131          * @since 1.25
1132          */
1133         public static function listExtensionDefinedTags() {
1134                 return ObjectCache::getMainWANInstance()->getWithSetCallback(
1135                         wfMemcKey( 'valid-tags-hook' ),
1136                         function() {
1137                                 $tags = array();
1138                                 Hooks::run( 'ListDefinedTags', array( &$tags ) );
1139                                 return array_filter( array_unique( $tags ) );
1140                         },
1141                         300,
1142                         array( wfMemcKey( 'valid-tags-hook' ) ),
1143                         array( 'lockTSE' => INF )
1144                 );
1145         }
1146
1147         /**
1148          * Invalidates the short-term cache of defined tags used by the
1149          * list*DefinedTags functions, as well as the tag statistics cache.
1150          * @since 1.25
1151          */
1152         public static function purgeTagCacheAll() {
1153                 $cache = ObjectCache::getMainWANInstance();
1154
1155                 $cache->touchCheckKey( wfMemcKey( 'active-tags' ) );
1156                 $cache->touchCheckKey( wfMemcKey( 'valid-tags-db' ) );
1157                 $cache->touchCheckKey( wfMemcKey( 'valid-tags-hook' ) );
1158
1159                 self::purgeTagUsageCache();
1160         }
1161
1162         /**
1163          * Invalidates the tag statistics cache only.
1164          * @since 1.25
1165          */
1166         public static function purgeTagUsageCache() {
1167                 $cache = ObjectCache::getMainWANInstance();
1168
1169                 $cache->touchCheckKey( wfMemcKey( 'change-tag-statistics' ) );
1170         }
1171
1172         /**
1173          * Returns a map of any tags used on the wiki to number of edits
1174          * tagged with them, ordered descending by the hitcount.
1175          * This does not include tags defined somewhere that have never been applied.
1176          *
1177          * Keeps a short-term cache in memory, so calling this multiple times in the
1178          * same request should be fine.
1179          *
1180          * @return array Array of string => int
1181          */
1182         public static function tagUsageStatistics() {
1183                 static $cachedStats = null;
1184
1185                 // Process cache to avoid I/O and repeated regens during holdoff
1186                 if ( $cachedStats !== null ) {
1187                         return $cachedStats;
1188                 }
1189
1190                 $fname = __METHOD__;
1191                 $cachedStats = ObjectCache::getMainWANInstance()->getWithSetCallback(
1192                         wfMemcKey( 'change-tag-statistics' ),
1193                         function() use ( $fname ) {
1194                                 $out = array();
1195
1196                                 $dbr = wfGetDB( DB_SLAVE, 'vslow' );
1197                                 $res = $dbr->select(
1198                                         'change_tag',
1199                                         array( 'ct_tag', 'hitcount' => 'count(*)' ),
1200                                         array(),
1201                                         $fname,
1202                                         array( 'GROUP BY' => 'ct_tag', 'ORDER BY' => 'hitcount DESC' )
1203                                 );
1204
1205                                 foreach ( $res as $row ) {
1206                                         $out[$row->ct_tag] = $row->hitcount;
1207                                 }
1208
1209                                 return $out;
1210                         },
1211                         300,
1212                         array( wfMemcKey( 'change-tag-statistics' ) ),
1213                         array( 'lockTSE' => INF )
1214                 );
1215
1216                 return $cachedStats;
1217         }
1218
1219         /**
1220          * Indicate whether change tag editing UI is relevant
1221          *
1222          * Returns true if the user has the necessary right and there are any
1223          * editable tags defined.
1224          *
1225          * This intentionally doesn't check "any addable || any deletable", because
1226          * it seems like it would be more confusing than useful if the checkboxes
1227          * suddenly showed up because some abuse filter stopped defining a tag and
1228          * then suddenly disappeared when someone deleted all uses of that tag.
1229          *
1230          * @param User $user
1231          * @return bool
1232          */
1233         public static function showTagEditingUI( User $user ) {
1234                 return $user->isAllowed( 'changetags' ) && (bool)self::listExplicitlyDefinedTags();
1235         }
1236 }