includes/collation/IcuCollation.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  */
  20
  21 /**
  22  * @since 1.16.3
  23  */
  24 class IcuCollation extends Collation {
  25         const FIRST_LETTER_VERSION = 2;
  26
  27         /** @var Collator */
  28         private $primaryCollator;
  29
  30         /** @var Collator */
  31         private $mainCollator;
  32
  33         /** @var string */
  34         private $locale;
  35
  36         /** @var Language */
  37         protected $digitTransformLanguage;
  38
  39         /** @var boolean */
  40         private $useNumericCollation = false;
  41
  42         /** @var array */
  43         private $firstLetterData;
  44
  45         /**
  46          * Unified CJK blocks.
  47          *
  48          * The same definition of a CJK block must be used for both Collation and
  49          * generateCollationData.php. These blocks are omitted from the first
  50          * letter data, as an optimisation measure and because the default UCA table
  51          * is pretty useless for sorting Chinese text anyway. Japanese and Korean
  52          * blocks are not included here, because they are smaller and more useful.
  53          */
  54         private static $cjkBlocks = [
  55                 [ 0x2E80, 0x2EFF ], // CJK Radicals Supplement
  56                 [ 0x2F00, 0x2FDF ], // Kangxi Radicals
  57                 [ 0x2FF0, 0x2FFF ], // Ideographic Description Characters
  58                 [ 0x3000, 0x303F ], // CJK Symbols and Punctuation
  59                 [ 0x31C0, 0x31EF ], // CJK Strokes
  60                 [ 0x3200, 0x32FF ], // Enclosed CJK Letters and Months
  61                 [ 0x3300, 0x33FF ], // CJK Compatibility
  62                 [ 0x3400, 0x4DBF ], // CJK Unified Ideographs Extension A
  63                 [ 0x4E00, 0x9FFF ], // CJK Unified Ideographs
  64                 [ 0xF900, 0xFAFF ], // CJK Compatibility Ideographs
  65                 [ 0xFE30, 0xFE4F ], // CJK Compatibility Forms
  66                 [ 0x20000, 0x2A6DF ], // CJK Unified Ideographs Extension B
  67                 [ 0x2A700, 0x2B73F ], // CJK Unified Ideographs Extension C
  68                 [ 0x2B740, 0x2B81F ], // CJK Unified Ideographs Extension D
  69                 [ 0x2F800, 0x2FA1F ], // CJK Compatibility Ideographs Supplement
  70         ];
  71
  72         /**
  73          * Additional characters (or character groups) to be considered separate
  74          * letters for given languages, or to be removed from the list of such
  75          * letters (denoted by keys starting with '-').
  76          *
  77          * These are additions to (or subtractions from) the data stored in the
  78          * first-letters-root.ser file (which among others includes full basic latin,
  79          * cyrillic and greek alphabets).
  80          *
  81          * "Separate letter" is a letter that would have a separate heading/section
  82          * for it in a dictionary or a phone book in this language. This data isn't
  83          * used for sorting (the ICU library handles that), only for deciding which
  84          * characters (or character groups) to use as headings.
  85          *
  86          * Initially generated based on the primary level of Unicode collation
  87          * tailorings available at http://developer.mimer.com/charts/tailorings.htm ,
  88          * later modified.
  89          *
  90          * Empty arrays are intended; this signifies that the data for the language is
  91          * available and that there are, in fact, no additional letters to consider.
  92          */
  93         private static $tailoringFirstLetters = [
  94                 'af' => [],
  95                 'am' => [],
  96                 'ar' => [],
  97                 'as' => [ "\xe0\xa6\x82", "\xe0\xa6\x81", "\xe0\xa6\x83", "\xe0\xa7\x8e", "ক্ষ " ],
  98                 'ast' => [ "Ch", "Ll", "Ñ" ], // not in libicu
  99                 'az' => [ "Ç", "Ə", "Ğ", "İ", "Ö", "Ş", "Ü" ],
 100                 'be' => [ "Ё" ],
 101                 'be-tarask' => [ "Ё" ],
 102                 'bg' => [],
 103                 'bn' => [ 'ং', 'ঃ', 'ঁ' ],
 104                 'bn@collation=traditional' => [
 105                         'ং', 'ঃ', 'ঁ', 'ক্', 'খ্', 'গ্', 'ঘ্', 'ঙ্', 'চ্', 'ছ্', 'জ্', 'ঝ্',
 106                         'ঞ্', 'ট্', 'ঠ্', 'ড্', 'ঢ্', 'ণ্', 'ৎ', 'থ্', 'দ্', 'ধ্', 'ন্', 'প্',
 107                         'ফ্', 'ব্', 'ভ্', 'ম্', 'য্', 'র্', 'ৰ্', 'ল্', 'ৱ্', 'শ্', 'ষ্', 'স্', 'হ্'
 108                 ],
 109                 'bo' => [],
 110                 'br' => [ "Ch", "C'h" ],
 111                 'bs' => [ "Č", "Ć", "Dž", "Đ", "Lj", "Nj", "Š", "Ž" ],
 112                 'bs-Cyrl' => [],
 113                 'ca' => [],
 114                 'chr' => [],
 115                 'co' => [], // not in libicu
 116                 'cs' => [ "Č", "Ch", "Ř", "Š", "Ž" ],
 117                 'cy' => [ "Ch", "Dd", "Ff", "Ng", "Ll", "Ph", "Rh", "Th" ],
 118                 'da' => [ "Æ", "Ø", "Å" ],
 119                 'de' => [],
 120                 'de-AT@collation=phonebook' => [ 'ä', 'ö', 'ü', 'ß' ],
 121                 'dsb' => [ "Č", "Ć", "Dź", "Ě", "Ch", "Ł", "Ń", "Ŕ", "Š", "Ś", "Ž", "Ź" ],
 122                 'ee' => [ "Dz", "Ɖ", "Ɛ", "Ƒ", "Gb", "Ɣ", "Kp", "Ny", "Ŋ", "Ɔ", "Ts", "Ʋ" ],
 123                 'el' => [],
 124                 'en' => [],
 125                 'eo' => [ "Ĉ", "Ĝ", "Ĥ", "Ĵ", "Ŝ", "Ŭ" ],
 126                 'es' => [ "Ñ" ],
 127                 'et' => [ "Š", "Ž", "Õ", "Ä", "Ö", "Ü", "W" ], // added W for CollationEt (xx-uca-et)
 128                 'eu' => [ "Ñ" ], // not in libicu
 129                 'fa' => [
 130                         // RTL, let's put each letter on a new line
 131                         "آ",
 132                         "ء",
 133                         "ه",
 134                         "ا",
 135                         "و"
 136                 ],
 137                 'fi' => [ "Å", "Ä", "Ö" ],
 138                 'fil' => [ "Ñ", "Ng" ],
 139                 'fo' => [ "Á", "Ð", "Í", "Ó", "Ú", "Ý", "Æ", "Ø", "Å" ],
 140                 'fr' => [],
 141                 'fr-CA' => [], // fr-CA sorts accents slightly different from fr.
 142                 'fur' => [ "À", "Á", "Â", "È", "Ì", "Ò", "Ù" ], // not in libicu
 143                 'fy' => [], // not in libicu
 144                 'ga' => [],
 145                 'gd' => [], // not in libicu
 146                 'gl' => [ "Ch", "Ll", "Ñ" ],
 147                 'gu' => [ "\xe0\xaa\x82", "\xe0\xaa\x83", "\xe0\xaa\x81", "\xe0\xaa\xb3" ],
 148                 'ha' => [ 'Ɓ', 'Ɗ', 'Ƙ', 'Sh', 'Ts', 'Ƴ' ],
 149                 'haw' => [ 'ʻ' ],
 150                 'he' => [],
 151                 'hi' => [ "\xe0\xa4\x82", "\xe0\xa4\x83" ],
 152                 'hr' => [ "Č", "Ć", "Dž", "Đ", "Lj", "Nj", "Š", "Ž" ],
 153                 'hsb' => [ "Č", "Dź", "Ě", "Ch", "Ł", "Ń", "Ř", "Š", "Ć", "Ž" ],
 154                 'hu' => [ "Cs", "Dz", "Dzs", "Gy", "Ly", "Ny", "Ö", "Sz", "Ty", "Ü", "Zs" ],
 155                 'hy' => [ "և" ],
 156                 'id' => [],
 157                 'ig' => [ "Ch", "Gb", "Gh", "Gw", "Ị", "Kp", "Kw", "Ṅ", "Nw", "Ny", "Ọ", "Sh", "Ụ" ],
 158                 'is' => [ "Á", "Ð", "É", "Í", "Ó", "Ú", "Ý", "Þ", "Æ", "Ö", "Å" ],
 159                 'it' => [],
 160                 'ka' => [],
 161                 'kk' => [ "Ү", "І" ],
 162                 'kl' => [ "Æ", "Ø", "Å" ],
 163                 'km' => [
 164                         "រ", "ឫ", "ឬ", "ល", "ឭ", "ឮ", "\xe1\x9e\xbb\xe1\x9f\x86",
 165                         "\xe1\x9f\x86", "\xe1\x9e\xb6\xe1\x9f\x86", "\xe1\x9f\x87",
 166                         "\xe1\x9e\xb7\xe1\x9f\x87", "\xe1\x9e\xbb\xe1\x9f\x87",
 167                         "\xe1\x9f\x81\xe1\x9f\x87", "\xe1\x9f\x84\xe1\x9f\x87",
 168                 ],
 169                 'kn' => [ "\xe0\xb2\x81", "\xe0\xb2\x83", "\xe0\xb3\xb1", "\xe0\xb3\xb2" ],
 170                 'kok' => [ "\xe0\xa4\x82", "\xe0\xa4\x83", "ळ", "क्ष" ],
 171                 'ku' => [ "Ç", "Ê", "Î", "Ş", "Û" ], // not in libicu
 172                 'ky' => [ "Ё" ],
 173                 'la' => [], // not in libicu
 174                 'lb' => [],
 175                 'lkt' => [ 'Č', 'Ǧ', 'Ȟ', 'Š', 'Ž' ],
 176                 'ln' => [ 'Ɛ' ],
 177                 'lo' => [],
 178                 'lt' => [ "Č", "Š", "Ž" ],
 179                 'lv' => [ "Č", "Ģ", "Ķ", "Ļ", "Ņ", "Š", "Ž" ],
 180                 'mk' => [ "Ѓ", "Ќ" ],
 181                 'ml' => [],
 182                 'mn' => [],
 183                 'mo' => [ "Ă", "Â", "Î", "Ş", "Ţ" ], // not in libicu
 184                 'mr' => [ "\xe0\xa4\x82", "\xe0\xa4\x83", "ळ", "क्ष", "ज्ञ" ],
 185                 'ms' => [],
 186                 'mt' => [ "Ċ", "Ġ", "Għ", "Ħ", "Ż" ],
 187                 'nb' => [ "Æ", "Ø", "Å" ],
 188                 'ne' => [],
 189                 'nl' => [],
 190                 'nn' => [ "Æ", "Ø", "Å" ],
 191                 'no' => [ "Æ", "Ø", "Å" ], // not in libicu. You should probably use nb or nn instead.
 192                 'oc' => [], // not in libicu
 193                 'om' => [ 'Ch', 'Dh', 'Kh', 'Ny', 'Ph', 'Sh' ],
 194                 'or' => [ "\xe0\xac\x81", "\xe0\xac\x82", "\xe0\xac\x83", "କ୍ଷ" ],
 195                 'pa' => [ "\xe0\xa9\x8d" ],
 196                 'pl' => [ "Ą", "Ć", "Ę", "Ł", "Ń", "Ó", "Ś", "Ź", "Ż" ],
 197                 'pt' => [],
 198                 'rm' => [], // not in libicu
 199                 'ro' => [ "Ă", "Â", "Î", "Ş", "Ţ" ],
 200                 'ru' => [],
 201                 'rup' => [ "Ă", "Â", "Î", "Ľ", "Ń", "Ş", "Ţ" ], // not in libicu
 202                 'sco' => [],
 203                 'se' => [
 204                         'Á', 'Č', 'Ʒ', 'Ǯ', 'Đ', 'Ǧ', 'Ǥ', 'Ǩ', 'Ŋ',
 205                         'Š', 'Ŧ', 'Ž', 'Ø', 'Æ', 'Ȧ', 'Ä', 'Ö'
 206                 ],
 207                 'si' => [ "\xe0\xb6\x82", "\xe0\xb6\x83", "\xe0\xb6\xa4" ],
 208                 'sk' => [ "Ä", "Č", "Ch", "Ô", "Š", "Ž" ],
 209                 'sl' => [ "Č", "Š", "Ž" ],
 210                 'smn' => [ "Á", "Č", "Đ", "Ŋ", "Š", "Ŧ", "Ž", "Æ", "Ø", "Å", "Ä", "Ö" ],
 211                 'sq' => [ "Ç", "Dh", "Ë", "Gj", "Ll", "Nj", "Rr", "Sh", "Th", "Xh", "Zh" ],
 212                 'sr' => [],
 213                 'sr-Latn' => [ "Č", "Ć", "Dž", "Đ", "Lj", "Nj", "Š", "Ž" ],
 214                 'sv' => [ "Å", "Ä", "Ö" ],
 215                 'sv@collation=standard' => [ "Å", "Ä", "Ö" ],
 216                 'sw' => [],
 217                 'ta' => [
 218                         "\xE0\xAE\x82", "ஃ", "க்ஷ", "க்", "ங்", "ச்", "ஞ்", "ட்", "ண்", "த்", "ந்",
 219                         "ப்", "ம்", "ய்", "ர்", "ல்", "வ்", "ழ்", "ள்", "ற்", "ன்", "ஜ்", "ஶ்", "ஷ்",
 220                         "ஸ்", "ஹ்", "க்ஷ்"
 221                 ],
 222                 'te' => [ "\xe0\xb0\x81", "\xe0\xb0\x82", "\xe0\xb0\x83" ],
 223                 'th' => [ "ฯ", "\xe0\xb9\x86", "\xe0\xb9\x8d", "\xe0\xb8\xba" ],
 224                 'tk' => [ "Ç", "Ä", "Ž", "Ň", "Ö", "Ş", "Ü", "Ý" ],
 225                 'tl' => [ "Ñ", "Ng" ], // not in libicu
 226                 'to' => [ "Ng", "ʻ" ],
 227                 'tr' => [ "Ç", "Ğ", "İ", "Ö", "Ş", "Ü" ],
 228                 'tt' => [ "Ә", "Ө", "Ү", "Җ", "Ң", "Һ" ], // not in libicu
 229                 'uk' => [ "Ґ", "Ь" ],
 230                 'uz' => [ "Ch", "G'", "Ng", "O'", "Sh" ], // not in libicu
 231                 'vi' => [ "Ă", "Â", "Đ", "Ê", "Ô", "Ơ", "Ư" ],
 232                 'vo' => [ "Ä", "Ö", "Ü" ],
 233                 'yi' => [
 234                         "\xd7\x91\xd6\xbf", "\xd7\x9b\xd6\xbc", "\xd7\xa4\xd6\xbc",
 235                         "\xd7\xa9\xd7\x82", "\xd7\xaa\xd6\xbc"
 236                 ],
 237                 'yo' => [ "Ẹ", "Gb", "Ọ", "Ṣ" ],
 238                 'zu' => [],
 239         ];
 240
 241         /**
 242          * @since 1.16.3
 243          */
 244         const RECORD_LENGTH = 14;
 245
 246         public function __construct( $locale ) {
 247                 if ( !extension_loaded( 'intl' ) ) {
 248                         throw new MWException( 'An ICU collation was requested, ' .
 249                                 'but the intl extension is not available.' );
 250                 }
 251
 252                 $this->locale = $locale;
 253                 // Drop everything after the '@' in locale's name
 254                 $localeParts = explode( '@', $locale );
 255                 $this->digitTransformLanguage = Language::factory( $locale === 'root' ? 'en' : $localeParts[0] );
 256
 257                 $this->mainCollator = Collator::create( $locale );
 258                 if ( !$this->mainCollator ) {
 259                         throw new MWException( "Invalid ICU locale specified for collation: $locale" );
 260                 }
 261
 262                 $this->primaryCollator = Collator::create( $locale );
 263                 $this->primaryCollator->setStrength( Collator::PRIMARY );
 264
 265                 // If the special suffix for numeric collation is present, turn on numeric collation.
 266                 if ( substr( $locale, -5, 5 ) === '-u-kn' ) {
 267                         $this->useNumericCollation = true;
 268                         // Strip off the special suffix so it doesn't trip up fetchFirstLetterData().
 269                         $this->locale = substr( $this->locale, 0, -5 );
 270                         $this->mainCollator->setAttribute( Collator::NUMERIC_COLLATION, Collator::ON );
 271                         $this->primaryCollator->setAttribute( Collator::NUMERIC_COLLATION, Collator::ON );
 272                 }
 273         }
 274
 275         public function getSortKey( $string ) {
 276                 return $this->mainCollator->getSortKey( $string );
 277         }
 278
 279         public function getPrimarySortKey( $string ) {
 280                 return $this->primaryCollator->getSortKey( $string );
 281         }
 282
 283         public function getFirstLetter( $string ) {
 284                 $string = strval( $string );
 285                 if ( $string === '' ) {
 286                         return '';
 287                 }
 288
 289                 $firstChar = mb_substr( $string, 0, 1, 'UTF-8' );
 290
 291                 // If the first character is a CJK character, just return that character.
 292                 if ( ord( $firstChar ) > 0x7f && self::isCjk( UtfNormal\Utils::utf8ToCodepoint( $firstChar ) ) ) {
 293                         return $firstChar;
 294                 }
 295
 296                 $sortKey = $this->getPrimarySortKey( $string );
 297
 298                 // Do a binary search to find the correct letter to sort under
 299                 $min = ArrayUtils::findLowerBound(
 300                         [ $this, 'getSortKeyByLetterIndex' ],
 301                         $this->getFirstLetterCount(),
 302                         'strcmp',
 303                         $sortKey );
 304
 305                 if ( $min === false ) {
 306                         // Before the first letter
 307                         return '';
 308                 }
 309
 310                 $sortLetter = $this->getLetterByIndex( $min );
 311
 312                 if ( $this->useNumericCollation ) {
 313                         // If the sort letter is a number, return '0–9' (or localized equivalent).
 314                         // ASCII value of 0 is 48. ASCII value of 9 is 57.
 315                         // Note that this also applies to non-Arabic numerals since they are
 316                         // mapped to Arabic numeral sort letters. For example, ২ sorts as 2.
 317                         if ( ord( $sortLetter ) >= 48 && ord( $sortLetter ) <= 57 ) {
 318                                 $sortLetter = wfMessage( 'category-header-numerals' )->numParams( 0, 9 )->text();
 319                         }
 320                 }
 321                 return $sortLetter;
 322         }
 323
 324         /**
 325          * @since 1.16.3
 326          * @return array
 327          */
 328         public function getFirstLetterData() {
 329                 if ( $this->firstLetterData === null ) {
 330                         $cache = ObjectCache::getLocalServerInstance( CACHE_ANYTHING );
 331                         $cacheKey = $cache->makeKey(
 332                                 'first-letters',
 333                                 $this->locale,
 334                                 $this->digitTransformLanguage->getCode(),
 335                                 self::getICUVersion(),
 336                                 self::FIRST_LETTER_VERSION
 337                         );
 338                         $this->firstLetterData = $cache->getWithSetCallback( $cacheKey, $cache::TTL_WEEK, function () {
 339                                 return $this->fetchFirstLetterData();
 340                         } );
 341                 }
 342                 return $this->firstLetterData;
 343         }
 344
 345         /**
 346          * @return array
 347          * @throws MWException
 348          */
 349         private function fetchFirstLetterData() {
 350                 // Generate data from serialized data file
 351                 if ( isset( self::$tailoringFirstLetters[$this->locale] ) ) {
 352                         $letters = wfGetPrecompiledData( 'first-letters-root.ser' );
 353                         // Append additional characters
 354                         $letters = array_merge( $letters, self::$tailoringFirstLetters[$this->locale] );
 355                         // Remove unnecessary ones, if any
 356                         if ( isset( self::$tailoringFirstLetters['-' . $this->locale] ) ) {
 357                                 $letters = array_diff( $letters, self::$tailoringFirstLetters['-' . $this->locale] );
 358                         }
 359                         // Apply digit transforms
 360                         $digits = [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' ];
 361                         $letters = array_diff( $letters, $digits );
 362                         foreach ( $digits as $digit ) {
 363                                 $letters[] = $this->digitTransformLanguage->formatNum( $digit, true );
 364                         }
 365                 } else {
 366                         $letters = wfGetPrecompiledData( "first-letters-{$this->locale}.ser" );
 367                         if ( $letters === false ) {
 368                                 throw new MWException( "MediaWiki does not support ICU locale " .
 369                                         "\"{$this->locale}\"" );
 370                         }
 371                 }
 372
 373                 /* Sort the letters.
 374                  *
 375                  * It's impossible to have the precompiled data file properly sorted,
 376                  * because the sort order changes depending on ICU version. If the
 377                  * array is not properly sorted, the binary search will return random
 378                  * results.
 379                  *
 380                  * We also take this opportunity to remove primary collisions.
 381                  */
 382                 $letterMap = [];
 383                 foreach ( $letters as $letter ) {
 384                         $key = $this->getPrimarySortKey( $letter );
 385                         if ( isset( $letterMap[$key] ) ) {
 386                                 // Primary collision
 387                                 // Keep whichever one sorts first in the main collator
 388                                 if ( $this->mainCollator->compare( $letter, $letterMap[$key] ) < 0 ) {
 389                                         $letterMap[$key] = $letter;
 390                                 }
 391                         } else {
 392                                 $letterMap[$key] = $letter;
 393                         }
 394                 }
 395                 ksort( $letterMap, SORT_STRING );
 396
 397                 /* Remove duplicate prefixes. Basically if something has a sortkey
 398                  * which is a prefix of some other sortkey, then it is an
 399                  * expansion and probably should not be considered a section
 400                  * header.
 401                  *
 402                  * For example 'þ' is sometimes sorted as if it is the letters
 403                  * 'th'. Other times it is its own primary element. Another
 404                  * example is '₨'. Sometimes its a currency symbol. Sometimes it
 405                  * is an 'R' followed by an 's'.
 406                  *
 407                  * Additionally an expanded element should always sort directly
 408                  * after its first element due to they way sortkeys work.
 409                  *
 410                  * UCA sortkey elements are of variable length but no collation
 411                  * element should be a prefix of some other element, so I think
 412                  * this is safe. See:
 413                  * - https://ssl.icu-project.org/repos/icu/icuhtml/trunk/design/collation/ICU_collation_design.htm
 414                  * - http://site.icu-project.org/design/collation/uca-weight-allocation
 415                  *
 416                  * Additionally, there is something called primary compression to
 417                  * worry about. Basically, if you have two primary elements that
 418                  * are more than one byte and both start with the same byte then
 419                  * the first byte is dropped on the second primary. Additionally
 420                  * either \x03 or \xFF may be added to mean that the next primary
 421                  * does not start with the first byte of the first primary.
 422                  *
 423                  * This shouldn't matter much, as the first primary is not
 424                  * changed, and that is what we are comparing against.
 425                  *
 426                  * tl;dr: This makes some assumptions about how icu implements
 427                  * collations. It seems incredibly unlikely these assumptions
 428                  * will change, but nonetheless they are assumptions.
 429                  */
 430
 431                 $prev = false;
 432                 $duplicatePrefixes = [];
 433                 foreach ( $letterMap as $key => $value ) {
 434                         // Remove terminator byte. Otherwise the prefix
 435                         // comparison will get hung up on that.
 436                         $trimmedKey = rtrim( $key, "\0" );
 437                         if ( $prev === false || $prev === '' ) {
 438                                 $prev = $trimmedKey;
 439                                 // We don't yet have a collation element
 440                                 // to compare against, so continue.
 441                                 continue;
 442                         }
 443
 444                         // Due to the fact the array is sorted, we only have
 445                         // to compare with the element directly previous
 446                         // to the current element (skipping expansions).
 447                         // An element "X" will always sort directly
 448                         // before "XZ" (Unless we have "XY", but we
 449                         // do not update $prev in that case).
 450                         if ( substr( $trimmedKey, 0, strlen( $prev ) ) === $prev ) {
 451                                 $duplicatePrefixes[] = $key;
 452                                 // If this is an expansion, we don't want to
 453                                 // compare the next element to this element,
 454                                 // but to what is currently $prev
 455                                 continue;
 456                         }
 457                         $prev = $trimmedKey;
 458                 }
 459                 foreach ( $duplicatePrefixes as $badKey ) {
 460                         wfDebug( "Removing '{$letterMap[$badKey]}' from first letters.\n" );
 461                         unset( $letterMap[$badKey] );
 462                         // This code assumes that unsetting does not change sort order.
 463                 }
 464                 $data = [
 465                         'chars' => array_values( $letterMap ),
 466                         'keys' => array_keys( $letterMap ),
 467                 ];
 468
 469                 // Reduce memory usage before caching
 470                 unset( $letterMap );
 471
 472                 return $data;
 473         }
 474
 475         /**
 476          * @since 1.16.3
 477          */
 478         public function getLetterByIndex( $index ) {
 479                 return $this->getFirstLetterData()['chars'][$index];
 480         }
 481
 482         /**
 483          * @since 1.16.3
 484          */
 485         public function getSortKeyByLetterIndex( $index ) {
 486                 return $this->getFirstLetterData()['keys'][$index];
 487         }
 488
 489         /**
 490          * @since 1.16.3
 491          */
 492         public function getFirstLetterCount() {
 493                 return count( $this->getFirstLetterData()['chars'] );
 494         }
 495
 496         /**
 497          * Test if a code point is a CJK (Chinese, Japanese, Korean) character
 498          * @since 1.16.3
 499          */
 500         public static function isCjk( $codepoint ) {
 501                 foreach ( self::$cjkBlocks as $block ) {
 502                         if ( $codepoint >= $block[0] && $codepoint <= $block[1] ) {
 503                                 return true;
 504                         }
 505                 }
 506                 return false;
 507         }
 508
 509         /**
 510          * Return the version of ICU library used by PHP's intl extension,
 511          * or false when the extension is not installed of the version
 512          * can't be determined.
 513          *
 514          * The constant INTL_ICU_VERSION this function refers to isn't really
 515          * documented. It is available since PHP 5.3.7 (see PHP bug 54561).
 516          * This function will return false on older PHPs.
 517          *
 518          * @since 1.21
 519          * @return string|bool
 520          */
 521         static function getICUVersion() {
 522                 return defined( 'INTL_ICU_VERSION' ) ? INTL_ICU_VERSION : false;
 523         }
 524
 525         /**
 526          * Return the version of Unicode appropriate for the version of ICU library
 527          * currently in use, or false when it can't be determined.
 528          *
 529          * @since 1.21
 530          * @return string|bool
 531          */
 532         static function getUnicodeVersionForICU() {
 533                 $icuVersion = IcuCollation::getICUVersion();
 534                 if ( !$icuVersion ) {
 535                         return false;
 536                 }
 537
 538                 $versionPrefix = substr( $icuVersion, 0, 3 );
 539                 // Source: http://site.icu-project.org/download
 540                 $map = [
 541                         '57.' => '8.0',
 542                         '56.' => '8.0',
 543                         '55.' => '7.0',
 544                         '54.' => '7.0',
 545                         '53.' => '6.3',
 546                         '52.' => '6.3',
 547                         '51.' => '6.2',
 548                         '50.' => '6.2',
 549                         '49.' => '6.1',
 550                         '4.8' => '6.0',
 551                         '4.6' => '6.0',
 552                         '4.4' => '5.2',
 553                         '4.2' => '5.1',
 554                         '4.0' => '5.1',
 555                         '3.8' => '5.0',
 556                         '3.6' => '5.0',
 557                         '3.4' => '4.1',
 558                 ];
 559
 560                 if ( isset( $map[$versionPrefix] ) ) {
 561                         return $map[$versionPrefix];
 562                 } else {
 563                         return false;
 564                 }
 565         }
 566 }