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 = 3;
  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 bool */
  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", "Ș", "Ț" ], // 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", "Ș", "Ț" ],
 200                 'ru' => [],
 201                 'rup' => [ "Ă", "Â", "Î", "Ľ", "Ń", "Ș", "Ț" ], // 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                                 static::class,
 334                                 $this->locale,
 335                                 $this->digitTransformLanguage->getCode(),
 336                                 self::getICUVersion(),
 337                                 self::FIRST_LETTER_VERSION
 338                         );
 339                         $this->firstLetterData = $cache->getWithSetCallback( $cacheKey, $cache::TTL_WEEK, function () {
 340                                 return $this->fetchFirstLetterData();
 341                         } );
 342                 }
 343                 return $this->firstLetterData;
 344         }
 345
 346         /**
 347          * @return array
 348          * @throws MWException
 349          */
 350         private function fetchFirstLetterData() {
 351                 // Generate data from serialized data file
 352                 if ( isset( self::$tailoringFirstLetters[$this->locale] ) ) {
 353                         $letters = wfGetPrecompiledData( 'first-letters-root.ser' );
 354                         // Append additional characters
 355                         $letters = array_merge( $letters, self::$tailoringFirstLetters[$this->locale] );
 356                         // Remove unnecessary ones, if any
 357                         if ( isset( self::$tailoringFirstLetters['-' . $this->locale] ) ) {
 358                                 $letters = array_diff( $letters, self::$tailoringFirstLetters['-' . $this->locale] );
 359                         }
 360                         // Apply digit transforms
 361                         $digits = [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' ];
 362                         $letters = array_diff( $letters, $digits );
 363                         foreach ( $digits as $digit ) {
 364                                 $letters[] = $this->digitTransformLanguage->formatNum( $digit, true );
 365                         }
 366                 } else {
 367                         $letters = wfGetPrecompiledData( "first-letters-{$this->locale}.ser" );
 368                         if ( $letters === false ) {
 369                                 throw new MWException( "MediaWiki does not support ICU locale " .
 370                                         "\"{$this->locale}\"" );
 371                         }
 372                 }
 373
 374                 /* Sort the letters.
 375                  *
 376                  * It's impossible to have the precompiled data file properly sorted,
 377                  * because the sort order changes depending on ICU version. If the
 378                  * array is not properly sorted, the binary search will return random
 379                  * results.
 380                  *
 381                  * We also take this opportunity to remove primary collisions.
 382                  */
 383                 $letterMap = [];
 384                 foreach ( $letters as $letter ) {
 385                         $key = $this->getPrimarySortKey( $letter );
 386                         if ( isset( $letterMap[$key] ) ) {
 387                                 // Primary collision
 388                                 // Keep whichever one sorts first in the main collator
 389                                 if ( $this->mainCollator->compare( $letter, $letterMap[$key] ) < 0 ) {
 390                                         $letterMap[$key] = $letter;
 391                                 }
 392                         } else {
 393                                 $letterMap[$key] = $letter;
 394                         }
 395                 }
 396                 ksort( $letterMap, SORT_STRING );
 397
 398                 /* Remove duplicate prefixes. Basically if something has a sortkey
 399                  * which is a prefix of some other sortkey, then it is an
 400                  * expansion and probably should not be considered a section
 401                  * header.
 402                  *
 403                  * For example 'þ' is sometimes sorted as if it is the letters
 404                  * 'th'. Other times it is its own primary element. Another
 405                  * example is '₨'. Sometimes its a currency symbol. Sometimes it
 406                  * is an 'R' followed by an 's'.
 407                  *
 408                  * Additionally an expanded element should always sort directly
 409                  * after its first element due to they way sortkeys work.
 410                  *
 411                  * UCA sortkey elements are of variable length but no collation
 412                  * element should be a prefix of some other element, so I think
 413                  * this is safe. See:
 414                  * - https://ssl.icu-project.org/repos/icu/icuhtml/trunk/design/collation/ICU_collation_design.htm
 415                  * - http://site.icu-project.org/design/collation/uca-weight-allocation
 416                  *
 417                  * Additionally, there is something called primary compression to
 418                  * worry about. Basically, if you have two primary elements that
 419                  * are more than one byte and both start with the same byte then
 420                  * the first byte is dropped on the second primary. Additionally
 421                  * either \x03 or \xFF may be added to mean that the next primary
 422                  * does not start with the first byte of the first primary.
 423                  *
 424                  * This shouldn't matter much, as the first primary is not
 425                  * changed, and that is what we are comparing against.
 426                  *
 427                  * tl;dr: This makes some assumptions about how icu implements
 428                  * collations. It seems incredibly unlikely these assumptions
 429                  * will change, but nonetheless they are assumptions.
 430                  */
 431
 432                 $prev = false;
 433                 $duplicatePrefixes = [];
 434                 foreach ( $letterMap as $key => $value ) {
 435                         // Remove terminator byte. Otherwise the prefix
 436                         // comparison will get hung up on that.
 437                         $trimmedKey = rtrim( $key, "\0" );
 438                         if ( $prev === false || $prev === '' ) {
 439                                 $prev = $trimmedKey;
 440                                 // We don't yet have a collation element
 441                                 // to compare against, so continue.
 442                                 continue;
 443                         }
 444
 445                         // Due to the fact the array is sorted, we only have
 446                         // to compare with the element directly previous
 447                         // to the current element (skipping expansions).
 448                         // An element "X" will always sort directly
 449                         // before "XZ" (Unless we have "XY", but we
 450                         // do not update $prev in that case).
 451                         if ( substr( $trimmedKey, 0, strlen( $prev ) ) === $prev ) {
 452                                 $duplicatePrefixes[] = $key;
 453                                 // If this is an expansion, we don't want to
 454                                 // compare the next element to this element,
 455                                 // but to what is currently $prev
 456                                 continue;
 457                         }
 458                         $prev = $trimmedKey;
 459                 }
 460                 foreach ( $duplicatePrefixes as $badKey ) {
 461                         wfDebug( "Removing '{$letterMap[$badKey]}' from first letters.\n" );
 462                         unset( $letterMap[$badKey] );
 463                         // This code assumes that unsetting does not change sort order.
 464                 }
 465                 $data = [
 466                         'chars' => array_values( $letterMap ),
 467                         'keys' => array_keys( $letterMap ),
 468                 ];
 469
 470                 // Reduce memory usage before caching
 471                 unset( $letterMap );
 472
 473                 return $data;
 474         }
 475
 476         /**
 477          * @param string $index
 478          * @return string
 479          * @since 1.16.3
 480          */
 481         public function getLetterByIndex( $index ) {
 482                 return $this->getFirstLetterData()['chars'][$index];
 483         }
 484
 485         /**
 486          * @param string $index
 487          * @return string
 488          * @since 1.16.3
 489          */
 490         public function getSortKeyByLetterIndex( $index ) {
 491                 return $this->getFirstLetterData()['keys'][$index];
 492         }
 493
 494         /**
 495          * @param string $index
 496          * @return string
 497          * @since 1.16.3
 498          */
 499         public function getFirstLetterCount() {
 500                 return count( $this->getFirstLetterData()['chars'] );
 501         }
 502
 503         /**
 504          * Test if a code point is a CJK (Chinese, Japanese, Korean) character
 505          * @param int $codepoint
 506          * @return bool
 507          * @since 1.16.3
 508          */
 509         public static function isCjk( $codepoint ) {
 510                 foreach ( self::$cjkBlocks as $block ) {
 511                         if ( $codepoint >= $block[0] && $codepoint <= $block[1] ) {
 512                                 return true;
 513                         }
 514                 }
 515                 return false;
 516         }
 517
 518         /**
 519          * Return the version of ICU library used by PHP's intl extension,
 520          * or false when the extension is not installed of the version
 521          * can't be determined.
 522          *
 523          * The constant INTL_ICU_VERSION this function refers to isn't really
 524          * documented. It is available since PHP 5.3.7 (see PHP 54561
 525          * https://bugs.php.net/bug.php?id=54561). This function will return
 526          * false on older PHPs.
 527          *
 528          * TODO: Remove the backwards-compatibility as MediaWiki now requires
 529          * higher levels of PHP.
 530          *
 531          * @since 1.21
 532          * @return string|bool
 533          */
 534         static function getICUVersion() {
 535                 return defined( 'INTL_ICU_VERSION' ) ? INTL_ICU_VERSION : false;
 536         }
 537
 538         /**
 539          * Return the version of Unicode appropriate for the version of ICU library
 540          * currently in use, or false when it can't be determined.
 541          *
 542          * @since 1.21
 543          * @return string|bool
 544          */
 545         static function getUnicodeVersionForICU() {
 546                 $icuVersion = self::getICUVersion();
 547                 if ( !$icuVersion ) {
 548                         return false;
 549                 }
 550
 551                 $versionPrefix = substr( $icuVersion, 0, 3 );
 552                 // Source: http://site.icu-project.org/download
 553                 $map = [
 554                         '57.' => '8.0',
 555                         '56.' => '8.0',
 556                         '55.' => '7.0',
 557                         '54.' => '7.0',
 558                         '53.' => '6.3',
 559                         '52.' => '6.3',
 560                         '51.' => '6.2',
 561                         '50.' => '6.2',
 562                         '49.' => '6.1',
 563                         '4.8' => '6.0',
 564                         '4.6' => '6.0',
 565                         '4.4' => '5.2',
 566                         '4.2' => '5.1',
 567                         '4.0' => '5.1',
 568                         '3.8' => '5.0',
 569                         '3.6' => '5.0',
 570                         '3.4' => '4.1',
 571                 ];
 572
 573                 if ( isset( $map[$versionPrefix] ) ) {
 574                         return $map[$versionPrefix];
 575                 } else {
 576                         return false;
 577                 }
 578         }
 579 }