// Copyright 2019 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef V8_REGEXP_SPECIAL_CASE_H_ #define V8_REGEXP_SPECIAL_CASE_H_ #ifdef V8_INTL_SUPPORT #include "irregexp/RegExpShim.h" #include "unicode/uchar.h" #include "unicode/uniset.h" #include "unicode/unistr.h" namespace v8 { namespace internal { // Sets of Unicode characters that need special handling under "i" mode // For non-unicode ignoreCase matches (aka "i", not "iu"), ECMA 262 // defines slightly different case-folding rules than Unicode. An // input character should match a pattern character if the result of // the Canonicalize algorithm is the same for both characters. // // Roughly speaking, for "i" regexps, Canonicalize(c) is the same as // c.toUpperCase(), unless a) c.toUpperCase() is a multi-character // string, or b) c is non-ASCII, and c.toUpperCase() is ASCII. See // https://tc39.es/ecma262/#sec-runtime-semantics-canonicalize-ch for // the precise definition. // // While compiling such regular expressions, we need to compute the // set of characters that should match a given input character. (See // GetCaseIndependentLetters and CharacterRange::AddCaseEquivalents.) // For almost all characters, this can be efficiently computed using // UnicodeSet::closeOver(USET_CASE_INSENSITIVE). These sets represent // the remaining special cases. // // For a character c, the rules are as follows: // // 1. If c is in neither IgnoreSet nor SpecialAddSet, then calling // UnicodeSet::closeOver(USET_CASE_INSENSITIVE) on a UnicodeSet // containing c will produce the set of characters that should // match /c/i (or /[c]/i), and only those characters. // // 2. If c is in IgnoreSet, then the only character it should match is // itself. However, closeOver will add additional incorrect // matches. For example, consider SHARP S: 'ß' (U+00DF) and 'ẞ' // (U+1E9E). Although closeOver('ß') = "ßẞ", uppercase('ß') is // "SS". Step 3.e therefore requires that 'ß' canonicalizes to // itself, and should not match 'ẞ'. In these cases, we can skip // the closeOver entirely, because it will never add an equivalent // character. // // 3. If c is in SpecialAddSet, then it should match at least one // character other than itself. However, closeOver will add at // least one additional incorrect match. For example, consider the // letter 'k'. Closing over 'k' gives "kKK" (lowercase k, uppercase // K, U+212A KELVIN SIGN). However, because of step 3.g, KELVIN // SIGN should not match either of the other two characters. As a // result, "k" and "K" are in SpecialAddSet (and KELVIN SIGN is in // IgnoreSet). To find the correct matches for characters in // SpecialAddSet, we closeOver the original character, but filter // out the results that do not have the same canonical value. // // The contents of these sets are calculated at build time by // src/regexp/gen-regexp-special-case.cc, which generates // gen/src/regexp/special-case.cc. This is done by iterating over the // result of closeOver for each BMP character, and finding sets for // which at least one character has a different canonical value than // another character. Characters that match no other characters in // their equivalence class are added to IgnoreSet. Characters that // match at least one other character are added to SpecialAddSet. class RegExpCaseFolding final : public AllStatic { public: static const icu::UnicodeSet& IgnoreSet(); static const icu::UnicodeSet& SpecialAddSet(); // This implements ECMAScript 2020 21.2.2.8.2 (Runtime Semantics: // Canonicalize) step 3, which is used to determine whether // characters match when ignoreCase is true and unicode is false. static UChar32 Canonicalize(UChar32 ch) { // a. Assert: ch is a UTF-16 code unit. CHECK_LE(ch, 0xffff); // b. Let s be the String value consisting of the single code unit ch. icu::UnicodeString s(ch); // c. Let u be the same result produced as if by performing the algorithm // for String.prototype.toUpperCase using s as the this value. // d. Assert: Type(u) is String. icu::UnicodeString& u = s.toUpper(); // e. If u does not consist of a single code unit, return ch. if (u.length() != 1) { return ch; } // f. Let cu be u's single code unit element. UChar32 cu = u.char32At(0); // g. If the value of ch >= 128 and the value of cu < 128, return ch. if (ch >= 128 && cu < 128) { return ch; } // h. Return cu. return cu; } }; } // namespace internal } // namespace v8 #endif // V8_INTL_SUPPORT #endif // V8_REGEXP_SPECIAL_CASE_H_