llvm/lib/Support/Regex.cpp

   1 //===-- Regex.cpp - Regular Expression matcher implementation -------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements a POSIX regular expression matcher.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Support/Regex.h"
  14 #include "llvm/ADT/SmallVector.h"
  15 #include "llvm/ADT/StringRef.h"
  16 #include "llvm/ADT/Twine.h"
  17 #include "regex_impl.h"
  18
  19 #include <cassert>
  20 #include <string>
  21
  22 using namespace llvm;
  23
  24 Regex::Regex() : preg(nullptr), error(REG_BADPAT) {}
  25
  26 Regex::Regex(StringRef regex, RegexFlags Flags) {
  27   unsigned flags = 0;
  28   preg = new llvm_regex();
  29   preg->re_endp = regex.end();
  30   if (Flags & IgnoreCase)
  31     flags |= REG_ICASE;
  32   if (Flags & Newline)
  33     flags |= REG_NEWLINE;
  34   if (!(Flags & BasicRegex))
  35     flags |= REG_EXTENDED;
  36   error = llvm_regcomp(preg, regex.data(), flags|REG_PEND);
  37 }
  38
  39 Regex::Regex(StringRef regex, unsigned Flags)
  40     : Regex(regex, static_cast<RegexFlags>(Flags)) {}
  41
  42 Regex::Regex(Regex &&regex) {
  43   preg = regex.preg;
  44   error = regex.error;
  45   regex.preg = nullptr;
  46   regex.error = REG_BADPAT;
  47 }
  48
  49 Regex::~Regex() {
  50   if (preg) {
  51     llvm_regfree(preg);
  52     delete preg;
  53   }
  54 }
  55
  56 namespace {
  57
  58 /// Utility to convert a regex error code into a human-readable string.
  59 void RegexErrorToString(int error, struct llvm_regex *preg,
  60                         std::string &Error) {
  61   size_t len = llvm_regerror(error, preg, nullptr, 0);
  62
  63   Error.resize(len - 1);
  64   llvm_regerror(error, preg, &Error[0], len);
  65 }
  66
  67 } // namespace
  68
  69 bool Regex::isValid(std::string &Error) const {
  70   if (!error)
  71     return true;
  72
  73   RegexErrorToString(error, preg, Error);
  74   return false;
  75 }
  76
  77 /// getNumMatches - In a valid regex, return the number of parenthesized
  78 /// matches it contains.
  79 unsigned Regex::getNumMatches() const {
  80   return preg->re_nsub;
  81 }
  82
  83 bool Regex::match(StringRef String, SmallVectorImpl<StringRef> *Matches,
  84                   std::string *Error) const {
  85   // Reset error, if given.
  86   if (Error && !Error->empty())
  87     *Error = "";
  88
  89   // Check if the regex itself didn't successfully compile.
  90   if (Error ? !isValid(*Error) : !isValid())
  91     return false;
  92
  93   unsigned nmatch = Matches ? preg->re_nsub+1 : 0;
  94
  95   // Update null string to empty string.
  96   if (String.data() == nullptr)
  97     String = "";
  98
  99   // pmatch needs to have at least one element.
 100   SmallVector<llvm_regmatch_t, 8> pm;
 101   pm.resize(nmatch > 0 ? nmatch : 1);
 102   pm[0].rm_so = 0;
 103   pm[0].rm_eo = String.size();
 104
 105   int rc = llvm_regexec(preg, String.data(), nmatch, pm.data(), REG_STARTEND);
 106
 107   // Failure to match is not an error, it's just a normal return value.
 108   // Any other error code is considered abnormal, and is logged in the Error.
 109   if (rc == REG_NOMATCH)
 110     return false;
 111   if (rc != 0) {
 112     if (Error)
 113       RegexErrorToString(error, preg, *Error);
 114     return false;
 115   }
 116
 117   // There was a match.
 118
 119   if (Matches) { // match position requested
 120     Matches->clear();
 121
 122     for (unsigned i = 0; i != nmatch; ++i) {
 123       if (pm[i].rm_so == -1) {
 124         // this group didn't match
 125         Matches->push_back(StringRef());
 126         continue;
 127       }
 128       assert(pm[i].rm_eo >= pm[i].rm_so);
 129       Matches->push_back(StringRef(String.data()+pm[i].rm_so,
 130                                    pm[i].rm_eo-pm[i].rm_so));
 131     }
 132   }
 133
 134   return true;
 135 }
 136
 137 std::string Regex::sub(StringRef Repl, StringRef String,
 138                        std::string *Error) const {
 139   SmallVector<StringRef, 8> Matches;
 140
 141   // Return the input if there was no match.
 142   if (!match(String, &Matches, Error))
 143     return std::string(String);
 144
 145   // Otherwise splice in the replacement string, starting with the prefix before
 146   // the match.
 147   std::string Res(String.begin(), Matches[0].begin());
 148
 149   // Then the replacement string, honoring possible substitutions.
 150   while (!Repl.empty()) {
 151     // Skip to the next escape.
 152     std::pair<StringRef, StringRef> Split = Repl.split('\\');
 153
 154     // Add the skipped substring.
 155     Res += Split.first;
 156
 157     // Check for terminimation and trailing backslash.
 158     if (Split.second.empty()) {
 159       if (Repl.size() != Split.first.size() &&
 160           Error && Error->empty())
 161         *Error = "replacement string contained trailing backslash";
 162       break;
 163     }
 164
 165     // Otherwise update the replacement string and interpret escapes.
 166     Repl = Split.second;
 167
 168     // FIXME: We should have a StringExtras function for mapping C99 escapes.
 169     switch (Repl[0]) {
 170
 171       // Backreference with the "\g<ref>" syntax
 172     case 'g':
 173       if (Repl.size() >= 4 && Repl[1] == '<') {
 174         size_t End = Repl.find('>');
 175         StringRef Ref = Repl.slice(2, End);
 176         unsigned RefValue;
 177         if (End != StringRef::npos && !Ref.getAsInteger(10, RefValue)) {
 178           Repl = Repl.substr(End + 1);
 179           if (RefValue < Matches.size())
 180             Res += Matches[RefValue];
 181           else if (Error && Error->empty())
 182             *Error =
 183                 ("invalid backreference string 'g<" + Twine(Ref) + ">'").str();
 184           break;
 185         }
 186       }
 187       [[fallthrough]];
 188
 189       // Treat all unrecognized characters as self-quoting.
 190     default:
 191       Res += Repl[0];
 192       Repl = Repl.substr(1);
 193       break;
 194
 195       // Single character escapes.
 196     case 't':
 197       Res += '\t';
 198       Repl = Repl.substr(1);
 199       break;
 200     case 'n':
 201       Res += '\n';
 202       Repl = Repl.substr(1);
 203       break;
 204
 205       // Decimal escapes are backreferences.
 206     case '0': case '1': case '2': case '3': case '4':
 207     case '5': case '6': case '7': case '8': case '9': {
 208       // Extract the backreference number.
 209       StringRef Ref = Repl.slice(0, Repl.find_first_not_of("0123456789"));
 210       Repl = Repl.substr(Ref.size());
 211
 212       unsigned RefValue;
 213       if (!Ref.getAsInteger(10, RefValue) &&
 214           RefValue < Matches.size())
 215         Res += Matches[RefValue];
 216       else if (Error && Error->empty())
 217         *Error = ("invalid backreference string '" + Twine(Ref) + "'").str();
 218       break;
 219     }
 220     }
 221   }
 222
 223   // And finally the suffix.
 224   Res += StringRef(Matches[0].end(), String.end() - Matches[0].end());
 225
 226   return Res;
 227 }
 228
 229 // These are the special characters matched in functions like "p_ere_exp".
 230 static const char RegexMetachars[] = "()^$|*+?.[]\\{}";
 231
 232 bool Regex::isLiteralERE(StringRef Str) {
 233   // Check for regex metacharacters.  This list was derived from our regex
 234   // implementation in regcomp.c and double checked against the POSIX extended
 235   // regular expression specification.
 236   return Str.find_first_of(RegexMetachars) == StringRef::npos;
 237 }
 238
 239 std::string Regex::escape(StringRef String) {
 240   std::string RegexStr;
 241   for (char C : String) {
 242     if (strchr(RegexMetachars, C))
 243       RegexStr += '\\';
 244     RegexStr += C;
 245   }
 246
 247   return RegexStr;
 248 }