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
22using namespace llvm;
23
24Regex::Regex() : preg(nullptr), error(REG_BADPAT) {}
25
26Regex::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
39Regex::Regex(StringRef regex, unsigned Flags)
40    : Regex(regex, static_cast<RegexFlags>(Flags)) {}
41
42Regex::Regex(Regex &&regex) {
43  preg = regex.preg;
44  error = regex.error;
45  regex.preg = nullptr;
46  regex.error = REG_BADPAT;
47}
48
49Regex::~Regex() {
50  if (preg) {
51    llvm_regfree(preg);
52    delete preg;
53  }
54}
55
56namespace {
57
58/// Utility to convert a regex error code into a human-readable string.
59void 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
69bool 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.
79unsigned Regex::getNumMatches() const {
80  return preg->re_nsub;
81}
82
83bool 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
137std::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".
230static const char RegexMetachars[] = "()^$|*+?.[]\\{}";
231
232bool 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
239std::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}
249