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   // pmatch needs to have at least one element.
96   SmallVector<llvm_regmatch_t, 8> pm;
97   pm.resize(nmatch > 0 ? nmatch : 1);
98   pm[0].rm_so = 0;
99   pm[0].rm_eo = String.size();
100 
101   int rc = llvm_regexec(preg, String.data(), nmatch, pm.data(), REG_STARTEND);
102 
103   // Failure to match is not an error, it's just a normal return value.
104   // Any other error code is considered abnormal, and is logged in the Error.
105   if (rc == REG_NOMATCH)
106     return false;
107   if (rc != 0) {
108     if (Error)
109       RegexErrorToString(error, preg, *Error);
110     return false;
111   }
112 
113   // There was a match.
114 
115   if (Matches) { // match position requested
116     Matches->clear();
117 
118     for (unsigned i = 0; i != nmatch; ++i) {
119       if (pm[i].rm_so == -1) {
120         // this group didn't match
121         Matches->push_back(StringRef());
122         continue;
123       }
124       assert(pm[i].rm_eo >= pm[i].rm_so);
125       Matches->push_back(StringRef(String.data()+pm[i].rm_so,
126                                    pm[i].rm_eo-pm[i].rm_so));
127     }
128   }
129 
130   return true;
131 }
132 
133 std::string Regex::sub(StringRef Repl, StringRef String,
134                        std::string *Error) const {
135   SmallVector<StringRef, 8> Matches;
136 
137   // Return the input if there was no match.
138   if (!match(String, &Matches, Error))
139     return std::string(String);
140 
141   // Otherwise splice in the replacement string, starting with the prefix before
142   // the match.
143   std::string Res(String.begin(), Matches[0].begin());
144 
145   // Then the replacement string, honoring possible substitutions.
146   while (!Repl.empty()) {
147     // Skip to the next escape.
148     std::pair<StringRef, StringRef> Split = Repl.split('\\');
149 
150     // Add the skipped substring.
151     Res += Split.first;
152 
153     // Check for terminimation and trailing backslash.
154     if (Split.second.empty()) {
155       if (Repl.size() != Split.first.size() &&
156           Error && Error->empty())
157         *Error = "replacement string contained trailing backslash";
158       break;
159     }
160 
161     // Otherwise update the replacement string and interpret escapes.
162     Repl = Split.second;
163 
164     // FIXME: We should have a StringExtras function for mapping C99 escapes.
165     switch (Repl[0]) {
166       // Treat all unrecognized characters as self-quoting.
167     default:
168       Res += Repl[0];
169       Repl = Repl.substr(1);
170       break;
171 
172       // Single character escapes.
173     case 't':
174       Res += '\t';
175       Repl = Repl.substr(1);
176       break;
177     case 'n':
178       Res += '\n';
179       Repl = Repl.substr(1);
180       break;
181 
182       // Decimal escapes are backreferences.
183     case '0': case '1': case '2': case '3': case '4':
184     case '5': case '6': case '7': case '8': case '9': {
185       // Extract the backreference number.
186       StringRef Ref = Repl.slice(0, Repl.find_first_not_of("0123456789"));
187       Repl = Repl.substr(Ref.size());
188 
189       unsigned RefValue;
190       if (!Ref.getAsInteger(10, RefValue) &&
191           RefValue < Matches.size())
192         Res += Matches[RefValue];
193       else if (Error && Error->empty())
194         *Error = ("invalid backreference string '" + Twine(Ref) + "'").str();
195       break;
196     }
197     }
198   }
199 
200   // And finally the suffix.
201   Res += StringRef(Matches[0].end(), String.end() - Matches[0].end());
202 
203   return Res;
204 }
205 
206 // These are the special characters matched in functions like "p_ere_exp".
207 static const char RegexMetachars[] = "()^$|*+?.[]\\{}";
208 
209 bool Regex::isLiteralERE(StringRef Str) {
210   // Check for regex metacharacters.  This list was derived from our regex
211   // implementation in regcomp.c and double checked against the POSIX extended
212   // regular expression specification.
213   return Str.find_first_of(RegexMetachars) == StringRef::npos;
214 }
215 
216 std::string Regex::escape(StringRef String) {
217   std::string RegexStr;
218   for (char C : String) {
219     if (strchr(RegexMetachars, C))
220       RegexStr += '\\';
221     RegexStr += C;
222   }
223 
224   return RegexStr;
225 }
226