Add regex module

Move regular expression matching into a function in its own module.

No functional change.

CMakeLists.txt

@@ -111,6 +111,7 @@ add_llvm_executable(include-what-you-use
   iwyu_output.cc
   iwyu_path_util.cc
   iwyu_preprocessor.cc
+  iwyu_regex.cc
   iwyu_verrs.cc
 )
 

iwyu_include_picker.cc

@@ -16,7 +16,6 @@
 // not hash_map: it's not as portable and needs hash<string>.
 #include <map>                          // for map, map<>::mapped_type, etc
 #include <memory>
-#include <regex>
 #include <string>                       // for string, basic_string, etc
 #include <system_error>                 // for error_code
 #include <utility>                      // for pair, make_pair
@@ -25,6 +24,7 @@
 #include "iwyu_location_util.h"
 #include "iwyu_path_util.h"
 #include "iwyu_port.h"
+#include "iwyu_regex.h"
 #include "iwyu_stl_util.h"
 #include "iwyu_string_util.h"
 #include "iwyu_verrs.h"
@@ -1436,17 +1436,16 @@ void IncludePicker::ExpandRegexes() {
     for (const string& regex_key : filepath_include_map_regex_keys) {
       const vector<MappedInclude>& map_to = filepath_include_map_[regex_key];
       // Enclose the regex in ^(...)$ for full match.
-      std::regex regex(std::string("^(" + regex_key.substr(1) + ")$"));
-      if (std::regex_match(hdr, regex) &&
-          !ContainsQuotedInclude(map_to, hdr)) {
+      std::string regex("^(" + regex_key.substr(1) + ")$");
+      if (RegexMatch(hdr, regex) && !ContainsQuotedInclude(map_to, hdr)) {
         Extend(&filepath_include_map_[hdr], filepath_include_map_[regex_key]);
         MarkVisibility(&include_visibility_map_, hdr,
                        include_visibility_map_[regex_key]);
       }
     }
     for (const string& regex_key : friend_to_headers_map_regex_keys) {
-      std::regex regex(std::string("^(" + regex_key.substr(1) + ")$"));
-      if (std::regex_match(hdr, regex)) {
+      std::string regex("^(" + regex_key.substr(1) + ")$");
+      if (RegexMatch(hdr, regex)) {
         InsertAllInto(friend_to_headers_map_[regex_key],
                       &friend_to_headers_map_[hdr]);
       }

iwyu_regex.cc

@@ -0,0 +1,21 @@
+//===--- iwyu_regex.cc - iwyu regex implementation ------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "iwyu_regex.h"
+
+#include <regex>
+
+namespace include_what_you_use {
+
+bool RegexMatch(const std::string& str, const std::string& pattern) {
+  std::regex r(pattern);
+  return std::regex_match(str, r);
+}
+
+}  // namespace include_what_you_use

iwyu_regex.h

@@ -0,0 +1,22 @@
+//===--- iwyu_regex.h - iwyu regex implementation -------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef INCLUDE_WHAT_YOU_USE_IWYU_REGEX_H_
+#define INCLUDE_WHAT_YOU_USE_IWYU_REGEX_H_
+
+#include <string>
+
+namespace include_what_you_use {
+
+// Returns true if str matches regular expression pattern.
+bool RegexMatch(const std::string& str, const std::string& pattern);
+
+}  // namespace include_what_you_use
+
+#endif  // INCLUDE_WHAT_YOU_USE_IWYU_REGEX_H_