Make regexp flag parsing stricter.

src/regexp.js

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 32 matching lines @@
         + (pattern.multiline ? 'm' : '');
     pattern = pattern.source;
   }
 
   pattern = IS_UNDEFINED(pattern) ? '' : ToString(pattern);
   flags = IS_UNDEFINED(flags) ? '' : ToString(flags);
 
   var global = false;
   var ignoreCase = false;
   var multiline = false;
-
   for (var i = 0; i < flags.length; i++) {
     var c = %_CallFunction(flags, i, StringCharAt);
     switch (c) {
       case 'g':
-        // Allow duplicate flags to be consistent with JSC and others.
+        if (global) {
+          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
+        }
         global = true;
         break;
       case 'i':
+        if (ignoreCase) {
+          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
+        }
         ignoreCase = true;
         break;
       case 'm':
+        if (multiline) {
+          throw MakeSyntaxError("invalid_regexp_flags", [flags]);
+        }
         multiline = true;
         break;
       default:
-        // Ignore flags that have no meaning to be consistent with
-        // JSC.
-        break;
+        throw MakeSyntaxError("invalid_regexp_flags", [flags]);
     }
   }
 
   %RegExpInitializeObject(object, pattern, global, ignoreCase, multiline);
 
   // Call internal function to compile the pattern.
   %RegExpCompile(object, pattern, flags);
 }
 
 
@@ skipping 393 matching lines @@
   %DefineAccessor($RegExp, "$'", SETTER, NoOpSetter, DONT_ENUM | DONT_DELETE);
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessor($RegExp, '$' + i, GETTER, RegExpMakeCaptureGetter(i), DONT_DELETE);
     %DefineAccessor($RegExp, '$' + i, SETTER, NoOpSetter, DONT_DELETE);
   }
 }
 
 
 SetupRegExp();