Make failed capturing parenthesis produce null instead of "".

runtime/lib/regexp_jsc.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // This file encapsulates all the interaction with the
 // JSC regular expression library also referred to as pcre
 
 #include "lib/regexp_jsc.h"
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
@@ skipping 136 matching lines @@
     const String& pattern = String::Handle(regex.pattern());
     const int kErrorLength = 256;
     char error_msg[kErrorLength];
     OS::SNPrint(error_msg, kErrorLength,
                 "jscre::jsRegExpExecute error : %d", retval);
     ThrowExceptionOnError(pattern, error_msg);
     UNREACHABLE();
     return Array::null();
   }
 
   const int kMatchPair = 2;

[siva, 2012/03/19 18:29:14]

ASSERT(retval <= (num_bracket_expressions + 1));

   Array& array =
-      Array::Handle(Array::New(kMatchPair * (num_bracket_expressions + 1)));
+      Array::Handle(Array::New(kMatchPair * retval));
   // The matches come in (start, end + 1) pairs for each bracketted expression.
   Smi& start = Smi::Handle();
   Smi& end = Smi::Handle();
-  for (intptr_t i = 0;
-       i < (kMatchPair * (num_bracket_expressions + 1));
-       i += kMatchPair) {
+  for (intptr_t i = 0; i < (kMatchPair * retval); i += kMatchPair) {
     start = Smi::New(offsets[i]);
     end = Smi::New(offsets[i + 1]);
     array.SetAt(i, start);
     array.SetAt(i+1, end);
   }
   return array.raw();
 }
 
 }  // namespace dart