[Bug c++/59681] New: SVN 197248 adding N3582 support broke Boost.Regex with -std=c++1y

[pab at pabigot dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59681

            Bug ID: 59681
           Summary: SVN 197248 adding N3582 support broke Boost.Regex with
                    -std=c++1y
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pab at pabigot dot com

In this commit 
http://gcc.gnu.org/viewcvs/gcc/trunk/gcc/cp/parser.c?r1=197248&r2=197247&pathrev=197248
the first diff (line 4109 of c/parser.c) fixed a problem where the
return value from finish_parenthesized_expr() was discarded.  As a side
effect, this small program:

#include <boost/regex.hpp>
const boost::regex e("AB");

produces these diagnostics with gcc -std=c++1y and Boost 1.55:

llc[45]$ /usr/local/gcc/bin/g++ --version
g++ (GCC) 4.9.0 20140104 (experimental)
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

llc[46]$ /usr/local/gcc/bin/g++ -std=c++1y -c /tmp/bre.cc 
In file included from
/usr/local/gcc-20140104/include/boost/regex/v4/regex.hpp:70:0,
                 from /usr/local/gcc-20140104/include/boost/regex.hpp:31,
                 from /tmp/bre.cc:1:
/usr/local/gcc-20140104/include/boost/regex/v4/basic_regex_creator.hpp: In
member function ‘boost::re_detail::re_literal*
boost::re_detail::basic_regex_creator<charT, traits>::append_literal(charT)’:
/usr/local/gcc-20140104/include/boost/regex/v4/basic_regex_creator.hpp:349:24:
error: lvalue required as increment operand
       ++(result->length);
                        ^
In file included from
/usr/local/gcc-20140104/include/boost/regex/v4/regex.hpp:73:0,
                 from /usr/local/gcc-20140104/include/boost/regex.hpp:31,
                 from /tmp/bre.cc:1:
/usr/local/gcc-20140104/include/boost/regex/v4/basic_regex_parser.hpp: In
member function ‘bool boost::re_detail::basic_regex_parser<charT,
traits>::parse_repeat(std::size_t, std::size_t)’:
/usr/local/gcc-20140104/include/boost/regex/v4/basic_regex_parser.hpp:974:21:
error: lvalue required as decrement operand
       --(lit->length);
                     ^
llc[47]$

The problem goes away if that line of the patch is reverted, but since
the change appears to be correct there's some other problem somewhere.