[Bug libstdc++/39407] New: Parse error in <stack> when user declares template-name c

["jwakely dot gcc at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

It was just brought to my attention that this fails to compile:

template <typename> void c();
#include <stack>


In file included from
/sbcimp/run/pd/gcc/32-bit/4.3.2/lib/gcc/i686-pc-linux-gnu/4.3.2/../../../../include/c++/4.3.2/stack:67,
                 from mark.cc:2:
/sbcimp/run/pd/gcc/32-bit/4.3.2/lib/gcc/i686-pc-linux-gnu/4.3.2/../../../../include/c++/4.3.2/bits/stl_stack.h:
In function ?bool std::operator<(const std::stack<_Tp, _Seq>&, const
std::stack<_Tp, _Seq>&)?:
/sbcimp/run/pd/gcc/32-bit/4.3.2/lib/gcc/i686-pc-linux-gnu/4.3.2/../../../../include/c++/4.3.2/bits/stl_stack.h:257:
error: `.' cannot appear in a constant-expression
/sbcimp/run/pd/gcc/32-bit/4.3.2/lib/gcc/i686-pc-linux-gnu/4.3.2/../../../../include/c++/4.3.2/bits/stl_stack.h:257:
error: parse error in template argument list

The problem is here:

  template<typename _Tp, typename _Seq>
    inline bool
    operator<(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
    { return __x.c < __y.c; }

The presence of the template ::c means that "c <" is parsed as the start of a
template-id, which then fails.

I *think* the compiler is doing the right thing here, but that doesn't help
users who've declared a template 'c'.  libstdc++ could make it a non-issue by
using parentheses to prevent __x.c being parsed as a template-id:

    { return (__x.c) < __y.c; }

I've only tested it with 4.3.2 but it apparently fails with 3.2 - 4.3.3, and I
assume with 4.4 too.


-- 
           Summary: Parse error in <stack> when user declares template-name
                    c
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jwakely dot gcc at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39407