[Bug c++/49520] New: [C++0x] using-declaration and operator&& confuses constexpr

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49520

           Summary: [C++0x] using-declaration and operator&& confuses
                    constexpr
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: redi@gcc.gnu.org
                CC: jason@gcc.gnu.org


namespace x { void foo(); }

template<typename T>
struct traits
{
    static constexpr bool f() { return true; }

    static constexpr bool g()
    {
        using x::foo;
        return f() && noexcept(foo());
    }
};

template struct traits<int>;


constexpr.cc: In static member function 'static constexpr bool traits<T>::g()
[with T = int]':
constexpr.cc:15:17:   required from here
constexpr.cc:12:5: error: body of constexpr function 'static constexpr bool
traits<T>::g() [with T = int]' not a return-statement


(I'm trying to use something of this form to make vector's move-assignment
operator noexcept when using std::allocator, an important QoI issue.  'f' is
propagate_on_container_move_assignment and 'x::foo' is 'std::swap' which needs
to be called unqualified.)