[Bug libstdc++/83538] New: std::match_results C++14 conformance issue: reference != value_type&

["andrey.y.guskov at intel dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83538

            Bug ID: 83538
           Summary: std::match_results C++14 conformance issue: reference
                    != value_type&
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andrey.y.guskov at intel dot com
  Target Milestone: ---

C++14 standard (page 1123, see here:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf#1137) says:

namespace std {
template <class BidirectionalIterator,
class Allocator = allocator<sub_match<BidirectionalIterator>>>
class match_results {
public:
typedef sub_match<BidirectionalIterator> value_type;
typedef const value_type& const_reference;
typedef value_type& reference;
...

As of now, std::match_results implementation disagrees with the standard in
that it does not consider 'reference' equal to 'value_type&'.
I made a reproducer to prove that:

#include <regex>
template <class T1, class T2> struct diff { static const bool s = true; };
template <class T1> struct diff<T1, T1> { static const bool s = false; };
typedef std::match_results<wchar_t*, std::allocator<std::sub_match<wchar_t> > >
m;
int main() { return !printf((diff<m::reference, m::value_type&>::s)? "FAIL\n" :
"PASS\n"); }