[LLVMbugs] [Bug 22085] New: fails to copy an std::pair

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22085

            Bug ID: 22085
           Summary: fails to copy an std::pair
           Product: clang
           Version: 3.5
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: marc.glisse at normalesup.org
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

http://stackoverflow.com/q/27748442/1918193
g++ and Intel accept the code just fine. Oracle rejects it with a message
similar to clang. This code is quite possibly invalid, but that would mean that
the meta-programming that is accumulating in the standard library is making it
harder and harder to use CRTP. In any case, the error message could do with
some improvement.

Here is a reduced version:

struct A { static constexpr bool value = true; };
template <bool> struct conditional {};
template <typename _B1, typename _B2>
struct B : conditional<_B1::value> {};
template <typename _Tp> _Tp declval();
template <typename _From > struct C {
  template <typename _To1> static void __test_aux(_To1);
  template <typename _From1,
            typename = decltype(__test_aux(declval<_From1>()))>
  static A __test(int);
  typedef decltype(__test<_From>(0)) type;
};
template <typename _From> struct is_convertible : C<_From >::type {};
template <bool> struct I;
template <class, class> struct J {
  template <class _U1, class _U2,
            class = typename I<
                B<is_convertible<_U1>, _U2>::value>::type>
  J(J<_U1, _U2>);
};
template <class R_> struct F : R_::Kernel_base::Point_3 {};
template <typename K_base, typename Kernel_> struct G : K_base {
  typedef K_base Kernel_base;
  typedef F<Kernel_> Point_3;
};
template <class R_> class P { typename R_::Vector_3 base; };
template <class R_> class L { J<typename R_::Point_3, R_> base; };
template <class R_> class V { V(typename R_::Line_3); };

struct H;
struct D {
  typedef P<H> Point_3;
  typedef V<H> Vector_3;
  typedef L<H> Line_3;
};
struct H : G<D, H> {};
void fn1() { J<F<H>, int> x(x); }





And here is a less reduced version to show that the same happens with libc++ /
libstdc++:

#include <utility>
template <class R_> struct F : R_::Kernel_base::Point_3 {};
template <typename K_base, typename Kernel_> struct G : K_base {
  typedef K_base Kernel_base;
  typedef F<Kernel_> Point_3;
};
template <class R_> class P { typename R_::Vector_3 base; };
template <class R_> class L {
  typedef typename R_::Point_3 Point_3;
  typedef R_ Vector_3;
  typedef std::pair<Point_3, Vector_3> Base;
  Base base;
};
template <class R_> class V { V(typename R_::Line_3); };
struct H;
struct D {
  typedef P<H> Point_3;
  typedef V<H> Vector_3;
  typedef L<H> Line_3;
};
struct H : G<D, H> {};

typedef std::pair<F<H>, int> X;
void fn1() { X x(x); }

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