[Bug c++/59056] enable_if turns a non-ambiguous template into an ambiguous one

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59056

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I must be misunderstanding something, because rewriting the class template
partial specializations as function templates (as per [temp.class.order]) shows
that one is more specialized than the other, as the functions are not
ambiguous:

#include <type_traits>

template <class T> class Foo {};

template <class X>
constexpr bool check()
{
  return true;
}

template <class X, class Enable = void>
struct Bar {};

template<class X>
void func(Bar<X, typename std::enable_if< check<X>() >::type>) { }

template<class T>
int func(Bar<Foo<T>>) {  return 0; }

void instance()
{
  Bar< Foo<int> > av;
  int i = func(av);
}

I thought if the partial specializations were ambiguous then these function
overloads should be too.