msvc bug: expr sfinae on private

test.cpp

#include <type_traits>

template <typename T, typename=void> struct Direct : std::false_type {};
template <typename T> struct Direct<T, std::void_t<decltype(std::declval<T>().f())>> : std::true_type {};

template <typename T> using Op = decltype(std::declval<T>().f());
template <typename T, typename=void> struct ViaAlias : std::false_type {};
template <typename T> struct ViaAlias<T, std::void_t<Op<T>>> : std::true_type {};


class X { void f(); };
static_assert(!Direct<X>::value,"Direct<X>");   // PASSES
static_assert(!ViaAlias<X>::value,"ViaAlias<X>");  // FAILS