MSVC fails to deduce template argument

November 7, 2023

This C++17 code compiles with clang and g++ but MSVC fails to deduce the template argument:

#include <type_traits>

struct Prop {
  constexpr Prop() {};
};

constexpr const Prop i;

struct Klass {
  template <auto Klass::*MEMBER, const Prop &P,
            std::enable_if_t<std::is_member_pointer_v<decltype(MEMBER)>, bool> = true>
  void def() {}
  void fn();
  int var;
};

void Klass::fn() {}

int main() {
  Klass k;

  k.def<&Klass::fn, i>();
  k.def<&Klass::var, i>();
}

Removing only the std::enable_if fixes it, as well as removing only the second template argument (the non-type reference). This makes me think that this is a bug. Does anyone see anything that is ill-formed or does anyone have any tips for making it work with MSVC?

I need the enable_if because I have multiple similar templates (that are more complex, this is only a minimal repro).