Are enum values allowed in a std::integer_sequence?

This code compiles and executes fine using GCC 13 and Clang 17, but fails to compile on MSVC. I am wondering if the code is required to work according to the standard or if this is a problem with MSVC. Demo

#include <utility>
#include <iostream>

enum e : int { A=5, B, C, D };

auto x = std::integer_sequence<e, A, B, C, D>{};
auto y = std::integer_sequence<unsigned, 9, 4, 3, 8>{};
auto z = std::integer_sequence<int, 0, 1, 2, 3>{};

template<typename T, T... ints>
void print_sequence(std::integer_sequence<T, ints...> int_seq)
{
    std::cout << "The sequence of size " << int_seq.size() << ": ";
    ((std::cout << ints << ' '), ...);
    std::cout << '\n';
}

int main(int, char**)
{
    print_sequence(x);
    print_sequence(y);
    print_sequence(z);
    return 0;
}

MSVC gives this error:

error C2338: static_assert failed: 'integer_sequence<T, I...> requires T to be an integral type.'

Solution

Update:

I submitted PR 112473 and this has been fixed in GCC-trunk.

MSVC-STL and libc++† are right, as e is not an integral type (i.e. std::is_integral_v<e> is false).

From [intseq.intseq]:

namespace std {
  template<class T, T... I> struct integer_sequence {
    using value_type = T;
    static constexpr size_t size() noexcept { return sizeof...(I); }
  };
}

Mandates: T is an integer type.

It is worth noting that, in contrast, integral_constant has no requirement for T, so things like integral_constant<pair<int, int>, pair{0, 0}> are perfectly fine in C++20.

† Clang's libc++ needs to be enabled through the -stdlib=libc++ flag, and it also has a corresponding static_assert in the integer_sequence implementation.