[clang] fails to compile print("{}", 5s) when using libstdc++

[Taw3e8]

This fails to compile without adding libc++:

#include <chrono>
#include <print>

int main() {
	using namespace std::chrono_literals;
	std::print("{}", 5s);
}

[frederick-vs-ja]

Reduced example (Godbolt link):

template <class R>
constexpr auto kind =
  primary_template_not_defined(
    kind<R> // How can this hack be valid!
  );

template <class T, decltype(sizeof(0)) N>
constexpr int kind<T[N]> = 0;

This was accepted by old versions of Clang, but not the trunk...

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Jan Piotrowicz (Taw3e8)

This [fails to compile](https://godbolt.org/z/EWrMKdd3o) without adding libc++:

#include <chrono>
#include <print>

int main() {
	using namespace std::chrono_literals;
	std::print("{}", 5s);
}

[erichkeane]

Reduced example (Godbolt link):

template <class R>
constexpr auto kind =
  primary_template_not_defined(
    kind<R> // How can this hack be valid!
  );

template <class T, decltype(sizeof(0)) N>
constexpr int kind<T[N]> = 0;

This was accepted by old versions of Clang, but not the trunk...

Looks like this example fails in GCC as well if you instantiate kind for the same reason. So assuming this is accurate, this is a case of Clang diagnosing a 'never valid' template immediately, which I believe is correct behavior.