std::byte formatting with compile-time API is broken

[alexezeder]

Right now formatting of std::byte using compile-time API like so:

fmt::format(FMT_COMPILE("{}"), std::byte{42})

ends up with compilation error, proof on Compiler Explorer. Because there are 2 write functions which satisfy for the passed type std::byte:

fmt/include/fmt/format.h

Lines 2114 to 2120 in 5a37e18

	template <typename Char, typename OutputIt, typename T,
	FMT_ENABLE_IF(std::is_enum<T>::value &&
	!std::is_same<T, Char>::value)>
	FMT_CONSTEXPR OutputIt write(OutputIt out, T value) {
	return write<Char>(
	out, static_cast<typename std::underlying_type<T>::type>(value));
	}

fmt/include/fmt/format.h

Lines 2150 to 2162 in 5a37e18

	template <typename Char, typename OutputIt, typename T>
	auto write(OutputIt out, const T& value) -> typename std::enable_if<
	mapped_type_constant<T, basic_format_context<OutputIt, Char>>::value ==
	type::custom_type,
	OutputIt>::type {
	using context_type = basic_format_context<OutputIt, Char>;
	using formatter_type =
	conditional_t<has_formatter<T, context_type>::value,
	typename context_type::template formatter_type<T>,
	fallback_formatter<T, Char>>;
	context_type ctx(out, {}, {});
	return formatter_type().format(value, ctx);
	}

I tried to fix that in the PR #2072 and with the SFINAE check for the enum-specific write function I ended up with a failed format-test because of a strange MSVC compiler error, which I cannot properly debug.

So feel free to create a new PR to fix that std::byte formatting bug with some MSVC workaround.

[alexezeder]

It turned out that there are some workarounds for MSVC - https://godbolt.org/z/dvcTjj