[libc++] __cpp_lib_ranges is defined without all views being available

[philnik777]

We've but views::join behind _LIBCPP_ENABLE_EXPERIMENTAL, but we didn't put __cpp_lib_ranges behind _LIBCPP_ENABLE_EXPERIMENTAL.

[changkhothuychung]

I am not sure how difficult this can be, but if there is some instruction I would like to take this one.

[ldionne]

I would suggest closing this without any resolution -- we're about to take join_view out of experimental state with #66033.

[frederick-vs-ja]

Maybe related: __cpp_lib_ranges is currently defined as 202207L but std::ranges::range_adaptor_closure is not yet implemented.

[h-2]

Maybe related: __cpp_lib_ranges is currently defined as 202207L but std::ranges::range_adaptor_closure is not yet implemented.

I have just run into this 😭

I previously had:

#if defined(__cpp_lib_ranges) && __cpp_lib_ranges >= 202202L
template <typename T>
using range_adaptor_closure = std::ranges::range_adaptor_closure<T>;
#elif defined(__GLIBCXX__)
template <typename T>
    requires(std::is_class_v<T> && std::same_as<T, std::remove_cv_t<T>>)
struct range_adaptor_closure : std::ranges::views::__adaptor::_RangeAdaptorClosure
{};
#elif defined(_LIBCPP_VERSION)
template <typename T>
using range_adaptor_closure = std::__range_adaptor_closure<T>;
#else
#    error "Requires modern standard library or older libstdc++ or libc++."
#endif

Now, I will need to add more checks...