cdata, including tests

drive-by: remove the `__ranges/data.h` header and merge it with
`__ranges/access.h` (for `ranges::data`), or `__ranges/const_access.h`
(for `ranges::cdata`). I felt comfortable doing this as every use of
`__ranges/access.h` included either `__ranges/data.h` itself, or
`__ranges/concepts.h` which itself included `__ranges/data.h`.

Author: strega-nil

libcxx/include/CMakeLists.txt

@@ -644,7 +644,6 @@ set(files
   __ranges/container_compatible_range.h
   __ranges/counted.h
   __ranges/dangling.h
-  __ranges/data.h
   __ranges/drop_view.h
   __ranges/drop_while_view.h
   __ranges/elements_view.h

libcxx/include/__format/range_default_formatter.h

@@ -22,8 +22,8 @@
 #include <__format/formatter.h>
 #include <__format/range_formatter.h>
 #include <__iterator/back_insert_iterator.h>
+#include <__ranges/access.h>
 #include <__ranges/concepts.h>
-#include <__ranges/data.h>
 #include <__ranges/from_range.h>
 #include <__ranges/size.h>
 #include <__type_traits/conditional.h>

libcxx/include/__format/range_formatter.h

@@ -26,8 +26,8 @@
 #include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
 #include <__iterator/back_insert_iterator.h>
+#include <__ranges/access.h>
 #include <__ranges/concepts.h>
-#include <__ranges/data.h>
 #include <__ranges/from_range.h>
 #include <__ranges/size.h>
 #include <__type_traits/remove_cvref.h>

libcxx/include/__ranges/access.h

@@ -14,10 +14,13 @@
 #include <__config>
 #include <__iterator/concepts.h>
 #include <__iterator/readable_traits.h>
+#include <__memory/pointer_traits.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__type_traits/decay.h>
+#include <__type_traits/is_pointer.h>
 #include <__type_traits/is_reference.h>
 #include <__type_traits/remove_cvref.h>
+#include <__type_traits/remove_pointer.h>
 #include <__type_traits/remove_reference.h>
 #include <__utility/auto_cast.h>
 #include <__utility/declval.h>
@@ -148,6 +151,42 @@ inline constexpr auto end = __end::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
+// [range.prim.data]
+
+namespace ranges {
+namespace __data {
+template <class _Tp>
+concept __ptr_to_object = is_pointer_v<_Tp> && is_object_v<remove_pointer_t<_Tp>>;
+
+template <class _Tp>
+concept __member_data = __can_borrow<_Tp> && requires(_Tp&& __t) {
+  { _LIBCPP_AUTO_CAST(__t.data()) } -> __ptr_to_object;
+};
+
+template <class _Tp>
+concept __ranges_begin_invocable = !__member_data<_Tp> && __can_borrow<_Tp> && requires(_Tp&& __t) {
+  { ranges::begin(__t) } -> contiguous_iterator;
+};
+
+struct __fn {
+  template <__member_data _Tp>
+  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const noexcept(noexcept(__t.data())) {
+    return __t.data();
+  }
+
+  template <__ranges_begin_invocable _Tp>
+  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(std::to_address(ranges::begin(__t)))) {
+    return std::to_address(ranges::begin(__t));
+  }
+};
+} // namespace __data
+
+inline namespace __cpo {
+inline constexpr auto data = __data::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
 #endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__ranges/concepts.h

@@ -21,7 +21,6 @@
 #include <__iterator/iterator_traits.h>
 #include <__iterator/readable_traits.h>
 #include <__ranges/access.h>
-#include <__ranges/data.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__ranges/enable_view.h>
 #include <__ranges/size.h>

libcxx/include/__ranges/const_access.h

@@ -213,6 +213,48 @@ inline constexpr auto crend = __crend::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
+// [range.prim.cdata]
+
+namespace ranges {
+namespace __cdata {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI constexpr static auto __as_const_pointer(const _Tp* __ptr) noexcept {
+    return __ptr;
+  }
+
+  template <__const_accessible_range _Rng>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static auto
+  operator()(_Rng&& __rng) noexcept(noexcept(__as_const_pointer(ranges::data(ranges::__possibly_const_range(__rng)))))
+      -> decltype(__as_const_pointer(ranges::data(ranges::__possibly_const_range(__rng)))) {
+    return __as_const_pointer(ranges::data(ranges::__possibly_const_range(__rng)));
+  }
+
+#  else  // ^^^ _LIBCPP_STD_VER >= 23 / _LIBCPP_STD_VER < 23 vvv
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::data(static_cast<const remove_reference_t<_Tp>&>(__t))))
+          -> decltype(ranges::data(static_cast<const remove_reference_t<_Tp>&>(__t))) {
+    return ranges::data(static_cast<const remove_reference_t<_Tp>&>(__t));
+  }
+
+  template <class _Tp>
+    requires is_rvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const noexcept(
+      noexcept(ranges::data(static_cast<const _Tp&&>(__t)))) -> decltype(ranges::data(static_cast<const _Tp&&>(__t))) {
+    return ranges::data(static_cast<const _Tp&&>(__t));
+  }
+#  endif // ^^^ _LIBCPP_STD_VER < 23
+};
+} // namespace __cdata
+
+inline namespace __cpo {
+inline constexpr auto cdata = __cdata::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
 #endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__ranges/data.h

@@ -15,7 +15,6 @@
 #include <__config>
 #include <__ranges/access.h>
 #include <__ranges/concepts.h>
-#include <__ranges/data.h>
 #include <__ranges/empty.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__ranges/size.h>

libcxx/include/__ranges/owning_view.h

@@ -19,7 +19,6 @@
 #include <__memory/addressof.h>
 #include <__ranges/access.h>
 #include <__ranges/concepts.h>
-#include <__ranges/data.h>
 #include <__ranges/empty.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__ranges/size.h>

libcxx/include/__ranges/ref_view.h

@@ -1714,7 +1714,6 @@ module std_private_ranges_counted                    [system] {
   export std_span
 }
 module std_private_ranges_dangling                   [system] { header "__ranges/dangling.h" }
-module std_private_ranges_data                       [system] { header "__ranges/data.h" }
 module std_private_ranges_drop_view                  [system] { header "__ranges/drop_view.h" }
 module std_private_ranges_drop_while_view            [system] { header "__ranges/drop_while_view.h" }
 module std_private_ranges_elements_view              [system] { header "__ranges/elements_view.h" }