1 files changed, 134 insertions, 0 deletions
diff --git a/libcxx/include/__ranges/rend.h b/libcxx/include/__ranges/rend.h
new file mode 100644
index 000000000000..e507b2587277
--- /dev/null
+++ b/libcxx/include/__ranges/rend.h
@@ -0,0 +1,134 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef _LIBCPP___RANGES_REND_H
+#define _LIBCPP___RANGES_REND_H
+
+#include <__concepts/class_or_enum.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/readable_traits.h>
+#include <__iterator/reverse_iterator.h>
+#include <__ranges/access.h>
+#include <__ranges/rbegin.h>
+#include <__utility/auto_cast.h>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+// [range.access.rend]
+
+namespace ranges {
+namespace __rend {
+template <class _Tp>
+concept __member_rend =
+  __can_borrow<_Tp> &&
+  __workaround_52970<_Tp> &&
+  requires(_Tp&& __t) {
+    ranges::rbegin(__t);
+    { _LIBCPP_AUTO_CAST(__t.rend()) } -> sentinel_for<decltype(ranges::rbegin(__t))>;
+  };
+
+void rend(auto&) = delete;
+void rend(const auto&) = delete;
+
+template <class _Tp>
+concept __unqualified_rend =
+  !__member_rend<_Tp> &&
+  __can_borrow<_Tp> &&
+  __class_or_enum<remove_cvref_t<_Tp>> &&
+  requires(_Tp&& __t) {
+    ranges::rbegin(__t);
+    { _LIBCPP_AUTO_CAST(rend(__t)) } -> sentinel_for<decltype(ranges::rbegin(__t))>;
+  };
+
+template <class _Tp>
+concept __can_reverse =
+  __can_borrow<_Tp> &&
+  !__member_rend<_Tp> &&
+  !__unqualified_rend<_Tp> &&
+  requires(_Tp&& __t) {
+    { ranges::begin(__t) } -> same_as<decltype(ranges::end(__t))>;
+    { ranges::begin(__t) } -> bidirectional_iterator;
+  };
+
+class __fn {
+public:
+  template <class _Tp>
+    requires __member_rend<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(_LIBCPP_AUTO_CAST(__t.rend())))
+  {
+    return _LIBCPP_AUTO_CAST(__t.rend());
+  }
+
+  template <class _Tp>
+    requires __unqualified_rend<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(_LIBCPP_AUTO_CAST(rend(__t))))
+  {
+    return _LIBCPP_AUTO_CAST(rend(__t));
+  }
+
+  template <class _Tp>
+    requires __can_reverse<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(ranges::begin(__t)))
+  {
+    return std::make_reverse_iterator(ranges::begin(__t));
+  }
+
+  void operator()(auto&&) const = delete;
+};
+} // namespace __rend
+
+inline namespace __cpo {
+  inline constexpr auto rend = __rend::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.access.crend]
+
+namespace ranges {
+namespace __crend {
+struct __fn {
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
+  constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(ranges::rend(static_cast<const remove_reference_t<_Tp>&>(__t))))
+    -> decltype(      ranges::rend(static_cast<const remove_reference_t<_Tp>&>(__t)))
+    { return          ranges::rend(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::rend(static_cast<const _Tp&&>(__t))))
+    -> decltype(      ranges::rend(static_cast<const _Tp&&>(__t)))
+    { return          ranges::rend(static_cast<const _Tp&&>(__t)); }
+};
+} // namespace __crend
+
+inline namespace __cpo {
+  inline constexpr auto crend = __crend::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_REND_H