[libc++][ranges] Implement rbegin, rend, crbegin and crend.

Differential Revision: https://reviews.llvm.org/D119057

libcxx/docs/Status/RangesPaper.csv

@@ -100,15 +100,15 @@ Section,Description,Dependencies,Assignee,Complete
 | `ranges::end <https://llvm.org/D100255>`_
 | `range::cbegin <https://llvm.org/D100255>`_
 | `ranges::cend <https://llvm.org/D100255>`_
-| ranges::rbegin
-| ranges::rend
-| ranges::crbegin
-| ranges::crend
+| `ranges::rbegin <https://llvm.org/D119057>`_
+| `ranges::rend <https://llvm.org/D119057>`_
+| `ranges::crbegin <https://llvm.org/D119057>`_
+| `ranges::crend <https://llvm.org/D119057>`_
 | `ranges::size <https://llvm.org/D101079>`_
 | `ranges::ssize <https://llvm.org/D101189>`_
 | `ranges::empty <https://llvm.org/D101193>`_
 | `ranges::data <https://llvm.org/D101476>`_
-| `ranges::cdata <https://llvm.org/D117044>`_",[iterator.concepts],Christopher Di Bella and Zoe Carver,In progress
+| `ranges::cdata <https://llvm.org/D117044>`_",[iterator.concepts],Various,✅
 `[range.range] <https://wg21.link/range.range>`_,"| `ranges::range <https://llvm.org/D100269>`_
 | `ranges::borrowed_range <https://llvm.org/D102426>`_
 | `ranges::enable_borrowed_range <https://llvm.org/D90999>`_

libcxx/include/CMakeLists.txt

@@ -346,7 +346,9 @@ set(files
   __ranges/non_propagating_cache.h
   __ranges/owning_view.h
   __ranges/range_adaptor.h
+  __ranges/rbegin.h
   __ranges/ref_view.h
+  __ranges/rend.h
   __ranges/reverse_view.h
   __ranges/single_view.h
   __ranges/size.h

libcxx/include/__concepts/class_or_enum.h

@@ -26,6 +26,7 @@ template<class _Tp>
 concept __class_or_enum = is_class_v<_Tp> || is_union_v<_Tp> || is_enum_v<_Tp>;
 
 // Work around Clang bug https://llvm.org/PR52970
+// TODO: remove this workaround once libc++ no longer has to support Clang 13 (it was fixed in Clang 14).
 template<class _Tp>
 concept __workaround_52970 = is_class_v<__uncvref_t<_Tp>> || is_union_v<__uncvref_t<_Tp>>;
 

libcxx/include/__ranges/access.h

@@ -15,7 +15,6 @@
 #include <__iterator/readable_traits.h>
 #include <__ranges/enable_borrowed_range.h>
 #include <__utility/auto_cast.h>
-#include <concepts>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/__ranges/rbegin.h

@@ -0,0 +1,130 @@
+// -*- 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_RBEGIN_H
+#define _LIBCPP___RANGES_RBEGIN_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 <__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 !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+// [ranges.access.rbegin]
+
+namespace ranges {
+namespace __rbegin {
+template <class _Tp>
+concept __member_rbegin =
+  __can_borrow<_Tp> &&
+  __workaround_52970<_Tp> &&
+  requires(_Tp&& __t) {
+    { _LIBCPP_AUTO_CAST(__t.rbegin()) } -> input_or_output_iterator;
+  };
+
+void rbegin(auto&) = delete;
+void rbegin(const auto&) = delete;
+
+template <class _Tp>
+concept __unqualified_rbegin =
+  !__member_rbegin<_Tp> &&
+  __can_borrow<_Tp> &&
+  __class_or_enum<remove_cvref_t<_Tp>> &&
+  requires(_Tp&& __t) {
+    { _LIBCPP_AUTO_CAST(rbegin(__t)) } -> input_or_output_iterator;
+  };
+
+template <class _Tp>
+concept __can_reverse =
+  __can_borrow<_Tp> &&
+  !__member_rbegin<_Tp> &&
+  !__unqualified_rbegin<_Tp> &&
+  requires(_Tp&& __t) {
+    { ranges::begin(__t) } -> same_as<decltype(ranges::end(__t))>;
+    { ranges::begin(__t) } -> bidirectional_iterator;
+  };
+
+struct __fn {
+  template <class _Tp>
+    requires __member_rbegin<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(_LIBCPP_AUTO_CAST(__t.rbegin())))
+  {
+    return _LIBCPP_AUTO_CAST(__t.rbegin());
+  }
+
+  template <class _Tp>
+    requires __unqualified_rbegin<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(_LIBCPP_AUTO_CAST(rbegin(__t))))
+  {
+    return _LIBCPP_AUTO_CAST(rbegin(__t));
+  }
+
+  template <class _Tp>
+    requires __can_reverse<_Tp>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+    noexcept(noexcept(ranges::end(__t)))
+  {
+    return std::make_reverse_iterator(ranges::end(__t));
+  }
+
+  void operator()(auto&&) const = delete;
+};
+} // namespace __rbegin
+
+inline namespace __cpo {
+  inline constexpr auto rbegin = __rbegin::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.access.crbegin]
+
+namespace ranges {
+namespace __crbegin {
+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::rbegin(static_cast<const remove_reference_t<_Tp>&>(__t))))
+    -> decltype(      ranges::rbegin(static_cast<const remove_reference_t<_Tp>&>(__t)))
+    { return          ranges::rbegin(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::rbegin(static_cast<const _Tp&&>(__t))))
+    -> decltype(      ranges::rbegin(static_cast<const _Tp&&>(__t)))
+    { return          ranges::rbegin(static_cast<const _Tp&&>(__t)); }
+};
+} // namespace __crbegin
+
+inline namespace __cpo {
+  inline constexpr auto crbegin = __crbegin::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+#endif // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_RBEGIN_H

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 !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+// [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 // !defined(_LIBCPP_HAS_NO_CONCEPTS)
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_REND_H

libcxx/include/module.modulemap

@@ -815,7 +815,9 @@ module std [system] {
       module non_propagating_cache  { private header "__ranges/non_propagating_cache.h" }
       module owning_view            { private header "__ranges/owning_view.h" }
       module range_adaptor          { private header "__ranges/range_adaptor.h" }
+      module rbegin                 { private header "__ranges/rbegin.h" }
       module ref_view               { private header "__ranges/ref_view.h" }
+      module rend                   { private header "__ranges/rend.h" }
       module reverse_view           { private header "__ranges/reverse_view.h" }
       module single_view            { private header "__ranges/single_view.h" }
       module size                   { private header "__ranges/size.h" }

libcxx/include/ranges

@@ -250,7 +250,9 @@ namespace std {
 #include <__ranges/enable_view.h>
 #include <__ranges/iota_view.h>
 #include <__ranges/join_view.h>
+#include <__ranges/rbegin.h>
 #include <__ranges/ref_view.h>
+#include <__ranges/rend.h>
 #include <__ranges/reverse_view.h>
 #include <__ranges/single_view.h>
 #include <__ranges/size.h>

libcxx/test/libcxx/diagnostics/detail.headers/ranges/rbegin.module.verify.cpp

@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__ranges/rbegin.h'}}
+#include <__ranges/rbegin.h>

libcxx/test/libcxx/diagnostics/detail.headers/ranges/rend.module.verify.cpp

@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__ranges/rend.h'}}
+#include <__ranges/rend.h>