[libc++][ranges] P1223R5: find_last (#99312)

Implements [P1223R5][] completely.

Includes an implementation of `find_last`, `find_last_if`, and
`find_last_if_not`.

[P1223R5]: https://wg21.link/p1223r5

libcxx/docs/FeatureTestMacroTable.rst

@@ -360,6 +360,8 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_ranges_contains``                              ``202207L``
     ---------------------------------------------------------- -----------------
+    ``__cpp_lib_ranges_find_last``                             ``202207L``
+    ---------------------------------------------------------- -----------------
     ``__cpp_lib_ranges_iota``                                  *unimplemented*
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_ranges_join_with``                             *unimplemented*

libcxx/docs/ReleaseNotes/19.rst

@@ -58,6 +58,7 @@ Implemented Papers
 - P2231R1 - Missing ``constexpr`` in ``std::optional`` and ``std::variant``
 - P0019R8 - ``std::atomic_ref``
 - P2389R2 - Alias template ``dims`` for the ``extents`` of ``mdspan``
+- P1223R5 - ``ranges::find_last()``, ``ranges::find_last_if()``, and ``ranges::find_last_if_not()``
 
 Improvements and New Features
 -----------------------------

libcxx/docs/Status/Cxx23Papers.csv

@@ -55,7 +55,7 @@
 "`P0429R9 <https://wg21.link/P0429R9>`__","LWG","A Standard ``flat_map``","July 2022","",""
 "`P1169R4 <https://wg21.link/P1169R4>`__","LWG","``static operator()``","July 2022","|Complete|","16.0"
 "`P1222R4 <https://wg21.link/P1222R4>`__","LWG","A Standard ``flat_set``","July 2022","",""
-"`P1223R5 <https://wg21.link/P1223R5>`__","LWG","``ranges::find_last()``, ``ranges::find_last_if()``, and ``ranges::find_last_if_not()``","July 2022","","","|ranges|"
+"`P1223R5 <https://wg21.link/P1223R5>`__","LWG","``ranges::find_last()``, ``ranges::find_last_if()``, and ``ranges::find_last_if_not()``","July 2022","|Complete|","19.0","|ranges|"
 "`P1467R9 <https://wg21.link/P1467R9>`__","LWG","Extended ``floating-point`` types and standard names","July 2022","",""
 "`P1642R11 <https://wg21.link/P1642R11>`__","LWG","Freestanding ``[utilities]``, ``[ranges]``, and ``[iterators]``","July 2022","",""
 "`P1899R3 <https://wg21.link/P1899R3>`__","LWG","``stride_view``","July 2022","","","|ranges|"

libcxx/docs/Status/RangesAlgorithms.csv

@@ -1,8 +1,8 @@
 Standard,Algorithm,Assignee,CL,Status
 C++20,all C++20 algorithms,N/A,N/A,✅
-C++23,`find_last <https://wg21.link/P1223R5>`_,Unassigned,No patch yet,Not started
-C++23,`find_last_if <https://wg21.link/P1223R5>`_,Unassigned,No patch yet,Not started
-C++23,`find_last_if_not <https://wg21.link/P1223R5>`_,Unassigned,No patch yet,Not started
+C++23,`find_last <https://wg21.link/P1223R5>`_,Nicole Mazzuca,`#99312 <https://github.com/llvm/llvm-project/pull/99312>`_,Complete
+C++23,`find_last_if <https://wg21.link/P1223R5>`_,Nicole Mazzuca,`#99312 <https://github.com/llvm/llvm-project/pull/99312>`_,Complete
+C++23,`find_last_if_not <https://wg21.link/P1223R5>`_,Nicole Mazzuca,`#99312 <https://github.com/llvm/llvm-project/pull/99312>`_,Complete
 C++23,`starts_with <https://wg21.link/P1659R3>`_,Zijun Zhao,`D150735 <https://llvm.org/D150735>`_,Complete
 C++23,`ends_with <https://wg21.link/P1659R3>`_,Zijun Zhao, `D150831 <https://llvm.org/D150831>`_,Complete
 C++23,`shift_left <https://wg21.link/p2440r1>`_,Unassigned,No patch yet,Not started

libcxx/include/CMakeLists.txt

@@ -97,6 +97,7 @@ set(files
   __algorithm/ranges_find_first_of.h
   __algorithm/ranges_find_if.h
   __algorithm/ranges_find_if_not.h
+  __algorithm/ranges_find_last.h
   __algorithm/ranges_for_each.h
   __algorithm/ranges_for_each_n.h
   __algorithm/ranges_generate.h

libcxx/include/__algorithm/ranges_find_last.h

@@ -0,0 +1,175 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___ALGORITHM_RANGES_FIND_LAST_H
+#define _LIBCPP___ALGORITHM_RANGES_FIND_LAST_H
+
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/indirectly_comparable.h>
+#include <__iterator/next.h>
+#include <__iterator/prev.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if _LIBCPP_STD_VER >= 23
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _Iter, class _Sent, class _Pred, class _Proj>
+_LIBCPP_HIDE_FROM_ABI constexpr subrange<_Iter>
+__find_last_impl(_Iter __first, _Sent __last, _Pred __pred, _Proj& __proj) {
+  if (__first == __last) {
+    return subrange<_Iter>(__first, __first);
+  }
+
+  if constexpr (bidirectional_iterator<_Iter>) {
+    auto __last_it = ranges::next(__first, __last);
+    for (auto __it = ranges::prev(__last_it); __it != __first; --__it) {
+      if (__pred(std::invoke(__proj, *__it))) {
+        return subrange<_Iter>(std::move(__it), std::move(__last_it));
+      }
+    }
+    if (__pred(std::invoke(__proj, *__first))) {
+      return subrange<_Iter>(std::move(__first), std::move(__last_it));
+    }
+    return subrange<_Iter>(__last_it, __last_it);
+  } else {
+    bool __found = false;
+    _Iter __found_it;
+    for (; __first != __last; ++__first) {
+      if (__pred(std::invoke(__proj, *__first))) {
+        __found    = true;
+        __found_it = __first;
+      }
+    }
+
+    if (__found) {
+      return subrange<_Iter>(std::move(__found_it), std::move(__first));
+    } else {
+      return subrange<_Iter>(__first, __first);
+    }
+  }
+}
+
+namespace __find_last {
+struct __fn {
+  template <class _Type>
+  struct __op {
+    const _Type& __value;
+    template <class _Elem>
+    _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator()(_Elem&& __elem) const {
+      return std::forward<_Elem>(__elem) == __value;
+    }
+  };
+
+  template <forward_iterator _Iter, sentinel_for<_Iter> _Sent, class _Type, class _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<_Iter, _Proj>, const _Type*>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, const _Type& __value, _Proj __proj = {}) {
+    return ranges::__find_last_impl(std::move(__first), std::move(__last), __op<_Type>{__value}, __proj);
+  }
+
+  template <forward_range _Range, class _Type, class _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static borrowed_subrange_t<_Range>
+  operator()(_Range&& __range, const _Type& __value, _Proj __proj = {}) {
+    return ranges::__find_last_impl(ranges::begin(__range), ranges::end(__range), __op<_Type>{__value}, __proj);
+  }
+};
+} // namespace __find_last
+
+namespace __find_last_if {
+struct __fn {
+  template <class _Pred>
+  struct __op {
+    _Pred& __pred;
+    template <class _Elem>
+    _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator()(_Elem&& __elem) const {
+      return std::invoke(__pred, std::forward<_Elem>(__elem));
+    }
+  };
+
+  template <forward_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
+            indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) {
+    return ranges::__find_last_impl(std::move(__first), std::move(__last), __op<_Pred>{__pred}, __proj);
+  }
+
+  template <forward_range _Range,
+            class _Proj = identity,
+            indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static borrowed_subrange_t<_Range>
+  operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) {
+    return ranges::__find_last_impl(ranges::begin(__range), ranges::end(__range), __op<_Pred>{__pred}, __proj);
+  }
+};
+} // namespace __find_last_if
+
+namespace __find_last_if_not {
+struct __fn {
+  template <class _Pred>
+  struct __op {
+    _Pred& __pred;
+    template <class _Elem>
+    _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator()(_Elem&& __elem) const {
+      return !std::invoke(__pred, std::forward<_Elem>(__elem));
+    }
+  };
+
+  template <forward_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
+            indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) {
+    return ranges::__find_last_impl(std::move(__first), std::move(__last), __op<_Pred>{__pred}, __proj);
+  }
+
+  template <forward_range _Range,
+            class _Proj = identity,
+            indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static borrowed_subrange_t<_Range>
+  operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) {
+    return ranges::__find_last_impl(ranges::begin(__range), ranges::end(__range), __op<_Pred>{__pred}, __proj);
+  }
+};
+} // namespace __find_last_if_not
+
+inline namespace __cpo {
+inline constexpr auto find_last        = __find_last::__fn{};
+inline constexpr auto find_last_if     = __find_last_if::__fn{};
+inline constexpr auto find_last_if_not = __find_last_if_not::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_RANGES_FIND_LAST_H

libcxx/include/algorithm

@@ -102,6 +102,31 @@ namespace ranges {
     constexpr borrowed_iterator_t<R>
       find_if_not(R&& r, Pred pred, Proj proj = {});                                                      // since C++20
 
+  template<forward_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+    constexpr subrange<I> find_last(I first, S last, const T& value, Proj proj = {});                     // since C++23
+
+  template<forward_range R, class T, class Proj = identity>
+    requires
+      indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+    constexpr borrowed_subrange_t<R> find_last(R&& r, const T& value, Proj proj = {});                   // since C++23
+
+  template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
+           indirect_unary_predicate<projected<I, Proj>> Pred>
+    constexpr subrange<I> find_last_if(I first, S last, Pred pred, Proj proj = {});                      // since C++23
+
+  template<forward_range R, class Proj = identity,
+           indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+    constexpr borrowed_subrange_t<R> find_last_if(R&& r, Pred pred, Proj proj = {});                     // since C++23
+
+  template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
+           indirect_unary_predicate<projected<I, Proj>> Pred>
+    constexpr subrange<I> find_last_if_not(I first, S last, Pred pred, Proj proj = {});                  // since C++23
+
+  template<forward_range R, class Proj = identity,
+           indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+    constexpr borrowed_subrange_t<R> find_last_if_not(R&& r, Pred pred, Proj proj = {});                 // since C++23
+
   template<class T, class Proj = identity,
            indirect_strict_weak_order<projected<const T*, Proj>> Comp = ranges::less>
     constexpr const T& min(const T& a, const T& b, Comp comp = {}, Proj proj = {});                       // since C++20
@@ -1989,6 +2014,7 @@ template <class BidirectionalIterator, class Compare>
 #  include <__algorithm/fold.h>
 #  include <__algorithm/ranges_contains_subrange.h>
 #  include <__algorithm/ranges_ends_with.h>
+#  include <__algorithm/ranges_find_last.h>
 #  include <__algorithm/ranges_starts_with.h>
 #endif // _LIBCPP_STD_VER >= 23
 

libcxx/include/module.modulemap

@@ -764,6 +764,7 @@ module std_private_algorithm_ranges_find_end                             [system
 module std_private_algorithm_ranges_find_first_of                        [system] { header "__algorithm/ranges_find_first_of.h" }
 module std_private_algorithm_ranges_find_if                              [system] { header "__algorithm/ranges_find_if.h" }
 module std_private_algorithm_ranges_find_if_not                          [system] { header "__algorithm/ranges_find_if_not.h" }
+module std_private_algorithm_ranges_find_last                            [system] { header "__algorithm/ranges_find_last.h" }
 module std_private_algorithm_ranges_for_each                             [system] {
   header "__algorithm/ranges_for_each.h"
   export std_private_algorithm_in_fun_result

libcxx/include/version

@@ -190,6 +190,7 @@ __cpp_lib_ranges_chunk                                  202202L <ranges>
 __cpp_lib_ranges_chunk_by                               202202L <ranges>
 __cpp_lib_ranges_concat                                 202403L <ranges>
 __cpp_lib_ranges_contains                               202207L <algorithm>
+__cpp_lib_ranges_find_last                              202207L <algorithm>
 __cpp_lib_ranges_iota                                   202202L <numeric>
 __cpp_lib_ranges_join_with                              202202L <ranges>
 __cpp_lib_ranges_repeat                                 202207L <ranges>
@@ -484,6 +485,7 @@ __cpp_lib_void_t                                        201411L <type_traits>
 // # define __cpp_lib_ranges_chunk                         202202L
 # define __cpp_lib_ranges_chunk_by                      202202L
 # define __cpp_lib_ranges_contains                      202207L
+# define __cpp_lib_ranges_find_last                     202207L
 // # define __cpp_lib_ranges_iota                          202202L
 // # define __cpp_lib_ranges_join_with                     202202L
 # define __cpp_lib_ranges_repeat                        202207L

libcxx/modules/std/algorithm.inc

@@ -77,13 +77,14 @@ export namespace std {
     using std::ranges::find_if_not;
   } // namespace ranges
 
+#if _LIBCPP_STD_VER >= 23
+  // [alg.find.last], find last
   namespace ranges {
-#if 0
     using std::ranges::find_last;
     using std::ranges::find_last_if;
     using std::ranges::find_last_if_not;
-#endif
   } // namespace ranges
+#endif
 
   // [alg.find.end], find end
   using std::find_end;

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp

@@ -119,6 +119,16 @@ constexpr bool all_the_algorithms()
     (void)std::ranges::find_if(a, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::find_if_not(first, last, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::find_if_not(a, UnaryTrue(&copies)); assert(copies == 0);
+#if TEST_STD_VER >= 23
+    (void)std::ranges::find_last_if(first, last, UnaryTrue(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if(a, UnaryTrue(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if_not(first, last, UnaryTrue(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if_not(a, UnaryTrue(&copies));
+    assert(copies == 0);
+#endif
     (void)std::ranges::for_each(first, last, UnaryVoid(&copies)); assert(copies == 1); copies = 0;
     (void)std::ranges::for_each(a, UnaryVoid(&copies)); assert(copies == 1); copies = 0;
     (void)std::ranges::for_each_n(first, count, UnaryVoid(&copies)); assert(copies == 1); copies = 0;

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp

@@ -115,6 +115,20 @@ constexpr bool all_the_algorithms()
     (void)std::ranges::find_if(a, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::find_if_not(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::find_if_not(a, UnaryTrue(), Proj(&copies)); assert(copies == 0);
+#if TEST_STD_VER >= 23
+    (void)std::ranges::find_last(first, last, value, Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last(a, value, Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if(first, last, UnaryTrue(), Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if(a, UnaryTrue(), Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if_not(first, last, UnaryTrue(), Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::find_last_if_not(a, UnaryTrue(), Proj(&copies));
+    assert(copies == 0);
+#endif
     (void)std::ranges::for_each(first, last, UnaryVoid(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::for_each(a, UnaryVoid(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::for_each_n(first, count, UnaryVoid(), Proj(&copies)); assert(copies == 0);

libcxx/test/libcxx/diagnostics/algorithm.nodiscard.verify.cpp

@@ -372,6 +372,18 @@ void test() {
   // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
   std::ranges::contains_subrange(iter, iter, iter, iter);
   // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last_if_not(iter, iter, pred);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last_if_not(range, pred);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last_if(iter, iter, pred);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last_if(range, pred);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last(iter, iter, 1);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::find_last(range, 1);
+  // expected-warning@-1 {{ignoring return value of function declared with 'nodiscard' attribute}}
   std::ranges::fold_left(range, 0, std::plus());
   // expected-warning@-1{{ignoring return value of function declared with 'nodiscard' attribute}}
   std::ranges::fold_left(iter, iter, 0, std::plus());