diff --git a/libcxx/docs/Status/RangesAlgorithms.csv b/libcxx/docs/Status/RangesAlgorithms.csv
--- a/libcxx/docs/Status/RangesAlgorithms.csv
+++ b/libcxx/docs/Status/RangesAlgorithms.csv
@@ -26,7 +26,7 @@
Search,search,Not assigned,n/a,Not started
Search,search_n,Not assigned,n/a,Not started
Search,find_end,Not assigned,n/a,Not started
-Read-only,is_partitioned,Christopher Di Bella,`D105794 <https://llvm.org/D105794>`_,Under review
+Read-only,is_partitioned,Nikolas Klauser,`D124440 <https://llvm.org/D124440>`_,✅
Read-only,is_sorted,Not assigned,n/a,Not started
Read-only,is_sorted_unitl,Not assigned,n/a,Not started
Read-only,includes,Not assigned,n/a,Not started
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -75,6 +75,7 @@
__algorithm/ranges_find.h
__algorithm/ranges_find_if.h
__algorithm/ranges_find_if_not.h
+ __algorithm/ranges_is_partitioned.h
__algorithm/ranges_max.h
__algorithm/ranges_max_element.h
__algorithm/ranges_min.h
diff --git a/libcxx/include/__algorithm/ranges_is_partitioned.h b/libcxx/include/__algorithm/ranges_is_partitioned.h
new file mode 100644
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_is_partitioned.h
@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_IS_PARTITIONED_H
+#define _LIBCPP___ALGORITHM_RANGES_IS_PARTITIONED_H
+
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__iterator/concepts.h>
+#include <__iterator/indirectly_comparable.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __is_partitioned {
+struct __fn {
+
+ template <class _Iter, class _Sent, class _Proj, class _Pred>
+ _LIBCPP_HIDE_FROM_ABI constexpr static
+ bool __is_parititioned_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
+ for (; __first != __last; ++__first) {
+ if (!std::invoke(__pred, std::invoke(__proj, *__first)))
+ break;
+ }
+
+ if (__first == __last)
+ return true;
+ ++__first;
+
+ for (; __first != __last; ++__first) {
+ if (std::invoke(__pred, std::invoke(__proj, *__first)))
+ return false;
+ }
+
+ return true;
+ }
+
+ template <input_iterator _Iter, sentinel_for<_Iter> _Sent,
+ class _Proj = identity,
+ indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ bool operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) const {
+ return __is_parititioned_impl(std::move(__first), std::move(__last), __pred, __proj);
+ }
+
+ template <input_range _Range,
+ class _Proj = identity,
+ indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
+ _LIBCPP_HIDE_FROM_ABI constexpr
+ bool operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
+ return __is_parititioned_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
+ }
+};
+} // namespace __is_partitioned
+
+inline namespace __cpo {
+ inline constexpr auto is_partitioned = __is_partitioned::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_IS_PARTITIONED_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -238,6 +238,15 @@
requires indirectly_copyable<iterator_t<R>, I>
constexpr ranges::copy_backward_result<borrowed_iterator_t<R>, I>
ranges::copy_backward(R&& r, I result); // since C++20
+
+ template<input_iterator I, sentinel_for<I> S, class Proj = identity,
+ indirect_unary_predicate<projected<I, Proj>> Pred>
+ constexpr bool ranges::is_partitioned(I first, S last, Pred pred, Proj proj = {}); // since C++20
+
+ template<input_range R, class Proj = identity,
+ indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+ constexpr bool ranges::is_partitioned(R&& r, Pred pred, Proj proj = {}); // since C++20
+
}
constexpr bool // constexpr in C++20
@@ -964,6 +973,7 @@
#include <__algorithm/ranges_find.h>
#include <__algorithm/ranges_find_if.h>
#include <__algorithm/ranges_find_if_not.h>
+#include <__algorithm/ranges_is_partitioned.h>
#include <__algorithm/ranges_max.h>
#include <__algorithm/ranges_max_element.h>
#include <__algorithm/ranges_min.h>
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -303,6 +303,7 @@
module ranges_find { private header "__algorithm/ranges_find.h" }
module ranges_find_if { private header "__algorithm/ranges_find_if.h" }
module ranges_find_if_not { private header "__algorithm/ranges_find_if_not.h" }
+ module ranges_is_partitioned { private header "__algorithm/ranges_is_partitioned.h" }
module ranges_max { private header "__algorithm/ranges_max.h" }
module ranges_max_element { private header "__algorithm/ranges_max_element.h" }
module ranges_min { private header "__algorithm/ranges_min.h" }
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -112,6 +112,7 @@
#include <__algorithm/ranges_find.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_find.h'}}
#include <__algorithm/ranges_find_if.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_find_if.h'}}
#include <__algorithm/ranges_find_if_not.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_find_if_not.h'}}
+#include <__algorithm/ranges_is_partitioned.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_is_partitioned.h'}}
#include <__algorithm/ranges_max.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_max.h'}}
#include <__algorithm/ranges_max_element.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_max_element.h'}}
#include <__algorithm/ranges_min.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_min.h'}}
diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.partitions/ranges.is_partitioned.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.partitions/ranges.is_partitioned.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.partitions/ranges.is_partitioned.pass.cpp
@@ -0,0 +1,225 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// <algorithm>
+
+// template<input_iterator I, sentinel_for<I> S, class Proj = identity,
+// indirect_unary_predicate<projected<I, Proj>> Pred>
+// constexpr bool ranges::is_partitioned(I first, S last, Pred pred, Proj proj = {});
+// template<input_range R, class Proj = identity,
+// indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+// constexpr bool ranges::is_partitioned(R&& r, Pred pred, Proj proj = {});
+
+
+#include <algorithm>
+#include <cassert>
+
+#include "almost_satisfies_types.h"
+#include "test_iterators.h"
+
+template <class Iter, class Sent = sentinel_wrapper<Iter>>
+concept HasIsPartitionedIt = requires(Iter iter, Sent sent) {
+ std::ranges::is_partitioned(iter, sent, std::identity{});
+};
+
+static_assert(HasIsPartitionedIt<int*>);
+static_assert(!HasIsPartitionedIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasIsPartitionedIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasIsPartitionedIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasIsPartitionedIt<int*, SentinelForNotSemiregular>);
+static_assert(!HasIsPartitionedIt<int*, SentinelForNotWeaklyEqualityComparableWith>);
+
+template <class Pred>
+concept HasIsPartitionedItPred = requires(int* first, int* last, Pred pred) {
+ std::ranges::is_partitioned(first, last, pred);
+};
+
+static_assert(HasIsPartitionedItPred<std::identity>);
+static_assert(!HasIsPartitionedItPred<IndirectUnaryPredicateNotCopyConstructible>);
+static_assert(!HasIsPartitionedItPred<IndirectUnaryPredicateNotPredicate>);
+
+template <class Range>
+concept HasIsPartitionedR = requires (Range range) {
+ std::ranges::is_partitioned(range, std::identity{});
+};
+
+static_assert(HasIsPartitionedR<UncheckedRange<int*>>);
+static_assert(!HasIsPartitionedR<InputRangeNotDerivedFrom>);
+static_assert(!HasIsPartitionedR<InputRangeNotIndirectlyReadable>);
+static_assert(!HasIsPartitionedR<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasIsPartitionedR<InputRangeNotSentinelSemiregular>);
+static_assert(!HasIsPartitionedR<InputRangeNotSentinelEqualityComparableWith>);
+
+template <class Pred>
+concept HasIsPartitionedRPred = requires(Pred pred) {
+ std::ranges::is_partitioned(UncheckedRange<int*>{}, pred);
+};
+
+static_assert(HasIsPartitionedRPred<std::identity>);
+static_assert(!HasIsPartitionedRPred<IndirectUnaryPredicateNotCopyConstructible>);
+static_assert(!HasIsPartitionedRPred<IndirectUnaryPredicateNotPredicate>);
+
+template <class Iter, class Sent = Iter>
+constexpr void test_iterators() {
+ { // simple test
+ {
+ int a[] = {1, 2, 3, 4, 5};
+ std::same_as<bool> decltype(auto) ret =
+ std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 5)), [](int i) { return i < 3; });
+ assert(ret);
+ }
+ {
+ int a[] = {1, 2, 3, 4, 5};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 5)));
+ std::same_as<bool> decltype(auto) ret = std::ranges::is_partitioned(range, [](int i) { return i < 3; });
+ assert(ret);
+ }
+ }
+
+ { // check that it's partitoned if the predicate is true for all elements
+ {
+ int a[] = {1, 2, 3, 4};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 4)), [](int) { return true; });
+ assert(ret);
+ }
+ {
+ int a[] = {1, 2, 3, 4};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 4)));
+ auto ret = std::ranges::is_partitioned(range, [](int) { return true; });
+ assert(ret);
+ }
+ }
+
+ { // check that it's partitioned if the predicate is false for all elements
+ {
+ int a[] = {1, 2, 3, 4};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 4)), [](int) { return false; });
+ assert(ret);
+ }
+ {
+ int a[] = {1, 2, 3, 4};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 4)));
+ auto ret = std::ranges::is_partitioned(range, [](int) { return false; });
+ assert(ret);
+ }
+ }
+
+ { // check that false is returned if the range isn't partitioned
+ {
+ int a[] = {1, 3, 2, 4};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 4)), [](int i) { return i < 3; });
+ assert(!ret);
+ }
+ {
+ int a[] = {1, 3, 2, 4};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 4)));
+ auto ret = std::ranges::is_partitioned(range, [](int i) { return i < 3; });
+ assert(!ret);
+ }
+ }
+
+ { // check that an empty range is partitioned
+ {
+ int a[] = {};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a)), [](int i) { return i < 3; });
+ assert(ret);
+ }
+ {
+ int a[] = {};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a)));
+ auto ret = std::ranges::is_partitioned(range, [](int i) { return i < 3; });
+ assert(ret);
+ }
+ }
+
+ { // check that a single element is partitioned
+ {
+ int a[] = {1};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 1)), [](int i) { return i < 3; });
+ assert(ret);
+ }
+ {
+ int a[] = {1};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 1)));
+ auto ret = std::ranges::is_partitioned(range, [](int i) { return i < 3; });
+ assert(ret);
+ }
+ }
+
+ { // check that it is partitioned when the first element is the partition point
+ {
+ int a[] = {0, 1, 1};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 3)), [](int i) { return i < 1; });
+ assert(ret);
+ }
+ {
+ int a[] = {0, 1, 1};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 3)));
+ auto ret = std::ranges::is_partitioned(range, [](int i) { return i < 1; });
+ assert(ret);
+ }
+ }
+
+ { // check that it is partitioned when the last element is the partition point
+ {
+ int a[] = {0, 0, 1};
+ auto ret = std::ranges::is_partitioned(Iter(a), Sent(Iter(a + 3)), [](int i) { return i < 1; });
+ assert(ret);
+ }
+ {
+ int a[] = {0, 0, 1};
+ auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 3)));
+ auto ret = std::ranges::is_partitioned(range, [](int i) { return i < 1; });
+ assert(ret);
+ }
+ }
+}
+
+constexpr bool test() {
+ test_iterators<cpp17_input_iterator<int*>, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+ test_iterators<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+ test_iterators<forward_iterator<int*>>();
+ test_iterators<bidirectional_iterator<int*>>();
+ test_iterators<random_access_iterator<int*>>();
+ test_iterators<contiguous_iterator<int*>>();
+ test_iterators<int*>();
+ test_iterators<const int*>();
+
+ { // check that std:invoke is used
+ struct S {
+ int check;
+ int other;
+
+ constexpr S& identity() {
+ return *this;
+ }
+ };
+ {
+ S a[] = {{1, 2}, {3, 4}, {5, 6}};
+ auto ret = std::ranges::is_partitioned(a, a + 3, &S::check, &S::identity);
+ assert(ret);
+ }
+ {
+ S a[] = {{1, 2}, {3, 4}, {5, 6}};
+ auto ret = std::ranges::is_partitioned(a, &S::check, &S::identity);
+ assert(ret);
+ }
+ }
+
+ return true;
+}
+
+int main(int, char**) {
+ test();
+ static_assert(test());
+
+ return 0;
+}