[libc++][ranges] implement `std::ranges::unique{_copy}`

implement `std::ranges::unique` and `std::ranges::unique_copy`

Differential Revision: https://reviews.llvm.org/D130404

(cherry picked from commit 72f57e3a30d597346feec74cf626796b0055680f)

19 files changed, 889 insertions, 174 deletions

diff --git a/libcxx/docs/Status/RangesAlgorithms.csv b/libcxx/docs/Status/RangesAlgorithms.csv
index 3ae87225c3eb..176ece9ae047 100644
--- a/libcxx/docs/Status/RangesAlgorithms.csv
+++ b/libcxx/docs/Status/RangesAlgorithms.csv
@@ -57,7 +57,7 @@ Write,swap_ranges,Nikolas Klauser,`D116303 <https://llvm.org/D116303>`_,✅
 Write,reverse_copy,Nikolas Klauser,`D127211 <https://llvm.org/D127211>`_,✅
 Write,rotate_copy,Nikolas Klauser,`D127211 <https://llvm.org/D127211>`_,✅
 Write,sample,Not assigned,n/a,Not started
-Write,unique_copy,Not assigned,n/a,Not started
+Write,unique_copy,Hui Xie,`D130404 <https://llvm.org/D130404>`,✅
 Write,partition_copy,Konstantin Varlamov,`D130070 <https://llvm.org/D130070>`_,✅
 Write,partial_sort_copy,Konstantin Varlamov,n/a,In progress
 Merge,merge,Hui Xie,`D128611 <https://llvm.org/D128611>`_,✅
@@ -70,7 +70,7 @@ Permutation,remove_if,Nikolas Klauser,`D128618 <https://llvm.org/D128618>`_,✅
 Permutation,reverse,Nikolas Klauser,`D125752 <https://llvm.org/D125752>`_,✅
 Permutation,rotate,Nikolas Klauser,`D124122 <https://llvm.org/D124122>`_,Under review
 Permutation,shuffle,Konstantin Varlamov,`D130321 <https://llvm.org/D130321>`_,✅
-Permutation,unique,Not assigned,n/a,Not started
+Permutation,unique,Hui Xie,`D130404 <https://llvm.org/D130404>`,✅
 Permutation,partition,Konstantin Varlamov,`D129624 <https://llvm.org/D129624>`_,✅
 Permutation,stable_partition,Konstantin Varlamov,`D129624 <https://llvm.org/D129624>`_,✅
 Permutation,sort,Konstantin Varlamov,`D127557 <https://llvm.org/D127557>`_,✅
diff --git a/libcxx/include/__algorithm/adjacent_find.h b/libcxx/include/__algorithm/adjacent_find.h
index 83d8c260f27a..1089bb20d5b2 100644
--- a/libcxx/include/__algorithm/adjacent_find.h
+++ b/libcxx/include/__algorithm/adjacent_find.h
@@ -11,8 +11,10 @@
 #define _LIBCPP___ALGORITHM_ADJACENT_FIND_H
 
 #include <__algorithm/comp.h>
+#include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -20,25 +22,31 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+template <class _Iter, class _Sent, class _BinaryPredicate>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _Iter
+__adjacent_find(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
+  if (__first == __last)
+    return __first;
+  _Iter __i = __first;
+  while (++__i != __last) {
+    if (__pred(*__first, *__i))
+      return __first;
+    __first = __i;
+  }
+  return __i;
+}
+
 template <class _ForwardIterator, class _BinaryPredicate>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
 adjacent_find(_ForwardIterator __first, _ForwardIterator __last, _BinaryPredicate __pred) {
-  if (__first != __last) {
-    _ForwardIterator __i = __first;
-    while (++__i != __last) {
-      if (__pred(*__first, *__i))
-        return __first;
-      __first = __i;
-    }
-  }
-  return __last;
+  return std::__adjacent_find(std::move(__first), std::move(__last), __pred);
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
 adjacent_find(_ForwardIterator __first, _ForwardIterator __last) {
   typedef typename iterator_traits<_ForwardIterator>::value_type __v;
-  return _VSTD::adjacent_find(__first, __last, __equal_to<__v>());
+  return std::adjacent_find(std::move(__first), std::move(__last), __equal_to<__v>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__algorithm/iterator_operations.h b/libcxx/include/__algorithm/iterator_operations.h
index 6ac5170b4a0e..e060574652d4 100644
--- a/libcxx/include/__algorithm/iterator_operations.h
+++ b/libcxx/include/__algorithm/iterator_operations.h
@@ -17,6 +17,7 @@
 #include <__iterator/iter_swap.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
+#include <__iterator/readable_traits.h>
 #include <__utility/declval.h>
 #include <__utility/forward.h>
 #include <__utility/move.h>
@@ -35,6 +36,10 @@ struct _RangeAlgPolicy {};
 
 template <>
 struct _IterOps<_RangeAlgPolicy> {
+
+  template <class _Iter>
+  using __value_type = iter_value_t<_Iter>;
+
   static constexpr auto advance = ranges::advance;
   static constexpr auto distance = ranges::distance;
   static constexpr auto __iter_move = ranges::iter_move;
@@ -50,6 +55,9 @@ struct _ClassicAlgPolicy {};
 template <>
 struct _IterOps<_ClassicAlgPolicy> {
 
+  template <class _Iter>
+  using __value_type = typename iterator_traits<_Iter>::value_type;
+
   // advance
   template <class _Iter, class _Distance>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
diff --git a/libcxx/include/__algorithm/ranges_unique.h b/libcxx/include/__algorithm/ranges_unique.h
index bdf755e9406e..85185280724b 100644
--- a/libcxx/include/__algorithm/ranges_unique.h
+++ b/libcxx/include/__algorithm/ranges_unique.h
@@ -9,6 +9,7 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_UNIQUE_H
 #define _LIBCPP___ALGORITHM_RANGES_UNIQUE_H
 
+#include <__algorithm/iterator_operations.h>
 #include <__algorithm/make_projected.h>
 #include <__algorithm/unique.h>
 #include <__config>
@@ -37,28 +38,31 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 namespace ranges {
 namespace __unique {
 
-struct __fn {
+  struct __fn {
+    template <
+        permutable _Iter,
+        sentinel_for<_Iter> _Sent,
+        class _Proj                                                  = identity,
+        indirect_equivalence_relation<projected<_Iter, _Proj>> _Comp = ranges::equal_to>
+    _LIBCPP_HIDE_FROM_ABI constexpr subrange<_Iter>
+    operator()(_Iter __first, _Sent __last, _Comp __comp = {}, _Proj __proj = {}) const {
+      auto __ret = std::__unique<_RangeAlgPolicy>(
+          std::move(__first), std::move(__last), ranges::__make_projected_comp(__comp, __proj));
+      return {std::move(__ret.first), std::move(__ret.second)};
+    }
 
-  template <permutable _Iter, sentinel_for<_Iter> _Sent, class _Proj = identity,
-            indirect_equivalence_relation<projected<_Iter, _Proj>> _Comp = ranges::equal_to>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  subrange<_Iter> operator()(_Iter __first, _Sent __last, _Comp __comp = {}, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__comp; (void)__proj;
-    return {};
-  }
-
-  template <forward_range _Range, class _Proj = identity,
-            indirect_equivalence_relation<projected<iterator_t<_Range>, _Proj>> _Comp = ranges::equal_to>
-  requires permutable<iterator_t<_Range>>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  borrowed_subrange_t<_Range> operator()(_Range&& __range, _Comp __comp = {}, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__comp; (void)__proj;
-    return {};
-  }
-
-};
+    template <
+        forward_range _Range,
+        class _Proj                                                               = identity,
+        indirect_equivalence_relation<projected<iterator_t<_Range>, _Proj>> _Comp = ranges::equal_to>
+      requires permutable<iterator_t<_Range>>
+    _LIBCPP_HIDE_FROM_ABI constexpr borrowed_subrange_t<_Range>
+    operator()(_Range&& __range, _Comp __comp = {}, _Proj __proj = {}) const {
+      auto __ret = std::__unique<_RangeAlgPolicy>(
+          ranges::begin(__range), ranges::end(__range), ranges::__make_projected_comp(__comp, __proj));
+      return {std::move(__ret.first), std::move(__ret.second)};
+    }
+  };
 
 } // namespace __unique
 
diff --git a/libcxx/include/__algorithm/ranges_unique_copy.h b/libcxx/include/__algorithm/ranges_unique_copy.h
index 56361aa8ae2f..d047b444aa5e 100644
--- a/libcxx/include/__algorithm/ranges_unique_copy.h
+++ b/libcxx/include/__algorithm/ranges_unique_copy.h
@@ -10,6 +10,7 @@
 #define _LIBCPP___ALGORITHM_RANGES_UNIQUE_COPY_H
 
 #include <__algorithm/in_out_result.h>
+#include <__algorithm/iterator_operations.h>
 #include <__algorithm/make_projected.h>
 #include <__algorithm/unique_copy.h>
 #include <__concepts/same_as.h>
@@ -19,8 +20,8 @@
 #include <__functional/ranges_operations.h>
 #include <__iterator/concepts.h>
 #include <__iterator/iterator_traits.h>
-#include <__iterator/readable_traits.h>
 #include <__iterator/projected.h>
+#include <__iterator/readable_traits.h>
 #include <__ranges/access.h>
 #include <__ranges/concepts.h>
 #include <__ranges/dangling.h>
@@ -42,42 +43,68 @@ using unique_copy_result = in_out_result<_InIter, _OutIter>;
 
 namespace __unique_copy {
 
+template <class _InIter, class _OutIter>
+concept __can_reread_from_output = (input_iterator<_OutIter> && same_as<iter_value_t<_InIter>, iter_value_t<_OutIter>>);
+
 struct __fn {
+  template <class _InIter, class _OutIter>
+  static consteval auto __get_algo_tag() {
+    if constexpr (forward_iterator<_InIter>) {
+      return __unique_copy_tags::__reread_from_input_tag{};
+    } else if constexpr (__can_reread_from_output<_InIter, _OutIter>) {
+      return __unique_copy_tags::__reread_from_output_tag{};
+    } else if constexpr (indirectly_copyable_storable<_InIter, _OutIter>) {
+      return __unique_copy_tags::__read_from_tmp_value_tag{};
+    }
+  }
+
+  template <class _InIter, class _OutIter>
+  using __algo_tag_t = decltype(__get_algo_tag<_InIter, _OutIter>());
 
-  template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter, class _Proj = identity,
+  template <input_iterator _InIter,
+            sentinel_for<_InIter> _Sent,
+            weakly_incrementable _OutIter,
+            class _Proj                                                    = identity,
             indirect_equivalence_relation<projected<_InIter, _Proj>> _Comp = ranges::equal_to>
-  requires indirectly_copyable<_InIter, _OutIter> &&
-            (forward_iterator<_InIter> ||
-            (input_iterator<_OutIter> && same_as<iter_value_t<_InIter>, iter_value_t<_OutIter>>) ||
-            indirectly_copyable_storable<_InIter, _OutIter>)
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  unique_copy_result<_InIter, _OutIter>
+    requires indirectly_copyable<_InIter, _OutIter> &&
+             (forward_iterator<_InIter> ||
+              (input_iterator<_OutIter> && same_as<iter_value_t<_InIter>, iter_value_t<_OutIter>>) ||
+              indirectly_copyable_storable<_InIter, _OutIter>)
+  _LIBCPP_HIDE_FROM_ABI constexpr unique_copy_result<_InIter, _OutIter>
   operator()(_InIter __first, _Sent __last, _OutIter __result, _Comp __comp = {}, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__result; (void)__comp; (void)__proj;
-    return {};
+    auto __ret = std::__unique_copy<_RangeAlgPolicy>(
+        std::move(__first),
+        std::move(__last),
+        std::move(__result),
+        __make_projected_comp(__comp, __proj),
+        __algo_tag_t<_InIter, _OutIter>());
+    return {std::move(__ret.first), std::move(__ret.second)};
   }
 
-  template <input_range _Range, weakly_incrementable _OutIter, class _Proj = identity,
+  template <input_range _Range,
+            weakly_incrementable _OutIter,
+            class _Proj                                                               = identity,
             indirect_equivalence_relation<projected<iterator_t<_Range>, _Proj>> _Comp = ranges::equal_to>
-  requires indirectly_copyable<iterator_t<_Range>, _OutIter> &&
-            (forward_iterator<iterator_t<_Range>> ||
-            (input_iterator<_OutIter> && same_as<range_value_t<_Range>, iter_value_t<_OutIter>>) ||
-            indirectly_copyable_storable<iterator_t<_Range>, _OutIter>)
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  unique_copy_result<borrowed_iterator_t<_Range>, _OutIter>
+    requires indirectly_copyable<iterator_t<_Range>, _OutIter> &&
+      (forward_iterator<iterator_t<_Range>> ||
+       (input_iterator<_OutIter> && same_as<range_value_t<_Range>, iter_value_t<_OutIter>>) ||
+       indirectly_copyable_storable<iterator_t<_Range>, _OutIter>)
+  _LIBCPP_HIDE_FROM_ABI constexpr unique_copy_result<borrowed_iterator_t<_Range>, _OutIter>
   operator()(_Range&& __range, _OutIter __result, _Comp __comp = {}, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__result; (void)__comp; (void)__proj;
-    return {};
+    auto __ret = std::__unique_copy<_RangeAlgPolicy>(
+        ranges::begin(__range),
+        ranges::end(__range),
+        std::move(__result),
+        __make_projected_comp(__comp, __proj),
+        __algo_tag_t<iterator_t<_Range>, _OutIter>());
+    return {std::move(__ret.first), std::move(__ret.second)};
   }
-
 };
 
 } // namespace __unique_copy
 
 inline namespace __cpo {
-  inline constexpr auto unique_copy = __unique_copy::__fn{};
+inline constexpr auto unique_copy = __unique_copy::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
diff --git a/libcxx/include/__algorithm/unique.h b/libcxx/include/__algorithm/unique.h
index 264d727d93c8..1727225a91cd 100644
--- a/libcxx/include/__algorithm/unique.h
+++ b/libcxx/include/__algorithm/unique.h
@@ -11,9 +11,11 @@
 
 #include <__algorithm/adjacent_find.h>
 #include <__algorithm/comp.h>
+#include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__utility/move.h>
+#include <__utility/pair.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -23,32 +25,34 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 // unique
 
+template <class _AlgPolicy, class _Iter, class _Sent, class _BinaryPredicate>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 std::pair<_Iter, _Iter>
+__unique(_Iter __first, _Sent __last, _BinaryPredicate&& __pred) {
+  __first = std::__adjacent_find(__first, __last, __pred);
+  if (__first != __last) {
+    // ...  a  a  ?  ...
+    //      f     i
+    _Iter __i = __first;
+    for (++__i; ++__i != __last;)
+      if (!__pred(*__first, *__i))
+        *++__first = _IterOps<_AlgPolicy>::__iter_move(__i);
+    ++__first;
+    return std::pair<_Iter, _Iter>(std::move(__first), std::move(__i));
+  }
+  return std::pair<_Iter, _Iter>(__first, __first);
+}
+
 template <class _ForwardIterator, class _BinaryPredicate>
-_LIBCPP_NODISCARD_EXT _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
-unique(_ForwardIterator __first, _ForwardIterator __last, _BinaryPredicate __pred)
-{
-    __first = _VSTD::adjacent_find<_ForwardIterator, _BinaryPredicate&>(__first, __last, __pred);
-    if (__first != __last)
-    {
-        // ...  a  a  ?  ...
-        //      f     i
-        _ForwardIterator __i = __first;
-        for (++__i; ++__i != __last;)
-            if (!__pred(*__first, *__i))
-                *++__first = _VSTD::move(*__i);
-        ++__first;
-    }
-    return __first;
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
+unique(_ForwardIterator __first, _ForwardIterator __last, _BinaryPredicate __pred) {
+  return std::__unique<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __pred).first;
 }
 
 template <class _ForwardIterator>
-_LIBCPP_NODISCARD_EXT inline
-_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_ForwardIterator
-unique(_ForwardIterator __first, _ForwardIterator __last)
-{
-    typedef typename iterator_traits<_ForwardIterator>::value_type __v;
-    return _VSTD::unique(__first, __last, __equal_to<__v>());
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
+unique(_ForwardIterator __first, _ForwardIterator __last) {
+  typedef typename iterator_traits<_ForwardIterator>::value_type __v;
+  return std::unique(__first, __last, __equal_to<__v>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__algorithm/unique_copy.h b/libcxx/include/__algorithm/unique_copy.h
index f58517749f51..c7c8d8e9d8fd 100644
--- a/libcxx/include/__algorithm/unique_copy.h
+++ b/libcxx/include/__algorithm/unique_copy.h
@@ -10,8 +10,14 @@
 #define _LIBCPP___ALGORITHM_UNIQUE_COPY_H
 
 #include <__algorithm/comp.h>
+#include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/is_base_of.h>
+#include <__type_traits/is_same.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -19,88 +25,99 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _BinaryPredicate, class _InputIterator, class _OutputIterator>
-_LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator
-__unique_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _BinaryPredicate __pred,
-              input_iterator_tag, output_iterator_tag)
-{
-    if (__first != __last)
-    {
-        typename iterator_traits<_InputIterator>::value_type __t(*__first);
+namespace __unique_copy_tags {
+
+struct __reread_from_input_tag {};
+struct __reread_from_output_tag {};
+struct __read_from_tmp_value_tag {};
+
+} // namespace __unique_copy_tags
+
+template <class _AlgPolicy, class _BinaryPredicate, class _InputIterator, class _Sent, class _OutputIterator>
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _LIBCPP_HIDE_FROM_ABI pair<_InputIterator, _OutputIterator>
+__unique_copy(_InputIterator __first,
+              _Sent __last,
+              _OutputIterator __result,
+              _BinaryPredicate&& __pred,
+              __unique_copy_tags::__read_from_tmp_value_tag) {
+  if (__first != __last) {
+    typename _IterOps<_AlgPolicy>::template __value_type<_InputIterator> __t(*__first);
+    *__result = __t;
+    ++__result;
+    while (++__first != __last) {
+      if (!__pred(__t, *__first)) {
+        __t       = *__first;
         *__result = __t;
         ++__result;
-        while (++__first != __last)
-        {
-            if (!__pred(__t, *__first))
-            {
-                __t = *__first;
-                *__result = __t;
-                ++__result;
-            }
-        }
+      }
     }
-    return __result;
+  }
+  return pair<_InputIterator, _OutputIterator>(std::move(__first), std::move(__result));
 }
 
-template <class _BinaryPredicate, class _ForwardIterator, class _OutputIterator>
-_LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator
-__unique_copy(_ForwardIterator __first, _ForwardIterator __last, _OutputIterator __result, _BinaryPredicate __pred,
-              forward_iterator_tag, output_iterator_tag)
-{
-    if (__first != __last)
-    {
-        _ForwardIterator __i = __first;
-        *__result = *__i;
+template <class _AlgPolicy, class _BinaryPredicate, class _ForwardIterator, class _Sent, class _OutputIterator>
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _LIBCPP_HIDE_FROM_ABI pair<_ForwardIterator, _OutputIterator>
+__unique_copy(_ForwardIterator __first,
+              _Sent __last,
+              _OutputIterator __result,
+              _BinaryPredicate&& __pred,
+              __unique_copy_tags::__reread_from_input_tag) {
+  if (__first != __last) {
+    _ForwardIterator __i = __first;
+    *__result            = *__i;
+    ++__result;
+    while (++__first != __last) {
+      if (!__pred(*__i, *__first)) {
+        *__result = *__first;
         ++__result;
-        while (++__first != __last)
-        {
-            if (!__pred(*__i, *__first))
-            {
-                *__result = *__first;
-                ++__result;
-                __i = __first;
-            }
-        }
+        __i = __first;
+      }
     }
-    return __result;
+  }
+  return pair<_ForwardIterator, _OutputIterator>(std::move(__first), std::move(__result));
 }
 
-template <class _BinaryPredicate, class _InputIterator, class _ForwardIterator>
-_LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
-__unique_copy(_InputIterator __first, _InputIterator __last, _ForwardIterator __result, _BinaryPredicate __pred,
-              input_iterator_tag, forward_iterator_tag)
-{
-    if (__first != __last)
-    {
-        *__result = *__first;
-        while (++__first != __last)
-            if (!__pred(*__result, *__first))
-                *++__result = *__first;
-        ++__result;
-    }
-    return __result;
+template <class _AlgPolicy, class _BinaryPredicate, class _InputIterator, class _Sent, class _InputAndOutputIterator>
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _LIBCPP_HIDE_FROM_ABI pair<_InputIterator, _InputAndOutputIterator>
+__unique_copy(_InputIterator __first,
+              _Sent __last,
+              _InputAndOutputIterator __result,
+              _BinaryPredicate&& __pred,
+              __unique_copy_tags::__reread_from_output_tag) {
+  if (__first != __last) {
+    *__result = *__first;
+    while (++__first != __last)
+      if (!__pred(*__result, *__first))
+        *++__result = *__first;
+    ++__result;
+  }
+  return pair<_InputIterator, _InputAndOutputIterator>(std::move(__first), std::move(__result));
 }
 
 template <class _InputIterator, class _OutputIterator, class _BinaryPredicate>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_OutputIterator
-unique_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _BinaryPredicate __pred)
-{
-    return _VSTD::__unique_copy<_BinaryPredicate&>(__first, __last, __result, __pred,
-                               typename iterator_traits<_InputIterator>::iterator_category(),
-                               typename iterator_traits<_OutputIterator>::iterator_category());
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator
+unique_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _BinaryPredicate __pred) {
+  using __algo_tag = typename conditional<
+      is_base_of<forward_iterator_tag, typename iterator_traits<_InputIterator>::iterator_category>::value,
+      __unique_copy_tags::__reread_from_input_tag,
+      typename conditional<
+          is_base_of<forward_iterator_tag, typename iterator_traits<_OutputIterator>::iterator_category>::value &&
+              is_same< typename iterator_traits<_InputIterator>::value_type,
+                       typename iterator_traits<_OutputIterator>::value_type>::value,
+          __unique_copy_tags::__reread_from_output_tag,
+          __unique_copy_tags::__read_from_tmp_value_tag>::type >::type;
+  return std::__unique_copy<_ClassicAlgPolicy>(
+             std::move(__first), std::move(__last), std::move(__result), __pred, __algo_tag())
+      .second;
 }
 
 template <class _InputIterator, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_OutputIterator
-unique_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result)
-{
-    typedef typename iterator_traits<_InputIterator>::value_type __v;
-    return _VSTD::unique_copy(__first, __last, __result, __equal_to<__v>());
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator
+unique_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result) {
+  typedef typename iterator_traits<_InputIterator>::value_type __v;
+  return std::unique_copy(std::move(__first), std::move(__last), std::move(__result), __equal_to<__v>());
 }
 
-
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___ALGORITHM_UNIQUE_COPY_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 4fc353a8ce5d..7b510b5096af 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -865,6 +865,34 @@ namespace ranges {
     borrowed_iterator_t<R>
       inplace_merge(R&& r, iterator_t<R> middle, Comp comp = {},
                     Proj proj = {});                                                               // Since C++20
+
+  template<permutable I, sentinel_for<I> S, class Proj = identity,
+           indirect_equivalence_relation<projected<I, Proj>> C = ranges::equal_to>
+    constexpr subrange<I> unique(I first, S last, C comp = {}, Proj proj = {});                    // Since C++20
+
+  template<forward_range R, class Proj = identity,
+           indirect_equivalence_relation<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
+    requires permutable<iterator_t<R>>
+    constexpr borrowed_subrange_t<R>
+      unique(R&& r, C comp = {}, Proj proj = {});                                                  // Since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O, class Proj = identity,
+           indirect_equivalence_relation<projected<I, Proj>> C = ranges::equal_to>
+    requires indirectly_copyable<I, O> &&
+             (forward_iterator<I> ||
+              (input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>) ||
+              indirectly_copyable_storable<I, O>)
+    constexpr unique_copy_result<I, O>
+      unique_copy(I first, S last, O result, C comp = {}, Proj proj = {});                         // Since C++20
+
+  template<input_range R, weakly_incrementable O, class Proj = identity,
+           indirect_equivalence_relation<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
+    requires indirectly_copyable<iterator_t<R>, O> &&
+             (forward_iterator<iterator_t<R>> ||
+              (input_iterator<O> && same_as<range_value_t<R>, iter_value_t<O>>) ||
+              indirectly_copyable_storable<iterator_t<R>, O>)
+    constexpr unique_copy_result<borrowed_iterator_t<R>, O>
+      unique_copy(R&& r, O result, C comp = {}, Proj proj = {});                                   // Since C++20
 }
 
     constexpr bool     // constexpr in C++20
@@ -1665,6 +1693,8 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_stable_sort.h>
 #include <__algorithm/ranges_swap_ranges.h>
 #include <__algorithm/ranges_transform.h>
+#include <__algorithm/ranges_unique.h>
+#include <__algorithm/ranges_unique_copy.h>
 #include <__algorithm/ranges_upper_bound.h>
 #include <__algorithm/remove.h>
 #include <__algorithm/remove_copy.h>
diff --git a/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp b/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp
index 669fa9c1842e..b4328006539f 100644
--- a/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp
@@ -222,10 +222,10 @@ constexpr bool all_the_algorithms()
     (void)std::ranges::transform(a, first2, UnaryTransform(&copies)); assert(copies == 0);
     (void)std::ranges::transform(first, mid, mid, last, first2, BinaryTransform(&copies)); assert(copies == 0);
     (void)std::ranges::transform(a, b, first2, BinaryTransform(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique(first, last, Equal(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique(a, Equal(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique_copy(first, last, first2, Equal(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique_copy(a, first2, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::unique(first, last, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::unique(a, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::unique_copy(first, last, first2, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::unique_copy(a, first2, Equal(&copies)); assert(copies == 0);
     (void)std::ranges::upper_bound(first, last, value, Less(&copies)); assert(copies == 0);
     (void)std::ranges::upper_bound(a, value, Less(&copies)); assert(copies == 0);
 
diff --git a/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp b/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp
index 22fdf09888af..4eadbcc97a65 100644
--- a/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp
@@ -213,10 +213,10 @@ constexpr bool all_the_algorithms()
     (void)std::ranges::transform(a, first2, UnaryTransform(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::transform(first, mid, mid, last, first2, BinaryTransform(), Proj(&copies), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::transform(a, b, first2, BinaryTransform(), Proj(&copies), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique(first, last, Equal(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique(a, Equal(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique_copy(first, last, first2, Equal(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::unique_copy(a, first2, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::unique(first, last, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::unique(a, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::unique_copy(first, last, first2, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::unique_copy(a, first2, Equal(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::upper_bound(first, last, value, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::upper_bound(a, value, Less(), Proj(&copies)); assert(copies == 0);
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique.pass.cpp
index 216ae6a1b98e..bb60109e7735 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique.pass.cpp
@@ -28,14 +28,214 @@
 #include <ranges>
 
 #include "almost_satisfies_types.h"
+#include "counting_predicates.h"
+#include "counting_projection.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+template <class Iter = int*, class Sent = int*, class Comp = std::ranges::equal_to, class Proj = std::identity>
+concept HasUniqueIter =
+    requires(Iter&& iter, Sent&& sent, Comp&& comp, Proj&& proj) {
+      std::ranges::unique(
+          std::forward<Iter>(iter), std::forward<Sent>(sent), std::forward<Comp>(comp), std::forward<Proj>(proj));
+    };
+
+static_assert(HasUniqueIter<int*, int*>);
+
+// !permutable<I>
+static_assert(!HasUniqueIter<PermutableNotForwardIterator>);
+static_assert(!HasUniqueIter<PermutableNotSwappable>);
+
+// !sentinel_for<S, I>
+static_assert(!HasUniqueIter<int*, SentinelForNotSemiregular>);
+
+// !indirect_equivalence_relation<Comp, projected<I, Proj>>
+static_assert(!HasUniqueIter<int*, int*, ComparatorNotCopyable<int>>);
+
+template <class Range, class Comp = std::ranges::equal_to, class Proj = std::identity>
+concept HasUniqueRange =
+    requires(Range&& range, Comp&& comp, Proj&& proj) {
+      std::ranges::unique(std::forward<Range>(range), std::forward<Comp>(comp), std::forward<Proj>(proj));
+    };
+
+template <class T>
+using R = UncheckedRange<T>;
+
+static_assert(HasUniqueRange<R<int*>>);
+
+// !forward_range<R>
+static_assert(!HasUniqueRange<ForwardRangeNotDerivedFrom>);
+static_assert(!HasUniqueRange<ForwardRangeNotIncrementable>);
+
+// permutable<ranges::iterator_t<R>>
+static_assert(!HasUniqueRange<R<PermutableNotForwardIterator>>);
+static_assert(!HasUniqueRange<R<PermutableNotSwappable>>);
+
+// !indirect_equivalence_relation<Comp, projected<ranges::iterator_t<R>, Proj>>
+static_assert(!HasUniqueRange<R<int*>, ComparatorNotCopyable<int>>);
+
+template <class Iter, template <class> class SentWrapper, std::size_t N1, std::size_t N2>
+constexpr void testUniqueImpl(std::array<int, N1> input, std::array<int, N2> expected) {
+  using Sent = SentWrapper<Iter>;
+
+  // iterator overload
+  {
+    auto in = input;
+    std::same_as<std::ranges::subrange<Iter>> decltype(auto) result =
+        std::ranges::unique(Iter{in.data()}, Sent{Iter{in.data() + in.size()}});
+    assert(std::ranges::equal(std::ranges::subrange<Iter>{Iter{in.data()}, result.begin()}, expected));
+    assert(base(result.end()) == in.data() + in.size());
+  }
+
+  // range overload
+  {
+    auto in = input;
+    std::ranges::subrange r{Iter{in.data()}, Sent{Iter{in.data() + in.size()}}};
+    std::same_as<std::ranges::subrange<Iter>> decltype(auto) result = std::ranges::unique(r);
+    assert(std::ranges::equal(std::ranges::subrange<Iter>{Iter{in.data()}, result.begin()}, expected));
+    assert(base(result.end()) == in.data() + in.size());
+  }
+}
+
+template <class Iter, template <class> class SentWrapper>
+constexpr void testImpl() {
+  // no consecutive elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 3, 2, 1};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+  }
+
+  // one group of consecutive elements
+  {
+    std::array in{2, 3, 3, 3, 4, 3};
+    std::array expected{2, 3, 4, 3};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+  }
+
+  // multiple groups of consecutive elements
+  {
+    std::array in{2, 3, 3, 3, 4, 3, 3, 5, 5, 5};
+    std::array expected{2, 3, 4, 3, 5};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+  }
+
+  // all the same
+  {
+    std::array in{1, 1, 1, 1, 1, 1};
+    std::array expected{1};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+  }
+
+  // empty range
+  {
+    std::array<int, 0> in{};
+    std::array<int, 0> expected{};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+  }
+
+  // single element range
+    std::array in{1};
+    std::array expected{1};
+    testUniqueImpl<Iter, SentWrapper>(in, expected);
+}
+
+template <template <class> class SentWrapper>
+constexpr void withAllPermutationsOfIter() {
+  testImpl<forward_iterator<int*>, SentWrapper>();
+  testImpl<bidirectional_iterator<int*>, SentWrapper>();
+  testImpl<random_access_iterator<int*>, SentWrapper>();
+  testImpl<contiguous_iterator<int*>, SentWrapper>();
+  testImpl<int*, SentWrapper>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  withAllPermutationsOfIter<std::type_identity_t>();
+  withAllPermutationsOfIter<sentinel_wrapper>();
+
+  struct Data {
+    int data;
+  };
+
+  // Test custom comparator
+  {
+    std::array input{Data{4}, Data{8}, Data{8}, Data{8}};
+    std::array expected{Data{4}, Data{8}};
+    const auto comp = [](const Data& x, const Data& y) { return x.data == y.data; };
+
+    // iterator overload
+    {
+      auto in     = input;
+      auto result = std::ranges::unique(in.begin(), in.end(), comp);
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end(), comp));
+      assert(base(result.end()) == in.end());
+    }
+
+    // range overload
+    {
+      auto in     = input;
+      auto result = std::ranges::unique(in, comp);
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end(), comp));
+      assert(base(result.end()) == in.end());
+    }
+  }
+
+  // Test custom projection
+  {
+    std::array input{Data{4}, Data{8}, Data{8}, Data{8}};
+    std::array expected{Data{4}, Data{8}};
+
+    const auto proj = &Data::data;
+
+    // iterator overload
+    {
+      auto in     = input;
+      auto result = std::ranges::unique(in.begin(), in.end(), {}, proj);
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end(), {}, proj, proj));
+      assert(base(result.end()) == in.end());
+    }
+
+    // range overload
+    {
+      auto in     = input;
+      auto result = std::ranges::unique(in, {}, proj);
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end(), {}, proj, proj));
+      assert(base(result.end()) == in.end());
+    }
+  }
+
+  // Complexity: For nonempty ranges, exactly (last - first) - 1 applications of the corresponding predicate
+  // and no more than twice as many applications of any projection.
+  {
+    std::array input{1, 2, 3, 3, 3, 4, 3, 3, 5, 5, 6, 6, 1};
+    std::array expected{1, 2, 3, 4, 3, 5, 6, 1};
+    // iterator overload
+    {
+      auto in          = input;
+      int numberOfComp = 0;
+      int numberOfProj = 0;
+      auto result      = std::ranges::unique(
+          in.begin(),
+          in.end(),
+          counting_predicate{std::ranges::equal_to{}, numberOfComp},
+          counting_projection{numberOfProj});
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end()));
+      assert(base(result.end()) == in.end());
+      assert(numberOfComp == in.size() - 1);
+      assert(numberOfProj <= static_cast<int>(2 * (in.size() - 1)));
+    }
+    // range overload
+    {
+      auto in          = input;
+      int numberOfComp = 0;
+      int numberOfProj = 0;
+      auto result      = std::ranges::unique(
+          in, counting_predicate{std::ranges::equal_to{}, numberOfComp}, counting_projection{numberOfProj});
+      assert(std::ranges::equal(in.begin(), result.begin(), expected.begin(), expected.end()));
+      assert(base(result.end()) == in.end());
+      assert(numberOfComp == in.size() - 1);
+      assert(numberOfProj <= static_cast<int>(2 * (in.size() - 1)));
+    }
+  }
 
   return true;
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique_copy.pass.cpp
index 8ccff619b811..ac7965c8eb2c 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/ranges_unique_copy.pass.cpp
@@ -36,15 +36,409 @@
 #include <ranges>
 
 #include "almost_satisfies_types.h"
+#include "counting_predicates.h"
+#include "counting_projection.h"
+#include "MoveOnly.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+template <
+    class InIter  = int*,
+    class Sent    = int*,
+    class OutIter = int*,
+    class Comp    = std::ranges::equal_to,
+    class Proj    = std::identity>
+concept HasUniqueCopyIter =
+    requires(InIter&& in, Sent&& sent, OutIter&& out, Comp&& comp, Proj&& proj) {
+      std::ranges::unique_copy(
+          std::forward<InIter>(in),
+          std::forward<Sent>(sent),
+          std::forward<OutIter>(out),
+          std::forward<Comp>(comp),
+          std::forward<Proj>(proj));
+    };
+
+static_assert(HasUniqueCopyIter<int*, int*, int*>);
+
+// !input_iterator<I>
+static_assert(!HasUniqueCopyIter<InputIteratorNotDerivedFrom, sentinel_wrapper<InputIteratorNotDerivedFrom>>);
+
+// !sentinel_for<S, I>
+static_assert(!HasUniqueCopyIter<int*, SentinelForNotSemiregular>);
+
+// !weakly_incrementable<O>
+static_assert(!HasUniqueCopyIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+// !indirect_equivalence_relation<Comp, projected<I, Proj>>
+static_assert(!HasUniqueCopyIter<int*, int*, int*, ComparatorNotCopyable<int>>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasUniqueCopyIter<const int*, const int*, const int*>);
+
+// forward_iterator<I>
+// !(input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+// !indirectly_copyable_storable<I, O>
+struct AssignableFromMoveOnly {
+  int data;
+  constexpr AssignableFromMoveOnly& operator=(MoveOnly const& m) {
+    data = m.get();
+    return *this;
+  }
+};
+static_assert(HasUniqueCopyIter<MoveOnly*, MoveOnly*, AssignableFromMoveOnly*>);
+// because:
+static_assert(std::forward_iterator<MoveOnly*>);
+static_assert(!std::same_as<std::iter_value_t<MoveOnly*>, std::iter_value_t<AssignableFromMoveOnly*>>);
+static_assert(!std::indirectly_copyable_storable<MoveOnly*, AssignableFromMoveOnly*>);
+
+// !forward_iterator<I>
+// (input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+// !indirectly_copyable_storable<I, O>
+struct CopyAssignableNotCopyConstructible {
+  int data;
+  constexpr CopyAssignableNotCopyConstructible(int i = 0) : data(i) {}
+  CopyAssignableNotCopyConstructible(const CopyAssignableNotCopyConstructible&)            = delete;
+  CopyAssignableNotCopyConstructible& operator=(const CopyAssignableNotCopyConstructible&) = default;
+  friend constexpr bool
+  operator==(CopyAssignableNotCopyConstructible const&, CopyAssignableNotCopyConstructible const&) = default;
+};
+
+using InputAndOutputIterator = cpp17_input_iterator<CopyAssignableNotCopyConstructible*>;
+static_assert(std::input_iterator<InputAndOutputIterator>);
+static_assert(std::output_iterator<InputAndOutputIterator, CopyAssignableNotCopyConstructible>);
+
+static_assert(
+    HasUniqueCopyIter<
+        cpp20_input_iterator<CopyAssignableNotCopyConstructible*>,
+        sentinel_wrapper<cpp20_input_iterator<CopyAssignableNotCopyConstructible*>>,
+        InputAndOutputIterator>);
+// because:
+static_assert(!std::forward_iterator< cpp20_input_iterator<CopyAssignableNotCopyConstructible*>>);
+static_assert(
+    std::input_iterator<InputAndOutputIterator> &&
+    std::same_as<std::iter_value_t<cpp20_input_iterator<CopyAssignableNotCopyConstructible*>>,
+                 std::iter_value_t<InputAndOutputIterator>>);
+static_assert(
+    !std::indirectly_copyable_storable<
+        cpp20_input_iterator<CopyAssignableNotCopyConstructible*>,
+        InputAndOutputIterator>);
+
+// !forward_iterator<I>
+// !(input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+// indirectly_copyable_storable<I, O>
+static_assert(
+    HasUniqueCopyIter<
+        cpp20_input_iterator<int*>,
+        sentinel_wrapper<cpp20_input_iterator<int*>>,
+        cpp20_output_iterator<int*>>);
+// because:
+static_assert(!std::forward_iterator<cpp20_input_iterator<int*>>);
+static_assert(!std::input_iterator<cpp20_output_iterator<int*>>);
+static_assert(std::indirectly_copyable_storable<cpp20_input_iterator<int*>, cpp20_output_iterator<int*>>);
+
+// !forward_iterator<I>
+// !(input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+// !indirectly_copyable_storable<I, O>
+static_assert(
+    !HasUniqueCopyIter<
+        cpp20_input_iterator<MoveOnly*>,
+        sentinel_wrapper<cpp20_input_iterator<MoveOnly*>>,
+        cpp20_output_iterator<AssignableFromMoveOnly*>>);
+// because:
+static_assert(!std::forward_iterator<cpp20_input_iterator<MoveOnly*>>);
+static_assert(!std::input_iterator<cpp20_output_iterator<MoveOnly*>>);
+static_assert(
+    !std::
+        indirectly_copyable_storable<cpp20_input_iterator<MoveOnly*>, cpp20_output_iterator<AssignableFromMoveOnly*>>);
+
+template < class Range, class OutIter = int*, class Comp = std::ranges::equal_to, class Proj = std::identity>
+concept HasUniqueCopyRange =
+    requires(Range&& range, OutIter&& out, Comp&& comp, Proj&& proj) {
+      std::ranges::unique_copy(
+          std::forward<Range>(range), std::forward<OutIter>(out), std::forward<Comp>(comp), std::forward<Proj>(proj));
+    };
+
+template <class T>
+using R = UncheckedRange<T>;
+
+static_assert(HasUniqueCopyRange<R<int*>, int*>);
+
+// !input_range<R>
+static_assert(!HasUniqueCopyRange<R<InputIteratorNotDerivedFrom>>);
+
+// !weakly_incrementable<O>
+static_assert(!HasUniqueCopyIter<R<int*>, WeaklyIncrementableNotMovable>);
+
+// !indirect_equivalence_relation<Comp, projected<I, Proj>>
+static_assert(!HasUniqueCopyIter<R<int*>, int*, ComparatorNotCopyable<int>>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasUniqueCopyIter<R<const int*>, const int*>);
+
+// !forward_iterator<iterator_t<R>>
+// !(input_iterator<O> && same_as<range_value_t<R>, iter_value_t<O>>)
+// !indirectly_copyable_storable<iterator_t<R>, O>
+static_assert(!HasUniqueCopyIter< R<cpp20_input_iterator<MoveOnly*>>, cpp20_output_iterator<AssignableFromMoveOnly*>>);
+
+template <class InIter, class OutIter, template <class> class SentWrapper, std::size_t N1, std::size_t N2>
+constexpr void testUniqueCopyImpl(std::array<int, N1> in, std::array<int, N2> expected) {
+  using Sent = SentWrapper<InIter>;
+
+  // iterator overload
+  {
+    std::array<int, N2> out;
+    std::same_as<std::ranges::unique_copy_result<InIter, OutIter>> decltype(auto) result =
+        std::ranges::unique_copy(InIter{in.data()}, Sent{InIter{in.data() + in.size()}}, OutIter{out.begin()});
+    assert(std::ranges::equal(out, expected));
+    assert(base(result.in) == in.data() + in.size());
+    assert(base(result.out) == out.data() + out.size());
+  }
+
+  // range overload
+  {
+    std::array<int, N2> out;
+    std::ranges::subrange r{InIter{in.data()}, Sent{InIter{in.data() + in.size()}}};
+    std::same_as<std::ranges::unique_copy_result<InIter, OutIter>> decltype(auto) result =
+        std::ranges::unique_copy(r, OutIter{out.begin()});
+    assert(std::ranges::equal(out, expected));
+    assert(base(result.in) == in.data() + in.size());
+    assert(base(result.out) == out.data() + out.size());
+  }
+}
+
+template <class InIter, class OutIter, template <class> class SentWrapper>
+constexpr void testImpl() {
+  // no consecutive elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 3, 2, 1};
+    testUniqueCopyImpl<InIter, OutIter, SentWrapper>(in, expected);
+  }
+
+  // one group of consecutive elements
+  {
+    std::array in{2, 3, 3, 3, 4, 3};
+    std::array expected{2, 3, 4, 3};
+    testUniqueCopyImpl<InIter, OutIter, SentWrapper>(in, expected);
+  }
+
+  // multiple groups of consecutive elements
+  {
+    std::array in{2, 3, 3, 3, 4, 3, 3, 5, 5, 5};
+    std::array expected{2, 3, 4, 3, 5};
+    testUniqueCopyImpl<InIter, OutIter, SentWrapper>(in, expected);
+  }
+
+  // all the same
+  {
+    std::array in{1, 1, 1, 1, 1, 1};
+    std::array expected{1};
+    testUniqueCopyImpl<InIter, OutIter, SentWrapper>(in, expected);
+  }
+
+  // empty range
+  {
+    std::array<int, 0> in{};
+    std::array<int, 0> expected{};
+    testUniqueCopyImpl<InIter, OutIter, SentWrapper>(in, expected);
+  }
+}
+
+template <class OutIter, template <class> class SentWrapper>
+constexpr void withAllPermutationsOfInIter() {
+  testImpl<cpp20_input_iterator<int*>, OutIter, sentinel_wrapper>();
+  testImpl<forward_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<bidirectional_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<random_access_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<contiguous_iterator<int*>, OutIter, SentWrapper>();
+  testImpl<int*, OutIter, SentWrapper>();
+}
+
+template <template <class> class SentWrapper>
+constexpr void withAllPermutationsOfInIterAndOutIter() {
+  withAllPermutationsOfInIter<cpp20_output_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<forward_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<bidirectional_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<random_access_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<contiguous_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<int*, SentWrapper>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  withAllPermutationsOfInIterAndOutIter<std::type_identity_t>();
+  withAllPermutationsOfInIterAndOutIter<sentinel_wrapper>();
+
+  // Test the overload that re-reads from the input iterator
+  // forward_iterator<I>
+  // !(input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+  // !indirectly_copyable_storable<I, O>
+  {
+    MoveOnly in[5] = {1, 3, 3, 3, 1};
+    // iterator overload
+    {
+      AssignableFromMoveOnly out[3] = {};
+      auto result                   = std::ranges::unique_copy(in, in + 5, out);
+      assert(std::ranges::equal(out, std::array{1, 3, 1}, {}, &AssignableFromMoveOnly::data));
+      assert(result.in == in + 5);
+      assert(result.out == out + 3);
+    }
+    // range overload
+    {
+      AssignableFromMoveOnly out[3] = {};
+      auto result                   = std::ranges::unique_copy(std::ranges::subrange{in, in + 5}, out);
+      assert(std::ranges::equal(out, std::array{1, 3, 1}, {}, &AssignableFromMoveOnly::data));
+      assert(result.in == in + 5);
+      assert(result.out == out + 3);
+    }
+  }
+
+  // Test the overload that re-reads from the output iterator
+  // !forward_iterator<I>
+  // (input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+  // !indirectly_copyable_storable<I, O>
+  {
+    using InIter                             = cpp20_input_iterator<CopyAssignableNotCopyConstructible*>;
+    using Sent                               = sentinel_wrapper<InIter>;
+    CopyAssignableNotCopyConstructible in[6] = {1, 1, 2, 2, 3, 3};
+    // iterator overload
+    {
+      CopyAssignableNotCopyConstructible out[3];
+      auto result = std::ranges::unique_copy(InIter{in}, Sent{InIter{in + 6}}, InputAndOutputIterator{out});
+      assert(std::ranges::equal(out, std::array{1, 2, 3}, {}, &CopyAssignableNotCopyConstructible::data));
+      assert(base(result.in) == in + 6);
+      assert(base(result.out) == out + 3);
+    }
+    // range overload
+    {
+      CopyAssignableNotCopyConstructible out[3];
+      auto r      = std::ranges::subrange(InIter{in}, Sent{InIter{in + 6}});
+      auto result = std::ranges::unique_copy(r, InputAndOutputIterator{out});
+      assert(std::ranges::equal(out, std::array{1, 2, 3}, {}, &CopyAssignableNotCopyConstructible::data));
+      assert(base(result.in) == in + 6);
+      assert(base(result.out) == out + 3);
+    }
+  }
+
+  // Test the overload that reads from the temporary copy of the value
+  // !forward_iterator<I>
+  // !(input_iterator<O> && same_as<iter_value_t<I>, iter_value_t<O>>)
+  // indirectly_copyable_storable<I, O>
+  {
+    using InIter = cpp20_input_iterator<int*>;
+    using Sent   = sentinel_wrapper<InIter>;
+    int in[4]    = {1, 1, 1, 2};
+    // iterator overload
+    {
+      int out[2];
+      auto result = std::ranges::unique_copy(InIter{in}, Sent{InIter{in + 4}}, cpp20_output_iterator<int*>{out});
+      assert(std::ranges::equal(out, std::array{1, 2}));
+      assert(base(result.in) == in + 4);
+      assert(base(result.out) == out + 2);
+    }
+    // range overload
+    {
+      int out[2];
+      auto r      = std::ranges::subrange(InIter{in}, Sent{InIter{in + 4}});
+      auto result = std::ranges::unique_copy(r, cpp20_output_iterator<int*>{out});
+      assert(std::ranges::equal(out, std::array{1, 2}));
+      assert(base(result.in) == in + 4);
+      assert(base(result.out) == out + 2);
+    }
+  }
+
+  struct Data {
+    int data;
+  };
+
+  // Test custom comparator
+  {
+    std::array in{Data{4}, Data{8}, Data{8}, Data{8}};
+    std::array expected{Data{4}, Data{8}};
+    const auto comp = [](const Data& x, const Data& y) { return x.data == y.data; };
+
+    // iterator overload
+    {
+      std::array<Data, 2> out;
+      auto result = std::ranges::unique_copy(in.begin(), in.end(), out.begin(), comp);
+      assert(std::ranges::equal(out, expected, comp));
+      assert(base(result.in) == in.begin() + 4);
+      assert(base(result.out) == out.begin() + 2);
+    }
+
+    // range overload
+    {
+      std::array<Data, 2> out;
+      auto result = std::ranges::unique_copy(in, out.begin(), comp);
+      assert(std::ranges::equal(out, expected, comp));
+      assert(base(result.in) == in.begin() + 4);
+      assert(base(result.out) == out.begin() + 2);
+    }
+  }
+
+  // Test custom projection
+  {
+    std::array in{Data{4}, Data{8}, Data{8}, Data{8}};
+    std::array expected{Data{4}, Data{8}};
+
+    const auto proj = &Data::data;
+
+    // iterator overload
+    {
+      std::array<Data, 2> out;
+      auto result = std::ranges::unique_copy(in.begin(), in.end(), out.begin(), {}, proj);
+      assert(std::ranges::equal(out, expected, {}, proj, proj));
+      assert(base(result.in) == in.begin() + 4);
+      assert(base(result.out) == out.begin() + 2);
+    }
+
+    // range overload
+    {
+      std::array<Data, 2> out;
+      auto result = std::ranges::unique_copy(in, out.begin(), {}, proj);
+      assert(std::ranges::equal(out, expected, {}, proj, proj));
+      assert(base(result.in) == in.begin() + 4);
+      assert(base(result.out) == out.begin() + 2);
+    }
+  }
 
+  // Exactly last - first - 1 applications of the corresponding predicate and no
+  // more than twice as many applications of any projection.
+  {
+    std::array in{1, 2, 3, 3, 3, 4, 3, 3, 5, 5, 6, 6, 1};
+    std::array expected{1, 2, 3, 4, 3, 5, 6, 1};
+    // iterator overload
+    {
+      std::array<int, 8> out;
+      int numberOfComp = 0;
+      int numberOfProj = 0;
+      auto result      = std::ranges::unique_copy(
+          in.begin(),
+          in.end(),
+          out.begin(),
+          counting_predicate{std::ranges::equal_to{}, numberOfComp},
+          counting_projection{numberOfProj});
+      assert(std::ranges::equal(out, expected));
+      assert(base(result.in) == in.end());
+      assert(base(result.out) == out.end());
+      assert(numberOfComp == in.size() - 1);
+      assert(numberOfProj <= static_cast<int>(2 * (in.size() - 1)));
+    }
+    // range overload
+    {
+      std::array<int, 8> out;
+      int numberOfComp = 0;
+      int numberOfProj = 0;
+      auto result      = std::ranges::unique_copy(
+          in,
+          out.begin(),
+          counting_predicate{std::ranges::equal_to{}, numberOfComp},
+          counting_projection{numberOfProj});
+      assert(std::ranges::equal(out, expected));
+      assert(base(result.in) == in.end());
+      assert(base(result.out) == out.end());
+      assert(numberOfComp == in.size() - 1);
+      assert(numberOfProj <= static_cast<int>(2 * (in.size() - 1)));
+    }
+  }
   return true;
 }
 
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/unique_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/unique_copy.pass.cpp
index bda304cd7493..bcf9c99e24c2 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/unique_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.unique/unique_copy.pass.cpp
@@ -19,9 +19,21 @@
 #include <algorithm>
 #include <cassert>
 
+#include "MoveOnly.h"
 #include "test_macros.h"
 #include "test_iterators.h"
 
+struct AssignableFromMoveOnly {
+  AssignableFromMoveOnly(int i) : data(i) {}
+  AssignableFromMoveOnly() : data(0) {}
+  int data;
+  AssignableFromMoveOnly& operator=(MoveOnly const& m) {
+    data = m.get();
+    return *this;
+  }
+  bool operator==(AssignableFromMoveOnly const& rhs) const { return data == rhs.data; }
+};
+
 #if TEST_STD_VER > 17
 TEST_CONSTEXPR bool test_constexpr() {
           int ia[]       = {0, 1, 2, 2, 4};
@@ -107,6 +119,7 @@ test()
 
 int main(int, char**)
 {
+    test<cpp17_input_iterator<const int*>, cpp17_input_iterator<int*> >();
     test<cpp17_input_iterator<const int*>, cpp17_output_iterator<int*> >();
     test<cpp17_input_iterator<const int*>, forward_iterator<int*> >();
     test<cpp17_input_iterator<const int*>, bidirectional_iterator<int*> >();
@@ -137,6 +150,16 @@ int main(int, char**)
     test<const int*, random_access_iterator<int*> >();
     test<const int*, int*>();
 
+    // Move only inputs
+    {
+      MoveOnly in[5]                     = {1, 3, 3, 3, 1};
+      AssignableFromMoveOnly out[3]      = {};
+      auto result                        = std::unique_copy(in, in + 5, out);
+      AssignableFromMoveOnly expected[3] = {1, 3, 1};
+      assert(std::equal(out, out + 3, expected));
+      assert(result == out + 3);
+    }
+
 #if TEST_STD_VER > 17
     static_assert(test_constexpr());
 #endif
diff --git a/libcxx/test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp b/libcxx/test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp
index a694376ca6ec..875ca35b1265 100644
--- a/libcxx/test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_result_alias_declarations.compile.pass.cpp
@@ -43,7 +43,7 @@ static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_copy_result
 static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_copy_n_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_move_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, uninitialized_move_n_result<int, long>>);
-// static_assert(std::is_same_v<in_out_result<int, long>, unique_copy_result<int, long>>);
+static_assert(std::is_same_v<in_out_result<int, long>, unique_copy_result<int, long>>);
 
 static_assert(std::is_same_v<in_in_out_result<int, long, char>, binary_transform_result<int, long, char>>);
 static_assert(std::is_same_v<in_in_out_result<int, long, char>, merge_result<int, long, char>>);
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
index e147c875902c..b8625f5a3f44 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
@@ -88,7 +88,7 @@ constexpr bool test_all() {
   using std::ranges::set_union_result;
   using std::ranges::swap_ranges_result;
   using std::ranges::unary_transform_result;
-  //using std::ranges::unique_copy_result;
+  using std::ranges::unique_copy_result;
 
   auto unary_pred = [](int i) { return i > 0; };
   auto binary_pred = [](int i, int j) { return i < j; };
@@ -117,7 +117,7 @@ constexpr bool test_all() {
   dangling_1st(std::ranges::partition_point, in, unary_pred);
   dangling_1st(std::ranges::lower_bound, in, x);
   dangling_1st(std::ranges::upper_bound, in, x);
-  //dangling_1st(std::ranges::equal_range, in, x);
+  dangling_1st(std::ranges::equal_range, in, x);
   dangling_1st(std::ranges::min_element, in);
   dangling_1st(std::ranges::max_element, in);
   dangling_1st<minmax_result<dangling>>(std::ranges::minmax_element, in);
@@ -157,7 +157,7 @@ constexpr bool test_all() {
   dangling_both<swap_ranges_result<dangling, dangling>>(std::ranges::swap_ranges, in, in2);
   dangling_1st<reverse_copy_result<dangling, int*>>(std::ranges::reverse_copy, in, out);
   dangling_1st<rotate_copy_result<dangling, int*>>(std::ranges::rotate_copy, in, mid, out);
-  //dangling_1st<unique_copy_result<dangling, int*>>(std::ranges::unique_copy, in, out);
+  dangling_1st<unique_copy_result<dangling, int*>>(std::ranges::unique_copy, in, out);
   dangling_1st<partition_copy_result<dangling, int*, int*>>(std::ranges::partition_copy, in, out, out2, unary_pred);
   //dangling_1st<partial_sort_copy_result<dangling, int*>>(std::ranges::partial_sort_copy, in, in2);
   //dangling_2nd<partial_sort_copy_result<int*, dangling>>(std::ranges::partial_sort_copy, in, in2);
@@ -184,7 +184,7 @@ constexpr bool test_all() {
   //dangling_1st(std::ranges::rotate, in, mid);
   if (!std::is_constant_evaluated()) // `shuffle` isn't `constexpr`.
     dangling_1st(std::ranges::shuffle, in, rand_gen());
-  //dangling_1st(std::ranges::unique, in);
+  dangling_1st(std::ranges::unique, in);
   dangling_1st(std::ranges::partition, in, unary_pred);
   if (!std::is_constant_evaluated())
     dangling_1st(std::ranges::stable_partition, in, unary_pred);
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_nonbool_predicates.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_nonbool_predicates.pass.cpp
index eeeec9c1f57f..0d1e3990b3b1 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_nonbool_predicates.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_nonbool_predicates.pass.cpp
@@ -115,7 +115,7 @@ constexpr bool test_all() {
   //test(std::ranges::remove_copy_if, in, out, unary_pred);
   test(std::ranges::replace_if, in, unary_pred, x);
   //test(std::ranges::replace_copy_if, in, out, unary_pred, x);
-  //test(std::ranges::unique_copy, in, out, binary_pred);
+  test(std::ranges::unique_copy, in, out, binary_pred);
   test(std::ranges::partition_copy, in, out, out2, unary_pred);
   //test(std::ranges::partial_sort_copy, in, in2, binary_pred);
   test(std::ranges::merge, in, in2, out, binary_pred);
@@ -124,7 +124,7 @@ constexpr bool test_all() {
   test(std::ranges::set_symmetric_difference, in, in2, out, binary_pred);
   test(std::ranges::set_union, in, in2, out, binary_pred);
   test(std::ranges::remove_if, in, unary_pred);
-  //test(std::ranges::unique, in, binary_pred);
+  test(std::ranges::unique, in, binary_pred);
   test(std::ranges::partition, in, unary_pred);
   if (!std::is_constant_evaluated())
     test(std::ranges::stable_partition, in, unary_pred);
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
index aa0b15db6dee..c6fa8598e613 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
@@ -140,7 +140,7 @@ constexpr bool test_all() {
   // `reverse_copy` has neither a projection nor a predicate.
   // `rotate_copy` has neither a projection nor a predicate.
   // `sample` has no requirement that the given generator be invoked via `std::invoke`.
-  //test(std::ranges::unique_copy, in, out, &Foo::binary_pred, &Bar::val);
+  test(std::ranges::unique_copy, in, out, &Foo::binary_pred, &Bar::val);
   test(std::ranges::partition_copy, in, out, out2, &Foo::unary_pred, &Bar::val);
   //test(std::ranges::partial_sort_copy, in, in2, &Foo::binary_pred, &Bar::val);
   test(std::ranges::merge, in, in2, out, &Foo::binary_pred, &Bar::val, &Bar::val);
@@ -153,7 +153,7 @@ constexpr bool test_all() {
   // `reverse` has neither a projection nor a predicate.
   // `rotate` has neither a projection nor a predicate.
   // `shuffle` has neither a projection nor a predicate.
-  //test(std::ranges::unique, in, &Foo::binary_pred, &Bar::val);
+  test(std::ranges::unique, in, &Foo::binary_pred, &Bar::val);
   test(std::ranges::partition, in, &Foo::unary_pred, &Bar::val);
   if (!std::is_constant_evaluated())
     test(std::ranges::stable_partition, in, &Foo::unary_pred, &Bar::val);
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
index 4013065eb42a..191b4953f025 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
@@ -136,7 +136,7 @@ constexpr void run_tests() {
   if constexpr (std::copyable<T>) {
     test(std::ranges::reverse_copy, in, out);
     test_mid(std::ranges::rotate_copy, in, mid, out);
-    //test(std::ranges::unique_copy, in, out);
+    test(std::ranges::unique_copy, in, out);
     test(std::ranges::partition_copy, in, out, out2, unary_pred);
     //test_mid(std::ranges::partial_sort_copy, in, in2);
     test(std::ranges::merge, in, in2, out);
@@ -153,7 +153,7 @@ constexpr void run_tests() {
     test(std::ranges::shuffle, in, rand_gen());
   //if (!std::is_constant_evaluated())
   //  test(std::ranges::sample, in, out, count, rand_gen());
-  //test(std::ranges::unique, in);
+  test(std::ranges::unique, in);
   test(std::ranges::partition, in, unary_pred);
   // TODO(ranges): `stable_partition` requires `ranges::rotate` to be implemented.
   //if (!std::is_constant_evaluated())
diff --git a/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp b/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp
index 1fc6dfb89c4b..eac6eece9ac7 100644
--- a/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp
+++ b/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp
@@ -145,8 +145,8 @@ static_assert(test(std::ranges::stable_sort, a));
 //static_assert(test(std::ranges::starts_with, a, a));
 static_assert(test(std::ranges::swap_ranges, a, a));
 static_assert(test(std::ranges::transform, a, a, triple));
-//static_assert(test(std::ranges::unique, a));
-//static_assert(test(std::ranges::unique_copy, a, a));
+static_assert(test(std::ranges::unique, a));
+static_assert(test(std::ranges::unique_copy, a, a));
 static_assert(test(std::ranges::upper_bound, a, 42));
 
 // [memory.syn]