[libc++][ranges] Implement `ranges::remove_copy{, _if}`.

Co-authored-by: Hui Xie <hui.xie1990@gmail.com>

Differential Revision: https://reviews.llvm.org/D130599

(cherry picked from commit 760d2b462c04537d119d76d3cc37d2cb53774a05)

15 files changed, 578 insertions, 84 deletions

diff --git a/libcxx/docs/Status/RangesAlgorithms.csv b/libcxx/docs/Status/RangesAlgorithms.csv
index 4251b12463ac..4299410089df 100644
--- a/libcxx/docs/Status/RangesAlgorithms.csv
+++ b/libcxx/docs/Status/RangesAlgorithms.csv
@@ -47,8 +47,8 @@ Write,fill_n,Nikolas Klauser,`D123462 <https://llvm.org/D123462>`_,✅
 Write,transform,Nikolas Klauser,`D122173 <https://llvm.org/D122173>`_,✅
 Write,generate,Konstantin Varlamov,`D130552 <https://llvm.org/D130552>`_,✅
 Write,generate_n,Konstantin Varlamov,`D130552 <https://llvm.org/D130552>`_,✅
-Write,remove_copy,Nikolas Klauser,n/a,Not started
-Write,remove_copy_if,Nikolas Klauser,n/a,Not started
+Write,remove_copy,Nikolas Klauser,`D130599 <https://llvm.org/D130599>`_,✅
+Write,remove_copy_if,Nikolas Klauser,`D130599 <https://llvm.org/D130599>`_,✅
 Write,replace,Nikolas Klauser,`D126283 <https://llvm.org/D126283>`_,✅
 Write,replace_if,Nikolas Klauser,`D126283 <https://llvm.org/D126283>`_,✅
 Write,replace_copy,Nikolas Klauser,`D129806 <https://llvm.org/D129806>`_,Under review
diff --git a/libcxx/include/__algorithm/ranges_remove_copy.h b/libcxx/include/__algorithm/ranges_remove_copy.h
index 16e9009e7ef0..a8144ce0ecbf 100644
--- a/libcxx/include/__algorithm/ranges_remove_copy.h
+++ b/libcxx/include/__algorithm/ranges_remove_copy.h
@@ -10,19 +10,16 @@
 #define _LIBCPP___ALGORITHM_RANGES_REMOVE_COPY_H
 
 #include <__algorithm/in_out_result.h>
-#include <__algorithm/make_projected.h>
-#include <__algorithm/remove_copy.h>
+#include <__algorithm/ranges_remove_copy_if.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
 #include <__functional/ranges_operations.h>
 #include <__iterator/concepts.h>
-#include <__iterator/iterator_traits.h>
 #include <__iterator/projected.h>
 #include <__ranges/access.h>
 #include <__ranges/concepts.h>
 #include <__ranges/dangling.h>
-#include <__utility/forward.h>
 #include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -40,32 +37,30 @@ using remove_copy_result = in_out_result<_InIter, _OutIter>;
 
 namespace __remove_copy {
 
-struct __fn {
-
-  template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter, class _Type,
-            class _Proj = identity>
-  requires indirectly_copyable<_InIter, _OutIter> &&
-           indirect_binary_predicate<ranges::equal_to, projected<_InIter, _Proj>, const _Type*>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_result<_InIter, _OutIter>
-  operator()(_InIter __first, _Sent __last, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__result; (void)__value; (void)__proj;
-    return {};
-  }
-
-  template <input_range _Range, weakly_incrementable _OutIter, class _Type, class _Proj = identity>
-  requires indirectly_copyable<iterator_t<_Range>, _OutIter> &&
-           indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_result<borrowed_iterator_t<_Range>, _OutIter>
-  operator()(_Range&& __range, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__result; (void)__value; (void)__proj;
-    return {};
-  }
-
-};
+  struct __fn {
+    template <input_iterator _InIter,
+              sentinel_for<_InIter> _Sent,
+              weakly_incrementable _OutIter,
+              class _Type,
+              class _Proj = identity>
+      requires indirectly_copyable<_InIter, _OutIter> &&
+               indirect_binary_predicate<ranges::equal_to, projected<_InIter, _Proj>, const _Type*>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_result<_InIter, _OutIter>
+    operator()(_InIter __first, _Sent __last, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
+      auto __pred = [&](auto&& __val) { return __value == __val; };
+      return ranges::__remove_copy_if_impl(std::move(__first), std::move(__last), std::move(__result), __pred, __proj);
+    }
+
+    template <input_range _Range, weakly_incrementable _OutIter, class _Type, class _Proj = identity>
+      requires indirectly_copyable<iterator_t<_Range>, _OutIter> &&
+               indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_result<borrowed_iterator_t<_Range>, _OutIter>
+    operator()(_Range&& __range, _OutIter __result, const _Type& __value, _Proj __proj = {}) const {
+      auto __pred = [&](auto&& __val) { return __value == __val; };
+      return ranges::__remove_copy_if_impl(
+          ranges::begin(__range), ranges::end(__range), std::move(__result), __pred, __proj);
+    }
+  };
 
 } // namespace __remove_copy
 
diff --git a/libcxx/include/__algorithm/ranges_remove_copy_if.h b/libcxx/include/__algorithm/ranges_remove_copy_if.h
index 4eafe425b8e3..3f56693fa1f2 100644
--- a/libcxx/include/__algorithm/ranges_remove_copy_if.h
+++ b/libcxx/include/__algorithm/ranges_remove_copy_if.h
@@ -38,33 +38,43 @@ namespace ranges {
 template <class _InIter, class _OutIter>
 using remove_copy_if_result = in_out_result<_InIter, _OutIter>;
 
-namespace __remove_copy_if {
-
-struct __fn {
-
-  template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter,
-            class _Proj = identity, indirect_unary_predicate<projected<_InIter, _Proj>> _Pred>
-  requires indirectly_copyable<_InIter, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_if_result<_InIter, _OutIter>
-  operator()(_InIter __first, _Sent __last, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__first; (void)__last; (void)__result; (void)__pred; (void)__proj;
-    return {};
+template <class _InIter, class _Sent, class _OutIter, class _Proj, class _Pred>
+_LIBCPP_HIDE_FROM_ABI constexpr in_out_result<_InIter, _OutIter>
+__remove_copy_if_impl(_InIter __first, _Sent __last, _OutIter __result, _Pred& __pred, _Proj& __proj) {
+  for (; __first != __last; ++__first) {
+    if (!std::invoke(__pred, std::invoke(__proj, *__first))) {
+      *__result = *__first;
+      ++__result;
+    }
   }
+  return {std::move(__first), std::move(__result)};
+}
 
-  template <input_range _Range, weakly_incrementable _OutIter, class _Proj = identity,
-            indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
-  requires indirectly_copyable<iterator_t<_Range>, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
-  remove_copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
-  operator()(_Range&& __range, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
-    // TODO: implement
-    (void)__range; (void)__result; (void)__pred; (void)__proj;
-    return {};
-  }
+namespace __remove_copy_if {
 
-};
+  struct __fn {
+    template <input_iterator _InIter,
+              sentinel_for<_InIter> _Sent,
+              weakly_incrementable _OutIter,
+              class _Proj = identity,
+              indirect_unary_predicate<projected<_InIter, _Proj>> _Pred>
+      requires indirectly_copyable<_InIter, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_if_result<_InIter, _OutIter>
+    operator()(_InIter __first, _Sent __last, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
+      return ranges::__remove_copy_if_impl(std::move(__first), std::move(__last), std::move(__result), __pred, __proj);
+    }
+
+    template <input_range _Range,
+              weakly_incrementable _OutIter,
+              class _Proj = identity,
+              indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
+      requires indirectly_copyable<iterator_t<_Range>, _OutIter>
+    _LIBCPP_HIDE_FROM_ABI constexpr remove_copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
+    operator()(_Range&& __range, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
+      return ranges::__remove_copy_if_impl(
+          ranges::begin(__range), ranges::end(__range), std::move(__result), __pred, __proj);
+    }
+  };
 
 } // namespace __remove_copy_if
 
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 92e9327442ff..b4e1b82350f2 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -912,6 +912,38 @@ namespace ranges {
               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
+
+  template<class I, class O>
+      using remove_copy_result = in_out_result<I, O>;                                              // Since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O, class T,
+           class Proj = identity>
+             indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+    constexpr remove_copy_result<I, O>
+      remove_copy(I first, S last, O result, const T& value, Proj proj = {});                      // Since C++20
+
+  template<input_range R, weakly_incrementable O, class T, class Proj = identity>
+    requires indirectly_copyable<iterator_t<R>, O> &&
+             indirect_binary_predicate<ranges::equal_to,
+                                       projected<iterator_t<R>, Proj>, const T*>
+    constexpr remove_copy_result<borrowed_iterator_t<R>, O>
+      remove_copy(R&& r, O result, const T& value, Proj proj = {});                                // Since C++20
+
+  template<class I, class O>
+      using remove_copy_if_result = in_out_result<I, O>;                                           // Since C++20
+
+  template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
+           class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred>
+    requires indirectly_copyable<I, O>
+    constexpr remove_copy_if_result<I, O>
+      remove_copy_if(I first, S last, O result, Pred pred, Proj proj = {});                        // Since C++20
+
+  template<input_range R, weakly_incrementable O, class Proj = identity,
+           indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
+    requires indirectly_copyable<iterator_t<R>, O>
+    constexpr remove_copy_if_result<borrowed_iterator_t<R>, O>
+      remove_copy_if(R&& r, O result, Pred pred, Proj proj = {});                                  // Since C++20
+
 }
 
     constexpr bool     // constexpr in C++20
@@ -1694,6 +1726,8 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_pop_heap.h>
 #include <__algorithm/ranges_push_heap.h>
 #include <__algorithm/ranges_remove.h>
+#include <__algorithm/ranges_remove_copy.h>
+#include <__algorithm/ranges_remove_copy_if.h>
 #include <__algorithm/ranges_remove_if.h>
 #include <__algorithm/ranges_replace.h>
 #include <__algorithm/ranges_replace_if.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 6e64454358b1..b809db91e42e 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
@@ -187,8 +187,8 @@ constexpr bool all_the_algorithms()
     //(void)std::ranges::prev_permutation(a, Less(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(first, last, Less(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(a, Less(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(a, first2, UnaryTrue(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(a, first2, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(first, last, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(a, UnaryTrue(&copies)); assert(copies == 0);
     //(void)std::ranges::replace_copy_if(first, last, first2, UnaryTrue(&copies), value); 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 7f0015456d75..687d4fa18d66 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
@@ -170,10 +170,10 @@ constexpr bool all_the_algorithms()
     //(void)std::ranges::prev_permutation(a, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(first, last, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::push_heap(a, Less(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy(first, last, first2, value, Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy(a, first2, value, Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::remove_copy_if(a, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy(first, last, first2, value, Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy(a, first2, value, Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(first, last, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::remove_copy_if(a, first2, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove(first, last, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove(a, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::remove_if(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy.pass.cpp
index fb8a615f682d..f31734417bfa 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy.pass.cpp
@@ -30,16 +30,223 @@
 #include <concepts>
 #include <functional>
 #include <ranges>
+#include <utility>
 
 #include "almost_satisfies_types.h"
+#include "counting_projection.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+struct ToPtr {
+  int* operator()(int) const;
+};
+
+template <class Iter = int*, class Sent = int*, class OutIter = int*, class Proj = std::identity>
+concept HasRemoveCopyIter =
+  requires(Iter&& iter, Sent&& sent, OutIter&& out, Proj&& proj) {
+    std::ranges::remove_copy(
+        std::forward<Iter>(iter), std::forward<Sent>(sent), std::forward<OutIter>(out), 0, std::forward<Proj>(proj));
+};
+
+static_assert(HasRemoveCopyIter<int*>);
+
+// !input_iterator<I>
+static_assert(!HasRemoveCopyIter<InputIteratorNotDerivedFrom>);
+static_assert(!HasRemoveCopyIter<cpp20_output_iterator<int*>>);
+
+// !sentinel_for<S, I>
+static_assert(!HasRemoveCopyIter<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(!HasRemoveCopyIter<int*, SentinelForNotSemiregular>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+// !indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+static_assert(!HasRemoveCopyIter<int*, int*, int*, ToPtr>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasRemoveCopyIter<int*, int*, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIter<const int*, const int*, const int*>);
+
+template <class Range, class OutIter = int*, class Proj = std::identity>
+concept HasRemoveCopyRange =
+  requires(Range&& range, OutIter&& out, Proj&& proj) {
+    std::ranges::remove_copy(
+        std::forward<Range>(range), std::forward<OutIter>(out), 0, std::forward<Proj>(proj));
+};
+
+template <class T>
+using R = UncheckedRange<T>;
+
+static_assert(HasRemoveCopyRange<R<int*>>);
+
+// !input_range<R>
+static_assert(!HasRemoveCopyRange<InputRangeNotDerivedFrom>);
+static_assert(!HasRemoveCopyRange<InputRangeNotIndirectlyReadable>);
+static_assert(!HasRemoveCopyRange<InputRangeNotInputOrOutputIterator>);
+static_assert(!HasRemoveCopyRange<InputRangeNotSentinelSemiregular>);
+static_assert(!HasRemoveCopyRange<InputRangeNotSentinelEqualityComparableWith>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyRange<R<int*>, WeaklyIncrementableNotMovable>);
+
+// !indirect_binary_predicate<ranges::equal_to, projected<iterator_t<I>, Proj>, const T*>
+static_assert(!HasRemoveCopyRange<R<int*>, int*, ToPtr>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasRemoveCopyRange<R<int*>, int*, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyRange<const int*, const int*, const int*>);
+
+template <int N, int M>
+struct Data {
+  std::array<int, N> input;
+  std::array<int, M> expected;
+  int val;
+};
+
+template <class InIter, class Sent, class OutIter, int N, int M>
+constexpr void test(Data<N, M> d) {
+  using Result = std::ranges::remove_copy_result<InIter, OutIter>;
+
+  { // iterator overload
+    std::array<int, M> output;
+
+    std::same_as<Result> decltype(auto) ret = std::ranges::remove_copy(
+        InIter(d.input.data()), Sent(InIter(d.input.data() + d.input.size())), OutIter(output.data()), d.val);
+
+    assert(base(ret.in) == d.input.data() + N);
+    assert(base(ret.out) == output.data() + M);
+    assert(d.expected == output);
+  }
+
+  { // range overload
+    std::array<int, M> output;
+    auto range = std::ranges::subrange(InIter(d.input.data()), Sent(InIter(d.input.data() + d.input.size())));
+
+    std::same_as<Result> decltype(auto) ret =
+        std::ranges::remove_copy(range, OutIter(output.data()), d.val);
+
+    assert(base(ret.in) == d.input.data() + N);
+    assert(base(ret.out) == output.data() + M);
+    assert(d.expected == output);
+  }
+}
+
+template <class Iter, class Sent, class OutIter>
+constexpr void tests() {
+  // simple test
+  test<Iter, Sent, OutIter, 6, 5>({.input = {1, 2, 3, 4, 5, 6}, .expected = {1, 2, 3, 4, 6}, .val = 5});
+  // empty range
+  test<Iter, Sent, OutIter, 0, 0>({});
+  // single element range - match
+  test<Iter, Sent, OutIter, 1, 0>({.input = {1}, .expected = {}, .val = 1});
+  // single element range - no match
+  test<Iter, Sent, OutIter, 1, 1>({.input = {1}, .expected = {1}, .val = 2});
+  // two element range - same order
+  test<Iter, Sent, OutIter, 2, 1>({.input = {1, 2}, .expected = {1}, .val = 2});
+  // two element range - reversed order
+  test<Iter, Sent, OutIter, 2, 1>({.input = {1, 2}, .expected = {2}, .val = 1});
+  // all elements match
+  test<Iter, Sent, OutIter, 5, 0>({.input = {1, 1, 1, 1, 1}, .expected = {}, .val = 1});
+  // the relative order of elements isn't changed
+  test<Iter, Sent, OutIter, 8, 5>({.input = {1, 2, 3, 2, 3, 4, 2, 5}, .expected = {1, 3, 3, 4, 5}, .val = 2});
+}
+
+template <class InIter, class Sent>
+constexpr void test_output_iterators() {
+  tests<InIter, Sent, cpp17_output_iterator<int*>>();
+  tests<InIter, Sent, forward_iterator<int*>>();
+  tests<InIter, Sent, bidirectional_iterator<int*>>();
+  tests<InIter, Sent, random_access_iterator<int*>>();
+  tests<InIter, Sent, contiguous_iterator<int*>>();
+  tests<InIter, Sent, int*>();
+}
+
+template <class Iter>
+constexpr void test_sentinels() {
+  test_output_iterators<Iter, Iter>();
+  test_output_iterators<Iter, sentinel_wrapper<Iter>>();
+  test_output_iterators<Iter, sized_sentinel<Iter>>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  test_output_iterators<cpp17_input_iterator<int*>, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  test_output_iterators<cpp17_input_iterator<int*>, sized_sentinel<cpp17_input_iterator<int*>>>();
+  test_output_iterators<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  test_output_iterators<cpp20_input_iterator<int*>, sized_sentinel<cpp20_input_iterator<int*>>>();
+  test_sentinels<forward_iterator<int*>>();
+  test_sentinels<bidirectional_iterator<int*>>();
+  test_sentinels<random_access_iterator<int*>>();
+  test_sentinels<contiguous_iterator<int*>>();
+  test_sentinels<int*>();
+
+  { // check that passing a different type works
+    struct S {
+      constexpr operator int() const { return 3; }
+    };
+
+    { // iterator overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(std::begin(a), std::end(a), std::begin(b), S{});
+    }
+
+    { // range overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(a, std::begin(b), S{});
+    }
+  }
+
+  { // check that a custom projection works
+    struct S {
+      constexpr operator int() const { return 3; }
+    };
+
+    { // iterator overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(std::begin(a), std::end(a), std::begin(b), S{});
+
+    }
+    { // range overload
+      int a[] = {1, 2, 3, 4};
+      int b[3];
+      std::ranges::remove_copy(a, std::begin(b), S{});
+    }
+  }
+
+  // Complexity: Exactly last - first applications of the corresponding predicate and any projection.
+
+  {
+    std::array in{4, 4, 5, 6};
+    std::array expected{5, 6};
+
+    // iterator overload
+    {
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy(
+          in.begin(),
+          in.end(),
+          out.begin(),
+          4,
+          counting_projection(numberOfProj));
+
+      assert(numberOfProj == static_cast<int>(in.size()));
+
+      assert(std::ranges::equal(out, expected));
+    }
+
+    // range overload
+    {
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy(
+          in, out.begin(), 4, counting_projection(numberOfProj));
+      assert(numberOfProj == static_cast<int>(in.size()));
+      assert(std::ranges::equal(out, expected));
+    }
+  }
 
   return true;
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy_if.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy_if.pass.cpp
index 8e3e46e12192..3a0d1ea424fd 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy_if.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/ranges_remove_copy_if.pass.cpp
@@ -28,16 +28,264 @@
 #include <concepts>
 #include <functional>
 #include <ranges>
+#include <type_traits>
+#include <utility>
 
 #include "almost_satisfies_types.h"
+#include "counting_predicates.h"
+#include "counting_projection.h"
 #include "test_iterators.h"
 
-// TODO: SFINAE tests.
+struct AlwaysTrue {
+  constexpr bool operator()(auto&&...) const { return true; }
+};
+
+template <
+    class I,
+    class S    = sentinel_wrapper<std::decay_t<I>>,
+    class O    = int*,
+    class Pred = AlwaysTrue>
+concept HasRemoveCopyIfIter =
+  requires(I&& iter, S&& sent, O&& out, Pred&& pred) {
+    std::ranges::remove_copy_if(std::forward<I>(iter), std::forward<S>(sent),
+                                std::forward<O>(out), std::forward<Pred>(pred));
+};
+
+static_assert(HasRemoveCopyIfIter<int*, int*, int*>);
+
+// !input_iterator<I>
+static_assert(!HasRemoveCopyIfIter<InputIteratorNotDerivedFrom>);
+static_assert(!HasRemoveCopyIfIter<cpp20_output_iterator<int*>>);
+
+// !sentinel_for<S, I>
+static_assert(!HasRemoveCopyIfIter<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(!HasRemoveCopyIfIter<int*, SentinelForNotSemiregular>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyIfIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+// !indirect_unary_predicate<Pred, projected<I, Proj>>
+static_assert(!HasRemoveCopyIfIter<int*, int*, int*, IndirectUnaryPredicateNotPredicate>);
+static_assert(!HasRemoveCopyIfIter<int*, int*, int*, IndirectUnaryPredicateNotCopyConstructible>);
+
+// !indirectly_copyable<I, O>
+static_assert(!HasRemoveCopyIfIter<int*, int*, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIfIter<const int*, const int*, const int*>);
+
+template < class R, class O = int*, class Pred = AlwaysTrue, class Proj = std::identity>
+concept HasRemoveCopyIfRange =
+    requires(R&& r, O&& out, Pred&& pred, Proj&& proj) {
+      std::ranges::remove_copy_if(
+          std::forward<R>(r), std::forward<O>(out), std::forward<Pred>(pred), std::forward<Proj>(proj));
+    };
+
+template <class T>
+using R = UncheckedRange<T>;
+
+static_assert(HasRemoveCopyIfRange<R<int*>>);
+
+// !input_range<R>
+static_assert(!HasRemoveCopyIfRange<R<InputIteratorNotDerivedFrom>>);
+static_assert(!HasRemoveCopyIfRange<R<cpp20_output_iterator<int*>>>);
+
+// !weakly_incrementable<O>
+static_assert(!HasRemoveCopyIfRange<R<int*>, WeaklyIncrementableNotMovable>);
+
+// !indirect_unary_predicate<Pred, projected<iterator_t<R>, Proj>>
+static_assert(!HasRemoveCopyIfRange<R<int*>, int*, IndirectUnaryPredicateNotPredicate>);
+static_assert(!HasRemoveCopyIfRange<R<int*>, int*, IndirectUnaryPredicateNotCopyConstructible>);
+
+// !indirectly_copyable<iterator_t<R>, O>
+static_assert(!HasRemoveCopyIfRange<R<int*>, OutputIteratorNotIndirectlyWritable>);
+static_assert(!HasRemoveCopyIfRange<R<const int*>, const int*>);
+
+template <class InIter, class OutIter, template <class> class SentWrapper, std::size_t N1, std::size_t N2, class Pred>
+constexpr void testRemoveCopyIfImpl(std::array<int, N1> in, std::array<int, N2> expected, Pred pred) {
+  using Sent = SentWrapper<InIter>;
+  using Result = std::ranges::remove_copy_if_result<InIter, OutIter>;
+
+  // iterator overload
+  {
+    std::array<int, N2> out;
+    std::same_as<Result> decltype(auto) result =
+        std::ranges::remove_copy_if(InIter{in.data()}, Sent{InIter{in.data() + in.size()}}, OutIter{out.data()}, pred);
+    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<Result> decltype(auto) result =
+        std::ranges::remove_copy_if(r, OutIter{out.data()}, pred);
+    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() {
+  // remove multiple elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 3, 1};
+    auto pred = [](int i) { return i == 2; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove single elements
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 2, 1};
+    auto pred = [](int i) { return i == 3; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // nothing removed
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array expected{1, 2, 3, 2, 1};
+    auto pred = [](int) { return false; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // all removed
+  {
+    std::array in{1, 2, 3, 2, 1};
+    std::array<int, 0> expected{};
+    auto pred = [](int) { return true; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove first
+  {
+    std::array in{1, 2, 3, 2};
+    std::array expected{2, 3, 2};
+    auto pred = [](int i) { return i < 2; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // remove last
+  {
+    std::array in{1, 2, 3, 2, 5};
+    std::array expected{1, 2, 3, 2};
+    auto pred = [](int i) { return i > 3; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // stable
+  {
+    std::array in{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+    std::array expected{6, 7, 8, 9, 10};
+    auto pred = [](int i) { return i < 6; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // empty range
+  {
+    std::array<int, 0> in{};
+    std::array<int, 0> expected{};
+    auto pred = [](int) { return false; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+
+  // one element range
+  {
+    std::array in{1};
+    std::array<int, 0> expected{};
+    auto pred = [](int i) { return i == 1; };
+    testRemoveCopyIfImpl<InIter, OutIter, SentWrapper>(in, expected, pred);
+  }
+}
+
+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 withAllPermutationsOfInIterOutIter() {
+  withAllPermutationsOfInIter<cpp20_output_iterator<int*>, SentWrapper>();
+  withAllPermutationsOfInIter<int*, SentWrapper>();
+}
 
 constexpr bool test() {
-  // TODO: main tests.
-  // TODO: A custom comparator works.
-  // TODO: A custom projection works.
+  withAllPermutationsOfInIterOutIter<std::type_identity_t>();
+  withAllPermutationsOfInIterOutIter<sentinel_wrapper>();
+
+  // Test custom projection
+  {
+    struct Data {
+      int data;
+    };
+
+    std::array in{Data{4}, Data{8}, Data{12}, Data{12}};
+    std::array expected{Data{4}, Data{12}, Data{12}};
+
+    const auto proj = &Data::data;
+    const auto pred = [](int i) { return i == 8; };
+
+    const auto equals = [](const Data& x, const Data& y) { return x.data == y.data; };
+    // iterator overload
+    {
+      std::array<Data, 3> out;
+      auto result = std::ranges::remove_copy_if(in.begin(), in.end(), out.begin(), pred, proj);
+      assert(std::ranges::equal(out, expected, equals));
+      assert(result.in == in.end());
+      assert(result.out == out.end());
+    }
+
+    // range overload
+    {
+      std::array<Data, 3> out;
+      auto result = std::ranges::remove_copy_if(in, out.begin(), pred, proj);
+      assert(std::ranges::equal(out, expected, equals));
+      assert(result.in == in.end());
+      assert(result.out == out.end());
+    }
+  }
+
+  // Complexity: Exactly last - first applications of the corresponding predicate and any projection.
+  {
+    std::array in{4, 4, 5, 6};
+    std::array expected{5, 6};
+
+    const auto pred = [](int i) { return i == 4; };
+
+    // iterator overload
+    {
+      int numberOfPred = 0;
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy_if(
+          in.begin(), in.end(), out.begin(), counting_predicate(pred, numberOfPred), counting_projection(numberOfProj));
+
+      assert(numberOfPred == static_cast<int>(in.size()));
+      assert(numberOfProj == static_cast<int>(in.size()));
+
+      assert(std::ranges::equal(out, expected));
+    }
+
+    // range overload
+    {
+      int numberOfPred = 0;
+      int numberOfProj = 0;
+      std::array<int, 2> out;
+      std::ranges::remove_copy_if(
+          in, out.begin(), counting_predicate(pred, numberOfPred), counting_projection(numberOfProj));
+      assert(numberOfPred == static_cast<int>(in.size()));
+      assert(numberOfProj == static_cast<int>(in.size()));
+      assert(std::ranges::equal(out, expected));
+    }
+  }
 
   return true;
 }
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 7198a3408e28..6a0fa1ac0b03 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
@@ -32,8 +32,8 @@ static_assert(std::is_same_v<in_out_result<int, long>, copy_backward_result<int,
 static_assert(std::is_same_v<in_out_result<int, long>, move_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, move_backward_result<int, long>>);
 static_assert(std::is_same_v<in_out_result<int, long>, partial_sort_copy_result<int, long>>);
-// static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_result<int, long>>);
-// static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_if_result<int, long>>);
+static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_result<int, long>>);
+static_assert(std::is_same_v<in_out_result<int, long>, remove_copy_if_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, replace_copy_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, replace_copy_if_result<int, long>>);
 // static_assert(std::is_same_v<in_out_result<int, long>, reverse_copy_result<int, long>>);
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 c0468de8365c..b280dca05ad9 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
@@ -78,8 +78,8 @@ constexpr bool test_all() {
   //using std::ranges::move_backward_result;
   using std::ranges::partial_sort_copy_result;
   using std::ranges::partition_copy_result;
-  //using std::ranges::remove_copy_result;
-  //using std::ranges::remove_copy_if_result;
+  using std::ranges::remove_copy_result;
+  using std::ranges::remove_copy_if_result;
   using std::ranges::reverse_copy_result;
   using std::ranges::rotate_copy_result;
   using std::ranges::set_difference_result;
@@ -146,8 +146,8 @@ constexpr bool test_all() {
         std::ranges::transform, in, in2, out_transform.begin(), binary_pred);
   }
   dangling_1st(std::ranges::generate, in, gen);
-  //dangling_1st<remove_copy_result<dangling, int*>>(std::ranges::remove_copy, in, out, x);
-  //dangling_1st<remove_copy_if_result<dangling, int*>>(std::ranges::remove_copy_if, in, out, unary_pred);
+  dangling_1st<remove_copy_result<dangling, int*>>(std::ranges::remove_copy, in, out, x);
+  dangling_1st<remove_copy_if_result<dangling, int*>>(std::ranges::remove_copy_if, in, out, unary_pred);
   dangling_1st(std::ranges::replace, in, x, x);
   dangling_1st(std::ranges::replace_if, in, std::identity{}, x);
   //dangling_1st(std::ranges::replace_copy, in, out, x, x);
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 a38891792a82..37d454ca4979 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
@@ -112,7 +112,7 @@ constexpr bool test_all() {
   //std::ranges::clamp(2, 1, 3, binary_pred);
   //test(std::ranges::is_permutation, in, in2, binary_pred);
   test(std::ranges::copy_if, in, out, unary_pred);
-  //test(std::ranges::remove_copy_if, in, out, unary_pred);
+  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);
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 0c39e901f275..120c0bc7e225 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
@@ -129,8 +129,8 @@ constexpr bool test_all() {
     test(std::ranges::transform, in, out_transform.begin(), &Foo::unary_pred, &Bar::val);
   }
   // Whether `ranges::generate{,_n}` invokes `gen` via `std::invoke` is not observable.
-  //test(std::ranges::remove_copy, in, out, x, &Bar::val);
-  //test(std::ranges::remove_copy_if, in, out, &Foo::unary_pred, &Bar::val);
+  test(std::ranges::remove_copy, in, out, x, &Bar::val);
+  test(std::ranges::remove_copy_if, in, out, &Foo::unary_pred, &Bar::val);
   // `replace*` algorithms only use the projection to compare the elements, not to write them.
   test(std::ranges::replace, in, x, a, &Bar::val);
   test(std::ranges::replace_if, in, &Foo::unary_pred, a, &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 e77153ae828c..9193333457a9 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
@@ -125,8 +125,8 @@ constexpr void run_tests() {
   test(std::ranges::generate, in, gen);
   std::ranges::generate_n(in.begin(), count, gen);
   if constexpr (std::copyable<T>) {
-  //test(std::ranges::remove_copy, in, out, x);
-  //test(std::ranges::remove_copy_if, in, out, unary_pred);
+    test(std::ranges::remove_copy, in, out, x);
+    test(std::ranges::remove_copy_if, in, out, unary_pred);
     test(std::ranges::replace, in, x, x);
     test(std::ranges::replace_if, in, unary_pred, x);
     //test(std::ranges::replace_copy, in, out, x, x);
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 5e9d9f27ff2e..0f8272896db8 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
@@ -119,8 +119,8 @@ static_assert(test(std::ranges::pop_heap, a));
 //static_assert(test(std::ranges::prev_permutation, a));
 static_assert(test(std::ranges::push_heap, a));
 static_assert(test(std::ranges::remove, a, 42));
-//static_assert(test(std::ranges::remove_copy, a, a, 42));
-//static_assert(test(std::ranges::remove_copy_if, a, a, odd));
+static_assert(test(std::ranges::remove_copy, a, a, 42));
+static_assert(test(std::ranges::remove_copy_if, a, a, odd));
 static_assert(test(std::ranges::remove_if, a, odd));
 static_assert(test(std::ranges::replace, a, 42, 43));
 //static_assert(test(std::ranges::replace_copy, a, a, 42, 43));
diff --git a/libcxx/test/support/counting_projection.h b/libcxx/test/support/counting_projection.h
index 714058c1c045..1af2c80f244d 100644
--- a/libcxx/test/support/counting_projection.h
+++ b/libcxx/test/support/counting_projection.h
@@ -28,7 +28,7 @@ public:
   template <class T>
   constexpr decltype(auto) operator()(T&& value) const {
     ++(*count_);
-    return proj_(std::forward<T>(value));
+    return std::invoke(proj_, std::forward<T>(value));
   }
 };