[libc++] Implement ranges::starts_with

10 files changed, 374 insertions, 5 deletions

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index ead9693b5f7d..3e210323e51d 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -166,6 +166,7 @@ set(files
   __algorithm/ranges_sort_heap.h
   __algorithm/ranges_stable_partition.h
   __algorithm/ranges_stable_sort.h
+  __algorithm/ranges_starts_with.h
   __algorithm/ranges_swap_ranges.h
   __algorithm/ranges_transform.h
   __algorithm/ranges_unique.h
diff --git a/libcxx/include/__algorithm/ranges_starts_with.h b/libcxx/include/__algorithm/ranges_starts_with.h
new file mode 100644
index 000000000000..4c37756f6720
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_starts_with.h
@@ -0,0 +1,90 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_RANGES_STARTS_WITH_H
+#define _LIBCPP___ALGORITHM_RANGES_STARTS_WITH_H
+
+#include "ranges_mismatch.h"
+#include <__algorithm/in_in_result.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/indirectly_comparable.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 23
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __starts_with {
+struct __fn {
+  template <input_iterator _Iter1,
+            sentinel_for<_Iter1> _Sent1,
+            input_iterator _Iter2,
+            sentinel_for<_Iter2> _Sent2,
+            class _Pred  = ranges::equal_to,
+            class _Proj1 = identity,
+            class _Proj2 = identity>
+    requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(
+      _Iter1 __first1,
+      _Sent1 __last1,
+      _Iter2 __first2,
+      _Sent2 __last2,
+      _Pred __pred   = {},
+      _Proj1 __proj1 = {},
+      _Proj2 __proj2 = {}) const {
+    return __mismatch::__fn::__go(
+               std::move(__first1),
+               std::move(__last1),
+               std::move(__first2),
+               std::move(__last2),
+               __pred,
+               __proj1,
+               __proj2)
+               .in2 == __last2;
+  }
+
+  template <input_range _Range1,
+            input_range _Range2,
+            class _Pred  = ranges::equal_to,
+            class _Proj1 = identity,
+            class _Proj2 = identity>
+    requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>, _Pred, _Proj1, _Proj2>
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(
+      _Range1&& __range1, _Range2&& __range2, _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const {
+    return __mismatch::__fn::__go(
+               ranges::begin(__range1),
+               ranges::end(__range1),
+               ranges::begin(__range2),
+               ranges::end(__range2),
+               __pred,
+               __proj1,
+               __proj2)
+               .in2 == ranges::end(__range2);
+  }
+};
+} // namespace __starts_with
+inline namespace __cpo {
+inline constexpr auto starts_with = __starts_with::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 23
+
+#endif // _LIBCPP___ALGORITHM_RANGES_STARTS_WITH_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 18a89eb1a4dc..280333e5b33d 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -446,6 +446,18 @@ namespace ranges {
            indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
     constexpr bool ranges::none_of(R&& r, Pred pred, Proj proj = {});                       // since C++20
 
+  template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+          class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
+    requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
+    constexpr bool ranges::starts_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
+                                      Proj1 proj1 = {}, Proj2 proj2 = {});                 // since C++23
+
+  template<input_range R1, input_range R2, class Pred = ranges::equal_to, class Proj1 = identity,
+          class Proj2 = identity>
+    requires indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
+    constexpr bool ranges::starts_with(R1&& r1, R2&& r2, Pred pred = {},
+                                      Proj1 proj1 = {}, Proj2 proj2 = {});                // since C++23
+
   template<input_iterator I1, sentinel_for<I1> S1,
           random_access_iterator I2, sentinel_for<I2> S2,
           class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
@@ -1874,6 +1886,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_sort_heap.h>
 #include <__algorithm/ranges_stable_partition.h>
 #include <__algorithm/ranges_stable_sort.h>
+#include <__algorithm/ranges_starts_with.h>
 #include <__algorithm/ranges_swap_ranges.h>
 #include <__algorithm/ranges_transform.h>
 #include <__algorithm/ranges_unique.h>
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index d6419daff675..af65d60227af 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -578,6 +578,7 @@ module std [system] {
         private header "__algorithm/ranges_stable_sort.h"
         export functional.__functional.ranges_operations
       }
+      module ranges_starts_with         { private header "__algorithm/ranges_starts_with.h" }
       module ranges_swap_ranges {
         private header "__algorithm/ranges_swap_ranges.h"
         export algorithm.__algorithm.in_in_result
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 d5d978d6a09d..0a70bd2a2434 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
@@ -215,7 +215,8 @@ constexpr bool all_the_algorithms()
     if (!std::is_constant_evaluated()) { (void)std::ranges::stable_sort(first, last, Less(&copies)); assert(copies == 0); }
     if (!std::is_constant_evaluated()) { (void)std::ranges::stable_sort(a, Less(&copies)); assert(copies == 0); }
 #if TEST_STD_VER > 20
-    //(void)std::ranges::starts_with(first, last, first2, last2, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::starts_with(first, last, first2, last2, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::starts_with(a, b, Equal(&copies)); assert(copies == 0);
 #endif
     (void)std::ranges::transform(first, last, first2, UnaryTransform(&copies)); assert(copies == 0);
     (void)std::ranges::transform(a, first2, UnaryTransform(&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 23d02f04c835..111b0ff655f5 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
@@ -206,7 +206,8 @@ constexpr bool all_the_algorithms()
     if (!std::is_constant_evaluated()) { (void)std::ranges::stable_sort(first, last, Less(), Proj(&copies)); assert(copies == 0); }
     if (!std::is_constant_evaluated()) { (void)std::ranges::stable_sort(a, Less(), Proj(&copies)); assert(copies == 0); }
 #if TEST_STD_VER > 20
-    //(void)std::ranges::starts_with(first, last, first2, last2, Equal(), Proj(&copies), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::starts_with(first, last, first2, last2, Equal(), Proj(&copies), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::starts_with(a, b, Equal(), Proj(&copies), Proj(&copies)); assert(copies == 0);
 #endif
     (void)std::ranges::transform(first, last, first2, UnaryTransform(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::transform(a, first2, UnaryTransform(), Proj(&copies)); assert(copies == 0);
diff --git a/libcxx/test/libcxx/private_headers.verify.cpp b/libcxx/test/libcxx/private_headers.verify.cpp
index cb80edfd0694..6762913512c7 100644
--- a/libcxx/test/libcxx/private_headers.verify.cpp
+++ b/libcxx/test/libcxx/private_headers.verify.cpp
@@ -204,6 +204,7 @@ END-SCRIPT
 #include <__algorithm/ranges_sort_heap.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_sort_heap.h'}}
 #include <__algorithm/ranges_stable_partition.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_stable_partition.h'}}
 #include <__algorithm/ranges_stable_sort.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_stable_sort.h'}}
+#include <__algorithm/ranges_starts_with.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_starts_with.h'}}
 #include <__algorithm/ranges_swap_ranges.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_swap_ranges.h'}}
 #include <__algorithm/ranges_transform.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_transform.h'}}
 #include <__algorithm/ranges_unique.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_unique.h'}}
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.starts_with/ranges.starts_with.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.starts_with/ranges.starts_with.pass.cpp
new file mode 100644
index 000000000000..3a9c1aeeaf87
--- /dev/null
+++ b/libcxx/test/std/algorithms/alg.nonmodifying/alg.starts_with/ranges.starts_with.pass.cpp
@@ -0,0 +1,255 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+//          class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity>
+//   requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2>
+//   constexpr bool ranges::starts_with(I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {},
+//                                      Proj1 proj1 = {}, Proj2 proj2 = {});
+// template<input_range R1, input_range R2, class Pred = ranges::equal_to, class Proj1 = identity,
+//          class Proj2 = identity>
+//   requires indirectly_comparable<iterator_t<R1>, iterator_t<R2>, Pred, Proj1, Proj2>
+//   constexpr bool ranges::starts_with(R1&& r1, R2&& r2, Pred pred = {},
+//                                      Proj1 proj1 = {}, Proj2 proj2 = {});
+
+#include <algorithm>
+#include <array>
+#include <ranges>
+
+#include "almost_satisfies_types.h"
+#include "test_iterators.h"
+
+template <class Iter1, class Sent1 = Iter1, class Iter2 = int*, class Sent2 = Iter2>
+concept HasStartsWithIt = requires (Iter1 first1, Sent1 last1, Iter2 first2, Sent2 last2) {
+  std::ranges::starts_with(first1, last1, first2, last2);
+};
+
+static_assert(HasStartsWithIt<int*>);
+static_assert(HasStartsWithIt<ForwardIteratorNotDerivedFrom>);
+static_assert(HasStartsWithIt<ForwardIteratorNotIncrementable>);
+static_assert(!HasStartsWithIt<int*, SentinelForNotSemiregular>);
+static_assert(!HasStartsWithIt<int*, int*, int**>); // not indirectly comparable
+static_assert(!HasStartsWithIt<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(HasStartsWithIt<int*, int*, ForwardIteratorNotDerivedFrom>);
+static_assert(HasStartsWithIt<int*, int*, ForwardIteratorNotIncrementable>);
+static_assert(!HasStartsWithIt<int*, int*, int*, SentinelForNotSemiregular>);
+static_assert(!HasStartsWithIt<int*, int*, int*, SentinelForNotWeaklyEqualityComparableWith>);
+
+template <class Range1, class Range2 = UncheckedRange<int*>>
+concept HasStartsWithR = requires (Range1 range1, Range2 range2) {
+  std::ranges::starts_with(range1, range2);
+};
+
+static_assert(HasStartsWithR<UncheckedRange<int*>>);
+static_assert(HasStartsWithR<ForwardRangeNotDerivedFrom>);
+static_assert(!HasStartsWithR<ForwardIteratorNotIncrementable>);
+static_assert(!HasStartsWithR<ForwardRangeNotSentinelSemiregular>);
+static_assert(!HasStartsWithR<ForwardRangeNotSentinelEqualityComparableWith>);
+static_assert(!HasStartsWithR<UncheckedRange<int*>, UncheckedRange<int**>>); // not indirectly comparable
+static_assert(HasStartsWithR<UncheckedRange<int*>, ForwardRangeNotDerivedFrom>);
+static_assert(HasStartsWithR<UncheckedRange<int*>, ForwardRangeNotIncrementable>);
+static_assert(!HasStartsWithR<UncheckedRange<int*>, ForwardRangeNotSentinelSemiregular>);
+static_assert(!HasStartsWithR<UncheckedRange<int*>, ForwardRangeNotSentinelEqualityComparableWith>);
+
+template <class Iter1, class Sent1 = Iter1, class Iter2, class Sent2 = Iter2>
+constexpr void test_iterators() {
+  {// simply tests
+   {int a[] = {1, 2, 3, 4, 5, 6};
+    int p[] = {1, 2};
+    std::same_as<bool> decltype(auto) ret =
+        std::ranges::starts_with(Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p + 2)));
+    assert(ret);
+   }
+   {
+    int a[]                               = {1, 2, 3, 4, 5, 6};
+    int p[]                               = {1, 2};
+    auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+    auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 2)));
+    std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+    assert(ret);
+   }
+  }
+
+  {// prefix doesn't match
+   {
+    int a[] = {1, 2, 3, 4, 5, 6};
+    int p[] = {4, 5, 6};
+    std::same_as<bool> decltype(auto) ret =
+    std::ranges::starts_with(Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p + 3)));
+    assert(!ret);
+   }
+   {
+    int a[]                               = {1, 2, 3, 4, 5, 6};
+    int p[]                               = {4, 5, 6};
+    auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+    auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 3)));
+    std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+    assert(!ret);
+   }
+  }
+
+  {// range and prefix are identical
+   {
+    int a[] = {1, 2, 3, 4, 5, 6};
+    int p[] = {1, 2, 3, 4, 5, 6};
+    std::same_as<bool> decltype(auto) ret =
+    std::ranges::starts_with(Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p + 6)));
+    assert(ret);
+   }
+   {
+    int a[]                               = {1, 2, 3, 4, 5, 6};
+    int p[]                               = {1, 2, 3, 4, 5, 6};
+    auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+    auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 6)));
+    std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+    assert(ret);
+   }
+  }
+
+ {// prefix is longer than range
+  {
+   int a[] = {1, 2, 3, 4, 5, 6};
+   int p[] = {1, 2, 3, 4, 5, 6, 7, 8};
+   std::same_as<bool> decltype(auto) ret =
+   std::ranges::starts_with(Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p + 8)));
+   assert(!ret);
+  }
+  {
+   int a[]                               = {1, 2, 3, 4, 5, 6};
+   int p[]                               = {1, 2, 3, 4, 5, 6, 7, 8};
+   auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+   auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 8)));
+   std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+   assert(!ret);
+  }
+ }
+
+ {// prefix has zero length
+  {
+   int a[] = {1, 2, 3, 4, 5, 6};
+   int p[] = {};
+   std::same_as<bool> decltype(auto) ret =
+   std::ranges::starts_with(Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p)));
+   assert(ret);
+  }
+  {
+   int a[]                               = {1, 2, 3, 4, 5, 6};
+   int p[]                               = {};
+   auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+   auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p)));
+   std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+   assert(ret);
+  }
+ }
+
+ {// range has zero length
+  {
+   int a[] = {};
+   int p[] = {1, 2, 3, 4, 5, 6, 7, 8};
+   std::same_as<bool> decltype(auto) ret =
+   std::ranges::starts_with(Iter1(a), Sent1(Iter1(a)), Iter2(p), Sent2(Iter2(p + 8)));
+   assert(!ret);
+  }
+  {
+   int a[]                               = {};
+   int p[]                               = {1, 2, 3, 4, 5, 6, 7, 8};
+   auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a)));
+   auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 8)));
+   std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix);
+   assert(!ret);
+  }
+ }
+
+ {// check that the predicate is used
+  {
+   int a[] = {11, 8, 3, 4, 0, 6};
+   int p[] = {1, 12};
+   std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(
+   Iter1(a), Sent1(Iter1(a + 6)), Iter2(p), Sent2(Iter2(p + 2)), [](int l, int r) { return l > r; });
+   assert(!ret);
+  }
+  {
+   int a[]                               = {11, 8, 3, 4, 0, 6};
+   int p[]                               = {1, 12};
+   auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+   auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 2)));
+   std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(whole, prefix, [](int l, int r) { return l > r; });
+   assert(!ret);
+  }
+ }
+
+ {// check that the projections are used
+  {
+    int a[]                               = {1, 3, 5, 1, 5, 6};
+    int p[]                               = {2, 3, 4};
+    std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(
+        Iter1(a),
+        Sent1(Iter1(a + 6)),
+        Iter2(p),
+        Sent2(Iter2(p + 3)),
+        {},
+        [](int i) { return i + 3; },
+        [](int i) { return i * 2; });
+    assert(ret);
+  }
+  {
+    int a[]                               = {1, 3, 5, 1, 5, 6};
+    int p[]                               = {2, 3, 4};
+    auto whole                            = std::ranges::subrange(Iter1(a), Sent1(Iter1(a + 6)));
+    auto prefix                           = std::ranges::subrange(Iter2(p), Sent2(Iter2(p + 3)));
+    std::same_as<bool> decltype(auto) ret = std::ranges::starts_with(
+        whole, prefix, {}, [](int i) { return i + 3; }, [](int i) { return i * 2; });
+    assert(ret);
+  }
+ }
+}
+
+constexpr bool test() {
+  types::for_each(types::forward_iterator_list<int*>{}, []<class I2>() {
+    types::for_each(types::forward_iterator_list<int*>{}, []<class I1>() {
+      test_iterators<I1, I1, I2, I2>();
+      test_iterators<I1, sized_sentinel<I1>, I2, I2>();
+      test_iterators<I1, I1, I2, sized_sentinel<I2>>();
+      test_iterators<I1, sized_sentinel<I1>, I2, sized_sentinel<I2>>();
+    });
+});
+
+  { // check that std::invoke is used
+    struct S {
+      int i;
+
+      constexpr S identity() { return *this; }
+
+      constexpr bool compare(const S& s) { return i == s.i; }
+    };
+    {
+      S a[]    = {{1}, {2}, {3}, {4}};
+      S p[]    = {{1}, {2}};
+      auto ret = std::ranges::starts_with(a, a + 4, p, p + 2, &S::compare, &S::identity, &S::identity);
+      assert(ret);
+    }
+    {
+      S a[]    = {{1}, {2}, {3}, {4}};
+      S p[]    = {{1}, {2}};
+      auto ret = std::ranges::starts_with(a, p, &S::compare, &S::identity, &S::identity);
+      assert(ret);
+    }
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+  return 0;
+}
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_differing_projections.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_differing_projections.pass.cpp
index d940a7ab9700..4c90387443df 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_differing_projections.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_differing_projections.pass.cpp
@@ -20,6 +20,7 @@
 #include <iterator>
 #include <ranges>
 #include <utility>
+#include "test_macros.h"
 
 // (in1, in2, ...)
 template <class Func, std::ranges::range Input1, std::ranges::range Input2, class ...Args>
@@ -74,8 +75,10 @@ constexpr bool test_all() {
   test(std::ranges::set_symmetric_difference, in, in2, out2, less, proj1, proj2);
   test(std::ranges::set_union, in, in2, out, less, proj1, proj2);
   test(std::ranges::set_union, in, in2, out2, less, proj1, proj2);
-  //test(std::ranges::starts_with, in, in2, eq, proj1, proj2);
-  //test(std::ranges::ends_with, in, in2, eq, proj1, proj2);
+#if TEST_STD_VER > 20
+  test(std::ranges::starts_with, in, in2, eq, proj1, proj2);
+  // test(std::ranges::ends_with, in, in2, eq, proj1, proj2);
+#endif
 
   return true;
 }
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 c951b9be9869..9e00a57ba80c 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
@@ -20,6 +20,7 @@
 #include <ranges>
 #include <type_traits>
 #include <utility>
+#include "test_macros.h"
 
 // Niebloids, unlike CPOs, are *not* required to be semiregular or even to have
 // a declared type at all; they are specified as "magic" overload sets whose
@@ -140,7 +141,9 @@ static_assert(test(std::ranges::sort, a));
 static_assert(test(std::ranges::sort_heap, a));
 static_assert(test(std::ranges::stable_partition, a, odd));
 static_assert(test(std::ranges::stable_sort, a));
-//static_assert(test(std::ranges::starts_with, a, a));
+#if TEST_STD_VER > 20
+static_assert(test(std::ranges::starts_with, a, a));
+#endif
 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));