[libc++][spaceship] Implements X::iterator container requirements. (#99343)

This implements the requirements for the container iterator requirements
for array, deque, vector, and `vector<bool>`.

Implements:
- LWG3352 strong_equality isn't a thing

Implements parts of:
- P1614R2 The Mothership has Landed

Fixes: https://github.com/llvm/llvm-project/issues/62486

libcxx/docs/Status/Cxx20Issues.csv

@@ -264,7 +264,7 @@
 "`3349 <https://wg21.link/LWG3349>`__","Missing ``__cpp_lib_constexpr_complex``\  for P0415R1","Prague","|Complete|","16.0"
 "`3350 <https://wg21.link/LWG3350>`__","Simplify return type of ``lexicographical_compare_three_way``\ ","Prague","|Complete|","17.0","|spaceship|"
 "`3351 <https://wg21.link/LWG3351>`__","``ranges::enable_safe_range``\  should not be constrained","Prague","|Complete|","15.0","|ranges|"
-"`3352 <https://wg21.link/LWG3352>`__","``strong_equality``\  isn't a thing","Prague","|Nothing To Do|","","|spaceship|"
+"`3352 <https://wg21.link/LWG3352>`__","``strong_equality``\  isn't a thing","Prague","|Complete|","19.0","|spaceship|"
 "`3354 <https://wg21.link/LWG3354>`__","``has_strong_structural_equality``\  has a meaningless definition","Prague","|Nothing To Do|","","|spaceship|"
 "`3355 <https://wg21.link/LWG3355>`__","The memory algorithms should support move-only input iterators introduced by P1207","Prague","|Complete|","15.0","|ranges|"
 "`3356 <https://wg21.link/LWG3356>`__","``__cpp_lib_nothrow_convertible``\  should be ``__cpp_lib_is_nothrow_convertible``\ ","Prague","|Complete|","12.0"

libcxx/docs/Status/SpaceshipProjects.csv

@@ -83,7 +83,7 @@ Section,Description,Dependencies,Assignee,Complete
 "| `[string.view.synop] <https://wg21.link/string.view.synop>`_
 | `[string.view.comparison] <https://wg21.link/string.view.comparison>`_",| `basic_string_view <https://reviews.llvm.org/D130295>`_,None,Mark de Wever,|Complete|
 - `5.7 Clause 22: Containers library <https://wg21.link/p1614r2#clause-22-containers-library>`_,,,,
-| `[container.requirements.general] <https://wg21.link/container.requirements.general>`_,|,None,Unassigned,|Not Started|
+| `[container.requirements.general] <https://wg21.link/container.requirements.general>`_,|,None,Mark de Wever,|Complete|
 | `[array.syn] <https://wg21.link/array.syn>`_ (`general <https://wg21.link/container.opt.reqmts>`_),| `array <https://reviews.llvm.org/D132265>`_,[expos.only.func],"| Adrian Vogelsgesang
 | Hristo Hristov",|Complete|
 | `[deque.syn] <https://wg21.link/deque.syn>`_ (`general <https://wg21.link/container.opt.reqmts>`_),| `deque <https://reviews.llvm.org/D144821>`_,[expos.only.func],Hristo Hristov,|Complete|

libcxx/include/__bit_reference

@@ -16,6 +16,7 @@
 #include <__bit/countr.h>
 #include <__bit/invert_if.h>
 #include <__bit/popcount.h>
+#include <__compare/ordering.h>
 #include <__config>
 #include <__fwd/bit_reference.h>
 #include <__iterator/iterator_traits.h>
@@ -913,6 +914,7 @@ public:
     return __x.__seg_ == __y.__seg_ && __x.__ctz_ == __y.__ctz_;
   }
 
+#if _LIBCPP_STD_VER <= 17
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 friend bool
   operator!=(const __bit_iterator& __x, const __bit_iterator& __y) {
     return !(__x == __y);
@@ -937,6 +939,18 @@ public:
   operator>=(const __bit_iterator& __x, const __bit_iterator& __y) {
     return !(__x < __y);
   }
+#else  // _LIBCPP_STD_VER <= 17
+  _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering
+  operator<=>(const __bit_iterator& __x, const __bit_iterator& __y) {
+    if (__x.__seg_ < __y.__seg_)
+      return strong_ordering::less;
+
+    if (__x.__seg_ == __y.__seg_)
+      return __x.__ctz_ <=> __y.__ctz_;
+
+    return strong_ordering::greater;
+  }
+#endif // _LIBCPP_STD_VER <= 17
 
 private:
   _LIBCPP_HIDE_FROM_ABI

libcxx/include/__iterator/bounded_iter.h

@@ -11,6 +11,8 @@
 #define _LIBCPP___ITERATOR_BOUNDED_ITER_H
 
 #include <__assert>
+#include <__compare/ordering.h>
+#include <__compare/three_way_comparable.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__memory/pointer_traits.h>
@@ -201,10 +203,15 @@ public:
   operator==(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
     return __x.__current_ == __y.__current_;
   }
+
+#if _LIBCPP_STD_VER <= 17
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
   operator!=(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
     return __x.__current_ != __y.__current_;
   }
+#endif
+
+  // TODO(mordante) disable these overloads in the LLVM 20 release.
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR friend bool
   operator<(__bounded_iter const& __x, __bounded_iter const& __y) _NOEXCEPT {
     return __x.__current_ < __y.__current_;
@@ -222,6 +229,23 @@ public:
     return __x.__current_ >= __y.__current_;
   }
 
+#if _LIBCPP_STD_VER >= 20
+  _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering
+  operator<=>(__bounded_iter const& __x, __bounded_iter const& __y) noexcept {
+    if constexpr (three_way_comparable<_Iterator, strong_ordering>) {
+      return __x.__current_ <=> __y.__current_;
+    } else {
+      if (__x.__current_ < __y.__current_)
+        return strong_ordering::less;
+
+      if (__x.__current_ == __y.__current_)
+        return strong_ordering::equal;
+
+      return strong_ordering::greater;
+    }
+  }
+#endif // _LIBCPP_STD_VER >= 20
+
 private:
   template <class>
   friend struct pointer_traits;

libcxx/include/__iterator/wrap_iter.h

@@ -10,6 +10,8 @@
 #ifndef _LIBCPP___ITERATOR_WRAP_ITER_H
 #define _LIBCPP___ITERATOR_WRAP_ITER_H
 
+#include <__compare/ordering.h>
+#include <__compare/three_way_comparable.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__memory/addressof.h>
@@ -131,6 +133,7 @@ operator<(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEXC
   return __x.base() < __y.base();
 }
 
+#if _LIBCPP_STD_VER <= 17
 template <class _Iter1>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool
 operator!=(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter1>& __y) _NOEXCEPT {
@@ -142,7 +145,9 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool
 operator!=(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEXCEPT {
   return !(__x == __y);
 }
+#endif
 
+// TODO(mordante) disable these overloads in the LLVM 20 release.
 template <class _Iter1>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool
 operator>(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter1>& __y) _NOEXCEPT {
@@ -179,6 +184,24 @@ operator<=(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEX
   return !(__y < __x);
 }
 
+#if _LIBCPP_STD_VER >= 20
+template <class _Iter1, class _Iter2>
+_LIBCPP_HIDE_FROM_ABI constexpr strong_ordering
+operator<=>(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) noexcept {
+  if constexpr (three_way_comparable_with<_Iter1, _Iter2, strong_ordering>) {
+    return __x.base() <=> __y.base();
+  } else {
+    if (__x.base() < __y.base())
+      return strong_ordering::less;
+
+    if (__x.base() == __y.base())
+      return strong_ordering::equal;
+
+    return strong_ordering::greater;
+  }
+}
+#endif // _LIBCPP_STD_VER >= 20
+
 template <class _Iter1, class _Iter2>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 #ifndef _LIBCPP_CXX03_LANG

libcxx/include/deque

@@ -376,10 +376,13 @@ public:
     return __x.__ptr_ == __y.__ptr_;
   }
 
+#if _LIBCPP_STD_VER <= 17
   _LIBCPP_HIDE_FROM_ABI friend bool operator!=(const __deque_iterator& __x, const __deque_iterator& __y) {
     return !(__x == __y);
   }
+#endif
 
+  // TODO(mordante) disable these overloads in the LLVM 20 release.
   _LIBCPP_HIDE_FROM_ABI friend bool operator<(const __deque_iterator& __x, const __deque_iterator& __y) {
     return __x.__m_iter_ < __y.__m_iter_ || (__x.__m_iter_ == __y.__m_iter_ && __x.__ptr_ < __y.__ptr_);
   }
@@ -396,6 +399,29 @@ public:
     return !(__x < __y);
   }
 
+#if _LIBCPP_STD_VER >= 20
+  _LIBCPP_HIDE_FROM_ABI friend strong_ordering operator<=>(const __deque_iterator& __x, const __deque_iterator& __y) {
+    if (__x.__m_iter_ < __y.__m_iter_)
+      return strong_ordering::less;
+
+    if (__x.__m_iter_ == __y.__m_iter_) {
+      if constexpr (three_way_comparable<pointer, strong_ordering>) {
+        return __x.__ptr_ <=> __y.__ptr_;
+      } else {
+        if (__x.__ptr_ < __y.__ptr_)
+          return strong_ordering::less;
+
+        if (__x.__ptr_ == __y.__ptr_)
+          return strong_ordering::equal;
+
+        return strong_ordering::greater;
+      }
+    }
+
+    return strong_ordering::greater;
+  }
+#endif // _LIBCPP_STD_VER >= 20
+
 private:
   _LIBCPP_HIDE_FROM_ABI explicit __deque_iterator(__map_iterator __m, pointer __p) _NOEXCEPT
       : __m_iter_(__m),
@@ -2530,8 +2556,7 @@ inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const deque<_Tp, _Allocator>& __x,
 template <class _Tp, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI __synth_three_way_result<_Tp>
 operator<=>(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y) {
-  return std::lexicographical_compare_three_way(
-      __x.begin(), __x.end(), __y.begin(), __y.end(), std::__synth_three_way);
+  return std::lexicographical_compare_three_way(__x.begin(), __x.end(), __y.begin(), __y.end(), std::__synth_three_way);
 }
 
 #endif // _LIBCPP_STD_VER <= 17

libcxx/test/libcxx/iterators/bounded_iter/comparison.pass.cpp

@@ -11,6 +11,7 @@
 //
 // Comparison operators
 
+#include <concepts>
 #include <__iterator/bounded_iter.h>
 
 #include "test_iterators.h"
@@ -59,6 +60,12 @@ TEST_CONSTEXPR_CXX14 bool tests() {
     assert(iter1 >= iter1);
   }
 
+#if TEST_STD_VER >= 20
+  // P1614
+  std::same_as<std::strong_ordering> decltype(auto) r1 = iter1 <=> iter2;
+  assert(r1 == std::strong_ordering::less);
+#endif
+
   return true;
 }
 
@@ -69,8 +76,11 @@ int main(int, char**) {
 #endif
 
 #if TEST_STD_VER > 17
-  tests<contiguous_iterator<int*> >();
-  static_assert(tests<contiguous_iterator<int*> >(), "");
+  tests<contiguous_iterator<int*>>();
+  static_assert(tests<contiguous_iterator<int*>>());
+
+  tests<three_way_contiguous_iterator<int*>>();
+  static_assert(tests<three_way_contiguous_iterator<int*>>());
 #endif
 
   return 0;

libcxx/test/std/containers/sequences/array/iterators.pass.cpp

@@ -148,6 +148,15 @@ TEST_CONSTEXPR_CXX17 bool tests()
             assert(std::rbegin(c)  != std::rend(c));
             assert(std::cbegin(c)  != std::cend(c));
             assert(std::crbegin(c) != std::crend(c));
+
+#  if TEST_STD_VER >= 20
+            // P1614 + LWG3352
+            std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+            assert(r1 == std::strong_ordering::equal);
+
+            std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+            assert(r2 == std::strong_ordering::equal);
+#  endif
         }
         {
             typedef std::array<int, 0> C;
@@ -189,6 +198,15 @@ TEST_CONSTEXPR_CXX17 bool tests()
             assert(std::rbegin(c)  == std::rend(c));
             assert(std::cbegin(c)  == std::cend(c));
             assert(std::crbegin(c) == std::crend(c));
+
+#  if TEST_STD_VER >= 20
+            // P1614 + LWG3352
+            std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+            assert(r1 == std::strong_ordering::equal);
+
+            std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+            assert(r2 == std::strong_ordering::equal);
+#  endif
         }
     }
 #endif

libcxx/test/std/containers/sequences/deque/iterators.pass.cpp

@@ -41,7 +41,27 @@ int main(int, char**)
     i = c.begin();
     C::const_iterator j;
     j = c.cbegin();
+
     assert(i == j);
+    assert(!(i != j));
+
+    assert(!(i < j));
+    assert((i <= j));
+
+    assert(!(i > j));
+    assert((i >= j));
+
+#  if TEST_STD_VER >= 20
+    // P1614 + LWG3352
+    // When the allocator does not have operator<=> then the iterator uses a
+    // fallback to provide operator<=>.
+    // Make sure to test with an allocator that does not have operator<=>.
+    static_assert(!std::three_way_comparable<min_allocator<int>, std::strong_ordering>);
+    static_assert(std::three_way_comparable<typename C::iterator, std::strong_ordering>);
+
+    std::same_as<std::strong_ordering> decltype(auto) r1 = i <=> j;
+    assert(r1 == std::strong_ordering::equal);
+#  endif
     }
 #endif
 #if TEST_STD_VER > 11
@@ -74,6 +94,15 @@ int main(int, char**)
 //         assert ( cii != c.begin());
 //         assert ( cii != c.cend());
 //         assert ( ii1 != c.end());
+
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+        assert(r1 == std::strong_ordering::equal);
+
+        std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+        assert(r2 == std::strong_ordering::equal);
+#  endif // TEST_STD_VER > 20
     }
 #endif
 

libcxx/test/std/containers/sequences/vector.bool/iterators.pass.cpp

@@ -77,7 +77,21 @@ TEST_CONSTEXPR_CXX20 bool tests()
         C::iterator i = c.begin();
         C::iterator j = c.end();
         assert(std::distance(i, j) == 0);
+
         assert(i == j);
+        assert(!(i != j));
+
+        assert(!(i < j));
+        assert((i <= j));
+
+        assert(!(i > j));
+        assert((i >= j));
+
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        std::same_as<std::strong_ordering> decltype(auto) r = i <=> j;
+        assert(r == std::strong_ordering::equal);
+#  endif
     }
     {
         typedef bool T;
@@ -86,7 +100,21 @@ TEST_CONSTEXPR_CXX20 bool tests()
         C::const_iterator i = c.begin();
         C::const_iterator j = c.end();
         assert(std::distance(i, j) == 0);
+
         assert(i == j);
+        assert(!(i != j));
+
+        assert(!(i < j));
+        assert((i <= j));
+
+        assert(!(i > j));
+        assert((i >= j));
+
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        std::same_as<std::strong_ordering> decltype(auto) r = i <=> j;
+        assert(r == std::strong_ordering::equal);
+#  endif
     }
     {
         typedef bool T;
@@ -131,6 +159,15 @@ TEST_CONSTEXPR_CXX20 bool tests()
         assert ( (cii >= ii1 ));
         assert (cii - ii1 == 0);
         assert (ii1 - cii == 0);
+
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+        assert(r1 == std::strong_ordering::equal);
+
+        std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+        assert(r2 == std::strong_ordering::equal);
+#  endif // TEST_STD_VER > 20
     }
 #endif
 

libcxx/test/std/containers/sequences/vector/iterators.pass.cpp

@@ -87,7 +87,27 @@ TEST_CONSTEXPR_CXX20 bool tests()
         C::iterator i = c.begin();
         C::iterator j = c.end();
         assert(std::distance(i, j) == 0);
+
         assert(i == j);
+        assert(!(i != j));
+
+        assert(!(i < j));
+        assert((i <= j));
+
+        assert(!(i > j));
+        assert((i >= j));
+
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        // When the allocator does not have operator<=> then the iterator uses a
+        // fallback to provide operator<=>.
+        // Make sure to test with an allocator that does not have operator<=>.
+        static_assert(!std::three_way_comparable<min_allocator<int>, std::strong_ordering>);
+        static_assert(std::three_way_comparable<typename C::iterator, std::strong_ordering>);
+
+        std::same_as<std::strong_ordering> decltype(auto) r1 = i <=> j;
+        assert(r1 == std::strong_ordering::equal);
+#  endif
     }
     {
         typedef int T;
@@ -96,7 +116,26 @@ TEST_CONSTEXPR_CXX20 bool tests()
         C::const_iterator i = c.begin();
         C::const_iterator j = c.end();
         assert(std::distance(i, j) == 0);
+
         assert(i == j);
+        assert(!(i != j));
+
+        assert(!(i < j));
+        assert((i <= j));
+
+        assert(!(i > j));
+        assert((i >= j));
+
+#  if TEST_STD_VER >= 20
+        // When the allocator does not have operator<=> then the iterator uses a
+        // fallback to provide operator<=>.
+        // Make sure to test with an allocator that does not have operator<=>.
+        static_assert(!std::three_way_comparable<min_allocator<int>, std::strong_ordering>);
+        static_assert(std::three_way_comparable<typename C::iterator, std::strong_ordering>);
+
+        std::same_as<std::strong_ordering> decltype(auto) r1 = i <=> j;
+        assert(r1 == std::strong_ordering::equal);
+#  endif
     }
     {
         typedef int T;
@@ -164,8 +203,16 @@ TEST_CONSTEXPR_CXX20 bool tests()
         assert ( (cii >= ii1 ));
         assert (cii - ii1 == 0);
         assert (ii1 - cii == 0);
+#  if TEST_STD_VER >= 20
+        // P1614 + LWG3352
+        std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+        assert(r1 == std::strong_ordering::equal);
+
+        std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+        assert(r2 == std::strong_ordering::equal);
+#  endif // TEST_STD_VER > 20
     }
-#endif
+#endif // TEST_STD_VER > 11
 
     return true;
 }

libcxx/test/std/containers/views/views.span/span.iterators/iterator.pass.cpp

@@ -0,0 +1,92 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <span>
+
+// class iterator
+
+#include <cassert>
+#include <concepts>
+#include <iterator>
+#include <span>
+#include <string>
+#include <version> // __cpp_lib_ranges_as_const is not defined in span.
+
+#include "test_macros.h"
+
+template <class T>
+constexpr void test_type() {
+  using C = std::span<T>;
+  typename C::iterator ii1{}, ii2{};
+  typename C::iterator ii4 = ii1;
+  // TODO Test against C++23 after implementing
+  //  P2278R4 cbegin should always return a constant iterator
+  // The means adjusting the #ifdef to guard against C++23.
+#ifdef __cpp_lib_ranges_as_const
+  typename C::const_iterator cii{};
+#endif
+  assert(ii1 == ii2);
+  assert(ii1 == ii4);
+#ifdef __cpp_lib_ranges_as_const
+  assert(ii1 == cii);
+#endif
+
+  assert(!(ii1 != ii2));
+#ifdef __cpp_lib_ranges_as_const
+  assert(!(ii1 != cii));
+#endif
+
+  T v;
+  C c{&v, 1};
+  assert(c.begin() == std::begin(c));
+  assert(c.rbegin() == std::rbegin(c));
+#ifdef __cpp_lib_ranges_as_const
+  assert(c.cbegin() == std::cbegin(c));
+  assert(c.crbegin() == std::crbegin(c));
+#endif
+
+  assert(c.end() == std::end(c));
+  assert(c.rend() == std::rend(c));
+#ifdef __cpp_lib_ranges_as_const
+  assert(c.cend() == std::cend(c));
+  assert(c.crend() == std::crend(c));
+#endif
+
+  assert(std::begin(c) != std::end(c));
+  assert(std::rbegin(c) != std::rend(c));
+#ifdef __cpp_lib_ranges_as_const
+  assert(std::cbegin(c) != std::cend(c));
+  assert(std::crbegin(c) != std::crend(c));
+#endif
+
+  // P1614 + LWG3352
+  std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+  assert(r1 == std::strong_ordering::equal);
+
+#ifdef __cpp_lib_ranges_as_const
+  std::same_as<std::strong_ordering> decltype(auto) r2 = cii <=> ii2;
+  assert(r2 == std::strong_ordering::equal);
+#endif
+}
+
+constexpr bool test() {
+  test_type<char>();
+  test_type<int>();
+  test_type<std::string>();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test(), "");
+
+  return 0;
+}

libcxx/test/std/strings/string.view/string.view.iterators/iterators.pass.cpp

@@ -0,0 +1,85 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: !stdlib=libc++ && (c++03 || c++11 || c++14)
+
+// <string_view>
+
+// class iterator
+
+#include <cassert>
+#include <concepts>
+#include <iterator>
+#include <string_view>
+
+#include "test_macros.h"
+#include "make_string.h"
+
+template <class CharT>
+TEST_CONSTEXPR_CXX14 void test_type() {
+  using C                  = std::basic_string_view<CharT>;
+  typename C::iterator ii1 = typename C::iterator(), ii2 = typename C::iterator();
+  typename C::iterator ii4       = ii1;
+  typename C::const_iterator cii = typename C::const_iterator();
+  assert(ii1 == ii2);
+  assert(ii1 == ii4);
+  assert(ii1 == cii);
+
+  assert(!(ii1 != ii2));
+  assert(!(ii1 != cii));
+
+#if TEST_STD_VER >= 17
+  C c = MAKE_STRING_VIEW(CharT, "abc");
+  assert(c.begin() == std::begin(c));
+  assert(c.rbegin() == std::rbegin(c));
+  assert(c.cbegin() == std::cbegin(c));
+  assert(c.crbegin() == std::crbegin(c));
+
+  assert(c.end() == std::end(c));
+  assert(c.rend() == std::rend(c));
+  assert(c.cend() == std::cend(c));
+  assert(c.crend() == std::crend(c));
+
+  assert(std::begin(c) != std::end(c));
+  assert(std::rbegin(c) != std::rend(c));
+  assert(std::cbegin(c) != std::cend(c));
+  assert(std::crbegin(c) != std::crend(c));
+#endif
+
+#if TEST_STD_VER >= 20
+  // P1614 + LWG3352
+  std::same_as<std::strong_ordering> decltype(auto) r1 = ii1 <=> ii2;
+  assert(r1 == std::strong_ordering::equal);
+
+  std::same_as<std::strong_ordering> decltype(auto) r2 = ii1 <=> ii2;
+  assert(r2 == std::strong_ordering::equal);
+#endif
+}
+
+TEST_CONSTEXPR_CXX14 bool test() {
+  test_type<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test_type<wchar_t>();
+#endif
+#ifndef TEST_HAS_NO_CHAR8_T
+  test_type<char8_t>();
+#endif
+  test_type<char16_t>();
+  test_type<char32_t>();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 14
+  static_assert(test(), "");
+#endif
+
+  return 0;
+}

libcxx/test/support/test_iterators.h

@@ -389,6 +389,8 @@ public:
     friend TEST_CONSTEXPR bool operator> (const contiguous_iterator& x, const contiguous_iterator& y) {return x.it_ >  y.it_;}
     friend TEST_CONSTEXPR bool operator>=(const contiguous_iterator& x, const contiguous_iterator& y) {return x.it_ >= y.it_;}
 
+    // Note no operator<=>, use three_way_contiguous_iterator for testing operator<=>
+
     friend TEST_CONSTEXPR It base(const contiguous_iterator& i) { return i.it_; }
 
     template <class T>