diff --git a/libcxx/include/concepts b/libcxx/include/concepts
--- a/libcxx/include/concepts
+++ b/libcxx/include/concepts
@@ -243,6 +243,88 @@
 concept move_constructible =
   constructible_from<_Tp, _Tp> && convertible_to<_Tp, _Tp>;
 
+// [concept.swappable]
+namespace ranges::__swap {
+  // Deleted to inhibit ADL
+  template<class _Tp>
+  void swap(_Tp&, _Tp&) = delete;
+
+  template<class _Tp>
+  concept __class_or_enum = is_class_v<_Tp> || is_enum_v<_Tp>;
+
+  // [1]
+  template<class _Tp, class _Up>
+  concept __unqualified_swappable_with =
+    (__class_or_enum<remove_cvref_t<_Tp>> || __class_or_enum<remove_cvref_t<_Up>>) &&
+    requires(_Tp&& __t, _Up&& __u) {
+      swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u));
+    };
+
+  struct __fn;
+
+  template<class _Tp, class _Up, size_t _Size>
+  concept __swappable_arrays =
+    !__unqualified_swappable_with<_Tp(&)[_Size], _Up(&)[_Size]> &&
+    extent_v<_Tp> == extent_v<_Up> &&
+    requires(_Tp(& __t)[_Size], _Up(& __u)[_Size], const __fn& __swap) {
+      __swap(__t[0], __u[0]);
+    };
+
+  template<class _Tp>
+  concept __exchangeable =
+    !__unqualified_swappable_with<_Tp&, _Tp&> &&
+    move_constructible<_Tp> &&
+    assignable_from<_Tp&, _Tp>;
+
+  struct __fn {
+    // 2.1   `S` is `(void)swap(E1, E2)`* if `E1` or `E2` has class or enumeration type and...
+    // *The name `swap` is used here unqualified.
+    template<class _Tp, class _Up>
+    requires __unqualified_swappable_with<_Tp, _Up>
+    constexpr void operator()(_Tp&& __t, _Up&& __u) const
+    noexcept(noexcept(swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+    {
+      swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u));
+    }
+
+    // 2.2   Otherwise, if `E1` and `E2` are lvalues of array types with equal extent and...
+    template<class _Tp, class _Up, size_t _Size>
+    requires __swappable_arrays<_Tp, _Up, _Size>
+    constexpr void operator()(_Tp(& __t)[_Size], _Up(& __u)[_Size]) const
+    noexcept(noexcept((*this)(*__t, *__u)))
+    {
+      for (size_t __i = 0; __i < _Size; ++__i) {
+        (*this)(__t[__i], __u[__i]);
+      }
+    }
+
+    // 2.3   Otherwise, if `E1` and `E2` are lvalues of the same type `T` that models...
+    template<__exchangeable _Tp>
+    constexpr void operator()(_Tp& __x, _Tp& __y) const
+    noexcept(is_nothrow_move_constructible_v<_Tp> && is_nothrow_move_assignable_v<_Tp>)
+    {
+      __y = _VSTD::exchange(__x, std::move(__y));
+    }
+  };
+}
+
+namespace ranges::inline __cpo {
+  inline constexpr auto swap = __swap::__fn{};
+}
+
+template<class _Tp>
+concept swappable = requires(_Tp& __a, _Tp& __b) { ranges::swap(__a, __b); };
+
+template<class _Tp, class _Up>
+concept swappable_with =
+  common_reference_with<_Tp&, _Up&> &&
+  requires(_Tp&& __t, _Up&& __u) {
+    ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Tp>(__t));
+    ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Up>(__u));
+    ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u));
+    ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Tp>(__t));
+  };
+
 // [concept.copyconstructible]
 template<class _Tp>
 concept copy_constructible =
diff --git a/libcxx/test/std/concepts/lang/swappable.h b/libcxx/test/std/concepts/lang/swappable.h
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/concepts/lang/swappable.h
@@ -0,0 +1,266 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 TEST_STD_CONCEPTS_LANG_SWAPPABLE_H
+#define TEST_STD_CONCEPTS_LANG_SWAPPABLE_H
+
+#include <concepts>
+
+// `adl_swappable` indicates it's been swapped using ADL by maintaining a pointer to itself that
+// isn't a part of the exchange. This is well-formed since we say that two `adl_swappable` objects
+// are equal only if their respective `value` subobjects are equal and their respective `this`
+// subobjects store the addresses of those respective `adl_swappable` objects.
+class lvalue_adl_swappable {
+public:
+  lvalue_adl_swappable() = default;
+
+  constexpr lvalue_adl_swappable(int value) noexcept : value_(value) {}
+
+  constexpr lvalue_adl_swappable(lvalue_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr lvalue_adl_swappable(lvalue_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr lvalue_adl_swappable&
+  operator=(lvalue_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(lvalue_adl_swappable& x,
+                             lvalue_adl_swappable& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool operator==(lvalue_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  lvalue_adl_swappable* this_ = this;
+};
+
+class lvalue_rvalue_adl_swappable {
+public:
+  lvalue_rvalue_adl_swappable() = default;
+
+  constexpr lvalue_rvalue_adl_swappable(int value) noexcept : value_(value) {}
+
+  constexpr
+  lvalue_rvalue_adl_swappable(lvalue_rvalue_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr
+  lvalue_rvalue_adl_swappable(lvalue_rvalue_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr lvalue_rvalue_adl_swappable&
+  operator=(lvalue_rvalue_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(lvalue_rvalue_adl_swappable& x,
+                             lvalue_rvalue_adl_swappable&& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool
+  operator==(lvalue_rvalue_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  lvalue_rvalue_adl_swappable* this_ = this;
+};
+
+class rvalue_lvalue_adl_swappable {
+public:
+  rvalue_lvalue_adl_swappable() = default;
+
+  constexpr rvalue_lvalue_adl_swappable(int value) noexcept : value_(value) {}
+
+  constexpr
+  rvalue_lvalue_adl_swappable(rvalue_lvalue_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr
+  rvalue_lvalue_adl_swappable(rvalue_lvalue_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr rvalue_lvalue_adl_swappable&
+  operator=(rvalue_lvalue_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(rvalue_lvalue_adl_swappable&& x,
+                             rvalue_lvalue_adl_swappable& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool
+  operator==(rvalue_lvalue_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  rvalue_lvalue_adl_swappable* this_ = this;
+};
+
+class rvalue_adl_swappable {
+public:
+  rvalue_adl_swappable() = default;
+
+  constexpr rvalue_adl_swappable(int value) noexcept : value_(value) {}
+
+  constexpr rvalue_adl_swappable(rvalue_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr rvalue_adl_swappable(rvalue_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr rvalue_adl_swappable&
+  operator=(rvalue_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(rvalue_adl_swappable&& x,
+                             rvalue_adl_swappable&& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool operator==(rvalue_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  rvalue_adl_swappable* this_ = this;
+};
+
+class non_move_constructible_adl_swappable {
+public:
+  non_move_constructible_adl_swappable() = default;
+
+  constexpr non_move_constructible_adl_swappable(int value) noexcept
+      : value_(value) {}
+
+  constexpr non_move_constructible_adl_swappable(
+      non_move_constructible_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr non_move_constructible_adl_swappable(
+      non_move_constructible_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr non_move_constructible_adl_swappable&
+  operator=(non_move_constructible_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(non_move_constructible_adl_swappable& x,
+                             non_move_constructible_adl_swappable& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool
+  operator==(non_move_constructible_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  non_move_constructible_adl_swappable* this_ = this;
+};
+
+class non_move_assignable_adl_swappable {
+public:
+  non_move_assignable_adl_swappable() = default;
+
+  constexpr non_move_assignable_adl_swappable(int value) noexcept
+      : value_(value) {}
+
+  non_move_assignable_adl_swappable(non_move_assignable_adl_swappable&& other) =
+      delete;
+
+  constexpr non_move_assignable_adl_swappable(
+      non_move_assignable_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr non_move_assignable_adl_swappable&
+  operator=(non_move_assignable_adl_swappable&& other) noexcept = delete;
+
+  constexpr friend void swap(non_move_assignable_adl_swappable& x,
+                             non_move_assignable_adl_swappable& y) noexcept {
+    std::ranges::swap(x.value_, y.value_);
+  }
+
+  constexpr bool
+  operator==(non_move_assignable_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  non_move_assignable_adl_swappable* this_ = this;
+};
+
+class throwable_adl_swappable {
+public:
+  throwable_adl_swappable() = default;
+
+  constexpr throwable_adl_swappable(int value) noexcept : value_(value) {}
+
+  constexpr throwable_adl_swappable(throwable_adl_swappable&& other) noexcept
+      : value_(std::move(other.value_)),
+        this_(this) {}
+
+  constexpr
+  throwable_adl_swappable(throwable_adl_swappable const& other) noexcept
+      : value_(other.value_),
+        this_(this) {}
+
+  constexpr throwable_adl_swappable&
+  operator=(throwable_adl_swappable other) noexcept {
+    value_ = other.value_;
+    return *this;
+  }
+
+  constexpr friend void swap(throwable_adl_swappable& X,
+                             throwable_adl_swappable& Y) noexcept(false) {
+    std::ranges::swap(X.value_, Y.value_);
+  }
+
+  constexpr bool
+  operator==(throwable_adl_swappable const& other) const noexcept {
+    return value_ == other.value_ && this_ == this && other.this_ == &other;
+  }
+
+private:
+  int value_{};
+  throwable_adl_swappable* this_ = this;
+};
+
+#endif // TEST_STD_CONCEPTS_LANG_SWAPPABLE_H
diff --git a/libcxx/test/std/concepts/lang/swappable.pass.cpp b/libcxx/test/std/concepts/lang/swappable.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/concepts/lang/swappable.pass.cpp
@@ -0,0 +1,291 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class T>
+// concept swappable = // see below
+
+#include <concepts>
+
+#include <algorithm>
+#include <cassert>
+#include <deque>
+#include <map>
+#include <memory>
+#include <string>
+#include <optional>
+#include <unordered_map>
+#include <vector>
+
+#include "test_macros.h"
+#include "swappable.h"
+
+template <class T>
+struct expected {
+  T x;
+  T y;
+};
+
+// clang-format off
+// Checks [concept.swappable]/2.1
+template <class T, class U>
+requires std::same_as<std::remove_cvref_t<T>, std::remove_cvref_t<U> > &&
+         std::swappable<std::remove_cvref_t<T> >
+constexpr bool check_swap_21(T&& x, U&& y) {
+  expected<std::remove_cvref_t<T> > const e{y, x};
+  std::ranges::swap(std::forward<T>(x), std::forward<U>(y));
+  return x == e.x && y == e.y;
+}
+
+// Checks [concept.swappable]/2.2
+template <std::swappable T, std::size_t N>
+constexpr bool check_swap_22(T (&x)[N], T (&y)[N]) {
+  expected<T[N]> e;
+  std::copy(y, y + N, e.x);
+  std::copy(x, x + N, e.y);
+
+  std::ranges::swap(x, y);
+  return std::equal(x, x + N, e.x, e.x + N) &&
+         std::equal(y, y + N, e.y, e.y + N);
+}
+
+// Checks [concept.swappable]/2.3
+template <std::swappable T>
+requires std::copy_constructible<std::remove_cvref_t<T> >
+constexpr bool check_swap_23(T x, T y) {
+  expected<std::remove_cvref_t<T> > const e{y, x};
+  std::ranges::swap(x, y);
+  return x == e.x && y == e.y;
+}
+// clang-format on
+
+constexpr bool check_lvalue_adl_swappable() {
+  auto x = lvalue_adl_swappable(0);
+  auto y = lvalue_adl_swappable(1);
+  constexpr auto is_noexcept = noexcept(std::ranges::swap(x, y));
+  return check_swap_21(x, y) && is_noexcept;
+}
+static_assert(check_lvalue_adl_swappable());
+
+constexpr bool check_rvalue_adl_swappable() {
+  constexpr auto is_noexcept = noexcept(
+      std::ranges::swap(rvalue_adl_swappable(0), rvalue_adl_swappable(1)));
+  return check_swap_21(rvalue_adl_swappable(0), rvalue_adl_swappable(1)) &&
+         is_noexcept;
+}
+static_assert(check_rvalue_adl_swappable());
+
+constexpr bool check_lvalue_rvalue_adl_swappable() {
+  auto x = lvalue_rvalue_adl_swappable(0);
+  constexpr auto is_noexcept =
+      noexcept(std::ranges::swap(x, lvalue_rvalue_adl_swappable(1)));
+  return check_swap_21(x, lvalue_rvalue_adl_swappable(1)) && is_noexcept;
+}
+static_assert(check_lvalue_rvalue_adl_swappable());
+
+constexpr bool check_rvalue_lvalue_adl_swappable() {
+  auto x = rvalue_lvalue_adl_swappable(0);
+  constexpr auto is_noexcept =
+      noexcept(std::ranges::swap(rvalue_lvalue_adl_swappable(1), x));
+  return check_swap_21(rvalue_lvalue_adl_swappable(1), x) && is_noexcept;
+}
+static_assert(check_rvalue_lvalue_adl_swappable());
+
+constexpr bool check_throwable_swappable() {
+  auto x = throwable_adl_swappable{0};
+  auto y = throwable_adl_swappable{1};
+  constexpr auto not_noexcept = !noexcept(std::ranges::swap(x, y));
+  return check_swap_21(x, y) && not_noexcept;
+}
+static_assert(check_throwable_swappable());
+
+constexpr bool check_non_move_constructible_adl_swappable() {
+  auto x = non_move_constructible_adl_swappable{0};
+  auto y = non_move_constructible_adl_swappable{1};
+  constexpr auto is_noexcept = noexcept(std::ranges::swap(x, y));
+  return check_swap_21(x, y) && is_noexcept;
+}
+static_assert(check_non_move_constructible_adl_swappable());
+
+constexpr bool check_non_move_assignable_adl_swappable() {
+  auto x = non_move_assignable_adl_swappable{0};
+  auto y = non_move_assignable_adl_swappable{1};
+  return check_swap_21(x, y) && noexcept(std::ranges::swap(x, y));
+}
+static_assert(check_non_move_assignable_adl_swappable());
+
+namespace swappable_namespace {
+enum unscoped { hello, world };
+void swap(unscoped&, unscoped&);
+
+enum class scoped { hello, world };
+void swap(scoped&, scoped&);
+} // namespace swappable_namespace
+
+static_assert(std::swappable<swappable_namespace::unscoped>);
+static_assert(std::swappable<swappable_namespace::scoped>);
+
+constexpr bool check_swap_arrays() {
+  int x[] = {0, 1, 2, 3, 4};
+  int y[] = {5, 6, 7, 8, 9};
+  return check_swap_22(x, y) && noexcept(std::ranges::swap(x, y));
+}
+static_assert(check_swap_arrays());
+
+constexpr bool check_lvalue_adl_swappable_arrays() {
+  lvalue_adl_swappable x[] = {{0}, {1}, {2}, {3}};
+  lvalue_adl_swappable y[] = {{4}, {5}, {6}, {7}};
+  return check_swap_22(x, y) && noexcept(std::ranges::swap(x, y));
+}
+static_assert(check_lvalue_adl_swappable_arrays());
+
+constexpr bool check_throwable_adl_swappable_arrays() {
+  throwable_adl_swappable x[] = {{0}, {1}, {2}, {3}};
+  throwable_adl_swappable y[] = {{4}, {5}, {6}, {7}};
+  return check_swap_22(x, y) && !noexcept(std::ranges::swap(x, y));
+}
+static_assert(check_throwable_adl_swappable_arrays());
+
+inline auto global_x = 0;
+static_assert(check_swap_23(0, 0) &&
+              noexcept(std::ranges::swap(global_x, global_x)));
+static_assert(check_swap_23(0, 1) &&
+              noexcept(std::ranges::swap(global_x, global_x)));
+static_assert(check_swap_23(1, 0) &&
+              noexcept(std::ranges::swap(global_x, global_x)));
+
+constexpr bool check_swappable_references() {
+  int x = 42;
+  int y = 64;
+  return check_swap_23<int&>(x, y) && noexcept(std::ranges::swap(x, y));
+}
+static_assert(check_swappable_references());
+
+constexpr bool check_swappable_pointers() {
+  char const* x = "hello";
+  return check_swap_23<char const*>(x, nullptr) &&
+         noexcept(std::ranges::swap(x, x));
+}
+static_assert(check_swappable_pointers());
+
+// All tests for std::swappable<T> are implicitly confirmed by `check_swap`, so we only need to
+// sanity check for a few positive cases.
+static_assert(std::swappable<int volatile&>);
+static_assert(std::swappable<int&&>);
+static_assert(std::swappable<int (*)()>);
+static_assert(std::swappable<int rvalue_adl_swappable::*>);
+static_assert(std::swappable<int (rvalue_adl_swappable::*)()>);
+static_assert(std::swappable<std::unique_ptr<int> >);
+
+static_assert(!std::swappable<void>);
+static_assert(!std::swappable<int const>);
+static_assert(!std::swappable<int const&>);
+static_assert(!std::swappable<int const&&>);
+static_assert(!std::swappable<int const volatile>);
+static_assert(!std::swappable<int const volatile&>);
+static_assert(!std::swappable<int const volatile&&>);
+static_assert(!std::swappable<int (&)()>);
+
+struct non_move_constructible {
+  non_move_constructible(non_move_constructible&&) = delete;
+  non_move_constructible& operator=(non_move_constructible&&);
+};
+static_assert(!std::move_constructible<non_move_constructible>);
+static_assert(
+    std::assignable_from<non_move_constructible&, non_move_constructible>);
+static_assert(!std::swappable<non_move_constructible>);
+
+struct non_move_assignable {
+  non_move_assignable(non_move_assignable&&);
+  non_move_assignable& operator=(non_move_assignable&&) = delete;
+};
+static_assert(std::move_constructible<non_move_assignable>);
+static_assert(!std::assignable_from<non_move_assignable&, non_move_assignable>);
+static_assert(!std::swappable<non_move_assignable>);
+
+using swap_type = std::remove_const_t<decltype(std::ranges::swap)>;
+static_assert(std::default_initializable<swap_type>);
+static_assert(std::move_constructible<swap_type>);
+static_assert(std::copy_constructible<swap_type>);
+static_assert(std::assignable_from<swap_type&, swap_type>);
+static_assert(std::assignable_from<swap_type&, swap_type&>);
+static_assert(std::assignable_from<swap_type&, swap_type const&>);
+static_assert(std::assignable_from<swap_type&, swap_type const>);
+static_assert(std::swappable<swap_type>);
+
+template <bool is_noexcept, std::swappable T>
+void check_swap(expected<T> const& e) {
+  auto a = e.y;
+  auto b = e.x;
+
+  std::ranges::swap(a, b);
+  assert(a == e.x);
+  assert(b == e.y);
+
+  std::ranges::swap(a, b);
+  assert(a == e.y);
+  assert(b == e.x);
+
+  static_assert(noexcept(std::ranges::swap(a, b)) == is_noexcept);
+}
+
+int main(int, char**) {
+  {
+    auto const e = expected<std::deque<int> >{
+        .x = {6, 7, 8, 9},
+        .y = {0, 1, 2, 3, 4, 5},
+    };
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  {
+    auto const e = expected<std::map<int, std::string> >{
+        .x = {{0, "whole"}, {1, "cashews"}},
+        .y = {{-1, "roasted"}, {2, "&"}, {-3, "salted"}},
+    };
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  {
+    auto const e = expected<std::string>{
+        .x = "hello there",
+        .y = "general kenobi",
+    };
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  {
+    auto const e = expected<std::optional<lvalue_adl_swappable> >{
+        .x = {10},
+        .y = {20},
+    };
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  {
+    auto const e = expected<std::optional<throwable_adl_swappable> >{
+        .x = {10},
+        .y = {20},
+    };
+    check_swap</*is_noexcept=*/false>(e);
+  }
+  {
+    auto const e = expected<std::unordered_map<int, std::string> >{
+        .x = {{0, "whole"}, {1, "cashews"}},
+        .y = {{-1, "roasted"}, {2, "&"}, {-3, "salted"}},
+    };
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  {
+    auto const e = expected<std::vector<int> >{
+        .x = {0, 1, 2, 3, 4, 5},
+        .y = {6, 7, 8, 9},
+    };
+
+    check_swap</*is_noexcept=*/true>(e);
+  }
+  return 0;
+}
diff --git a/libcxx/test/std/concepts/lang/swappable_with.compile.pass.cpp b/libcxx/test/std/concepts/lang/swappable_with.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/concepts/lang/swappable_with.compile.pass.cpp
@@ -0,0 +1,613 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class T, class U>
+// concept swappable_with = // see below
+
+#include <concepts>
+
+#include <array>
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <memory>
+#include <mutex>
+#include <optional>
+#include <set>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "swappable.h"
+
+template <class T, class U>
+constexpr bool check_swappable_with_impl() {
+  static_assert(std::swappable_with<T, U> == std::swappable_with<U, T>);
+  return std::swappable_with<T, U>;
+}
+
+template <class T, class U>
+constexpr bool check_swappable_with() {
+  static_assert(!check_swappable_with_impl<T, U>());
+  static_assert(!check_swappable_with_impl<T, U const>());
+  static_assert(!check_swappable_with_impl<T const, U>());
+  static_assert(!check_swappable_with_impl<T const, U const>());
+
+  static_assert(!check_swappable_with_impl<T, U&>());
+  static_assert(!check_swappable_with_impl<T, U const&>());
+  static_assert(!check_swappable_with_impl<T, U volatile&>());
+  static_assert(!check_swappable_with_impl<T, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T const, U&>());
+  static_assert(!check_swappable_with_impl<T const, U const&>());
+  static_assert(!check_swappable_with_impl<T const, U volatile&>());
+  static_assert(!check_swappable_with_impl<T const, U const volatile&>());
+
+  static_assert(!check_swappable_with_impl<T&, U>());
+  static_assert(!check_swappable_with_impl<T&, U const>());
+  static_assert(!check_swappable_with_impl<T const&, U>());
+  static_assert(!check_swappable_with_impl<T const&, U const>());
+  static_assert(!check_swappable_with_impl<T volatile&, U>());
+  static_assert(!check_swappable_with_impl<T volatile&, U const>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U const>());
+
+  static_assert(!check_swappable_with_impl<T&, U const&>());
+  static_assert(!check_swappable_with_impl<T&, U volatile&>());
+  static_assert(!check_swappable_with_impl<T&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T const&, U&>());
+  static_assert(!check_swappable_with_impl<T const&, U const&>());
+  static_assert(!check_swappable_with_impl<T const&, U volatile&>());
+  static_assert(!check_swappable_with_impl<T const&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U const&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U const&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U volatile&>());
+  static_assert(
+      !check_swappable_with_impl<T const volatile&, U const volatile&>());
+
+  static_assert(!check_swappable_with_impl<T, U&&>());
+  static_assert(!check_swappable_with_impl<T, U const&&>());
+  static_assert(!check_swappable_with_impl<T, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T const, U&&>());
+  static_assert(!check_swappable_with_impl<T const, U const&&>());
+  static_assert(!check_swappable_with_impl<T const, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T const, U const volatile&&>());
+
+  static_assert(!check_swappable_with_impl<T&&, U>());
+  static_assert(!check_swappable_with_impl<T&&, U const>());
+  static_assert(!check_swappable_with_impl<T const&&, U>());
+  static_assert(!check_swappable_with_impl<T const&&, U const>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U const>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U const>());
+
+  static_assert(!check_swappable_with_impl<T&, U&&>());
+  static_assert(!check_swappable_with_impl<T&, U const&&>());
+  static_assert(!check_swappable_with_impl<T&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T const&, U&&>());
+  static_assert(!check_swappable_with_impl<T const&, U const&&>());
+  static_assert(!check_swappable_with_impl<T const&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T const&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U&&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U const&&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T volatile&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U const&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&, U volatile&&>());
+  static_assert(
+      !check_swappable_with_impl<T const volatile&, U const volatile&&>());
+
+  static_assert(!check_swappable_with_impl<T&&, U&>());
+  static_assert(!check_swappable_with_impl<T&&, U const&>());
+  static_assert(!check_swappable_with_impl<T&&, U volatile&>());
+  static_assert(!check_swappable_with_impl<T&&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T const&&, U&>());
+  static_assert(!check_swappable_with_impl<T const&&, U const&>());
+  static_assert(!check_swappable_with_impl<T const&&, U volatile&>());
+  static_assert(!check_swappable_with_impl<T const&&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U const&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U volatile&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U const volatile&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U const&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U volatile&>());
+  static_assert(
+      !check_swappable_with_impl<T const volatile&&, U const volatile&>());
+
+  static_assert(!check_swappable_with_impl<T&&, U&&>());
+  static_assert(!check_swappable_with_impl<T&&, U const&&>());
+  static_assert(!check_swappable_with_impl<T&&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T&&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T const&&, U&&>());
+  static_assert(!check_swappable_with_impl<T const&&, U const&&>());
+  static_assert(!check_swappable_with_impl<T const&&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T const&&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U&&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U const&&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U volatile&&>());
+  static_assert(!check_swappable_with_impl<T volatile&&, U const volatile&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U const&&>());
+  static_assert(!check_swappable_with_impl<T const volatile&&, U volatile&&>());
+  static_assert(
+      !check_swappable_with_impl<T const volatile&&, U const volatile&&>());
+  return check_swappable_with_impl<T&, U&>();
+}
+
+template <class T, class U>
+constexpr bool check_swappable_with_including_lvalue_ref_to_volatile() {
+  constexpr auto result = check_swappable_with<T, U>();
+  static_assert(check_swappable_with_impl<T volatile&, U volatile&>() ==
+                result);
+  return result;
+}
+
+namespace fundamental {
+static_assert(
+    check_swappable_with_including_lvalue_ref_to_volatile<int, int>());
+static_assert(
+    check_swappable_with_including_lvalue_ref_to_volatile<double, double>());
+static_assert(
+    !check_swappable_with_including_lvalue_ref_to_volatile<int, double>());
+
+static_assert(
+    check_swappable_with_including_lvalue_ref_to_volatile<int*, int*>());
+static_assert(
+    !check_swappable_with_including_lvalue_ref_to_volatile<int, int*>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (*)(), int (*)()>());
+static_assert(
+    !check_swappable_with_including_lvalue_ref_to_volatile<int, int (*)()>());
+
+struct S {};
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<int, S>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int S::*, int S::*>());
+static_assert(
+    !check_swappable_with_including_lvalue_ref_to_volatile<int, int S::*>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)(), int (S::*)()>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int, int (S::*)()>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() noexcept, int (S::*)() noexcept>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() noexcept, int (S::*)()>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const, int (S::*)() const>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const, int (S::*)()>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const noexcept, int (S::*)() const noexcept>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const, int (S::*)() const noexcept>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() volatile, int (S::*)() volatile>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() volatile, int (S::*)()>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const volatile, int (S::*)() const volatile>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int (S::*)() const volatile, int (S::*)()>());
+
+static_assert(
+    check_swappable_with_including_lvalue_ref_to_volatile<int[5], int[5]>());
+static_assert(
+    !check_swappable_with_including_lvalue_ref_to_volatile<int[5], int[6]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5], double[5]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5], double[6]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<int[5][6],
+                                                                     int[5]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<int[5][6],
+                                                                     int[6]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], double[5]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], double[6]>());
+static_assert(check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], int[5][6]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], int[5][4]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], int[6][5]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], double[5][6]>());
+static_assert(!check_swappable_with_including_lvalue_ref_to_volatile<
+              int[5][6], double[6][5]>());
+
+// always false
+static_assert(!check_swappable_with_impl<void, void>());
+static_assert(!check_swappable_with_impl<int, void>());
+static_assert(!check_swappable_with_impl<int&, void>());
+static_assert(!check_swappable_with_impl<void, int>());
+static_assert(!check_swappable_with_impl<void, int&>());
+static_assert(!check_swappable_with_impl<int, int()>());
+static_assert(!check_swappable_with_impl<int, int (&)()>());
+} // namespace fundamental
+
+namespace adl {
+static_assert(
+    check_swappable_with<lvalue_adl_swappable, lvalue_adl_swappable>());
+static_assert(check_swappable_with<lvalue_rvalue_adl_swappable,
+                                   lvalue_rvalue_adl_swappable>());
+static_assert(check_swappable_with<rvalue_lvalue_adl_swappable,
+                                   rvalue_lvalue_adl_swappable>());
+static_assert(
+    check_swappable_with_impl<rvalue_adl_swappable, rvalue_adl_swappable>());
+static_assert(!check_swappable_with_impl<lvalue_rvalue_adl_swappable&,
+                                         lvalue_rvalue_adl_swappable&&>());
+
+struct s1 {};
+struct no_common_reference_with_s1 {
+  friend void swap(s1&, no_common_reference_with_s1&);
+  friend void swap(no_common_reference_with_s1&, s1&);
+};
+static_assert(!check_swappable_with<s1, no_common_reference_with_s1>());
+
+struct one_way_swappable_with_s1 {
+  friend void swap(s1&, one_way_swappable_with_s1&);
+  operator s1();
+};
+static_assert(std::common_reference_with<one_way_swappable_with_s1, s1>);
+static_assert(!check_swappable_with<one_way_swappable_with_s1, s1>());
+
+struct one_way_swappable_with_s1_other_way {
+  friend void swap(one_way_swappable_with_s1_other_way&, s1&);
+  operator s1();
+};
+static_assert(
+    std::common_reference_with<one_way_swappable_with_s1_other_way, s1>);
+static_assert(!check_swappable_with<one_way_swappable_with_s1_other_way, s1>());
+
+struct can_swap_with_s1_but_not_swappable {
+  can_swap_with_s1_but_not_swappable(can_swap_with_s1_but_not_swappable&&) =
+      delete;
+  friend void swap(s1&, can_swap_with_s1_but_not_swappable&);
+  friend void swap(can_swap_with_s1_but_not_swappable&, s1&);
+
+  operator s1() const;
+};
+static_assert(
+    std::common_reference_with<can_swap_with_s1_but_not_swappable, s1>);
+static_assert(!std::swappable<can_swap_with_s1_but_not_swappable>);
+static_assert(
+    !check_swappable_with<can_swap_with_s1_but_not_swappable&, s1&>());
+
+struct swappable_with_s1 {
+  friend void swap(s1&, swappable_with_s1&);
+  friend void swap(swappable_with_s1&, s1&);
+  operator s1() const;
+};
+static_assert(check_swappable_with<swappable_with_s1, s1>());
+
+struct swappable_with_const_s1_but_not_swappable {
+  swappable_with_const_s1_but_not_swappable(
+      swappable_with_const_s1_but_not_swappable const&);
+  swappable_with_const_s1_but_not_swappable(
+      swappable_with_const_s1_but_not_swappable const&&);
+  swappable_with_const_s1_but_not_swappable&
+  operator=(swappable_with_const_s1_but_not_swappable const&);
+  swappable_with_const_s1_but_not_swappable&
+  operator=(swappable_with_const_s1_but_not_swappable const&&);
+
+  friend void swap(s1 const&, swappable_with_const_s1_but_not_swappable const&);
+  friend void swap(swappable_with_const_s1_but_not_swappable const&, s1 const&);
+
+  operator s1 const &() const;
+};
+static_assert(
+    !std::swappable<swappable_with_const_s1_but_not_swappable const&>);
+static_assert(!std::swappable_with<
+              swappable_with_const_s1_but_not_swappable const&, s1 const&>);
+
+struct swappable_with_volatile_s1_but_not_swappable {
+  swappable_with_volatile_s1_but_not_swappable(
+      swappable_with_volatile_s1_but_not_swappable volatile&);
+  swappable_with_volatile_s1_but_not_swappable(
+      swappable_with_volatile_s1_but_not_swappable volatile&&);
+  swappable_with_volatile_s1_but_not_swappable&
+  operator=(swappable_with_volatile_s1_but_not_swappable volatile&);
+  swappable_with_volatile_s1_but_not_swappable&
+  operator=(swappable_with_volatile_s1_but_not_swappable volatile&&);
+
+  friend void swap(s1 volatile&,
+                   swappable_with_volatile_s1_but_not_swappable volatile&);
+  friend void swap(swappable_with_volatile_s1_but_not_swappable volatile&,
+                   s1 volatile&);
+
+  operator s1 volatile &() volatile;
+};
+static_assert(
+    !std::swappable<swappable_with_volatile_s1_but_not_swappable volatile&>);
+static_assert(
+    !std::swappable_with<swappable_with_volatile_s1_but_not_swappable volatile&,
+                         s1 volatile&>);
+
+struct swappable_with_cv_s1_but_not_swappable {
+  swappable_with_cv_s1_but_not_swappable(
+      swappable_with_cv_s1_but_not_swappable const volatile&);
+  swappable_with_cv_s1_but_not_swappable(
+      swappable_with_cv_s1_but_not_swappable const volatile&&);
+  swappable_with_cv_s1_but_not_swappable&
+  operator=(swappable_with_cv_s1_but_not_swappable const volatile&);
+  swappable_with_cv_s1_but_not_swappable&
+  operator=(swappable_with_cv_s1_but_not_swappable const volatile&&);
+
+  friend void swap(s1 const volatile&,
+                   swappable_with_cv_s1_but_not_swappable const volatile&);
+  friend void swap(swappable_with_cv_s1_but_not_swappable const volatile&,
+                   s1 const volatile&);
+
+  operator s1 const volatile &() const volatile;
+};
+static_assert(
+    !std::swappable<swappable_with_cv_s1_but_not_swappable const volatile&>);
+static_assert(
+    !std::swappable_with<swappable_with_cv_s1_but_not_swappable const volatile&,
+                         s1 const volatile&>);
+
+struct s2 {
+  friend void swap(s2 const&, s2 const&);
+  friend void swap(s2 volatile&, s2 volatile&);
+  friend void swap(s2 const volatile&, s2 const volatile&);
+};
+
+struct swappable_with_const_s2 {
+  swappable_with_const_s2(swappable_with_const_s2 const&);
+  swappable_with_const_s2(swappable_with_const_s2 const&&);
+  swappable_with_const_s2& operator=(swappable_with_const_s2 const&);
+  swappable_with_const_s2& operator=(swappable_with_const_s2 const&&);
+
+  friend void swap(swappable_with_const_s2 const&,
+                   swappable_with_const_s2 const&);
+  friend void swap(s2 const&, swappable_with_const_s2 const&);
+  friend void swap(swappable_with_const_s2 const&, s2 const&);
+
+  operator s2 const &() const;
+};
+static_assert(std::swappable_with<swappable_with_const_s2 const&, s2 const&>);
+
+struct swappable_with_volatile_s2 {
+  swappable_with_volatile_s2(swappable_with_volatile_s2 volatile&);
+  swappable_with_volatile_s2(swappable_with_volatile_s2 volatile&&);
+  swappable_with_volatile_s2& operator=(swappable_with_volatile_s2 volatile&);
+  swappable_with_volatile_s2& operator=(swappable_with_volatile_s2 volatile&&);
+
+  friend void swap(swappable_with_volatile_s2 volatile&,
+                   swappable_with_volatile_s2 volatile&);
+  friend void swap(s2 volatile&, swappable_with_volatile_s2 volatile&);
+  friend void swap(swappable_with_volatile_s2 volatile&, s2 volatile&);
+
+  operator s2 volatile &() volatile;
+};
+static_assert(
+    std::swappable_with<swappable_with_volatile_s2 volatile&, s2 volatile&>);
+
+struct swappable_with_cv_s2 {
+  swappable_with_cv_s2(swappable_with_cv_s2 const volatile&);
+  swappable_with_cv_s2(swappable_with_cv_s2 const volatile&&);
+  swappable_with_cv_s2& operator=(swappable_with_cv_s2 const volatile&);
+  swappable_with_cv_s2& operator=(swappable_with_cv_s2 const volatile&&);
+
+  friend void swap(swappable_with_cv_s2 const volatile&,
+                   swappable_with_cv_s2 const volatile&);
+  friend void swap(s2 const volatile&, swappable_with_cv_s2 const volatile&);
+  friend void swap(swappable_with_cv_s2 const volatile&, s2 const volatile&);
+
+  operator s2 const volatile &() const volatile;
+};
+static_assert(std::swappable_with<swappable_with_cv_s2 const volatile&,
+                                  s2 const volatile&>);
+
+struct swappable_with_rvalue_ref_to_s1_but_not_swappable {
+  friend void swap(swappable_with_rvalue_ref_to_s1_but_not_swappable&&,
+                   swappable_with_rvalue_ref_to_s1_but_not_swappable&&);
+  friend void swap(s1&&, swappable_with_rvalue_ref_to_s1_but_not_swappable&&);
+  friend void swap(swappable_with_rvalue_ref_to_s1_but_not_swappable&&, s1&&);
+
+  operator s1() const;
+};
+static_assert(
+    !std::swappable<swappable_with_rvalue_ref_to_s1_but_not_swappable const&&>);
+static_assert(
+    !std::swappable_with<
+        swappable_with_rvalue_ref_to_s1_but_not_swappable const&&, s1 const&&>);
+
+struct swappable_with_rvalue_ref_to_const_s1_but_not_swappable {
+  friend void
+  swap(s1 const&&,
+       swappable_with_rvalue_ref_to_const_s1_but_not_swappable const&&);
+  friend void
+  swap(swappable_with_rvalue_ref_to_const_s1_but_not_swappable const&&,
+       s1 const&&);
+
+  operator s1 const() const;
+};
+static_assert(!std::swappable<
+              swappable_with_rvalue_ref_to_const_s1_but_not_swappable const&&>);
+static_assert(!std::swappable_with<
+              swappable_with_rvalue_ref_to_const_s1_but_not_swappable const&&,
+              s1 const&&>);
+
+struct swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable {
+  swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable(
+      swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&);
+  swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable(
+      swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&);
+  swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable& operator=(
+      swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&);
+  swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable& operator=(
+      swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&);
+
+  friend void
+  swap(s1 volatile&&,
+       swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&);
+  friend void
+  swap(swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&,
+       s1 volatile&&);
+
+  operator s1 volatile &&() volatile&&;
+};
+static_assert(
+    !std::swappable<
+        swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&>);
+static_assert(
+    !std::swappable_with<
+        swappable_with_rvalue_ref_to_volatile_s1_but_not_swappable volatile&&,
+        s1 volatile&&>);
+
+struct swappable_with_rvalue_ref_to_cv_s1_but_not_swappable {
+  swappable_with_rvalue_ref_to_cv_s1_but_not_swappable(
+      swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&);
+  swappable_with_rvalue_ref_to_cv_s1_but_not_swappable(
+      swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&);
+  swappable_with_rvalue_ref_to_cv_s1_but_not_swappable& operator=(
+      swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&);
+  swappable_with_rvalue_ref_to_cv_s1_but_not_swappable& operator=(
+      swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&);
+
+  friend void
+  swap(s1 const volatile&&,
+       swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&);
+  friend void
+  swap(swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&,
+       s1 const volatile&&);
+
+  operator s1 const volatile &&() const volatile&&;
+};
+static_assert(
+    !std::swappable<
+        swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&>);
+static_assert(
+    !std::swappable_with<
+        swappable_with_rvalue_ref_to_cv_s1_but_not_swappable const volatile&&,
+        s1 const volatile&&>);
+
+struct s3 {
+  friend void swap(s3&&, s3&&);
+  friend void swap(s3 const&&, s3 const&&);
+  friend void swap(s3 volatile&&, s3 volatile&&);
+  friend void swap(s3 const volatile&&, s3 const volatile&&);
+};
+
+struct swappable_with_rvalue_ref_to_s3 {
+  friend void swap(swappable_with_rvalue_ref_to_s3&&,
+                   swappable_with_rvalue_ref_to_s3&&);
+  friend void swap(s3&&, swappable_with_rvalue_ref_to_s3&&);
+  friend void swap(swappable_with_rvalue_ref_to_s3&&, s3&&);
+
+  operator s3() const;
+};
+static_assert(std::swappable_with<swappable_with_rvalue_ref_to_s3&&, s3&&>);
+
+struct swappable_with_rvalue_ref_to_const_s3 {
+  swappable_with_rvalue_ref_to_const_s3(
+      swappable_with_rvalue_ref_to_const_s3 const&);
+  swappable_with_rvalue_ref_to_const_s3(
+      swappable_with_rvalue_ref_to_const_s3 const&&);
+  swappable_with_rvalue_ref_to_const_s3&
+  operator=(swappable_with_rvalue_ref_to_const_s3 const&);
+  swappable_with_rvalue_ref_to_const_s3&
+  operator=(swappable_with_rvalue_ref_to_const_s3 const&&);
+
+  friend void swap(swappable_with_rvalue_ref_to_const_s3 const&&,
+                   swappable_with_rvalue_ref_to_const_s3 const&&);
+  friend void swap(s3 const&&, swappable_with_rvalue_ref_to_const_s3 const&&);
+  friend void swap(swappable_with_rvalue_ref_to_const_s3 const&&, s3 const&&);
+
+  operator s3() const;
+};
+static_assert(std::swappable_with<swappable_with_rvalue_ref_to_const_s3 const&&,
+                                  s3 const&&>);
+
+struct swappable_with_rvalue_ref_to_volatile_s3 {
+  swappable_with_rvalue_ref_to_volatile_s3(
+      swappable_with_rvalue_ref_to_volatile_s3 volatile&);
+  swappable_with_rvalue_ref_to_volatile_s3(
+      swappable_with_rvalue_ref_to_volatile_s3 volatile&&);
+  swappable_with_rvalue_ref_to_volatile_s3&
+  operator=(swappable_with_rvalue_ref_to_volatile_s3 volatile&);
+  swappable_with_rvalue_ref_to_volatile_s3&
+  operator=(swappable_with_rvalue_ref_to_volatile_s3 volatile&&);
+
+  friend void swap(swappable_with_rvalue_ref_to_volatile_s3 volatile&&,
+                   swappable_with_rvalue_ref_to_volatile_s3 volatile&&);
+  friend void swap(s3 volatile&&,
+                   swappable_with_rvalue_ref_to_volatile_s3 volatile&&);
+  friend void swap(swappable_with_rvalue_ref_to_volatile_s3 volatile&&,
+                   s3 volatile&&);
+
+  operator s3 volatile &() volatile;
+};
+static_assert(
+    std::swappable_with<swappable_with_rvalue_ref_to_volatile_s3 volatile&&,
+                        s3 volatile&&>);
+
+// struct swappable_with_cv_s2 {
+//   swappable_with_cv_s2(swappable_with_cv_s2 const volatile&);
+//   swappable_with_cv_s2(swappable_with_cv_s2 const volatile&&);
+//   swappable_with_cv_s2& operator=(swappable_with_cv_s2 const volatile&);
+//   swappable_with_cv_s2& operator=(swappable_with_cv_s2 const volatile&&);
+
+//   friend void swap(swappable_with_cv_s2 const volatile&, swappable_with_cv_s2 const volatile&);
+//   friend void swap(s2 const volatile&, swappable_with_cv_s2 const volatile&);
+//   friend void swap(swappable_with_cv_s2 const volatile&, s2 const volatile&);
+
+//   operator s2 const volatile&() const volatile;
+// };
+// static_assert(std::swappable_with<swappable_with_cv_s2 const volatile&, s2 const volatile&>);
+} // namespace adl
+
+namespace standard_types {
+static_assert(
+    check_swappable_with<std::array<int, 10>, std::array<int, 10> >());
+static_assert(
+    !check_swappable_with<std::array<int, 10>, std::array<double, 10> >());
+static_assert(check_swappable_with<std::deque<int>, std::deque<int> >());
+static_assert(!check_swappable_with<std::deque<int>, std::vector<int> >());
+static_assert(
+    check_swappable_with<std::forward_list<int>, std::forward_list<int> >());
+static_assert(
+    !check_swappable_with<std::forward_list<int>, std::vector<int> >());
+static_assert(check_swappable_with<std::list<int>, std::list<int> >());
+static_assert(!check_swappable_with<std::list<int>, std::vector<int> >());
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+static_assert(!check_swappable_with<std::lock_guard<std::mutex>,
+                                    std::lock_guard<std::mutex> >());
+static_assert(
+    !check_swappable_with<std::lock_guard<std::mutex>, std::vector<int> >());
+static_assert(!check_swappable_with<std::mutex, std::mutex>());
+static_assert(!check_swappable_with<std::mutex, std::vector<int> >());
+#endif
+
+static_assert(
+    check_swappable_with<std::map<int, void*>, std::map<int, void*> >());
+static_assert(!check_swappable_with<std::map<int, void*>, std::vector<int> >());
+static_assert(check_swappable_with<std::optional<std::vector<int> >,
+                                   std::optional<std::vector<int> > >());
+static_assert(!check_swappable_with<std::optional<std::vector<int> >,
+                                    std::vector<int> >());
+static_assert(check_swappable_with<std::vector<int>, std::vector<int> >());
+static_assert(!check_swappable_with<std::vector<int>, int>());
+} // namespace standard_types
+
+int main(int, char**) { return 0; }