test/std/utilities/variant/variant.variant/variant.swap/swap.pass.cpp

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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++98, c++03, c++11, c++14

// XFAIL: dylib-has-no-bad_variant_access && !libcpp-no-exceptions

// <variant>

// template <class ...Types> class variant;

// void swap(variant& rhs) noexcept(see below)

#include <cassert>
#include <string>
#include <type_traits>
#include <variant>

#include "test_convertible.h"
#include "test_macros.h"
#include "variant_test_helpers.h"

struct NotSwappable {};
void swap(NotSwappable &, NotSwappable &) = delete;

struct NotCopyable {
  NotCopyable() = default;
  NotCopyable(const NotCopyable &) = delete;
  NotCopyable &operator=(const NotCopyable &) = delete;
};

struct NotCopyableWithSwap {
  NotCopyableWithSwap() = default;
  NotCopyableWithSwap(const NotCopyableWithSwap &) = delete;
  NotCopyableWithSwap &operator=(const NotCopyableWithSwap &) = delete;
};
void swap(NotCopyableWithSwap &, NotCopyableWithSwap) {}

struct NotMoveAssignable {
  NotMoveAssignable() = default;
  NotMoveAssignable(NotMoveAssignable &&) = default;
  NotMoveAssignable &operator=(NotMoveAssignable &&) = delete;
};

struct NotMoveAssignableWithSwap {
  NotMoveAssignableWithSwap() = default;
  NotMoveAssignableWithSwap(NotMoveAssignableWithSwap &&) = default;
  NotMoveAssignableWithSwap &operator=(NotMoveAssignableWithSwap &&) = delete;
};
void swap(NotMoveAssignableWithSwap &, NotMoveAssignableWithSwap &) noexcept {}

template <bool Throws> void do_throw() {}

template <> void do_throw<true>() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  throw 42;
#else
  std::abort();
#endif
}

template <bool NT_Copy, bool NT_Move, bool NT_CopyAssign, bool NT_MoveAssign,
          bool NT_Swap, bool EnableSwap = true>
struct NothrowTypeImp {
  static int move_called;
  static int move_assign_called;
  static int swap_called;
  static void reset() { move_called = move_assign_called = swap_called = 0; }
  NothrowTypeImp() = default;
  explicit NothrowTypeImp(int v) : value(v) {}
  NothrowTypeImp(const NothrowTypeImp &o) noexcept(NT_Copy) : value(o.value) {
    assert(false);
  } // never called by test
  NothrowTypeImp(NothrowTypeImp &&o) noexcept(NT_Move) : value(o.value) {
    ++move_called;
    do_throw<!NT_Move>();
    o.value = -1;
  }
  NothrowTypeImp &operator=(const NothrowTypeImp &) noexcept(NT_CopyAssign) {
    assert(false);
    return *this;
  } // never called by the tests
  NothrowTypeImp &operator=(NothrowTypeImp &&o) noexcept(NT_MoveAssign) {
    ++move_assign_called;
    do_throw<!NT_MoveAssign>();
    value = o.value;
    o.value = -1;
    return *this;
  }
  int value;
};
template <bool NT_Copy, bool NT_Move, bool NT_CopyAssign, bool NT_MoveAssign,
          bool NT_Swap, bool EnableSwap>
int NothrowTypeImp<NT_Copy, NT_Move, NT_CopyAssign, NT_MoveAssign, NT_Swap,
                   EnableSwap>::move_called = 0;
template <bool NT_Copy, bool NT_Move, bool NT_CopyAssign, bool NT_MoveAssign,
          bool NT_Swap, bool EnableSwap>
int NothrowTypeImp<NT_Copy, NT_Move, NT_CopyAssign, NT_MoveAssign, NT_Swap,
                   EnableSwap>::move_assign_called = 0;
template <bool NT_Copy, bool NT_Move, bool NT_CopyAssign, bool NT_MoveAssign,
          bool NT_Swap, bool EnableSwap>
int NothrowTypeImp<NT_Copy, NT_Move, NT_CopyAssign, NT_MoveAssign, NT_Swap,
                   EnableSwap>::swap_called = 0;

template <bool NT_Copy, bool NT_Move, bool NT_CopyAssign, bool NT_MoveAssign,
          bool NT_Swap>
void swap(NothrowTypeImp<NT_Copy, NT_Move, NT_CopyAssign, NT_MoveAssign,
                         NT_Swap, true> &lhs,
          NothrowTypeImp<NT_Copy, NT_Move, NT_CopyAssign, NT_MoveAssign,
                         NT_Swap, true> &rhs) noexcept(NT_Swap) {
  lhs.swap_called++;
  do_throw<!NT_Swap>();
  int tmp = lhs.value;
  lhs.value = rhs.value;
  rhs.value = tmp;
}

// throwing copy, nothrow move ctor/assign, no swap provided
using NothrowMoveable = NothrowTypeImp<false, true, false, true, false, false>;
// throwing copy and move assign, nothrow move ctor, no swap provided
using NothrowMoveCtor = NothrowTypeImp<false, true, false, false, false, false>;
// nothrow move ctor, throwing move assignment, swap provided
using NothrowMoveCtorWithThrowingSwap =
    NothrowTypeImp<false, true, false, false, false, true>;
// throwing move ctor, nothrow move assignment, no swap provided
using ThrowingMoveCtor =
    NothrowTypeImp<false, false, false, true, false, false>;
// throwing special members, nothrowing swap
using ThrowingTypeWithNothrowSwap =
    NothrowTypeImp<false, false, false, false, true, true>;
using NothrowTypeWithThrowingSwap =
    NothrowTypeImp<true, true, true, true, false, true>;
// throwing move assign with nothrow move and nothrow swap
using ThrowingMoveAssignNothrowMoveCtorWithSwap =
    NothrowTypeImp<false, true, false, false, true, true>;
// throwing move assign with nothrow move but no swap.
using ThrowingMoveAssignNothrowMoveCtor =
    NothrowTypeImp<false, true, false, false, false, false>;

struct NonThrowingNonNoexceptType {
  static int move_called;
  static void reset() { move_called = 0; }
  NonThrowingNonNoexceptType() = default;
  NonThrowingNonNoexceptType(int v) : value(v) {}
  NonThrowingNonNoexceptType(NonThrowingNonNoexceptType &&o) noexcept(false)
      : value(o.value) {
    ++move_called;
    o.value = -1;
  }
  NonThrowingNonNoexceptType &
  operator=(NonThrowingNonNoexceptType &&) noexcept(false) {
    assert(false); // never called by the tests.
    return *this;
  }
  int value;
};
int NonThrowingNonNoexceptType::move_called = 0;

struct ThrowsOnSecondMove {
  int value;
  int move_count;
  ThrowsOnSecondMove(int v) : value(v), move_count(0) {}
  ThrowsOnSecondMove(ThrowsOnSecondMove &&o) noexcept(false)
      : value(o.value), move_count(o.move_count + 1) {
    if (move_count == 2)
      do_throw<true>();
    o.value = -1;
  }
  ThrowsOnSecondMove &operator=(ThrowsOnSecondMove &&) {
    assert(false); // not called by test
    return *this;
  }
};

void test_swap_valueless_by_exception() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  using V = std::variant<int, MakeEmptyT>;
  { // both empty
    V v1;
    makeEmpty(v1);
    V v2;
    makeEmpty(v2);
    assert(MakeEmptyT::alive == 0);
    { // member swap
      v1.swap(v2);
      assert(v1.valueless_by_exception());
      assert(v2.valueless_by_exception());
      assert(MakeEmptyT::alive == 0);
    }
    { // non-member swap
      swap(v1, v2);
      assert(v1.valueless_by_exception());
      assert(v2.valueless_by_exception());
      assert(MakeEmptyT::alive == 0);
    }
  }
  { // only one empty
    V v1(42);
    V v2;
    makeEmpty(v2);
    { // member swap
      v1.swap(v2);
      assert(v1.valueless_by_exception());
      assert(std::get<0>(v2) == 42);
      // swap again
      v2.swap(v1);
      assert(v2.valueless_by_exception());
      assert(std::get<0>(v1) == 42);
    }
    { // non-member swap
      swap(v1, v2);
      assert(v1.valueless_by_exception());
      assert(std::get<0>(v2) == 42);
      // swap again
      swap(v1, v2);
      assert(v2.valueless_by_exception());
      assert(std::get<0>(v1) == 42);
    }
  }
#endif
}

void test_swap_same_alternative() {
  {
    using T = ThrowingTypeWithNothrowSwap;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>, 100);
    v1.swap(v2);
    assert(T::swap_called == 1);
    assert(std::get<0>(v1).value == 100);
    assert(std::get<0>(v2).value == 42);
    swap(v1, v2);
    assert(T::swap_called == 2);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<0>(v2).value == 100);
  }
  {
    using T = NothrowMoveable;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>, 100);
    v1.swap(v2);
    assert(T::swap_called == 0);
    assert(T::move_called == 1);
    assert(T::move_assign_called == 2);
    assert(std::get<0>(v1).value == 100);
    assert(std::get<0>(v2).value == 42);
    T::reset();
    swap(v1, v2);
    assert(T::swap_called == 0);
    assert(T::move_called == 1);
    assert(T::move_assign_called == 2);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<0>(v2).value == 100);
  }
#ifndef TEST_HAS_NO_EXCEPTIONS
  {
    using T = NothrowTypeWithThrowingSwap;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T::swap_called == 1);
    assert(T::move_called == 0);
    assert(T::move_assign_called == 0);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<0>(v2).value == 100);
  }
  {
    using T = ThrowingMoveCtor;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T::move_called == 1); // call threw
    assert(T::move_assign_called == 0);
    assert(std::get<0>(v1).value ==
           42); // throw happened before v1 was moved from
    assert(std::get<0>(v2).value == 100);
  }
  {
    using T = ThrowingMoveAssignNothrowMoveCtor;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T::move_called == 1);
    assert(T::move_assign_called == 1);  // call threw and didn't complete
    assert(std::get<0>(v1).value == -1); // v1 was moved from
    assert(std::get<0>(v2).value == 100);
  }
#endif
}

void test_swap_different_alternatives() {
  {
    using T = NothrowMoveCtorWithThrowingSwap;
    using V = std::variant<T, int>;
    T::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    v1.swap(v2);
    assert(T::swap_called == 0);
    // The libc++ implementation double copies the argument, and not
    // the variant swap is called on.
    LIBCPP_ASSERT(T::move_called == 1);
    assert(T::move_called <= 2);
    assert(T::move_assign_called == 0);
    assert(std::get<1>(v1) == 100);
    assert(std::get<0>(v2).value == 42);
    T::reset();
    swap(v1, v2);
    assert(T::swap_called == 0);
    LIBCPP_ASSERT(T::move_called == 2);
    assert(T::move_called <= 2);
    assert(T::move_assign_called == 0);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<1>(v2) == 100);
  }
#ifndef TEST_HAS_NO_EXCEPTIONS
  {
    using T1 = ThrowingTypeWithNothrowSwap;
    using T2 = NonThrowingNonNoexceptType;
    using V = std::variant<T1, T2>;
    T1::reset();
    T2::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T1::swap_called == 0);
    assert(T1::move_called == 1); // throws
    assert(T1::move_assign_called == 0);
    // FIXME: libc++ shouldn't move from T2 here.
    LIBCPP_ASSERT(T2::move_called == 1);
    assert(T2::move_called <= 1);
    assert(std::get<0>(v1).value == 42);
    if (T2::move_called != 0)
      assert(v2.valueless_by_exception());
    else
      assert(std::get<1>(v2).value == 100);
  }
  {
    using T1 = NonThrowingNonNoexceptType;
    using T2 = ThrowingTypeWithNothrowSwap;
    using V = std::variant<T1, T2>;
    T1::reset();
    T2::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    LIBCPP_ASSERT(T1::move_called == 0);
    assert(T1::move_called <= 1);
    assert(T2::swap_called == 0);
    assert(T2::move_called == 1); // throws
    assert(T2::move_assign_called == 0);
    if (T1::move_called != 0)
      assert(v1.valueless_by_exception());
    else
      assert(std::get<0>(v1).value == 42);
    assert(std::get<1>(v2).value == 100);
  }
// FIXME: The tests below are just very libc++ specific
#ifdef _LIBCPP_VERSION
  {
    using T1 = ThrowsOnSecondMove;
    using T2 = NonThrowingNonNoexceptType;
    using V = std::variant<T1, T2>;
    T2::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    v1.swap(v2);
    assert(T2::move_called == 2);
    assert(std::get<1>(v1).value == 100);
    assert(std::get<0>(v2).value == 42);
    assert(std::get<0>(v2).move_count == 1);
  }
  {
    using T1 = NonThrowingNonNoexceptType;
    using T2 = ThrowsOnSecondMove;
    using V = std::variant<T1, T2>;
    T1::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T1::move_called == 1);
    assert(v1.valueless_by_exception());
    assert(std::get<0>(v2).value == 42);
  }
#endif
// testing libc++ extension. If either variant stores a nothrow move
// constructible type v1.swap(v2) provides the strong exception safety
// guarantee.
#ifdef _LIBCPP_VERSION
  {

    using T1 = ThrowingTypeWithNothrowSwap;
    using T2 = NothrowMoveable;
    using V = std::variant<T1, T2>;
    T1::reset();
    T2::reset();
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<1>, 100);
    try {
      v1.swap(v2);
      assert(false);
    } catch (int) {
    }
    assert(T1::swap_called == 0);
    assert(T1::move_called == 1);
    assert(T1::move_assign_called == 0);
    assert(T2::swap_called == 0);
    assert(T2::move_called == 2);
    assert(T2::move_assign_called == 0);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<1>(v2).value == 100);
    // swap again, but call v2's swap.
    T1::reset();
    T2::reset();
    try {
      v2.swap(v1);
      assert(false);
    } catch (int) {
    }
    assert(T1::swap_called == 0);
    assert(T1::move_called == 1);
    assert(T1::move_assign_called == 0);
    assert(T2::swap_called == 0);
    assert(T2::move_called == 2);
    assert(T2::move_assign_called == 0);
    assert(std::get<0>(v1).value == 42);
    assert(std::get<1>(v2).value == 100);
  }
#endif // _LIBCPP_VERSION
#endif
}

template <class Var>
constexpr auto has_swap_member_imp(int)
    -> decltype(std::declval<Var &>().swap(std::declval<Var &>()), true) {
  return true;
}

template <class Var> constexpr auto has_swap_member_imp(long) -> bool {
  return false;
}

template <class Var> constexpr bool has_swap_member() {
  return has_swap_member_imp<Var>(0);
}

void test_swap_sfinae() {
  {
    // This variant type does not provide either a member or non-member swap
    // but is still swappable via the generic swap algorithm, since the
    // variant is move constructible and move assignable.
    using V = std::variant<int, NotSwappable>;
    LIBCPP_STATIC_ASSERT(!has_swap_member<V>(), "");
    static_assert(std::is_swappable_v<V>, "");
  }
  {
    using V = std::variant<int, NotCopyable>;
    LIBCPP_STATIC_ASSERT(!has_swap_member<V>(), "");
    static_assert(!std::is_swappable_v<V>, "");
  }
  {
    using V = std::variant<int, NotCopyableWithSwap>;
    LIBCPP_STATIC_ASSERT(!has_swap_member<V>(), "");
    static_assert(!std::is_swappable_v<V>, "");
  }
  {
    using V = std::variant<int, NotMoveAssignable>;
    LIBCPP_STATIC_ASSERT(!has_swap_member<V>(), "");
    static_assert(!std::is_swappable_v<V>, "");
  }
}

void test_swap_noexcept() {
  {
    using V = std::variant<int, NothrowMoveable>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    using V = std::variant<int, NothrowMoveCtor>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(!std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    using V = std::variant<int, ThrowingTypeWithNothrowSwap>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(!std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    using V = std::variant<int, ThrowingMoveAssignNothrowMoveCtor>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(!std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    using V = std::variant<int, ThrowingMoveAssignNothrowMoveCtorWithSwap>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    using V = std::variant<int, NotMoveAssignableWithSwap>;
    static_assert(std::is_swappable_v<V> && has_swap_member<V>(), "");
    static_assert(std::is_nothrow_swappable_v<V>, "");
    // instantiate swap
    V v1, v2;
    v1.swap(v2);
    swap(v1, v2);
  }
  {
    // This variant type does not provide either a member or non-member swap
    // but is still swappable via the generic swap algorithm, since the
    // variant is move constructible and move assignable.
    using V = std::variant<int, NotSwappable>;
    LIBCPP_STATIC_ASSERT(!has_swap_member<V>(), "");
    static_assert(std::is_swappable_v<V>, "");
    static_assert(std::is_nothrow_swappable_v<V>, "");
    V v1, v2;
    swap(v1, v2);
  }
}

#ifdef _LIBCPP_VERSION
// This is why variant should SFINAE member swap. :-)
template class std::variant<int, NotSwappable>;
#endif

int main(int, char**) {
  test_swap_valueless_by_exception();
  test_swap_same_alternative();
  test_swap_different_alternatives();
  test_swap_sfinae();
  test_swap_noexcept();

  return 0;
}