llvm-project/libcxx/test/std/utilities/variant/variant.variant/variant.assign/copy.pass.cpp

//===----------------------------------------------------------------------===//
//
// 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

// <variant>

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

// constexpr variant& operator=(variant const&);

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

#include "test_macros.h"

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

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

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

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

struct CopyAssign {
  constexpr CopyAssign(int v, int* alv, int* cpy_ctr, int* cpy_assi, int* move_ctr, int* move_assi)
      : value(v),
        alive(alv),
        copy_construct(cpy_ctr),
        copy_assign(cpy_assi),
        move_construct(move_ctr),
        move_assign(move_assi) {
    ++*alive;
  }
  constexpr CopyAssign(const CopyAssign& o)
      : value(o.value),
        alive(o.alive),
        copy_construct(o.copy_construct),
        copy_assign(o.copy_assign),
        move_construct(o.move_construct),
        move_assign(o.move_assign) {
    ++*alive;
    ++*copy_construct;
  }
  constexpr CopyAssign(CopyAssign&& o) noexcept
      : value(o.value),
        alive(o.alive),
        copy_construct(o.copy_construct),
        copy_assign(o.copy_assign),
        move_construct(o.move_construct),
        move_assign(o.move_assign) {
    o.value = -1;
    ++*alive;
    ++*move_construct;
  }
  constexpr CopyAssign& operator=(const CopyAssign& o) {
    value          = o.value;
    alive          = o.alive;
    copy_construct = o.copy_construct;
    copy_assign    = o.copy_assign;
    move_construct = o.move_construct;
    move_assign    = o.move_assign;
    ++*copy_assign;
    return *this;
  }
  constexpr CopyAssign& operator=(CopyAssign&& o) noexcept {
    value          = o.value;
    alive          = o.alive;
    copy_construct = o.copy_construct;
    copy_assign    = o.copy_assign;
    move_construct = o.move_construct;
    move_assign    = o.move_assign;
    o.value        = -1;
    ++*move_assign;
    return *this;
  }
  TEST_CONSTEXPR_CXX20 ~CopyAssign() { --*alive; }
  int value;
  int* alive;
  int* copy_construct;
  int* copy_assign;
  int* move_construct;
  int* move_assign;
};

struct CopyMaybeThrows {
  CopyMaybeThrows(const CopyMaybeThrows&);
  CopyMaybeThrows& operator=(const CopyMaybeThrows&);
};
struct CopyDoesThrow {
  CopyDoesThrow(const CopyDoesThrow&) noexcept(false);
  CopyDoesThrow& operator=(const CopyDoesThrow&) noexcept(false);
};

struct NTCopyAssign {
  constexpr NTCopyAssign(int v) : value(v) {}
  NTCopyAssign(const NTCopyAssign&) = default;
  NTCopyAssign(NTCopyAssign&&)      = default;
  NTCopyAssign& operator=(const NTCopyAssign& that) {
    value = that.value;
    return *this;
  };
  NTCopyAssign& operator=(NTCopyAssign&&) = delete;
  int value;
};

static_assert(!std::is_trivially_copy_assignable<NTCopyAssign>::value, "");
static_assert(std::is_copy_assignable<NTCopyAssign>::value, "");

struct TCopyAssign {
  constexpr TCopyAssign(int v) : value(v) {}
  TCopyAssign(const TCopyAssign&)            = default;
  TCopyAssign(TCopyAssign&&)                 = default;
  TCopyAssign& operator=(const TCopyAssign&) = default;
  TCopyAssign& operator=(TCopyAssign&&)      = delete;
  int value;
};

static_assert(std::is_trivially_copy_assignable<TCopyAssign>::value, "");

struct TCopyAssignNTMoveAssign {
  constexpr TCopyAssignNTMoveAssign(int v) : value(v) {}
  TCopyAssignNTMoveAssign(const TCopyAssignNTMoveAssign&)            = default;
  TCopyAssignNTMoveAssign(TCopyAssignNTMoveAssign&&)                 = default;
  TCopyAssignNTMoveAssign& operator=(const TCopyAssignNTMoveAssign&) = default;
  TCopyAssignNTMoveAssign& operator=(TCopyAssignNTMoveAssign&& that) {
    value      = that.value;
    that.value = -1;
    return *this;
  }
  int value;
};

static_assert(std::is_trivially_copy_assignable_v<TCopyAssignNTMoveAssign>, "");

#ifndef TEST_HAS_NO_EXCEPTIONS
struct CopyThrows {
  CopyThrows() = default;
  CopyThrows(const CopyThrows&) { throw 42; }
  CopyThrows& operator=(const CopyThrows&) { throw 42; }
};

struct CopyCannotThrow {
  static int alive;
  CopyCannotThrow() { ++alive; }
  CopyCannotThrow(const CopyCannotThrow&) noexcept { ++alive; }
  CopyCannotThrow(CopyCannotThrow&&) noexcept { assert(false); }
  CopyCannotThrow& operator=(const CopyCannotThrow&) noexcept = default;
  CopyCannotThrow& operator=(CopyCannotThrow&&) noexcept {
    assert(false);
    return *this;
  }
};

int CopyCannotThrow::alive = 0;

struct MoveThrows {
  static int alive;
  MoveThrows() { ++alive; }
  MoveThrows(const MoveThrows&) { ++alive; }
  MoveThrows(MoveThrows&&) { throw 42; }
  MoveThrows& operator=(const MoveThrows&) { return *this; }
  MoveThrows& operator=(MoveThrows&&) { throw 42; }
  ~MoveThrows() { --alive; }
};

int MoveThrows::alive = 0;

struct MakeEmptyT {
  static int alive;
  MakeEmptyT() { ++alive; }
  MakeEmptyT(const MakeEmptyT&) {
    ++alive;
    // Don't throw from the copy constructor since variant's assignment
    // operator performs a copy before committing to the assignment.
  }
  MakeEmptyT(MakeEmptyT&&) { throw 42; }
  MakeEmptyT& operator=(const MakeEmptyT&) { throw 42; }
  MakeEmptyT& operator=(MakeEmptyT&&) { throw 42; }
  ~MakeEmptyT() { --alive; }
};

int MakeEmptyT::alive = 0;

template <class Variant>
void makeEmpty(Variant& v) {
  Variant v2(std::in_place_type<MakeEmptyT>);
  try {
    v = std::move(v2);
    assert(false);
  } catch (...) {
    assert(v.valueless_by_exception());
  }
}
#endif // TEST_HAS_NO_EXCEPTIONS

constexpr void test_copy_assignment_not_noexcept() {
  {
    using V = std::variant<CopyMaybeThrows>;
    static_assert(!std::is_nothrow_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, CopyDoesThrow>;
    static_assert(!std::is_nothrow_copy_assignable<V>::value, "");
  }
}

constexpr void test_copy_assignment_sfinae() {
  {
    using V = std::variant<int, long>;
    static_assert(std::is_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, CopyOnly>;
    static_assert(std::is_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, NoCopy>;
    static_assert(!std::is_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, MoveOnly>;
    static_assert(!std::is_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, MoveOnlyNT>;
    static_assert(!std::is_copy_assignable<V>::value, "");
  }

  // Make sure we properly propagate triviality (see P0602R4).
  {
    using V = std::variant<int, long>;
    static_assert(std::is_trivially_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, NTCopyAssign>;
    static_assert(!std::is_trivially_copy_assignable<V>::value, "");
    static_assert(std::is_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, TCopyAssign>;
    static_assert(std::is_trivially_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, TCopyAssignNTMoveAssign>;
    static_assert(std::is_trivially_copy_assignable<V>::value, "");
  }
  {
    using V = std::variant<int, CopyOnly>;
    static_assert(std::is_trivially_copy_assignable<V>::value, "");
  }
}

void test_copy_assignment_empty_empty() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  using MET = MakeEmptyT;
  {
    using V = std::variant<int, long, MET>;
    V v1(std::in_place_index<0>);
    makeEmpty(v1);
    V v2(std::in_place_index<0>);
    makeEmpty(v2);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.valueless_by_exception());
    assert(v1.index() == std::variant_npos);
  }
#endif // TEST_HAS_NO_EXCEPTIONS
}

void test_copy_assignment_non_empty_empty() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  using MET = MakeEmptyT;
  {
    using V = std::variant<int, MET>;
    V v1(std::in_place_index<0>, 42);
    V v2(std::in_place_index<0>);
    makeEmpty(v2);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.valueless_by_exception());
    assert(v1.index() == std::variant_npos);
  }
  {
    using V = std::variant<int, MET, std::string>;
    V v1(std::in_place_index<2>, "hello");
    V v2(std::in_place_index<0>);
    makeEmpty(v2);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.valueless_by_exception());
    assert(v1.index() == std::variant_npos);
  }
#endif // TEST_HAS_NO_EXCEPTIONS
}

void test_copy_assignment_empty_non_empty() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  using MET = MakeEmptyT;
  {
    using V = std::variant<int, MET>;
    V v1(std::in_place_index<0>);
    makeEmpty(v1);
    V v2(std::in_place_index<0>, 42);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 0);
    assert(std::get<0>(v1) == 42);
  }
  {
    using V = std::variant<int, MET, std::string>;
    V v1(std::in_place_index<0>);
    makeEmpty(v1);
    V v2(std::in_place_type<std::string>, "hello");
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 2);
    assert(std::get<2>(v1) == "hello");
  }
#endif // TEST_HAS_NO_EXCEPTIONS
}

template <typename T>
struct Result {
  std::size_t index;
  T value;
};

TEST_CONSTEXPR_CXX20 void test_copy_assignment_same_index() {
  {
    using V = std::variant<int>;
    V v1(43);
    V v2(42);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 0);
    assert(std::get<0>(v1) == 42);
  }
  {
    using V = std::variant<int, long, unsigned>;
    V v1(43l);
    V v2(42l);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 1);
    assert(std::get<1>(v1) == 42);
  }
  {
    using V            = std::variant<int, CopyAssign, unsigned>;
    int alive          = 0;
    int copy_construct = 0;
    int copy_assign    = 0;
    int move_construct = 0;
    int move_assign    = 0;
    V v1(std::in_place_type<CopyAssign>, 43, &alive, &copy_construct, &copy_assign, &move_construct, &move_assign);
    V v2(std::in_place_type<CopyAssign>, 42, &alive, &copy_construct, &copy_assign, &move_construct, &move_assign);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 1);
    assert(std::get<1>(v1).value == 42);
    assert(copy_construct == 0);
    assert(move_construct == 0);
    assert(copy_assign == 1);
  }

  // Make sure we properly propagate triviality, which implies constexpr-ness (see P0602R4).
  {
    struct {
      constexpr Result<int> operator()() const {
        using V = std::variant<int>;
        V v(43);
        V v2(42);
        v = v2;
        return {v.index(), std::get<0>(v)};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 0, "");
    static_assert(result.value == 42, "");
  }
  {
    struct {
      constexpr Result<long> operator()() const {
        using V = std::variant<int, long, unsigned>;
        V v(43l);
        V v2(42l);
        v = v2;
        return {v.index(), std::get<1>(v)};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 1, "");
    static_assert(result.value == 42l, "");
  }
  {
    struct {
      constexpr Result<int> operator()() const {
        using V = std::variant<int, TCopyAssign, unsigned>;
        V v(std::in_place_type<TCopyAssign>, 43);
        V v2(std::in_place_type<TCopyAssign>, 42);
        v = v2;
        return {v.index(), std::get<1>(v).value};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 1, "");
    static_assert(result.value == 42, "");
  }
  {
    struct {
      constexpr Result<int> operator()() const {
        using V = std::variant<int, TCopyAssignNTMoveAssign, unsigned>;
        V v(std::in_place_type<TCopyAssignNTMoveAssign>, 43);
        V v2(std::in_place_type<TCopyAssignNTMoveAssign>, 42);
        v = v2;
        return {v.index(), std::get<1>(v).value};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 1, "");
    static_assert(result.value == 42, "");
  }
}

TEST_CONSTEXPR_CXX20 void test_copy_assignment_different_index() {
  {
    using V = std::variant<int, long, unsigned>;
    V v1(43);
    V v2(42l);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 1);
    assert(std::get<1>(v1) == 42);
  }
  {
    using V            = std::variant<int, CopyAssign, unsigned>;
    int alive          = 0;
    int copy_construct = 0;
    int copy_assign    = 0;
    int move_construct = 0;
    int move_assign    = 0;
    V v1(std::in_place_type<unsigned>, 43u);
    V v2(std::in_place_type<CopyAssign>, 42, &alive, &copy_construct, &copy_assign, &move_construct, &move_assign);
    assert(copy_construct == 0);
    assert(move_construct == 0);
    assert(alive == 1);
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 1);
    assert(std::get<1>(v1).value == 42);
    assert(alive == 2);
    assert(copy_construct == 1);
    assert(move_construct == 1);
    assert(copy_assign == 0);
  }

  // Make sure we properly propagate triviality, which implies constexpr-ness (see P0602R4).
  {
    struct {
      constexpr Result<long> operator()() const {
        using V = std::variant<int, long, unsigned>;
        V v(43);
        V v2(42l);
        v = v2;
        return {v.index(), std::get<1>(v)};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 1, "");
    static_assert(result.value == 42l, "");
  }
  {
    struct {
      constexpr Result<int> operator()() const {
        using V = std::variant<int, TCopyAssign, unsigned>;
        V v(std::in_place_type<unsigned>, 43u);
        V v2(std::in_place_type<TCopyAssign>, 42);
        v = v2;
        return {v.index(), std::get<1>(v).value};
      }
    } test;
    constexpr auto result = test();
    static_assert(result.index == 1, "");
    static_assert(result.value == 42, "");
  }
}

void test_assignment_throw() {
#ifndef TEST_HAS_NO_EXCEPTIONS
  using MET = MakeEmptyT;
  // same index
  {
    using V = std::variant<int, MET, std::string>;
    V v1(std::in_place_type<MET>);
    MET& mref = std::get<1>(v1);
    V v2(std::in_place_type<MET>);
    try {
      v1 = v2;
      assert(false);
    } catch (...) {
    }
    assert(v1.index() == 1);
    assert(&std::get<1>(v1) == &mref);
  }

  // difference indices
  {
    using V = std::variant<int, CopyThrows, std::string>;
    V v1(std::in_place_type<std::string>, "hello");
    V v2(std::in_place_type<CopyThrows>);
    try {
      v1 = v2;
      assert(false);
    } catch (...) { /* ... */
    }
    // Test that copy construction is used directly if move construction may throw,
    // resulting in a valueless variant if copy throws.
    assert(v1.valueless_by_exception());
  }
  {
    using V = std::variant<int, MoveThrows, std::string>;
    V v1(std::in_place_type<std::string>, "hello");
    V v2(std::in_place_type<MoveThrows>);
    assert(MoveThrows::alive == 1);
    // Test that copy construction is used directly if move construction may throw.
    v1 = v2;
    assert(v1.index() == 1);
    assert(v2.index() == 1);
    assert(MoveThrows::alive == 2);
  }
  {
    // Test that direct copy construction is preferred when it cannot throw.
    using V = std::variant<int, CopyCannotThrow, std::string>;
    V v1(std::in_place_type<std::string>, "hello");
    V v2(std::in_place_type<CopyCannotThrow>);
    assert(CopyCannotThrow::alive == 1);
    v1 = v2;
    assert(v1.index() == 1);
    assert(v2.index() == 1);
    assert(CopyCannotThrow::alive == 2);
  }
  {
    using V = std::variant<int, CopyThrows, std::string>;
    V v1(std::in_place_type<CopyThrows>);
    V v2(std::in_place_type<std::string>, "hello");
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 2);
    assert(std::get<2>(v1) == "hello");
    assert(v2.index() == 2);
    assert(std::get<2>(v2) == "hello");
  }
  {
    using V = std::variant<int, MoveThrows, std::string>;
    V v1(std::in_place_type<MoveThrows>);
    V v2(std::in_place_type<std::string>, "hello");
    V& vref = (v1 = v2);
    assert(&vref == &v1);
    assert(v1.index() == 2);
    assert(std::get<2>(v1) == "hello");
    assert(v2.index() == 2);
    assert(std::get<2>(v2) == "hello");
  }
#endif // TEST_HAS_NO_EXCEPTIONS
}

template <std::size_t NewIdx, class T, class ValueType>
constexpr void test_constexpr_assign_imp(T&& v, ValueType&& new_value) {
  using Variant = std::decay_t<T>;
  const Variant cp(std::forward<ValueType>(new_value));
  v = cp;
  assert(v.index() == NewIdx);
  assert(std::get<NewIdx>(v) == std::get<NewIdx>(cp));
}

constexpr void test_constexpr_copy_assignment_trivial() {
  // Make sure we properly propagate triviality, which implies constexpr-ness (see P0602R4).
  using V = std::variant<long, void*, int>;
  static_assert(std::is_trivially_copyable<V>::value, "");
  static_assert(std::is_trivially_copy_assignable<V>::value, "");
  test_constexpr_assign_imp<0>(V(42l), 101l);
  test_constexpr_assign_imp<0>(V(nullptr), 101l);
  test_constexpr_assign_imp<1>(V(42l), nullptr);
  test_constexpr_assign_imp<2>(V(42l), 101);
}

struct NonTrivialCopyAssign {
  int i = 0;
  constexpr NonTrivialCopyAssign(int ii) : i(ii) {}
  constexpr NonTrivialCopyAssign(const NonTrivialCopyAssign& other) : i(other.i) {}
  constexpr NonTrivialCopyAssign& operator=(const NonTrivialCopyAssign& o) {
    i = o.i;
    return *this;
  }
  TEST_CONSTEXPR_CXX20 ~NonTrivialCopyAssign() = default;
  friend constexpr bool operator==(const NonTrivialCopyAssign& x, const NonTrivialCopyAssign& y) { return x.i == y.i; }
};

constexpr void test_constexpr_copy_assignment_non_trivial() {
  // Make sure we properly propagate triviality, which implies constexpr-ness (see P0602R4).
  using V = std::variant<long, void*, NonTrivialCopyAssign>;
  static_assert(!std::is_trivially_copyable<V>::value, "");
  static_assert(!std::is_trivially_copy_assignable<V>::value, "");
  test_constexpr_assign_imp<0>(V(42l), 101l);
  test_constexpr_assign_imp<0>(V(nullptr), 101l);
  test_constexpr_assign_imp<1>(V(42l), nullptr);
  test_constexpr_assign_imp<2>(V(42l), NonTrivialCopyAssign(5));
  test_constexpr_assign_imp<2>(V(NonTrivialCopyAssign(3)), NonTrivialCopyAssign(5));
}

void non_constexpr_test() {
  test_copy_assignment_empty_empty();
  test_copy_assignment_non_empty_empty();
  test_copy_assignment_empty_non_empty();
  test_assignment_throw();
}

constexpr bool cxx17_constexpr_test() {
  test_copy_assignment_sfinae();
  test_copy_assignment_not_noexcept();
  test_constexpr_copy_assignment_trivial();

  return true;
}

TEST_CONSTEXPR_CXX20 bool cxx20_constexpr_test() {
  test_copy_assignment_same_index();
  test_copy_assignment_different_index();
  test_constexpr_copy_assignment_non_trivial();

  return true;
}

int main(int, char**) {
  non_constexpr_test();
  cxx17_constexpr_test();
  cxx20_constexpr_test();

  static_assert(cxx17_constexpr_test());
#if TEST_STD_VER >= 20
  static_assert(cxx20_constexpr_test());
#endif
  return 0;
}