sdk/lib/stdcompat/test/memory_test.cc

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/stdcompat/memory.h>
#include <lib/stdcompat/optional.h>

#include <array>
#include <memory>
#include <type_traits>

#include <gtest/gtest.h>

struct arrow {
  struct inner {
  } value;
  const inner* operator->() const { return &value; }
};

template <typename T>
struct weird_ptr {
  const T& operator->() const { return value; }
  T value;
};

namespace std {
template <>
struct pointer_traits<arrow> {
  using element_type = const typename arrow::inner;
};
template <typename T>
struct pointer_traits<weird_ptr<T>> {
  using element_type = const T;
};
}  // namespace std

namespace {

constexpr bool IsAddressOfConstexpr() {
  int a = 1;
  return cpp17::addressof(a) == &a;
}

TEST(MemoryTest, AddressOfReturnsCorrectPointer) {
  static_assert(IsAddressOfConstexpr() == true,
                "cpp17::addressof should be evaluated in constexpr.");
}

TEST(MemoryTest, AddressOfReturnsAddressNotOverridenOperator) {
  struct Misleading {
    constexpr Misleading* operator&() const { return nullptr; }
  };

  alignas(Misleading) std::array<char, sizeof(Misleading)> buffer;
  const Misleading* ptr = new (static_cast<void*>(buffer.data())) Misleading();
  const Misleading& misleading = *ptr;

  ASSERT_EQ(&misleading, nullptr);
  ASSERT_EQ(cpp17::addressof(misleading), ptr);
}

#if __cpp_lib_addressof_constexpr >= 201603L && !defined(LIB_STDCOMPAT_USE_POLYFILLS)

template <typename T>
constexpr void check_addressof_alias() {
  // Need so the compiler picks the right overload.
  constexpr T* (*cpp17_addressof)(T&) = &cpp17::addressof<T>;
  constexpr T* (*std_addressof)(T&) = &std::addressof<T>;
  static_assert(cpp17_addressof == std_addressof);
}

struct UserType {
  int var;
};

TEST(MemoryTest, AddressOfIsAliasForStdWhenAvailable) {
  check_addressof_alias<int>();
  check_addressof_alias<UserType>();
}
#endif

TEST(MemoryTest, ToAddressWithRawReturnsRightPointer) {
  constexpr int* a = nullptr;
  static_assert(cpp20::to_address(a) == nullptr, "To Address returns right raw ptr.");
}

TEST(MemoryTest, ToAddressWithFancyReturnsRightPointer) {
  std::unique_ptr<int> a = std::make_unique<int>(1);
  EXPECT_EQ(a.get(), cpp20::to_address(a));
}

TEST(MemoryTest, ToAddressWithArrowReturnsRightPointer) {
  cpp17::optional<const int> a(13);
  EXPECT_EQ(&*a, cpp20::to_address(a));

  arrow b;
  EXPECT_EQ(&b.value, cpp20::to_address(b));

  // We only go one level because cpp17::optional<T>::operator->() returns T*, which goes to the
  // first overload of cpp20::to_address and there is no recursion.
  cpp17::optional<const arrow> c;
  EXPECT_EQ(&*c, cpp20::to_address(c));

  // TODO(fxbug.dev/70523): libc++ and libstdc++ currently both have broken implementations of
  // std::to_address that require specializing std::pointer_traits and don't allow operator-> to
  // return non-raw-pointers, so the chaining in this test case (which seems to be intentionally
  // allowed by the standard, given that there is a recursive path through the function) is
  // impossible.
  //
  // Here we do go two levels because weird_ptr<T>::operator->() returns const T&, which goes back
  // to the overload for operator->() and then we get a raw pointer.
  // weird_ptr<cpp17::optional<const int>> e;
  // EXPECT_EQ(&*e.value, cpp20::to_address(e));
}

// TODO(fxbug.dev/70523): This is only to be bug-compatible with the standard library
// implementations; change asserts when the linked bug is resolved.
TEST(MemoryTest, BannedUses) {
  struct banned {
    const int* operator->() const { return &value; }
    int value;
  };

  // These tests must *not* compile to keep compatibility with the curent standard library
  // implementations. Uncomment them to verify that they error out both for the polyfill and the
  // standard version.

  // No std::pointer_traits specialization
  // banned a;
  // EXPECT_EQ(&a.value, cpp20::to_address(a));

  // Doesn't ever get to a raw pointer
  // weird_ptr<const int> b;
  // EXPECT_EQ(&b.value, cpp20::to_address(b));

  // Incorrect attempt at chaining
  // cpp17::optional<const cpp17::optional<int>> c(13);
  // EXPECT_EQ(&**c, cpp20::to_address(c));

  // No chaining
  // weird_ptr<cpp17::optional<const int>> d;
  // EXPECT_EQ(&*d.value, cpp20::to_address(d));
}

#if __cpp_lib_to_address >= 201711L && !defined(LIB_STDCOMPAT_USE_POLYFILLS)

template <typename T>
constexpr void check_to_address_alias() {
  // Need so the compiler picks the right overload.
  constexpr auto (*cpp20_to_address)(const T&) = &cpp20::to_address<T>;
  constexpr auto (*std_to_address)(const T&) = &std::to_address<T>;
  static_assert(cpp20_to_address == std_to_address);
}

TEST(MemoryTest, ToAddressIsAliasForStdWhenAvailable) {
  check_to_address_alias<int*>();
  check_to_address_alias<std::unique_ptr<int>>();
}

#endif

}  // namespace