third_party/libc++/src/test/std/ranges/range.adaptors/range.drop/dangling.cache.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, c++17

// If we have a copy-propagating cache, when we copy ZeroOnDestroy, we will get a
// dangling reference to the copied-from object. This test ensures that we do not
// propagate the cache on copy.

#include <ranges>

#include <cstddef>
#include <cstring>

#include "test_macros.h"
#include "types.h"

struct ZeroOnDestroy : std::ranges::view_base {
  unsigned count = 0;
  int buff[8] = {1, 2, 3, 4, 5, 6, 7, 8};

  constexpr ForwardIter begin() { return ForwardIter(buff); }
  constexpr ForwardIter begin() const { return ForwardIter(); }
  constexpr ForwardIter end() { return ForwardIter(buff + 8); }
  constexpr ForwardIter end() const { return ForwardIter(); }

  ZeroOnDestroy() = default;
  ZeroOnDestroy(const ZeroOnDestroy&) = default;
  ZeroOnDestroy& operator=(const ZeroOnDestroy&) = default;
  ~ZeroOnDestroy() {
    std::memset(buff, 0, sizeof(buff));
  }

  static auto dropFirstFour() {
    ZeroOnDestroy zod;
    std::ranges::drop_view dv(zod, 4);
    // Make sure we call begin here so the next call to begin will
    // use the cached iterator.
    assert(*dv.begin() == 5);
    // Intentionally invoke the copy ctor here.
    return std::ranges::drop_view(dv);
  }
};

int main(int, char**) {
  auto noDanlingCache = ZeroOnDestroy::dropFirstFour();
  // If we use the cached version, it will reference the copied-from view.
  // Worst case this is a segfault, best case it's an assertion fired.
  assert(*noDanlingCache.begin() == 5);

  return 0;
}