Extra requirement in `ranges::partial_sort_copy`: `d_first` must be constructible from `*first`

[SergeyKopienko]

oneDPL/include/oneapi/dpl/pstl/algorithm_impl.h

Line 2577 in e16a913

::new (__k) _T2(*__it);

The source comment: #2780 (comment)

This code is used from

struct __internal::__partial_sort_copy_fn
{
    template <typename _ExecutionPolicy, std::ranges::random_access_range _R, std::ranges::random_access_range _OutR,
              typename _Comp = std::ranges::less, typename _Proj1 = std::identity, typename _Proj2 = std::identity>
        requires oneapi::dpl::is_execution_policy_v<std::remove_cvref_t<_ExecutionPolicy>> &&
                 std::ranges::sized_range<_R> && std::ranges::sized_range<_OutR> &&
                 std::indirectly_copyable<std::ranges::iterator_t<_R>, std::ranges::iterator_t<_OutR>> &&
                 std::sortable<std::ranges::iterator_t<_OutR>, _Comp, _Proj2> &&
                 std::indirect_strict_weak_order<_Comp, std::projected<std::ranges::iterator_t<_R>, _Proj1>,
                                                 std::projected<std::ranges::iterator_t<_OutR>, _Proj2>>
    std::ranges::partial_sort_copy_result<std::ranges::borrowed_iterator_t<_R>, std::ranges::borrowed_iterator_t<_OutR>>
    operator()(_ExecutionPolicy&& __exec, _R&& __r, _OutR&& __result, _Comp __comp = {}, _Proj1 __proj1 = {},
               _Proj2 __proj2 = {}) const
    {
        const auto __dispatch_tag = oneapi::dpl::__ranges::__select_backend(__exec);
        return oneapi::dpl::__internal::__ranges::__pattern_partial_sort_copy_ranges(
            __dispatch_tag, std::forward<_ExecutionPolicy>(__exec), std::forward<_R>(__r),
            std::forward<_OutR>(__result), __comp, __proj1, __proj2);
    }
}; //__partial_sort_copy_fn
inline constexpr __internal::__partial_sort_copy_fn partial_sort_copy;

std::indirectly_copyable<std::ranges::iterator_t<_R>, std::ranges::iterator_t<_OutR>> check in the requires clause permits copy assignment, but it does not inherently allow copy via the constructor in placement new, which is used in the implementation.

The classic partial_sort_copy is also prone to this issue, because it only has an indirectly_copyable-like requirement in the standard:

*first must be writable to d_first