libstdc++: Include std::ranges::subrange definition in <tuple> [PR102301]

In order for std::make_from_tuple to work with tuple-like types, the
overloads of std::get for those types must have been declared before the
definition of std::make_from_tuple. That means we need to include the
definition of std::ranges::subrange in <tuple>.

The definitions of std::pair and its overloads of std::get are already
included in <tuple>. We provide forward declarations of std::array and
its std::get overloads in <tuple>. We could just declare subrange
without defining it, and give ranges::get a non-deduced return type,
like so:

  namespace ranges
  {
    enum class subrange_kind : bool { unsized, sized};

    template<input_or_output_iterator I, sentinel_for<I> S,
	     subrange_kind K>
      requires (K == subrange_kind::sized || !sized_sentinel_for<S, I>)
      class subrange;

    template<size_t _Num, class _It, class _Sent, subrange_kind _Kind>
      requires (_Num < 2)
      constexpr __conditional_t<_Num == 0, _It, _Sent>
      get(const subrange<_It, _Sent, _Kind>& __r);

    template<size_t _Num, class _It, class _Sent, subrange_kind _Kind>
      requires (_Num < 2)
      constexpr __conditional_t<_Num == 0, _It, _Sent>
      get(subrange<_It, _Sent, _Kind>&& __r)
  }
  using ranges::get;

It is a bit late in the GCC 13 dev cycle to do this, so just include the
right headers for now.

Also add the dangling check to std::make_from_tuple added by P2255.

libstdc++-v3/ChangeLog:

	PR libstdc++/102301
	* include/bits/ranges_base.h: Include <bits/stl_iterator.h> for
	std::make_reverse_iterator.
	* include/std/tuple: Include <bits/ranges_util.h> for subrange.
	(make_from_tuple): Add static assertion from P2255 to diagnose
	dangling references.
	* testsuite/20_util/tuple/make_from_tuple/dangling_ref.cc: New test.
	* testsuite/20_util/tuple/make_from_tuple/tuple_like.cc: New test.
This commit is contained in:
Jonathan Wakely 2023-01-23 12:25:36 +00:00
parent aba6416e95
commit 33ed110858
4 changed files with 61 additions and 5 deletions

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@ -34,7 +34,7 @@
#if __cplusplus > 201703L
#include <initializer_list>
#include <bits/iterator_concepts.h>
#include <bits/stl_iterator.h>
#include <ext/numeric_traits.h>
#include <bits/max_size_type.h>

View file

@ -37,10 +37,11 @@
#include <bits/stl_pair.h> // for std::pair
#include <bits/uses_allocator.h> // for std::allocator_arg_t
#include <bits/utility.h> // for std::get, std::tuple_size etc.
#include <bits/utility.h> // for std::tuple_size etc.
#include <bits/invoke.h> // for std::__invoke
#if __cplusplus > 201703L
# include <compare>
# include <bits/ranges_util.h> // for std::ranges::subrange
# define __cpp_lib_constexpr_tuple 201811L
#endif
@ -2312,9 +2313,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
make_from_tuple(_Tuple&& __t)
noexcept(__unpack_std_tuple<is_nothrow_constructible, _Tp, _Tuple>)
{
return __make_from_tuple_impl<_Tp>(
std::forward<_Tuple>(__t),
make_index_sequence<tuple_size_v<remove_reference_t<_Tuple>>>{});
constexpr size_t __n = tuple_size_v<remove_reference_t<_Tuple>>;
#if __has_builtin(__reference_constructs_from_temporary)
if constexpr (__n == 1)
{
using _Elt = decltype(std::get<0>(std::declval<_Tuple>()));
static_assert(!__reference_constructs_from_temporary(_Tp, _Elt));
}
#endif
return __make_from_tuple_impl<_Tp>(std::forward<_Tuple>(__t),
make_index_sequence<__n>{});
}
#endif // C++17

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@ -0,0 +1,5 @@
// { dg-do compile { target c++17 } }
#include <tuple>
std::tuple<short> f();
auto t = std::make_from_tuple<const int&>(f()); // { dg-error "here" }
// { dg-error "static assertion failed" "" { target *-*-* } 0 }

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@ -0,0 +1,43 @@
// { dg-do compile { target c++17 } }
#include <tuple>
#include <utility>
struct Two
{
Two(const char*, int);
};
void
test_pair()
{
auto two = std::make_from_tuple<Two>(std::pair("one", 2));
static_assert(std::is_same_v<decltype(two), Two>, "make from pair");
}
#include <array>
struct Three
{
Three(int, int, int);
};
void
test_array()
{
Three three = std::make_from_tuple<Three>(std::array<int, 3>{{1, 2, 3}});
static_assert(std::is_same_v<decltype(three), Three>, "make from array");
}
#if __cplusplus >= 202002L
#include <vector>
#include <ranges>
void
test_subrange() // PR libstdc++/102301
{
auto r = std::views::iota(0, 5);
auto v = std::make_from_tuple<std::vector<int>>(std::ranges::subrange(r));
static_assert(std::is_same_v<decltype(v), std::vector<int>>, "from subrange");
}
#endif