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.

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 26b3a983f72e8ca0630e89f47c7549718060c0a7..86952b340965c239f9a53505ed0b1c55bd0fe3ba 100644 (file)
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -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>
 

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 3d82ed1c3706bed3f6aeb453f997de234a0af50b..c773b3a348bc4dc364db9ea554cae4df5339d9cb 100644 (file)
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -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
 

diff --git a/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/dangling_ref.cc b/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/dangling_ref.cc
new file mode 100644 (file)
index 0000000..7958ec8
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/dangling_ref.cc
@@ -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 }

diff --git a/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/tuple_like.cc b/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/tuple_like.cc
new file mode 100644 (file)
index 0000000..de69455
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/tuple_like.cc
@@ -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