Implement LWG-3743 ranges::to's reserve may be ill-formed (#3269)

Co-authored-by: Casey Carter <[email protected]>
Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: 3 people

stl/inc/ranges

@@ -7720,7 +7720,7 @@ namespace ranges {
         } else if constexpr (_Converts_constructible_insertable<_Rng, _Container, _Types...>) {
             _Container _Cont(_STD forward<_Types>(_Args)...);
             if constexpr (_Sized_and_reservable<_Rng, _Container>) {
-                _Cont.reserve(_RANGES size(_Range));
+                _Cont.reserve(static_cast<range_size_t<_Container>>(_RANGES size(_Range)));
             }
             _RANGES copy(_Range, _Container_inserter<range_reference_t<_Rng>>(_Cont));
             return _Cont;

stl/inc/xutility

@@ -3630,6 +3630,10 @@ namespace ranges {
         constexpr explicit _Subrange_base(const _Size_type&) noexcept {}
     };
 
+#if 1 // TRANSITION, VSO-1695918 - Warning C4324 incorrectly firing in the presence of `pragma pack`
+#pragma warning(push)
+#pragma warning(disable : 4324) // structure was padded due to alignment specifier
+#endif // TRANSITION, VSO-1695918 - Warning C4324 incorrectly firing in the presence of `pragma pack`
     _EXPORT_STD template <input_or_output_iterator _It, sentinel_for<_It> _Se, subrange_kind _Ki>
         requires (_Ki == subrange_kind::sized || !sized_sentinel_for<_Se, _It>)
     class subrange : public _Subrange_base<_It, _Se, _Ki> {
@@ -3792,6 +3796,9 @@ namespace ranges {
             return *this;
         }
     };
+#if 1 // TRANSITION, VSO-1695918 - Warning C4324 incorrectly firing in the presence of `pragma pack`
+#pragma warning(pop)
+#endif // TRANSITION, VSO-1695918 - Warning C4324 incorrectly firing in the presence of `pragma pack`
 
     template <input_or_output_iterator _It, sentinel_for<_It> _Se>
     subrange(_It, _Se) -> subrange<_It, _Se>;

tests/std/tests/P1206R7_vector_from_range/test.cpp

@@ -161,6 +161,11 @@ void test_vso1591034() {
     assert(counted_item::count == 6);
 }
 
+void test_LWG_3743() { // COMPILE-ONLY
+    ranges::subrange r(views::iota(0ULL) | views::take(5), 5);
+    (void) ranges::to<vector<unsigned long long>>(r, size_t{0});
+}
+
 int main() {
     // Validate views
     test_copyable_views();