[PATCH] libstdc++: Fix forwarding in __take/drop_of_repeat_view [PR112453]

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk/13?  (The
&& overloads are also missing on earlier branches, but I don't think
it makes a difference there since all uses of that operator* are on
lvalues before this fix.)

-- >8 --

We need to respect the value category of the repeat_view passed to these
two functions when accessing its _M_value member.  This revealed that
the space-efficient partial specialization of __box lacks && overloads
of operator* to match std::optional's API.

        PR libstdc++/112453

libstdc++-v3/ChangeLog:

        * include/std/ranges (__detail::__box::operator*): Define &&
        overloads as well.
        (__detail::__take_of_repeat_view): Forward __r when accessing
        its _M_value member.
        (__detail::__drop_of_repeat_view): Likewise.
        * testsuite/std/ranges/repeat/1.cc (test07): New test.
---
 libstdc++-v3/include/std/ranges               | 20 ++++++++++++++-----
 libstdc++-v3/testsuite/std/ranges/repeat/1.cc | 13 ++++++++++++
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 7893e3a84c9..41f95dc8f78 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -250,13 +250,21 @@ namespace ranges
        { return true; };
 
        constexpr _Tp&
-       operator*() noexcept
+       operator*() & noexcept
        { return _M_value; }
 
        constexpr const _Tp&
-       operator*() const noexcept
+       operator*() const & noexcept
        { return _M_value; }
 
+       constexpr _Tp&&
+       operator*() && noexcept
+       { return std::move(_M_value); }
+
+       constexpr const _Tp&&
+       operator*() const && noexcept
+       { return std::move(_M_value); }
+
        constexpr _Tp*
        operator->() noexcept
        { return std::__addressof(_M_value); }
@@ -7799,9 +7807,10 @@ namespace views::__adaptor
          using _Tp = remove_cvref_t<_Range>;
          static_assert(__is_repeat_view<_Tp>);
          if constexpr (sized_range<_Tp>)
-           return views::repeat(*__r._M_value, std::min(ranges::distance(__r), 
__n));
+           return views::repeat(*std::forward<_Range>(__r)._M_value,
+                                std::min(ranges::distance(__r), __n));
          else
-           return views::repeat(*__r._M_value, __n);
+           return views::repeat(*std::forward<_Range>(__r)._M_value, __n);
        }
 
       template<typename _Range>
@@ -7813,7 +7822,8 @@ namespace views::__adaptor
          if constexpr (sized_range<_Tp>)
            {
              auto __sz = ranges::distance(__r);
-             return views::repeat(*__r._M_value, __sz - std::min(__sz, __n));
+             return views::repeat(*std::forward<_Range>(__r)._M_value,
+                                  __sz - std::min(__sz, __n));
            }
          else
            return __r;
diff --git a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc 
b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
index 30636407ee2..9551414e2c8 100644
--- a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
@@ -2,6 +2,7 @@
 
 #include <ranges>
 #include <algorithm>
+#include <memory>
 #include <testsuite_hooks.h>
 
 #if __cpp_lib_ranges_repeat != 202207L
@@ -137,6 +138,17 @@ test06()
   static_assert( requires { views::repeat(move_only{}, 2); } );
 }
 
+void
+test07()
+{
+  // PR libstdc++/112453
+  auto t = std::views::repeat(std::make_unique<int>(5)) | std::views::take(2);
+  auto d = std::views::repeat(std::make_unique<int>(5)) | std::views::drop(2);
+
+  auto t2 = std::views::repeat(std::make_unique<int>(5), 4) | 
std::views::take(2);
+  auto d2 = std::views::repeat(std::make_unique<int>(5), 4) | 
std::views::drop(2);
+}
+
 int
 main()
 {
@@ -146,4 +158,5 @@ main()
   static_assert(test04());
   test05();
   test06();
+  test07();
 }
-- 
2.43.0.rc1