[PATCH] libstdc++: ranges::rotate should use ranges::iter_move [PR121913]

[Jonathan Wakely]

Using std::move(*it) is incorrect for iterators that use proxy refs, we
should use ranges::iter_move(it) instead.

libstdc++-v3/ChangeLog:

        PR libstdc++/121913
        * include/bits/ranges_algo.h (__rotate_fn::operator()): Use
        ranges::iter_move(it) instead of std::move(*it).
        * testsuite/25_algorithms/rotate/121913.cc: New test.
---

The testcase is highly contrived, but the fix seems worth doing anyway.

Tested powerpc64le-linux.

 libstdc++-v3/include/bits/ranges_algo.h       |  4 +-
 .../testsuite/25_algorithms/rotate/121913.cc  | 45 +++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/25_algorithms/rotate/121913.cc

diff --git a/libstdc++-v3/include/bits/ranges_algo.h 
b/libstdc++-v3/include/bits/ranges_algo.h
index 609b82e26d8a..9b348d82ce55 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -1685,7 +1685,7 @@ namespace ranges
                        {
                          auto __mid = ranges::next(__p, __n - 1);
                          auto __end = ranges::next(__mid);
-                         auto __t = std::move(*__p);
+                         auto __t = ranges::iter_move(__p);
                          ranges::move(ranges::next(__p), __end, __p);
                          *__mid = std::move(__t);
                          return {std::move(__ret), std::move(__lasti)};
@@ -1713,7 +1713,7 @@ namespace ranges
                        {
                          auto __mid = ranges::next(__p, __n - 1);
                          auto __end = ranges::next(__mid);
-                         auto __t = std::move(*__mid);
+                         auto __t = ranges::iter_move(__mid);
                          ranges::move_backward(__p, __mid, __end);
                          *__p = std::move(__t);
                          return {std::move(__ret), std::move(__lasti)};
diff --git a/libstdc++-v3/testsuite/25_algorithms/rotate/121913.cc 
b/libstdc++-v3/testsuite/25_algorithms/rotate/121913.cc
new file mode 100644
index 000000000000..d648699adbda
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/rotate/121913.cc
@@ -0,0 +1,45 @@
+// { dg-do compile { target c++20 } }
+
+// Bug libstdc++/121913  ranges::rotate should use ranges::iter_move
+
+#include <algorithm>
+
+struct A { };
+
+struct B
+{
+  B& operator=(const B&) = delete;
+  B& operator=(const A&) const;
+
+  operator A() const;
+};
+
+struct I
+{
+  using value_type = A;
+  using difference_type = int;
+  B operator*() const;
+  B operator[](int) const;
+  I& operator++();
+  I operator++(int);
+  I& operator--();
+  I operator--(int);
+  I& operator+=(int);
+  I& operator-=(int);
+
+  auto operator<=>(const I&) const = default;
+
+  friend A iter_move(const I&);
+  friend I operator+(I, int);
+  friend I operator-(I, int);
+  friend I operator+(int, I);
+  friend int operator-(I, I);
+};
+
+static_assert( std::random_access_iterator<I> );
+
+void
+test_pr121913()
+{
+  std::ranges::rotate(I{}, I{}, I{});
+}
-- 
2.51.0