[libc++][ranges] LWG3736: move_iterator missing disable_sized_sentinel_for specialization (#85611)

This pull request implements LWG3736: move_iterator missing
disable_sized_sentinel_for specialization.

Author: Xiaoyang Liu

libcxx/docs/Status/Cxx23Issues.csv

@@ -201,7 +201,7 @@
 "`3677 <https://wg21.link/LWG3677>`__","Is a cv-qualified ``pair`` specially handled in uses-allocator construction?", "November 2022","|Complete|","18.0",""
 "`3717 <https://wg21.link/LWG3717>`__","``common_view::end`` should improve ``random_access_range`` case", "November 2022","","","|ranges|"
 "`3732 <https://wg21.link/LWG3732>`__","``prepend_range`` and ``append_range`` can't be amortized constant time", "November 2022","|Nothing to do|","","|ranges|"
-"`3736 <https://wg21.link/LWG3736>`__","``move_iterator`` missing ``disable_sized_sentinel_for`` specialization", "November 2022","","","|ranges|"
+"`3736 <https://wg21.link/LWG3736>`__","``move_iterator`` missing ``disable_sized_sentinel_for`` specialization", "November 2022","|Complete|","19.0","|ranges|"
 "`3737 <https://wg21.link/LWG3737>`__","``take_view::sentinel`` should provide ``operator-``", "November 2022","","","|ranges|"
 "`3738 <https://wg21.link/LWG3738>`__","Missing preconditions for ``take_view`` constructor", "November 2022","|Complete|","16.0","|ranges|"
 "`3743 <https://wg21.link/LWG3743>`__","``ranges::to``'s reserve may be ill-formed", "November 2022","","","|ranges|"

libcxx/include/__iterator/move_iterator.h

@@ -330,6 +330,12 @@ operator+(typename move_iterator<_Iter>::difference_type __n, const move_iterato
 }
 #endif // _LIBCPP_STD_VER >= 20
 
+#if _LIBCPP_STD_VER >= 20
+template <class _Iter1, class _Iter2>
+  requires(!sized_sentinel_for<_Iter1, _Iter2>)
+inline constexpr bool disable_sized_sentinel_for<move_iterator<_Iter1>, move_iterator<_Iter2>> = true;
+#endif // _LIBCPP_STD_VER >= 20
+
 template <class _Iter>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 move_iterator<_Iter> make_move_iterator(_Iter __i) {
   return move_iterator<_Iter>(std::move(__i));

libcxx/include/iterator

@@ -475,6 +475,11 @@ constexpr move_iterator<Iterator> operator+(   // constexpr in C++17
 template <class Iterator>   // constexpr in C++17
 constexpr  move_iterator<Iterator> make_move_iterator(const Iterator& i);
 
+template<class Iterator1, class Iterator2>
+    requires (!sized_sentinel_for<Iterator1, Iterator2>)
+  inline constexpr bool disable_sized_sentinel_for<move_iterator<Iterator1>,    // since C++20
+                                                    move_iterator<Iterator2>> = true;
+
 template<semiregular S>
 class move_sentinel {
 public:

libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+#include <iterator>
+
+#include "test_iterators.h"
+
+using sized_it = random_access_iterator<int*>;
+static_assert(std::sized_sentinel_for<sized_it, sized_it>);
+static_assert(std::sized_sentinel_for<std::move_iterator<sized_it>, std::move_iterator<sized_it>>);
+
+struct unsized_it {
+  using value_type      = int;
+  using difference_type = std::ptrdiff_t;
+
+  value_type& operator*() const;
+  bool operator==(const unsized_it&) const;
+  difference_type operator-(const unsized_it&) const { return 0; }
+};
+
+template <>
+inline constexpr bool std::disable_sized_sentinel_for<unsized_it, unsized_it> = true;
+
+static_assert(!std::sized_sentinel_for<unsized_it, unsized_it>);
+static_assert(!std::sized_sentinel_for<std::move_iterator<unsized_it>, std::move_iterator<unsized_it>>);