3 files changed, 33 insertions, 0 deletions
diff --git a/libcxx/include/__functional/is_transparent.h b/libcxx/include/__functional/is_transparent.h
index 567df1a..c2c6fbc 100644
--- a/libcxx/include/__functional/is_transparent.h
+++ b/libcxx/include/__functional/is_transparent.h
@@ -29,6 +29,14 @@ inline const bool __is_transparent_v<_Tp, _Key, __void_t<typename _Tp::is_transp
 
 #endif
 
+// Two types are considered transparently comparable if `comparator(key, arg)` is equivalent to `comparator(key,
+// <implicit cast to KeyT>(arg))`.
+//
+// This is different from `__is_transparent_v`, which is only a property of the comparator and doesn't provide
+// additional semantic guarantees.
+template <class _Comparator, class _KeyT, class _Arg, class = void>
+inline const bool __is_transparently_comparable_v = false;
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FUNCTIONAL_IS_TRANSPARENT
diff --git a/libcxx/include/__functional/operations.h b/libcxx/include/__functional/operations.h
index 7b0ea11..7f315ca 100644
--- a/libcxx/include/__functional/operations.h
+++ b/libcxx/include/__functional/operations.h
@@ -15,7 +15,9 @@
 #include <__functional/unary_function.h>
 #include <__fwd/functional.h>
 #include <__type_traits/desugars_to.h>
+#include <__type_traits/is_generic_transparent_comparator.h>
 #include <__type_traits/is_integral.h>
+#include <__type_traits/make_transparent.h>
 #include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -377,6 +379,14 @@ struct less<void> {
   typedef void is_transparent;
 };
 
+template <class _Tp>
+struct __make_transparent<less<_Tp> > {
+  using type _LIBCPP_NODEBUG = less<>;
+};
+
+template <>
+inline const bool __is_generic_transparent_comparator_v<less<>> = true;
+
 template <class _Tp, class _Up>
 inline const bool __desugars_to_v<__less_tag, less<>, _Tp, _Up> = true;
 
@@ -466,6 +476,14 @@ struct greater<void> {
 
 template <class _Tp, class _Up>
 inline const bool __desugars_to_v<__greater_tag, greater<>, _Tp, _Up> = true;
+
+template <class _Tp>
+struct __make_transparent<greater<_Tp>> {
+  using type _LIBCPP_NODEBUG = greater<>;
+};
+
+template <>
+inline const bool __is_generic_transparent_comparator_v<greater<>> = true;
 #endif
 
 // Logical operations
diff --git a/libcxx/include/__functional/ranges_operations.h b/libcxx/include/__functional/ranges_operations.h
index df95843..dc9da06 100644
--- a/libcxx/include/__functional/ranges_operations.h
+++ b/libcxx/include/__functional/ranges_operations.h
@@ -14,6 +14,7 @@
 #include <__concepts/totally_ordered.h>
 #include <__config>
 #include <__type_traits/desugars_to.h>
+#include <__type_traits/is_generic_transparent_comparator.h>
 #include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -108,6 +109,12 @@ inline const bool __desugars_to_v<__less_tag, ranges::less, _Tp, _Up> = true;
 template <class _Tp, class _Up>
 inline const bool __desugars_to_v<__greater_tag, ranges::greater, _Tp, _Up> = true;
 
+template <>
+inline const bool __is_generic_transparent_comparator_v<ranges::less> = true;
+
+template <>
+inline const bool __is_generic_transparent_comparator_v<ranges::greater> = true;
+
 #endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD