Deprecate and inline some historical inline variables in Abseil

PiperOrigin-RevId: 911711219
Change-Id: Icf6fa5f06d4c9f251d1f4139f942182c078db743

Author: Abseil Team

absl/types/variant.h

@@ -56,13 +56,17 @@ template <size_t I, typename T>
 using variant_alternative_t ABSL_REFACTOR_INLINE
     = std::variant_alternative_t<I, T>;
 
-using std::variant_npos;
+inline constexpr size_t variant_npos ABSL_REFACTOR_INLINE
+    = std::variant_npos;
 
 template <typename T>
 using variant_size ABSL_REFACTOR_INLINE
     = std::variant_size<T>;
 
-using std::variant_size_v;
+template <typename T>
+inline constexpr size_t variant_size_v ABSL_REFACTOR_INLINE
+    = std::variant_size_v<T>;
+
 using std::visit;
 
 namespace variant_internal {

absl/utility/utility.h

@@ -38,15 +38,22 @@ ABSL_NAMESPACE_BEGIN
 using std::apply;
 using std::exchange;
 using std::forward;
-using std::in_place;
-using std::in_place_index;
+
+inline constexpr const std::in_place_t& in_place ABSL_DEPRECATE_AND_INLINE() =
+    std::in_place;
+
+template <size_t I>
+inline constexpr const std::in_place_index_t<I>& in_place_index
+ABSL_DEPRECATE_AND_INLINE() = std::in_place_index<I>;
 
 template <size_t I>
 using in_place_index_t ABSL_DEPRECATE_AND_INLINE() = std::in_place_index_t<I>;
 
 using in_place_t ABSL_DEPRECATE_AND_INLINE() = std::in_place_t;
 
-using std::in_place_type;
+template <class T>
+inline constexpr const std::in_place_type_t<T>& in_place_type
+ABSL_DEPRECATE_AND_INLINE() = std::in_place_type<T>;
 
 template <class T>
 using in_place_type_t ABSL_DEPRECATE_AND_INLINE() = std::in_place_type_t<T>;