fix includes, macro guards, and test header

Author: guptapratykshh

libs/core/type_support/include/hpx/type_support/is_replaceable.hpp

@@ -11,16 +11,14 @@
 #include <cstddef>
 #include <type_traits>
 
-#include <hpx/type_support/is_trivially_relocatable.hpp>
-
 namespace hpx::experimental {
 
-// P2786R13 defines a single feature-test macro __cpp_trivial_relocatability
-// that covers both the core-language keyword and the associated library traits
-// (std::is_trivially_relocatable, std::is_replaceable, std::relocate_at).
-// The language and library features are bundled in one proposal, so guarding on
-// this macro is sufficient to confirm that std::is_replaceable is available.
-#if defined(__cpp_trivial_relocatability)
+// std::is_replaceable is a library trait introduced by P2786R13.
+// Guard its use on the library feature-test macro __cpp_lib_trivially_relocatable
+// rather than the core-language macro __cpp_trivial_relocatability, since the
+// standard library may not ship the trait even when the language keyword is
+// available (or vice versa).
+#if defined(__cpp_lib_trivially_relocatable)
     HPX_CXX_CORE_EXPORT template <typename T>
     struct is_replaceable : std::is_replaceable<T>
     {

libs/core/type_support/include/hpx/type_support/is_trivially_relocatable.hpp

@@ -12,13 +12,12 @@
 
 namespace hpx::experimental {
 
-// P2786R13 defines a single feature-test macro __cpp_trivial_relocatability
-// that covers both the core-language keyword and the associated library traits
-// (std::is_trivially_relocatable, std::is_replaceable, std::relocate_at).
-// The language and library features are bundled in one proposal, so guarding on
-// this macro is sufficient to confirm that std::is_trivially_relocatable is
-// available.
-#if defined(__cpp_trivial_relocatability)
+// std::is_trivially_relocatable is a library trait introduced by P2786R13.
+// Guard its use on the library feature-test macro __cpp_lib_trivially_relocatable
+// rather than the core-language macro __cpp_trivial_relocatability, since the
+// standard library may not ship the trait even when the language keyword is
+// available (or vice versa).
+#if defined(__cpp_lib_trivially_relocatable)
     template <typename T>
     struct is_trivially_relocatable : std::is_trivially_relocatable<T>
     {

libs/core/type_support/include/hpx/type_support/relocate_at.hpp

@@ -13,6 +13,7 @@
 
 #include <concepts>
 #include <cstring>
+#include <memory>
 #include <type_traits>
 
 namespace hpx::detail {

libs/core/type_support/tests/unit/is_replaceable.cpp

@@ -4,7 +4,7 @@
 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
-#include <hpx/type_support/is_replaceable.hpp>
+#include <hpx/modules/type_support.hpp>
 
 #include <cassert>
 #include <memory>