Fuse `<xstddef>` into `<type_traits>` (#3654)

stl/CMakeLists.txt

@@ -247,7 +247,6 @@ set(HEADERS
     ${CMAKE_CURRENT_LIST_DIR}/inc/xnode_handle.h
     ${CMAKE_CURRENT_LIST_DIR}/inc/xpolymorphic_allocator.h
     ${CMAKE_CURRENT_LIST_DIR}/inc/xsmf_control.h
-    ${CMAKE_CURRENT_LIST_DIR}/inc/xstddef
     ${CMAKE_CURRENT_LIST_DIR}/inc/xstring
     ${CMAKE_CURRENT_LIST_DIR}/inc/xthreads.h
     ${CMAKE_CURRENT_LIST_DIR}/inc/xtimec.h

stl/inc/header-units.json

@@ -153,7 +153,6 @@
         "xnode_handle.h",
         "xpolymorphic_allocator.h",
         "xsmf_control.h",
-        "xstddef",
         "xstring",
         "xthreads.h",
         "xtimec.h",

stl/inc/type_traits

@@ -8,8 +8,9 @@
 #define _TYPE_TRAITS_
 #include <yvals_core.h>
 #if _STL_COMPILER_PREPROCESSOR
+#include <cstddef>
 #include <cstdint>
-#include <xstddef>
+#include <xtr1common>
 
 #pragma pack(push, _CRT_PACKING)
 #pragma warning(push, _STL_WARNING_LEVEL)
@@ -19,6 +20,10 @@ _STL_DISABLE_CLANG_WARNINGS
 #undef new
 
 _STD_BEGIN
+template <class>
+// TRANSITION, CWG-2518: false value attached to a dependent name (for static_assert)
+_INLINE_VAR constexpr bool _Always_false = false;
+
 _EXPORT_STD template <class _Ty, _Ty... _Vals>
 struct integer_sequence { // sequence of integer parameters
     static_assert(is_integral_v<_Ty>, "integer_sequence<T, I...> requires T to be an integral type.");

stl/inc/xstddef

@@ -1,32 +0,0 @@
-// xstddef internal header (core)
-
-// Copyright (c) Microsoft Corporation.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#pragma once
-#ifndef _XSTDDEF_
-#define _XSTDDEF_
-#include <yvals_core.h>
-#if _STL_COMPILER_PREPROCESSOR
-#include <cstddef>
-#include <xtr1common>
-
-#pragma pack(push, _CRT_PACKING)
-#pragma warning(push, _STL_WARNING_LEVEL)
-#pragma warning(disable : _STL_DISABLED_WARNINGS)
-_STL_DISABLE_CLANG_WARNINGS
-#pragma push_macro("new")
-#undef new
-
-_STD_BEGIN
-template <class>
-// TRANSITION, CWG-2518: false value attached to a dependent name (for static_assert)
-_INLINE_VAR constexpr bool _Always_false = false;
-_STD_END
-
-#pragma pop_macro("new")
-_STL_RESTORE_CLANG_WARNINGS
-#pragma warning(pop)
-#pragma pack(pop)
-#endif // _STL_COMPILER_PREPROCESSOR
-#endif // _XSTDDEF_

tests/std/tests/GH_001411_core_headers/test.cpp

@@ -21,7 +21,6 @@
 
 // <__msvc_iter_core.hpp> is included by <tuple>
 // <xkeycheck.h> should not be included outside of <yvals_core.h>
-// <xstddef> is included by <type_traits>
 // <xtr1common> is included by <cstddef>
 // <yvals_core.h> is included by every public core header
 

tests/std/tests/VSO_0000000_instantiate_iterators_misc/test.compile.pass.cpp

@@ -1624,7 +1624,7 @@ void typeindex_test() {
 
 template <typename FunctorArg, typename Arg>
 void functors_test_impl(Arg val) {
-    // Following from <xstddef>:
+    // Following from <type_traits> and <xutility>:
     (void) plus<FunctorArg>()(val, val);
     (void) minus<FunctorArg>()(val, val);
     (void) multiplies<FunctorArg>()(val, val);

tests/std/tests/VSO_0000000_instantiate_type_traits/test.compile.pass.cpp

@@ -124,7 +124,7 @@ void type_traits_test_impl() {
     TRAIT_V(is_null_pointer, T);
     TRAIT_V(is_union, T);
     TRAIT_V(is_class, T);
-    TRAIT_V(is_function, T); // from xstddef
+    TRAIT_V(is_function, T);
     TRAIT_V(is_fundamental, T);
     TRAIT_V(is_arithmetic, T); // from xtr1common
     TRAIT_V(is_object, T);