[libc++] Bump the C++ Standard used to compile the dylib to C++23

This is necessary in order to implement some papers like P2467R1, which
require using C++23 declarations in the dylib. It is a good habit to keep
building the dylib with a recent standard version regardless.

Author: ldionne

libcxx/CMakeLists.txt

@@ -504,10 +504,9 @@ remove_flags(-Wno-pedantic -pedantic-errors -pedantic)
 # Required flags ==============================================================
 function(cxx_add_basic_build_flags target)
 
-  # Require C++20 for all targets. C++17 is needed to use aligned allocation
-  # in the dylib. C++20 is needed to use char8_t.
+  # Require C++23 for all targets.
   set_target_properties(${target} PROPERTIES
-    CXX_STANDARD 20
+    CXX_STANDARD 23
     CXX_STANDARD_REQUIRED YES
     CXX_EXTENSIONS NO)
 

libcxx/src/include/sso_allocator.h

@@ -11,6 +11,7 @@
 #define _LIBCPP_SSO_ALLOCATOR_H
 
 #include <__config>
+#include <cstddef>
 #include <memory>
 #include <new>
 #include <type_traits>
@@ -34,7 +35,7 @@ class _LIBCPP_HIDDEN __sso_allocator<void, _Np>
 template <class _Tp, size_t _Np>
 class _LIBCPP_HIDDEN __sso_allocator
 {
-    typename aligned_storage<sizeof(_Tp) * _Np>::type buf_;
+    alignas(_Tp) std::byte buf_[sizeof(_Tp) * _Np];
     bool __allocated_;
 public:
     typedef size_t            size_type;

libcxx/src/locale.cpp

@@ -10,6 +10,7 @@
 #include <algorithm>
 #include <clocale>
 #include <codecvt>
+#include <cstddef>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
@@ -87,7 +88,7 @@ struct release
 template <class T, class ...Args>
 T& make(Args ...args)
 {
-    static typename aligned_storage<sizeof(T)>::type buf;
+    alignas(T) static std::byte buf[sizeof(T)];
     auto *obj = ::new (&buf) T(args...);
     return *obj;
 }
@@ -541,7 +542,7 @@ const locale&
 locale::__imp::make_classic()
 {
     // only one thread can get in here and it only gets in once
-    static aligned_storage<sizeof(locale)>::type buf;
+    alignas(locale) static std::byte buf[sizeof(locale)];
     locale* c = reinterpret_cast<locale*>(&buf);
     c->__locale_ = &make<__imp>(1u);
     return *c;
@@ -558,7 +559,7 @@ locale&
 locale::__imp::make_global()
 {
     // only one thread can get in here and it only gets in once
-    static aligned_storage<sizeof(locale)>::type buf;
+    alignas(locale) static std::byte buf[sizeof(locale)];
     auto *obj = ::new (&buf) locale(locale::classic());
     return *obj;
 }

libcxx/test/tools/clang_tidy_checks/CMakeLists.txt

@@ -33,7 +33,7 @@ set(Clang_DIR "${Clang_DIR_SAVE}" CACHE PATH "The directory containing a CMake c
 
 message(STATUS "Found system-installed LLVM ${LLVM_PACKAGE_VERSION} with headers in ${LLVM_INCLUDE_DIRS}")
 
-set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD 23)
 
 # Link only against clangTidy itself, not anything that clangTidy uses; otherwise we run setup code multiple times
 # which results in clang-tidy crashing
@@ -58,7 +58,7 @@ add_library(cxx-tidy MODULE ${SOURCES})
 target_link_libraries(cxx-tidy clangTidy)
 
 set_target_properties(cxx-tidy PROPERTIES
-                      CXX_STANDARD 20
+                      CXX_STANDARD 23
                       CXX_STANDARD_REQUIRED YES
                       CXX_EXTENSIONS NO)
 

libcxxabi/src/CMakeLists.txt

@@ -171,7 +171,7 @@ target_link_libraries(cxxabi_shared_objects PUBLIC cxxabi-headers)
 set_target_properties(cxxabi_shared_objects
   PROPERTIES
     CXX_EXTENSIONS OFF
-    CXX_STANDARD 20
+    CXX_STANDARD 23
     CXX_STANDARD_REQUIRED OFF
     COMPILE_FLAGS "${LIBCXXABI_COMPILE_FLAGS}"
     DEFINE_SYMBOL ""
@@ -251,7 +251,7 @@ target_link_libraries(cxxabi_static_objects PUBLIC cxxabi-headers)
 set_target_properties(cxxabi_static_objects
   PROPERTIES
     CXX_EXTENSIONS OFF
-    CXX_STANDARD 20
+    CXX_STANDARD 23
     CXX_STANDARD_REQUIRED OFF
     COMPILE_FLAGS "${LIBCXXABI_COMPILE_FLAGS}"
 )