Make list constexpr as part of P3372R3

Author: winner245

libcxx/docs/FeatureTestMacroTable.rst

@@ -416,6 +416,8 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_bitset``                                       ``202306L``
     ---------------------------------------------------------- -----------------
+    ``__cpp_lib_constexpr_list``                               ``202502L``
+    ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_new``                                ``202406L``
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_constrained_equality``                         *unimplemented*

libcxx/include/__memory/allocation_guard.h

@@ -49,24 +49,26 @@ struct __allocation_guard {
   using _Size _LIBCPP_NODEBUG    = typename allocator_traits<_Alloc>::size_type;
 
   template <class _AllocT> // we perform the allocator conversion inside the constructor
-  _LIBCPP_HIDE_FROM_ABI explicit __allocation_guard(_AllocT __alloc, _Size __n)
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI explicit __allocation_guard(_AllocT __alloc, _Size __n)
       : __alloc_(std::move(__alloc)),
         __n_(__n),
         __ptr_(allocator_traits<_Alloc>::allocate(__alloc_, __n_)) // initialization order is important
   {}
 
-  _LIBCPP_HIDE_FROM_ABI ~__allocation_guard() _NOEXCEPT { __destroy(); }
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI ~__allocation_guard() _NOEXCEPT { __destroy(); }
 
-  _LIBCPP_HIDE_FROM_ABI __allocation_guard(const __allocation_guard&) = delete;
-  _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard(const __allocation_guard&) = delete;
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard(__allocation_guard&& __other) _NOEXCEPT
       : __alloc_(std::move(__other.__alloc_)),
         __n_(__other.__n_),
         __ptr_(__other.__ptr_) {
     __other.__ptr_ = nullptr;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(const __allocation_guard& __other) = delete;
-  _LIBCPP_HIDE_FROM_ABI __allocation_guard& operator=(__allocation_guard&& __other) _NOEXCEPT {
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard&
+  operator=(const __allocation_guard& __other) = delete;
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI __allocation_guard&
+  operator=(__allocation_guard&& __other) _NOEXCEPT {
     if (std::addressof(__other) != this) {
       __destroy();
 
@@ -79,17 +81,17 @@ struct __allocation_guard {
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI _Pointer
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI _Pointer
   __release_ptr() _NOEXCEPT { // not called __release() because it's a keyword in objective-c++
     _Pointer __tmp = __ptr_;
     __ptr_         = nullptr;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI _Pointer __get() const _NOEXCEPT { return __ptr_; }
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI _Pointer __get() const _NOEXCEPT { return __ptr_; }
 
 private:
-  _LIBCPP_HIDE_FROM_ABI void __destroy() _NOEXCEPT {
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI void __destroy() _NOEXCEPT {
     if (__ptr_ != nullptr) {
       allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_, __n_);
     }

libcxx/include/__memory/pointer_traits.h

@@ -302,6 +302,14 @@ concept __resettable_smart_pointer_with_args = requires(_Smart __s, _Pointer __p
 
 #endif
 
+template <class _PtrTo, class _PtrFrom>
+_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _PtrTo __static_fancy_pointer_cast(const _PtrFrom& __p) {
+  using __ptr_traits   = pointer_traits<_PtrTo>;
+  using __element_type = typename __ptr_traits::element_type;
+  return __p ? __ptr_traits::pointer_to(*static_cast<__element_type*>(std::addressof(*__p)))
+             : static_cast<_PtrTo>(nullptr);
+}
+
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS