[libc++] Make <map> std::map constexpr as part of P3372R3

libcxx/docs/FeatureTestMacroTable.rst

@@ -430,6 +430,8 @@ Status
  ---------------------------------------------------------- -----------------
  ``__cpp_lib_constexpr_list`` ``202502L``
  ---------------------------------------------------------- -----------------
+ ``__cpp_lib_constexpr_map`` ``202502L``
+ ---------------------------------------------------------- -----------------
  ``__cpp_lib_constexpr_new`` ``202406L``
  ---------------------------------------------------------- -----------------
  ``__cpp_lib_constexpr_queue`` ``202502L``

libcxx/docs/ReleaseNotes/22.rst

@@ -45,6 +45,7 @@ Implemented Papers
 - P3060R3: Add ``std::views::indices(n)`` (`Github <https://llvm.org/PR148175>`__)
 - P2835R7: Expose ``std::atomic_ref``'s object address (`Github <https://llvm.org/PR118377>`__)
 - P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)
+- P3372R3: ``constexpr map`` (`Github <https://llvm.org/PR134330>`__) (The paper is partially implemented. ``constexpr map`` is implemented in this release)
 
 Improvements and New Features
 -----------------------------

libcxx/include/__iterator/erase_if_container.h

@@ -22,7 +22,8 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Container, class _Predicate>
-_LIBCPP_HIDE_FROM_ABI typename _Container::size_type __libcpp_erase_if_container(_Container& __c, _Predicate& __pred) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 typename _Container::size_type
+__libcpp_erase_if_container(_Container& __c, _Predicate& __pred) {
  typename _Container::size_type __old_size = __c.size();
 
  const typename _Container::iterator __last = __c.end();

libcxx/include/__node_handle

@@ -31,29 +31,29 @@ private:
 public:
  // [container.node.cons], constructors, copy, and assignment
  constexpr node-handle() noexcept : ptr_(), alloc_() {}
- node-handle(node-handle&&) noexcept;
- node-handle& operator=(node-handle&&);
+ constexpr node-handle(node-handle&&) noexcept; // constexpr since C++26
+ constexpr node-handle& operator=(node-handle&&); // constexpr since C++26
 
  // [container.node.dtor], destructor
- ~node-handle();
+ constexpr ~node-handle(); // constexpr since C++26
 
  // [container.node.observers], observers
  value_type& value() const; // not present for map containers
  key_type& key() const; // not present for set containers
- mapped_type& mapped() const; // not present for set containers
+ constexpr mapped_type& mapped() const; // not present for set containers, constexpr since C++26
 
- allocator_type get_allocator() const;
- explicit operator bool() const noexcept;
- [[nodiscard]] bool empty() const noexcept; // nodiscard since C++20
+ constexpr allocator_type get_allocator() const; // constexpr since C++26
+ constexpr explicit operator bool() const noexcept; // constexpr since C++26
+ [[nodiscard]] constexpr bool empty() const noexcept; // nodiscard since C++20, constexpr since C++26
 
  // [container.node.modifiers], modifiers
- void swap(node-handle&)
+ constexpr void swap(node-handle&)
  noexcept(ator_traits::propagate_on_container_swap::value ||
- ator_traits::is_always_equal::value);
+ ator_traits::is_always_equal::value); // constexpr since C++26
 
- friend void swap(node-handle& x, node-handle& y) noexcept(noexcept(x.swap(y))) {
+ constexpr friend void swap(node-handle& x, node-handle& y) noexcept(noexcept(x.swap(y))) {
  x.swap(y);
- }
+ } // constexpr since C++26
 };
 
 */
@@ -99,12 +99,12 @@ private:
  __node_pointer_type __ptr_ = nullptr;
  optional<allocator_type> __alloc_;
 
- _LIBCPP_HIDE_FROM_ABI void __release_ptr() {
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __release_ptr() {
  __ptr_ = nullptr;
  __alloc_ = std::nullopt;
  }
 
- _LIBCPP_HIDE_FROM_ABI void __destroy_node_pointer() {
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __destroy_node_pointer() {
  if (__ptr_ != nullptr) {
  typedef typename __allocator_traits_rebind< allocator_type, _NodeType>::type __node_alloc_type;
  __node_alloc_type __alloc(*__alloc_);
@@ -113,19 +113,20 @@ private:
  }
  }
 
- _LIBCPP_HIDE_FROM_ABI __basic_node_handle(__node_pointer_type __ptr, allocator_type const& __alloc)
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+ __basic_node_handle(__node_pointer_type __ptr, allocator_type const& __alloc)
  : __ptr_(__ptr), __alloc_(__alloc) {}
 
 public:
- _LIBCPP_HIDE_FROM_ABI __basic_node_handle() = default;
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __basic_node_handle() = default;
 
- _LIBCPP_HIDE_FROM_ABI __basic_node_handle(__basic_node_handle&& __other) noexcept
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __basic_node_handle(__basic_node_handle&& __other) noexcept
  : __ptr_(__other.__ptr_), __alloc_(std::move(__other.__alloc_)) {
  __other.__ptr_ = nullptr;
  __other.__alloc_ = std::nullopt;
  }
 
- _LIBCPP_HIDE_FROM_ABI __basic_node_handle& operator=(__basic_node_handle&& __other) {
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __basic_node_handle& operator=(__basic_node_handle&& __other) {
  _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
  __alloc_ == std::nullopt || __alloc_traits::propagate_on_container_move_assignment::value ||
  __alloc_ == __other.__alloc_,
@@ -144,13 +145,13 @@ public:
  return *this;
  }
 
- _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const { return *__alloc_; }
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 allocator_type get_allocator() const { return *__alloc_; }
 
- _LIBCPP_HIDE_FROM_ABI explicit operator bool() const { return __ptr_ != nullptr; }
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit operator bool() const { return __ptr_ != nullptr; }
 
- [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool empty() const { return __ptr_ == nullptr; }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool empty() const { return __ptr_ == nullptr; }
 
- _LIBCPP_HIDE_FROM_ABI void swap(__basic_node_handle& __other) noexcept(
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(__basic_node_handle& __other) noexcept(
  __alloc_traits::propagate_on_container_swap::value || __alloc_traits::is_always_equal::value) {
  using std::swap;
  swap(__ptr_, __other.__ptr_);
@@ -159,12 +160,12 @@ public:
  swap(__alloc_, __other.__alloc_);
  }
 
- _LIBCPP_HIDE_FROM_ABI friend void
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend void
  swap(__basic_node_handle& __a, __basic_node_handle& __b) noexcept(noexcept(__a.swap(__b))) {
  __a.swap(__b);
  }
 
- _LIBCPP_HIDE_FROM_ABI ~__basic_node_handle() { __destroy_node_pointer(); }
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 ~__basic_node_handle() { __destroy_node_pointer(); }
 };
 
 template <class _NodeType, class _Derived>
@@ -179,6 +180,7 @@ struct __map_node_handle_specifics {
  using key_type = __remove_const_t<typename _NodeType::__node_value_type::first_type>;
  using mapped_type = typename _NodeType::__node_value_type::second_type;
 
+ // This method is not constexpr as per the standard.
  _LIBCPP_HIDE_FROM_ABI key_type& key() const {
  return const_cast<key_type&>(static_cast<_Derived const*>(this)->__ptr_->__get_value().first);
  }