[libc++] Make list constexpr as part of P3372R3 (#129799)

This patch makes `std::list` constexpr as part of P3372R3.

Fixes #128659.

Author: winner245

libcxx/docs/FeatureTestMacroTable.rst

@@ -422,6 +422,8 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_forward_list``                       ``202502L``
     ---------------------------------------------------------- -----------------
+    ``__cpp_lib_constexpr_list``                               ``202502L``
+    ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_new``                                ``202406L``
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_queue``                              ``202502L``

libcxx/include/list

@@ -71,6 +71,7 @@ __cpp_lib_constexpr_dynamic_alloc                       201907L <memory>
 __cpp_lib_constexpr_forward_list                        202502L <forward_list>
 __cpp_lib_constexpr_functional                          201907L <functional>
 __cpp_lib_constexpr_iterator                            201811L <iterator>
+__cpp_lib_constexpr_list                                202502L <list>
 __cpp_lib_constexpr_memory                              202202L <memory>
                                                         201811L // C++20
 __cpp_lib_constexpr_new                                 202406L <new>
@@ -545,6 +546,7 @@ __cpp_lib_void_t                                        201411L <type_traits>
 # undef  __cpp_lib_constexpr_algorithms
 # define __cpp_lib_constexpr_algorithms                 202306L
 # define __cpp_lib_constexpr_forward_list               202502L
+# define __cpp_lib_constexpr_list                       202502L
 # if !defined(_LIBCPP_ABI_VCRUNTIME)
 #   define __cpp_lib_constexpr_new                      202406L
 # endif

libcxx/include/version

@@ -10,34 +10,34 @@
 
 // template< class T, class Alloc >
 // bool operator==( const std::list<T,Alloc>& lhs,
-//                  const std::list<T,Alloc>& rhs );
+//                  const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 // template< class T, class Alloc >
 // bool operator!=( const std::list<T,Alloc>& lhs,
-//                  const std::list<T,Alloc>& rhs );
+//                  const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 // template< class T, class Alloc >
 // bool operator<( const std::list<T,Alloc>& lhs,
-//                 const std::list<T,Alloc>& rhs );
+//                 const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 // template< class T, class Alloc >
 // bool operator<=( const std::list<T,Alloc>& lhs,
-//                  const std::list<T,Alloc>& rhs );
+//                  const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 // template< class T, class Alloc >
 // bool operator>( const std::list<T,Alloc>& lhs,
-//                 const std::list<T,Alloc>& rhs );
+//                 const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 // template< class T, class Alloc >
 // bool operator>=( const std::list<T,Alloc>& lhs,
-//                  const std::list<T,Alloc>& rhs );
+//                  const std::list<T,Alloc>& rhs ); // constexpr since C++26
 
 #include <list>
 #include <cassert>
 
 #include "test_comparisons.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     const std::list<int> l1, l2;
     assert(testComparisons(l1, l2, true, false));
@@ -113,5 +113,15 @@ int main(int, char**) {
     const std::list<LessAndEqComp> l2(items2, items2 + 2);
     assert(testComparisons(l1, l2, false, false));
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }

libcxx/test/std/containers/sequences/list/compare.pass.cpp

@@ -11,7 +11,7 @@
 
 // template <class T, class Allocator> constexpr
 //   synth-three-way-result<T>
-//     operator<=>(const list<T, Allocator>& x, const list<T, Allocator>& y);
+//     operator<=>(const list<T, Allocator>& x, const list<T, Allocator>& y); // constexpr since C++26
 
 #include <list>
 #include <cassert>
@@ -20,6 +20,8 @@
 
 int main(int, char**) {
   assert(test_sequence_container_spaceship<std::list>());
-  // `std::list` is not constexpr, so no `static_assert` test here.
+#if TEST_STD_VER >= 26
+  static_assert(test_sequence_container_spaceship<std::list>());
+#endif
   return 0;
 }

libcxx/test/std/containers/sequences/list/compare.three_way.pass.cpp

@@ -10,15 +10,15 @@
 
 // class list
 
-// allocator_type get_allocator() const
+// allocator_type get_allocator() const // constexpr since C++26
 
 #include <list>
 #include <cassert>
 
 #include "test_allocator.h"
 #include "test_macros.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     std::allocator<int> alloc;
     const std::list<int> l(alloc);
@@ -30,5 +30,14 @@ int main(int, char**) {
     assert(l.get_allocator() == alloc);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }

libcxx/test/std/containers/sequences/list/get_allocator.pass.cpp

@@ -12,6 +12,7 @@
 // type.
 
 #include <list>
+#include <cassert>
 
 #include "test_macros.h"
 
@@ -23,8 +24,18 @@ struct A {
   std::list<A>::const_reverse_iterator crit;
 };
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   A a;
+  (void)a;
+
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }

libcxx/test/std/containers/sequences/list/incomplete_type.pass.cpp

@@ -8,12 +8,12 @@
 
 // <list>
 
-// iterator       begin();
-// iterator       end();
-// const_iterator begin()  const;
-// const_iterator end()    const;
-// const_iterator cbegin() const;
-// const_iterator cend()   const;
+// iterator       begin();        // constexpr since C++26
+// iterator       end();          // constexpr since C++26
+// const_iterator begin()  const; // constexpr since C++26
+// const_iterator end()    const; // constexpr since C++26
+// const_iterator cbegin() const; // constexpr since C++26
+// const_iterator cend()   const; // constexpr since C++26
 
 #include <list>
 #include <cassert>
@@ -27,7 +27,7 @@ struct A {
   int second;
 };
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef int T;
     typedef std::list<T> C;
@@ -74,6 +74,8 @@ int main(int, char**) {
     typedef std::list<T> C;
     C::iterator i;
     C::const_iterator j;
+    (void)i;
+    (void)j;
   }
 #if TEST_STD_VER >= 11
   {
@@ -122,6 +124,8 @@ int main(int, char**) {
     typedef std::list<T, min_allocator<T>> C;
     C::iterator i;
     C::const_iterator j;
+    (void)i;
+    (void)j;
   }
   {
     typedef A T;
@@ -150,5 +154,14 @@ int main(int, char**) {
   }
 #endif
 
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }

libcxx/test/std/containers/sequences/list/iterators.pass.cpp

@@ -10,15 +10,15 @@
 
 // class list
 
-// bool empty() const noexcept;
+// bool empty() const noexcept; // constexpr since C++26
 
 #include <list>
 #include <cassert>
 
 #include "test_macros.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::list<int> C;
     C c;
@@ -42,5 +42,14 @@ int main(int, char**) {
   }
 #endif
 
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }

libcxx/test/std/containers/sequences/list/list.capacity/empty.pass.cpp

@@ -8,7 +8,7 @@
 
 // <list>
 
-// size_type max_size() const noexcept
+// size_type max_size() const noexcept // constexpr since C++26
 
 #include <cassert>
 #include <limits>
@@ -18,7 +18,7 @@
 #include "test_allocator.h"
 #include "test_macros.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef limited_allocator<int, 10> A;
     typedef std::list<int, A> C;
@@ -42,5 +42,14 @@ int main(int, char**) {
     assert(c.max_size() <= alloc_max_size(c.get_allocator()));
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }