[libc++] Remove extension to support allocator<const T>

This extension is a portability trap for users, since no other standard
library supports it. Furthermore, the Standard explicitly allows
implementations to reject std::allocator<cv T>, so allowing it is
really going against the current.

This was discovered in D120684: this extension required `const_cast`ing
in `__construct_range_forward`, a fishy bit of code that can be removed
if we don't support the extension anymore.

Differential Revision: https://reviews.llvm.org/D120996

Author: ldionne

libcxx/docs/ReleaseNotes.rst

@@ -69,6 +69,11 @@ API Changes
 - The C++14 function ``std::quoted(const char*)`` is no longer supported in
   C++03 or C++11 modes.
 
+- libc++ no longer supports containers of ``const``-qualified element type,
+  such as ``vector<const T>`` and ``list<const T>``. This used to be supported
+  as an extension. Likewise, ``std::allocator<const T>`` is no longer supported.
+  If you were using ``vector<const T>``, replace it with ``vector<T>`` instead.
+
 ABI Changes
 -----------
 

libcxx/include/__memory/allocator.h

@@ -37,17 +37,6 @@ class _LIBCPP_TEMPLATE_VIS allocator<void>
 
     template <class _Up> struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {typedef allocator<_Up> other;};
 };
-
-template <>
-class _LIBCPP_TEMPLATE_VIS allocator<const void>
-{
-public:
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const void*       pointer;
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const void*       const_pointer;
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const void        value_type;
-
-    template <class _Up> struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {typedef allocator<_Up> other;};
-};
 #endif
 
 // This class provides a non-trivial default constructor to the class that derives from it
@@ -80,6 +69,7 @@ template <class _Tp>
 class _LIBCPP_TEMPLATE_VIS allocator
     : private __non_trivial_if<!is_void<_Tp>::value, allocator<_Tp> >
 {
+    static_assert(!is_const<_Tp>::value, "std::allocator does not support const types");
     static_assert(!is_volatile<_Tp>::value, "std::allocator does not support volatile types");
 public:
     typedef size_t      size_type;
@@ -158,84 +148,6 @@ class _LIBCPP_TEMPLATE_VIS allocator
 #endif
 };
 
-template <class _Tp>
-class _LIBCPP_TEMPLATE_VIS allocator<const _Tp>
-    : private __non_trivial_if<!is_void<_Tp>::value, allocator<const _Tp> >
-{
-    static_assert(!is_volatile<_Tp>::value, "std::allocator does not support volatile types");
-public:
-    typedef size_t      size_type;
-    typedef ptrdiff_t   difference_type;
-    typedef const _Tp   value_type;
-    typedef true_type   propagate_on_container_move_assignment;
-    typedef true_type   is_always_equal;
-
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    allocator() _NOEXCEPT = default;
-
-    template <class _Up>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    allocator(const allocator<_Up>&) _NOEXCEPT { }
-
-    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    const _Tp* allocate(size_t __n) {
-        if (__n > allocator_traits<allocator>::max_size(*this))
-            __throw_bad_array_new_length();
-        if (__libcpp_is_constant_evaluated()) {
-            return static_cast<const _Tp*>(::operator new(__n * sizeof(_Tp)));
-        } else {
-            return static_cast<const _Tp*>(_VSTD::__libcpp_allocate(__n * sizeof(_Tp), _LIBCPP_ALIGNOF(_Tp)));
-        }
-    }
-
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    void deallocate(const _Tp* __p, size_t __n) {
-        if (__libcpp_is_constant_evaluated()) {
-            ::operator delete(const_cast<_Tp*>(__p));
-        } else {
-            _VSTD::__libcpp_deallocate((void*) const_cast<_Tp *>(__p), __n * sizeof(_Tp), _LIBCPP_ALIGNOF(_Tp));
-        }
-    }
-
-    // C++20 Removed members
-#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS)
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp* pointer;
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp* const_pointer;
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp& reference;
-    _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp& const_reference;
-
-    template <class _Up>
-    struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {
-        typedef allocator<_Up> other;
-    };
-
-    _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_INLINE_VISIBILITY
-    const_pointer address(const_reference __x) const _NOEXCEPT {
-        return _VSTD::addressof(__x);
-    }
-
-    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY _LIBCPP_DEPRECATED_IN_CXX17
-    const _Tp* allocate(size_t __n, const void*) {
-        return allocate(__n);
-    }
-
-    _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_INLINE_VISIBILITY size_type max_size() const _NOEXCEPT {
-        return size_type(~0) / sizeof(_Tp);
-    }
-
-    template <class _Up, class... _Args>
-    _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_INLINE_VISIBILITY
-    void construct(_Up* __p, _Args&&... __args) {
-        ::new ((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
-    }
-
-    _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_INLINE_VISIBILITY
-    void destroy(pointer __p) {
-        __p->~_Tp();
-    }
-#endif
-};
-
 template <class _Tp, class _Up>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 bool operator==(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {return true;}

libcxx/include/__memory/shared_ptr.h

@@ -288,7 +288,7 @@ struct __shared_ptr_emplace
         : __storage_(_VSTD::move(__a))
     {
 #if _LIBCPP_STD_VER > 17
-        using _TpAlloc = typename __allocator_traits_rebind<_Alloc, _Tp>::type;
+        using _TpAlloc = typename __allocator_traits_rebind<_Alloc, remove_cv_t<_Tp>>::type;
         _TpAlloc __tmp(*__get_alloc());
         allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), _VSTD::forward<_Args>(__args)...);
 #else
@@ -305,7 +305,7 @@ struct __shared_ptr_emplace
 private:
     virtual void __on_zero_shared() _NOEXCEPT {
 #if _LIBCPP_STD_VER > 17
-        using _TpAlloc = typename __allocator_traits_rebind<_Alloc, _Tp>::type;
+        using _TpAlloc = typename __allocator_traits_rebind<_Alloc, remove_cv_t<_Tp>>::type;
         _TpAlloc __tmp(*__get_alloc());
         allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
 #else
@@ -960,7 +960,7 @@ template<class _Tp, class ..._Args, class = __enable_if_t<!is_array<_Tp>::value>
 _LIBCPP_HIDE_FROM_ABI
 shared_ptr<_Tp> make_shared(_Args&& ...__args)
 {
-    return _VSTD::allocate_shared<_Tp>(allocator<_Tp>(), _VSTD::forward<_Args>(__args)...);
+    return _VSTD::allocate_shared<_Tp>(allocator<typename remove_cv<_Tp>::type>(), _VSTD::forward<_Args>(__args)...);
 }
 
 template<class _Tp, class _Up>

libcxx/include/memory

@@ -895,19 +895,17 @@ void __construct_range_forward(_Alloc& __a, _Iter __begin1, _Iter __end1, _Ptr&
 }
 
 template <class _Alloc, class _Source, class _Dest,
-          class _RawSource = typename remove_const<_Source>::type,
-          class _RawDest = typename remove_const<_Dest>::type,
           class =
     typename enable_if<
         is_trivially_copy_constructible<_Dest>::value &&
-        is_same<_RawSource, _RawDest>::value &&
+        is_same<typename remove_const<_Source>::type, _Dest>::value &&
         (__is_default_allocator<_Alloc>::value || !__has_construct<_Alloc, _Dest*, _Source&>::value)
     >::type>
 _LIBCPP_INLINE_VISIBILITY
 void __construct_range_forward(_Alloc&, _Source* __begin1, _Source* __end1, _Dest*& __begin2) {
     ptrdiff_t _Np = __end1 - __begin1;
     if (_Np > 0) {
-        _VSTD::memcpy(const_cast<_RawDest*>(__begin2), __begin1, _Np * sizeof(_Dest));
+        _VSTD::memcpy(__begin2, __begin1, _Np * sizeof(_Dest));
         __begin2 += _Np;
     }
 }

libcxx/test/libcxx/containers/sequences/vector/const_value_type.pass.cpp

@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-// http://wg21.link/LWG2447 gives implementors freedom to reject volatile types in `std::allocator`.
+// http://wg21.link/LWG2447 gives implementors freedom to reject const or volatile types in `std::allocator`.
 
 #include <memory>
 
 std::allocator<volatile int> A1; // expected-error@*:* {{std::allocator does not support volatile types}}
-std::allocator<const volatile int> A2; // expected-error@*:* {{std::allocator does not support volatile types}}
+std::allocator<const int> A2; // expected-error@*:* {{std::allocator does not support const types}}

libcxx/test/libcxx/memory/allocator_volatile.verify.cpp renamed to libcxx/test/libcxx/memory/allocator.cv.verify.cpp

@@ -17,18 +17,10 @@
 #include <type_traits>
 
 typedef std::allocator<void> A1;
-typedef std::allocator<void const> A2;
-struct A3 : std::allocator<void> { };
-struct A4 : std::allocator<void const> { };
+struct A2 : std::allocator<void> { };
 
 static_assert(std::is_trivially_default_constructible<A1>::value, "");
 static_assert(std::is_trivial<A1>::value, "");
 
 static_assert(std::is_trivially_default_constructible<A2>::value, "");
 static_assert(std::is_trivial<A2>::value, "");
-
-static_assert(std::is_trivially_default_constructible<A3>::value, "");
-static_assert(std::is_trivial<A3>::value, "");
-
-static_assert(std::is_trivially_default_constructible<A4>::value, "");
-static_assert(std::is_trivial<A4>::value, "");

libcxx/test/libcxx/memory/allocator_void.trivial.compile.pass.cpp

@@ -202,9 +202,6 @@ void test()
     test_not_const<std::array<      volatile int, 1>>();
     test_false    <std::array<const volatile int, 1>>();
     test_true     <std::deque<               int>>();
-#ifdef _LIBCPP_VERSION
-    test_true     <std::deque<const          int>>();
-#endif // _LIBCPP_VERSION
     test_true     <std::forward_list<int>>();
     test_true     <std::list<int>>();
     test_true     <std::vector<int>>();
@@ -223,9 +220,6 @@ void test()
 
     // Container adaptors
     test_true     <std::stack<               int>>();
-#ifdef _LIBCPP_VERSION
-    test_true     <std::stack<const          int>>();
-#endif // _LIBCPP_VERSION
     test_true     <std::queue<int>>();
     test_true     <std::priority_queue<int>>();
 

libcxx/test/std/concepts/concepts.lang/concept.default.init/default_initializable.compile.pass.cpp

@@ -37,12 +37,12 @@ TEST_CONSTEXPR_CXX20 bool test() {
 
 int main(int, char**) {
   test<char>();
-  test<char const>();
+  test<int>();
   test<void>();
 
 #if TEST_STD_VER > 17
   static_assert(test<char>());
-  static_assert(test<char const>());
+  static_assert(test<int>());
   static_assert(test<void>());
 #endif
   return 0;

libcxx/test/std/utilities/memory/default.allocator/allocator.ctor.pass.cpp

@@ -26,15 +26,9 @@ int main(int, char**)
 {
     test<int>();
     test<void>();
-#ifdef _LIBCPP_VERSION // extension
-    test<int const>();
-#endif // _LIBCPP_VERSION
 
     static_assert(test<int>());
     static_assert(test<void>());
-#ifdef _LIBCPP_VERSION // extension
-    static_assert(test<int const>());
-#endif // _LIBCPP_VERSION
 
     return 0;
 }