[libcxx][NFC] Make sequence containers slightly more SFINAE-friendly during CTAD.

Disable the constructors taking `(size_type, const value_type&,
allocator_type)` if `allocator_type` is not a valid allocator.
Otherwise, these constructors are considered when resolving e.g.
`(int*, int*, NotAnAllocator())`, leading to a hard error during
instantiation. A hard error makes the Standard's requirement to not
consider deduction guides of the form `(Iterator, Iterator,
BadAllocator)` during overload resolution essentially non-functional.

The previous approach was to SFINAE away `allocator_traits`. This patch
SFINAEs away the specific constructors instead, for consistency with
`basic_string` -- see [LWG3076](wg21.link/lwg3076) which describes
a very similar problem for strings (note, however, that unlike LWG3076,
no valid constructor call is affected by the bad instantiation).

Differential Revision: https://reviews.llvm.org/D114311

libcxx/include/__memory/allocator_traits.h

@@ -349,14 +349,6 @@ struct _LIBCPP_TEMPLATE_VIS allocator_traits
     }
 };
 
-// A version of `allocator_traits` for internal usage that SFINAEs away if the
-// given allocator doesn't have a nested `value_type`. This helps avoid hard
-// errors when forming implicit deduction guides for a container that has an
-// invalid Allocator type. See https://wg21.link/LWGXXXXX.
-// TODO(varconst): use the actual link once available.
-template <class _Alloc, class _ValueType = typename _Alloc::value_type>
-struct _LIBCPP_TEMPLATE_VIS __allocator_traits : allocator_traits<_Alloc> {};
-
 template <class _Traits, class _Tp>
 struct __rebind_alloc_helper {
 #ifndef _LIBCPP_CXX03_LANG

libcxx/include/deque

@@ -1266,7 +1266,7 @@ public:
     typedef typename __base::const_reference              const_reference;
     typedef typename __base::iterator                     iterator;
     typedef typename __base::const_iterator               const_iterator;
-    typedef typename __allocator_traits<allocator_type>::size_type   size_type;
+    typedef typename __base::size_type                    size_type;
     typedef typename __base::difference_type              difference_type;
 
     typedef typename __base::pointer                      pointer;
@@ -1289,7 +1289,14 @@ public:
     explicit deque(size_type __n, const _Allocator& __a);
 #endif
     deque(size_type __n, const value_type& __v);
-    deque(size_type __n, const value_type& __v, const allocator_type& __a);
+
+    template <class = __enable_if_t<__is_allocator<_Allocator>::value> >
+    deque(size_type __n, const value_type& __v, const allocator_type& __a) : __base(__a)
+    {
+        if (__n > 0)
+            __append(__n, __v);
+    }
+
     template <class _InputIter>
         deque(_InputIter __f, _InputIter __l,
               typename enable_if<__is_cpp17_input_iterator<_InputIter>::value>::type* = 0);
@@ -1608,14 +1615,6 @@ deque<_Tp, _Allocator>::deque(size_type __n, const value_type& __v)
         __append(__n, __v);
 }
 
-template <class _Tp, class _Allocator>
-deque<_Tp, _Allocator>::deque(size_type __n, const value_type& __v, const allocator_type& __a)
-    : __base(__a)
-{
-    if (__n > 0)
-        __append(__n, __v);
-}
-
 template <class _Tp, class _Allocator>
 template <class _InputIter>
 deque<_Tp, _Allocator>::deque(_InputIter __f, _InputIter __l,

libcxx/include/forward_list

@@ -186,6 +186,7 @@ template <class T, class Allocator, class Predicate>
 #include <iterator>
 #include <limits>
 #include <memory>
+#include <type_traits>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -647,7 +648,7 @@ public:
     typedef const value_type&                                           const_reference;
     typedef typename allocator_traits<allocator_type>::pointer          pointer;
     typedef typename allocator_traits<allocator_type>::const_pointer    const_pointer;
-    typedef typename __allocator_traits<allocator_type>::size_type     size_type;
+    typedef typename allocator_traits<allocator_type>::size_type        size_type;
     typedef typename allocator_traits<allocator_type>::difference_type  difference_type;
 
     typedef typename base::iterator       iterator;
@@ -669,7 +670,13 @@ public:
     explicit forward_list(size_type __n, const allocator_type& __a);
 #endif
     forward_list(size_type __n, const value_type& __v);
-    forward_list(size_type __n, const value_type& __v, const allocator_type& __a);
+
+    template <class = __enable_if_t<__is_allocator<_Alloc>::value> >
+    forward_list(size_type __n, const value_type& __v, const allocator_type& __a) : base(__a)
+    {
+        insert_after(cbefore_begin(), __n, __v);
+    }
+
     template <class _InputIterator>
         forward_list(_InputIterator __f, _InputIterator __l,
                      typename enable_if<
@@ -943,14 +950,6 @@ forward_list<_Tp, _Alloc>::forward_list(size_type __n, const value_type& __v)
     insert_after(cbefore_begin(), __n, __v);
 }
 
-template <class _Tp, class _Alloc>
-forward_list<_Tp, _Alloc>::forward_list(size_type __n, const value_type& __v,
-                                        const allocator_type& __a)
-    : base(__a)
-{
-    insert_after(cbefore_begin(), __n, __v);
-}
-
 template <class _Tp, class _Alloc>
 template <class _InputIterator>
 forward_list<_Tp, _Alloc>::forward_list(_InputIterator __f, _InputIterator __l,

libcxx/include/list

@@ -853,7 +853,7 @@ public:
     typedef const value_type&                              const_reference;
     typedef typename base::pointer                         pointer;
     typedef typename base::const_pointer                   const_pointer;
-    typedef typename __allocator_traits<allocator_type>::size_type   size_type;
+    typedef typename base::size_type                       size_type;
     typedef typename base::difference_type                 difference_type;
     typedef typename base::iterator                        iterator;
     typedef typename base::const_iterator                  const_iterator;
@@ -885,7 +885,16 @@ public:
     explicit list(size_type __n, const allocator_type& __a);
 #endif
     list(size_type __n, const value_type& __x);
-    list(size_type __n, const value_type& __x, const allocator_type& __a);
+    template <class = __enable_if_t<__is_allocator<_Alloc>::value> >
+    list(size_type __n, const value_type& __x, const allocator_type& __a) : base(__a)
+    {
+#if _LIBCPP_DEBUG_LEVEL == 2
+        __get_db()->__insert_c(this);
+#endif
+        for (; __n > 0; --__n)
+            push_back(__x);
+    }
+
     template <class _InpIter>
         list(_InpIter __f, _InpIter __l,
              typename enable_if<__is_cpp17_input_iterator<_InpIter>::value>::type* = 0);
@@ -1241,17 +1250,6 @@ list<_Tp, _Alloc>::list(size_type __n, const value_type& __x)
         push_back(__x);
 }
 
-template <class _Tp, class _Alloc>
-list<_Tp, _Alloc>::list(size_type __n, const value_type& __x, const allocator_type& __a)
-    : base(__a)
-{
-#if _LIBCPP_DEBUG_LEVEL == 2
-    __get_db()->__insert_c(this);
-#endif
-    for (; __n > 0; --__n)
-        push_back(__x);
-}
-
 template <class _Tp, class _Alloc>
 template <class _InpIter>
 list<_Tp, _Alloc>::list(_InpIter __f, _InpIter __l,

libcxx/include/vector

@@ -359,7 +359,7 @@ public:
     typedef allocator_traits<allocator_type>                __alloc_traits;
     typedef value_type&                                     reference;
     typedef const value_type&                               const_reference;
-    typedef typename __allocator_traits<allocator_type>::size_type   size_type;
+    typedef typename __alloc_traits::size_type              size_type;
     typedef typename __alloc_traits::difference_type        difference_type;
     typedef typename __alloc_traits::pointer                pointer;
     typedef typename __alloc_traits::const_pointer          const_pointer;
@@ -395,7 +395,21 @@ public:
     explicit vector(size_type __n, const allocator_type& __a);
 #endif
     vector(size_type __n, const value_type& __x);
-    vector(size_type __n, const value_type& __x, const allocator_type& __a);
+
+    template <class = __enable_if_t<__is_allocator<_Allocator>::value> >
+    vector(size_type __n, const value_type& __x, const allocator_type& __a)
+        : __base(__a)
+    {
+#if _LIBCPP_DEBUG_LEVEL == 2
+      __get_db()->__insert_c(this);
+#endif
+      if (__n > 0)
+      {
+          __vallocate(__n);
+          __construct_at_end(__n, __x);
+      }
+    }
+
     template <class _InputIterator>
         vector(_InputIterator __first,
                typename enable_if<__is_cpp17_input_iterator  <_InputIterator>::value &&
@@ -1126,20 +1140,6 @@ vector<_Tp, _Allocator>::vector(size_type __n, const value_type& __x)
     }
 }
 
-template <class _Tp, class _Allocator>
-vector<_Tp, _Allocator>::vector(size_type __n, const value_type& __x, const allocator_type& __a)
-    : __base(__a)
-{
-#if _LIBCPP_DEBUG_LEVEL == 2
-    __get_db()->__insert_c(this);
-#endif
-    if (__n > 0)
-    {
-        __vallocate(__n);
-        __construct_at_end(__n, __x);
-    }
-}
-
 template <class _Tp, class _Allocator>
 template <class _InputIterator>
 vector<_Tp, _Allocator>::vector(_InputIterator __first,

libcxx/test/std/containers/sequences/deque/deque.cons/default_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/deque/deque.cons/dtor_noexcept.pass.cpp

@@ -25,6 +25,7 @@ struct some_alloc
     typedef T value_type;
     some_alloc(const some_alloc&);
     ~some_alloc() noexcept(false);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/deque/deque.cons/move_assign_noexcept.pass.cpp

@@ -29,6 +29,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/deque/deque.cons/move_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/deque/deque.special/swap_noexcept.pass.cpp

@@ -34,6 +34,7 @@ struct some_alloc
 
     some_alloc() {}
     some_alloc(const some_alloc&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::true_type propagate_on_container_swap;
@@ -46,6 +47,7 @@ struct some_alloc2
 
     some_alloc2() {}
     some_alloc2(const some_alloc2&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_swap;

libcxx/test/std/containers/sequences/forwardlist/forwardlist.cons/default_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/forwardlist/forwardlist.cons/dtor_noexcept.pass.cpp

@@ -25,6 +25,7 @@ struct some_alloc
     typedef T value_type;
     some_alloc(const some_alloc&);
     ~some_alloc() noexcept(false);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/forwardlist/forwardlist.cons/move_assign_noexcept.pass.cpp

@@ -29,6 +29,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/forwardlist/forwardlist.cons/move_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/forwardlist/forwardlist.spec/swap_noexcept.pass.cpp

@@ -35,6 +35,7 @@ struct some_alloc
 
     some_alloc() {}
     some_alloc(const some_alloc&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::true_type propagate_on_container_swap;
@@ -47,6 +48,7 @@ struct some_alloc2
 
     some_alloc2() {}
     some_alloc2(const some_alloc2&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_swap;

libcxx/test/std/containers/sequences/list/list.cons/default_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/list/list.cons/dtor_noexcept.pass.cpp

@@ -25,6 +25,7 @@ struct some_alloc
     typedef T value_type;
     some_alloc(const some_alloc&);
     ~some_alloc() noexcept(false);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/list/list.cons/move_assign_noexcept.pass.cpp

@@ -29,6 +29,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/list/list.cons/move_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/list/list.special/swap_noexcept.pass.cpp

@@ -34,6 +34,7 @@ struct some_alloc
 
     some_alloc() {}
     some_alloc(const some_alloc&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::true_type propagate_on_container_swap;
@@ -46,6 +47,7 @@ struct some_alloc2
 
     some_alloc2() {}
     some_alloc2(const some_alloc2&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_swap;

libcxx/test/std/containers/sequences/vector/vector.cons/default_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/vector/vector.cons/dtor_noexcept.pass.cpp

@@ -25,6 +25,7 @@ struct some_alloc
     typedef T value_type;
     some_alloc(const some_alloc&);
     ~some_alloc() noexcept(false);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/vector/vector.cons/move_assign_noexcept.pass.cpp

@@ -29,6 +29,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 template <class T>
@@ -38,6 +39,7 @@ struct some_alloc2
 
     some_alloc2() {}
     some_alloc2(const some_alloc2&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_move_assignment;
@@ -51,6 +53,7 @@ struct some_alloc3
 
     some_alloc3() {}
     some_alloc3(const some_alloc3&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_move_assignment;

libcxx/test/std/containers/sequences/vector/vector.cons/move_noexcept.pass.cpp

@@ -27,6 +27,7 @@ struct some_alloc
 {
     typedef T value_type;
     some_alloc(const some_alloc&);
+    void allocate(size_t);
 };
 
 int main(int, char**)

libcxx/test/std/containers/sequences/vector/vector.special/swap_noexcept.pass.cpp

@@ -35,6 +35,7 @@ struct some_alloc
 
     some_alloc() {}
     some_alloc(const some_alloc&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::true_type propagate_on_container_swap;
@@ -47,6 +48,7 @@ struct some_alloc2
 
     some_alloc2() {}
     some_alloc2(const some_alloc2&);
+    void allocate(size_t);
     void deallocate(void*, unsigned) {}
 
     typedef std::false_type propagate_on_container_swap;