[libc++] Move enable_if to 2nd argument of std::vector(iterator, iterator) ctor

[pcc]

Summary

If a pointer is passed as the third argument of the (iterator,
iterator, allocator) constructor with the intention of it being
implicitly converted to the allocator type, it is possible for overload
resolution to favour the (iterator, iterator, enable_if) constructor.
Eliminate this possibility by moving the enable_if to one of the
existing arguments and removing the third argument.

[rsmith]

include/vector

521–528

I don't believe this is a correct change.

std::vector<int> v( {}, my_weird_iterator );

... cannot deduce the type of _InputIterator.

include/vector

#endif
     {
 #if _LIBCPP_DEBUG_LEVEL >= 2
         __get_db()->__insert_c(this);
 #endif
     }
     explicit vector(size_type __n);
     vector(size_type __n, const_reference __x);
     vector(size_type __n, const_reference __x, const allocator_type& __a);
     template <class _InputIterator>
-        vector(_InputIterator __first, _InputIterator __last,
+        vector(_InputIterator __first,
                typename enable_if<__is_input_iterator  <_InputIterator>::value &&
                                  !__is_forward_iterator<_InputIterator>::value &&
                                  is_constructible<
                                     value_type,
-                                    typename iterator_traits<_InputIterator>::reference>::value>::type* = 0);
+                                    typename iterator_traits<_InputIterator>::reference>::value,
+                                 _InputIterator>::type __last);
     template <class _InputIterator>
         vector(_InputIterator __first, _InputIterator __last, const allocator_type& __a,
                typename enable_if<__is_input_iterator  <_InputIterator>::value &&
                                  !__is_forward_iterator<_InputIterator>::value &&
                                  is_constructible<
                                     value_type,
                                     typename iterator_traits<_InputIterator>::reference>::value>::type* = 0);
     template <class _ForwardIterator>
-        vector(_ForwardIterator __first, _ForwardIterator __last,
+        vector(_ForwardIterator __first,
                typename enable_if<__is_forward_iterator<_ForwardIterator>::value &&
                                  is_constructible<
                                     value_type,
-                                    typename iterator_traits<_ForwardIterator>::reference>::value>::type* = 0);
+                                    typename iterator_traits<_ForwardIterator>::reference>::value,
+                                 _ForwardIterator>::type __last);
     template <class _ForwardIterator>
         vector(_ForwardIterator __first, _ForwardIterator __last, const allocator_type& __a,
                typename enable_if<__is_forward_iterator<_ForwardIterator>::value &&
                                  is_constructible<
                                     value_type,
                                     typename iterator_traits<_ForwardIterator>::reference>::value>::type* = 0);
 #ifndef _LIBCPP_HAS_NO_GENERALIZED_INITIALIZERS
     _LIBCPP_INLINE_VISIBILITY
#endif
     {
         allocate(__n);
         __construct_at_end(__n, __x);
     }
 }
 
 template <class _Tp, class _Allocator>
 template <class _InputIterator>
-vector<_Tp, _Allocator>::vector(_InputIterator __first, _InputIterator __last,
+vector<_Tp, _Allocator>::vector(_InputIterator __first,
        typename enable_if<__is_input_iterator  <_InputIterator>::value &&
                          !__is_forward_iterator<_InputIterator>::value &&
                          is_constructible<
                             value_type,
-                            typename iterator_traits<_InputIterator>::reference>::value>::type*)
+                            typename iterator_traits<_InputIterator>::reference>::value,
+                          _InputIterator>::type __last)
 {
 #if _LIBCPP_DEBUG_LEVEL >= 2
     __get_db()->__insert_c(this);
 #endif
     for (; __first != __last; ++__first)
         push_back(*__first);
 }
 
#if _LIBCPP_DEBUG_LEVEL >= 2
     __get_db()->__insert_c(this);
 #endif
     for (; __first != __last; ++__first)
         push_back(*__first);
 }
 
 template <class _Tp, class _Allocator>
 template <class _ForwardIterator>
-vector<_Tp, _Allocator>::vector(_ForwardIterator __first, _ForwardIterator __last,
+vector<_Tp, _Allocator>::vector(_ForwardIterator __first,
                                 typename enable_if<__is_forward_iterator<_ForwardIterator>::value &&
                                 is_constructible<
                                    value_type,
-                                   typename iterator_traits<_ForwardIterator>::reference>::value>::type*)
+                                   typename iterator_traits<_ForwardIterator>::reference>::value,
+                                                   _ForwardIterator>::type __last)
 {
 #if _LIBCPP_DEBUG_LEVEL >= 2
     __get_db()->__insert_c(this);
 #endif
     size_type __n = static_cast<size_type>(_VSTD::distance(__first, __last));
     if (__n > 0)
     {
         allocate(__n);

test/containers/sequences/vector/vector.cons/construct_iter_iter_alloc.pass.cpp

 
 #include <vector>
 #include <cassert>
 
 #include "test_iterators.h"
 #include "../../../stack_allocator.h"
 #include "../../../min_allocator.h"
 
-template <class C, class Iterator>
+template <class C, class Iterator, class A>
 void
-test(Iterator first, Iterator last, const typename C::allocator_type& a)
+test(Iterator first, Iterator last, const A& a)
 {
     C c(first, last, a);
     assert(c.__invariants());
     assert(c.size() == std::distance(first, last));
     for (typename C::const_iterator i = c.cbegin(), e = c.cend(); i != e; ++i, ++first)
         assert(*i == *first);
 }
 
+template <class T>
+struct implicit_conv_allocator : min_allocator<T>
+{
+    implicit_conv_allocator(void* p) {}
+    implicit_conv_allocator(const implicit_conv_allocator&) = default;
+};
+
 int main()
 {
     {
     int a[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 8, 7, 6, 5, 4, 3, 1, 0};
     int* an = a + sizeof(a)/sizeof(a[0]);
     std::allocator<int> alloc;
     test<std::vector<int> >(input_iterator<const int*>(a), input_iterator<const int*>(an), alloc);
     test<std::vector<int> >(forward_iterator<const int*>(a), forward_iterator<const int*>(an), alloc);
     test<std::vector<int> >(bidirectional_iterator<const int*>(a), bidirectional_iterator<const int*>(an), alloc);
     test<std::vector<int> >(random_access_iterator<const int*>(a), random_access_iterator<const int*>(an), alloc);
     test<std::vector<int> >(a, an, alloc);
     }
 #if __cplusplus >= 201103L
     {
     int a[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 8, 7, 6, 5, 4, 3, 1, 0};
     int* an = a + sizeof(a)/sizeof(a[0]);
     min_allocator<int> alloc;
     test<std::vector<int, min_allocator<int>> >(input_iterator<const int*>(a), input_iterator<const int*>(an), alloc);
     test<std::vector<int, min_allocator<int>> >(forward_iterator<const int*>(a), forward_iterator<const int*>(an), alloc);
     test<std::vector<int, min_allocator<int>> >(bidirectional_iterator<const int*>(a), bidirectional_iterator<const int*>(an), alloc);
     test<std::vector<int, min_allocator<int>> >(random_access_iterator<const int*>(a), random_access_iterator<const int*>(an), alloc);
     test<std::vector<int, min_allocator<int>> >(a, an, alloc);
+    test<std::vector<int, implicit_conv_allocator<int>> >(a, an, nullptr);
     }
 #endif
 }