Narrows is_copy_constructible specialization for containers

Author: sdebionne

include/pybind11/cast.h

@@ -770,10 +770,32 @@ using movable_cast_op_type =
 // T is non-copyable, but code containing such a copy constructor fails to actually compile.
 template <typename T, typename SFINAE = void> struct is_copy_constructible : std::is_copy_constructible<T> {};
 
+// STL-like containers traits
+template <typename T, typename _ = void> struct is_container : std::false_type {};
+template <typename T> struct is_container<
+    T,
+    typename std::conditional<
+        false,
+        void_t<
+            typename T::value_type,
+            typename T::reference,
+            typename T::size_type,
+            typename T::iterator,
+            typename T::const_iterator,
+            decltype(std::declval<T>().size()),
+            decltype(std::declval<T>().begin()),
+            decltype(std::declval<T>().end()),
+            decltype(std::declval<T>().cbegin()),
+            decltype(std::declval<T>().cend())
+        >,
+        void
+    >::type> : public std::true_type {};
+
 // Specialization for types that appear to be copy constructible but also look like stl containers
 // (we specifically check for: has `value_type` and `reference` with `reference = value_type&`): if
 // so, copy constructability depends on whether the value_type is copy constructible.
 template <typename Container> struct is_copy_constructible<Container, enable_if_t<all_of<
+        is_container<Container>,
         std::is_copy_constructible<Container>,
         std::is_same<typename Container::value_type &, typename Container::reference>
     >::value>> : is_copy_constructible<typename Container::value_type> {};