Make buffer_type public

Reason: Failures from GCC and Clang. See the new code comment.

doc/mrdocs.yml

@@ -16,6 +16,7 @@ exclude-symbols:
   - 'boost::detail::**'
   - 'boost::to_string_helper'
   - 'boost::dynamic_bitset::bit_appender'
+  - 'boost::dynamic_bitset::buffer_type'
 file-patterns:
   - '*.hpp'
 multipage: true

include/boost/dynamic_bitset/dynamic_bitset.hpp

@@ -84,11 +84,6 @@ template< typename Block, typename AllocatorOrContainer >
 class dynamic_bitset
 {
     BOOST_STATIC_ASSERT( (bool)detail::dynamic_bitset_impl::allowed_block_type< Block >::value );
-    typedef typename std::conditional<
-            detail::dynamic_bitset_impl::is_container< AllocatorOrContainer, Block >::value,
-            AllocatorOrContainer,
-            std::vector< Block, AllocatorOrContainer >
-        >::type                             buffer_type;
 
 public:
     //!     The same type as `Block`.
@@ -105,6 +100,16 @@ public:
     // -----------------------------------------------------------------------
     typedef std::size_t                     size_type;
 
+    //!     Note: Made public to cope with failures from many GCC and
+    //!     Clang versions which seem to ignore the friend declarations
+    //!     of `bit_iterator` and `const_bit_iterator`.
+    // -----------------------------------------------------------------------
+    typedef typename std::conditional<
+            detail::dynamic_bitset_impl::is_container< AllocatorOrContainer, Block >::value,
+            AllocatorOrContainer,
+            std::vector< Block, AllocatorOrContainer >
+        >::type                             buffer_type;
+
     //!     The number of bits the type `Block` uses to represent
     //!     values, excluding any padding bits. Numerically equal to
     //!     `std::numeric_limits< Block >::digits`.