key_nodeptr_comp broken if the key type is void*

[Andrey Semashev]

This is a regression since 1.60. boost::intrusive::set::insert_check() fails to compile if called with a key that has type void*. The error is as follows:

/home/lastique/src/boost-xcoder/boost/intrusive/detail/key_nodeptr_comp.hpp:87: error: no match for call to ‘(MediaBufferBase::callback_list::callback_reference::order_by_key) (const MediaBufferBase::callback_list::callback_reference&)’
    {  return base().get()(key_of_value()(*traits_->to_value_ptr(t1)));  }
              ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The problem is in key_nodeptr_comp implementation, which has an overload of operator() whith two formal parameters, the second one being used for enable_if_c and having the type void*. This operator calls user's ordering predicate with only one argument, which is naturally not expected.

The suggested solution is to use SFINAE on the return type of the operators or use a more distinct type for the hidden argument of the operators.

[Andrey Semashev]

Here is a fix: ​https://github.com/boostorg/intrusive/pull/21.