# File lib/chef/mixin/deep_merge.rb, line 104
      def deep_merge!(source, dest, options = {})
        # turn on this line for stdout debugging text
        merge_debug = options[:merge_debug] || false
        overwrite_unmergeable = !options[:preserve_unmergeables]
        knockout_prefix = options[:knockout_prefix] || nil
        raise InvalidParameter, "knockout_prefix cannot be an empty string in deep_merge!" if knockout_prefix == ""
        raise InvalidParameter, "overwrite_unmergeable must be true if knockout_prefix is specified in deep_merge!" if knockout_prefix && !overwrite_unmergeable
        # if present: we will split and join arrays on this char before merging
        array_split_char = options[:unpack_arrays] || false
        # request that we sort together any arrays when they are merged
        sort_merged_arrays = options[:sort_merged_arrays] || false
        di = options[:debug_indent] || ''
        # do nothing if source is nil
        return dest if source.nil?
        # if dest doesn't exist, then simply copy source to it
        if dest.nil? && overwrite_unmergeable
          dest = source; return dest
        end

        puts "#{di}Source class: #{source.class.inspect} :: Dest class: #{dest.class.inspect}" if merge_debug
        if source.kind_of?(Hash)
          puts "#{di}Hashes: #{source.inspect} :: #{dest.inspect}" if merge_debug
          source.each do |src_key, src_value|
            if dest.kind_of?(Hash)
              puts "#{di} looping: #{src_key.inspect} => #{src_value.inspect} :: #{dest.inspect}" if merge_debug
              if dest[src_key]
                puts "#{di} ==>merging: #{src_key.inspect} => #{src_value.inspect} :: #{dest[src_key].inspect}" if merge_debug
                dest[src_key] = deep_merge!(src_value, dest[src_key], options.merge(:debug_indent => di + '  '))
              else # dest[src_key] doesn't exist so we want to create and overwrite it (but we do this via deep_merge!)
                puts "#{di} ==>merging over: #{src_key.inspect} => #{src_value.inspect}" if merge_debug
                # note: we rescue here b/c some classes respond to "dup" but don't implement it (Numeric, TrueClass, FalseClass, NilClass among maybe others)
                begin
                  src_dup = src_value.dup # we dup src_value if possible because we're going to merge into it (since dest is empty)
                rescue TypeError
                  src_dup = src_value
                end
                dest[src_key] = deep_merge!(src_value, src_dup, options.merge(:debug_indent => di + '  '))
              end
            else # dest isn't a hash, so we overwrite it completely (if permitted)
              if overwrite_unmergeable
                puts "#{di}  overwriting dest: #{src_key.inspect} => #{src_value.inspect} -over->  #{dest.inspect}" if merge_debug
                dest = overwrite_unmergeables(source, dest, options)
              end
            end
          end
        elsif source.kind_of?(Array)
          puts "#{di}Arrays: #{source.inspect} :: #{dest.inspect}" if merge_debug
          # if we are instructed, join/split any source arrays before processing
          if array_split_char
            puts "#{di} split/join on source: #{source.inspect}" if merge_debug
            source = source.join(array_split_char).split(array_split_char)
            if dest.kind_of?(Array)
              dest = dest.join(array_split_char).split(array_split_char)
            end
          end
          # if there's a naked knockout_prefix in source, that means we are to truncate dest
          ko_variants = [ knockout_prefix, "#{knockout_prefix}:" ]
          ko_variants.each do |ko|
            if source.index(ko)
              dest = clear_or_nil(dest); source.delete(ko)
            end
          end
          if dest.kind_of?(Array)
            if knockout_prefix
              print "#{di} knocking out: " if merge_debug
              # remove knockout prefix items from both source and dest
              source.delete_if do |ko_item|
                retval = false
                item = ko_item.respond_to?(:gsub) ? ko_item.gsub(%r{^#{knockout_prefix}:}, "") : ko_item
                if item != ko_item
                  print "#{ko_item} - " if merge_debug
                  dest.delete(item)
                  dest.delete(ko_item)
                  retval = true
                end
                retval
              end
              puts if merge_debug
            end
            puts "#{di} merging arrays: #{source.inspect} :: #{dest.inspect}" if merge_debug
            dest = dest | source
            dest.sort! if sort_merged_arrays
          elsif overwrite_unmergeable
            puts "#{di} overwriting dest: #{source.inspect} -over-> #{dest.inspect}" if merge_debug
            dest = overwrite_unmergeables(source, dest, options)
          end
        else # src_hash is not an array or hash, so we'll have to overwrite dest
          puts "#{di}Others: #{source.inspect} :: #{dest.inspect}" if merge_debug
          dest = overwrite_unmergeables(source, dest, options)
        end
        puts "#{di}Returning #{dest.inspect}" if merge_debug
        dest
      end