monkey patch to allow use of dynamic fields in boost function

sunspot_dynamic_fields_patch.rb

module Sunspot
  class FieldFactory::Dynamic
    # avoid use of : in field name
    def build(dynamic_name)
      AttributeField.new("#{@name}_#{dynamic_name}", @type, @options.dup)
    end
  end

  class Setup
    # support using dynamicfields by using function { :"dynamic_field:field_name"}
    def field(field_name)
      if m = field_name.to_s.match(/([^:]*):(.*)/)
        dynamic_field_factory(m[1]).build(m[2])
      elsif field_factory = @field_factories_cache[field_name.to_sym]
        field_factory.build
      else
        raise(
            UnrecognizedFieldError,
            "No field configured for #{@class_name} with name '#{field_name}'"
        )
      end
    end
  end
end