OCaml compiler library : Attr_helper

`sig
type error = Multiple_attributes of string | No_payload_expected of string
val get_no_payload_attribute :
string -> Parsetree.attributes -> string Asttypes.loc option
val has_no_payload_attribute : string -> Parsetree.attributes -> bool
exception Error of Location.t * Attr_helper.error
val report_error : Attr_helper.error Format_doc.format_printer
val report_error_doc : Attr_helper.error Format_doc.printer
end`