You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: signature.rb
    path of file: ./repos/steep/lib/steep/diagnostic
    
    the code of the file until where you have to start completion: module Steep
  module Diagnostic
    module Signature
      class Base
        include Helper

        attr_reader :location

        def initialize(location:)
          @location = location
        e
    
        def header_line
          expected_kind =
            case decl
            when RBS::AST::Declarations::ModuleAlias
              "module"
            when RBS::AST::Declarations::ClassAlias
              "class"
            else
              raise
            end