attr.rb

module Thor
  module ClassMethods
    def attr_reader(*)
      super
    end

    def attr_writer(*)
      super
    end

    def attr_accessor(*)
      super
    end
  end
end

class Foo
  extend Thor::ClassMethods

  class << self
    def method_visibility(method)
      case
      when private_method_defined?(method)
        :private
      when protected_method_defined?(method)
        :protected
      else
        :public
      end
    end
  end

  attr_reader :pub

  protected

  attr_reader :prot
  alias protalias prot
  alias_method :protaliasmethod, :prot

  private

  attr_reader :priv
  alias privalias priv
  alias_method :privaliasmethod, :priv
end


f = Foo.new

puts "Public"
f.pub

puts

puts "Protected"
puts "prot: #{Foo.method_visibility(:prot)}"
puts "protalias: #{Foo.method_visibility(:protalias)}"
puts "protaliasmethod #{Foo.method_visibility(:protaliasmethod)}"

puts

puts "Private"
puts "priv: #{Foo.method_visibility(:priv)}"
puts "privalias: #{Foo.method_visibility(:privalias)}"
puts "privaliasmethod#{Foo.method_visibility(:privaliasmethod)}"

result.txt

$ ruby -v attr.rb
ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]
Public

Protected
prot: public
protalias: public
protaliasmethod public

Private
priv: public
privalias: public
privaliasmethod: public