Lint/UselessMethodDefinition: false positive(?) with mixed in method

[leoarnold]

Expected behavior

Given the test script

require 'action_controller'

class A
  include ActiveSupport::Configurable
  include ActionController::RequestForgeryProtection

  def valid_authenticity_token?(session, encoded_masked_token)
    super
  end
end

class B
  include ActiveSupport::Configurable
  include ActionController::RequestForgeryProtection
end

the method definition in class A seems necessary

$ irb -I. -rtest.rb
2.5.8 :001 > A.new.respond_to?(:valid_authenticity_token?)
 => true 
2.5.8 :002 > B.new.respond_to?(:valid_authenticity_token?)
 => false 

and therefore is not an offense.

Actual behavior

$ rubocop --only Lint/UselessMethodDefinition test.rb 
Inspecting 1 file
W

Offenses:

test.rb:7:3: W: Lint/UselessMethodDefinition: Useless method definition detected.
  def valid_authenticity_token?(session, encoded_masked_token) ...
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 file inspected, 1 offense detected, 1 offense auto-correctable

Steps to reproduce the problem

See above

RuboCop version

$ [bundle exec] rubocop -V
0.90.0 (using Parser 2.7.1.4, rubocop-ast 0.3.0, running on ruby 2.5.8 x86_64-linux)

[marcandre]

You are correct it isn't useless in the sense of having no side-effect, so maybe we should change the wording, but the only thing this code does is make the method public (and slow it down a bit).

It should be replaced by public :valid_authenticity_token?