Incorrect example code for Lint/UselessAccessModifier

[Earlopain]

rubocop/lib/rubocop/cop/lint/useless_access_modifier.rb

Lines 114 to 126 in b4080d8

	# @example MethodCreatingMethods: delegate
	# # Lint/UselessAccessModifier:
	# # MethodCreatingMethods:
	# # - delegate
	#
	# # good
	# require 'active_support/core_ext/module/delegation'
	# class Foo
	# # this is not redundant because `delegate` creates methods
	# private
	#
	# delegate :method_a, to: :method_b
	# end

This says that the Rails method delegate respects access modifiers, however that doesn't seem to be the case:

require "active_support/core_ext/module/delegation"
require "ostruct"
class Bar
  def qux
    OpenStruct.new(baz: "bar")
  end
end

class Foo < Bar
  private
  delegate :baz, to: :qux # private: true is what you'd want
end

puts Foo.new.baz # works just fine

This is further supported by delegate having a keyword argument called private to achieve the desired behaviour: https://api.rubyonrails.org/classes/Module.html#method-i-delegate

I would change docs myself but can't actually think of a usecase for this config value.

[vlad-pisanov]

The delegate example is definitely wrong.

MethodCreatingMethods is for things like define_method that are aware of their current visibility. A somewhat contrived example would be:

class C
  private # wrongly flagged as Lint/UselessAccessModifier: Useless private access modifier
  
  send :define_method, :foo, -> { 'E621' } # `private` is respected when `foo` is defined
end

C.new.foo
# private method `foo' called for #<C:0x00007fa1770405b8> (NoMethodError)