Rails/Delegate false positive (arguments ignored)

[ryym]

Rails/Delegate warns incorrectly about a method call with arguments.

Sample code (a.rb):

# frozen_string_literal: true

# A
class A
  def b; end
end

# Foo
class Foo
  def a(n)
    p n
    A.new
  end

  def b
    a(1).b
  end
end

Foo.new.b

---

Expected behavior

rubocop a.rb reports no offenses.

Actual behavior

It reports an offense like this:

a.rb:13:3: C: Rails/Delegate: Use delegate to define delegations.
  def b
  ^^^

But obviously Foo#b method cannot be delegate to a.b. In fact, auto-fixed code raises an error.

$ bin/rails runner "load 'a.rb'"
1

$ rubocop -a a.rb
$ bin/rails runner "load 'a.rb'"
a.rb:10:in `a': wrong number of arguments (given 0, expected 1) (ArgumentError)
        from a.rb:15:in `b'
        ...

Auto-fixed code:

 # frozen_string_literal: true
 
 # A
 class A
   def b; end
 end
 
 # Foo
 class Foo
   def a(n)
     p n
     A.new
   end
 
-  def b
-    a(1).b
-  end
+  delegate :b, to: :a
 end
 
 Foo.new.b

Steps to reproduce the problem

Run rubocop a.rb using this .rubocop.yml:

AllCops:
  TargetRailsVersion: 5.1

Rails:
  Enabled: true

RuboCop version

$ rubocop -V
0.52.1 (using Parser 2.4.0.2, running on ruby 2.4.2 x86_64-darwin16)