Rubocop Style/Alias cop breaks code with nonsensical fix when autocorrecting

[preetpalS]

Rubocop Style/Alias cop breaks working ruby code with nonsensical fix when autocorrecting.

The following working code:

# frozen_string_literal: true

# Sample class
class SampleClass
  MY_CONSTANT = 1

  CONSTANT_HASH = {
    MY_CONSTANT => :sample
  }.freeze

  class << self
    def sample?
      (1..100).to_a.sample
    end
    alias_method CONSTANT_HASH[MY_CONSTANT], :'sample?'
  end
end

puts SampleClass.sample?
puts SampleClass.sample

Is autocorrected to following broken code:

# frozen_string_literal: true

# Sample class
class SampleClass
  MY_CONSTANT = 1

  CONSTANT_HASH = {
    MY_CONSTANT => :sample
  }.freeze

  class << self
    def sample?
      (1..100).to_a.sample
    end
    alias (const nil :CONSTANT_HASH) sample?
  end
end

puts SampleClass.sample?
puts SampleClass.sample

When using the following rubocop configuration (.rubocop.yml in same directory as source file):

AllCops:
  DisplayCopNames: true
  DisplayStyleGuide: true
  TargetRubyVersion: 2.4

---

Expected behavior

Rubocop (when autocorrecting) should not attempt to replace alias_method with alias when the first argument to alias_method is not a literal.

Actual behavior

Rubocop attempts (when autocorrecting) to replace alias_method with alias even the first argument to alias_method is not a literal. It converts alias_method CONSTANT_HASH[MY_CONSTANT], :'sample?' to alias (const nil :CONSTANT_HASH) sample? which is not valid code.

Steps to reproduce the problem

Full command line session (on Windows 10 in Emacs eshell using the Ruby from RubyInstaller2; this should not matter though) shown below to reproduce:

~/Projects/TMP $ cat .rubocop.yml 

AllCops:
  DisplayCopNames: true
  DisplayStyleGuide: true
  TargetRubyVersion: 2.4
~/Projects/TMP $ ruby -v
ruby 2.4.1p111 (2017-03-22 revision 58053) [x64-mingw32]
~/Projects/TMP $ cat alias_rubocop_test_case.rb 
# frozen_string_literal: true

# Sample class
class SampleClass
  MY_CONSTANT = 1

  CONSTANT_HASH = {
    MY_CONSTANT => :sample
  }.freeze

  class << self
    def sample?
      (1..100).to_a.sample
    end
    alias_method CONSTANT_HASH[MY_CONSTANT], :'sample?'
  end
end

puts SampleClass.sample?
puts SampleClass.sample
~/Projects/TMP $ rubocop --version
0.49.0
~/Projects/TMP $ ruby alias_rubocop_test_case.rb 
35
79
~/Projects/TMP $ rubocop -a alias_rubocop_test_case.rb 
Inspecting 1 file
E

Offenses:

alias_rubocop_test_case.rb:15:5: C: [Corrected] Style/Alias: Use alias instead of alias_method in a class body. (https://github.com/bbatsov/ruby-style-guide#alias-method)
    alias_method CONSTANT_HASH[MY_CONSTANT], :'sample?'
    ^^^^^^^^^^^^
alias_rubocop_test_case.rb:15:11: E: unexpected token tLPAREN2
(Using Ruby 2.4 parser; configure using TargetRubyVersion parameter, under AllCops)
    alias (const nil :CONSTANT_HASH) sample?
          ^

1 file inspected, 2 offenses detected, 1 offense corrected
~/Projects/TMP $ cat alias_rubocop_test_case.rb 
# frozen_string_literal: true

# Sample class
class SampleClass
  MY_CONSTANT = 1

  CONSTANT_HASH = {
    MY_CONSTANT => :sample
  }.freeze

  class << self
    def sample?
      (1..100).to_a.sample
    end
    alias (const nil :CONSTANT_HASH) sample?
  end
end

puts SampleClass.sample?
puts SampleClass.sample
~/Projects/TMP $ ruby alias_rubocop_test_case.rb 
alias_rubocop_test_case.rb:15: syntax error, unexpected '('
    alias (const nil :CONSTANT_HASH) samp
           ^
~/Projects/TMP $ 

RuboCop version

~/Projects/TMP $ rubocop -V
0.49.0 (using Parser 2.4.0.0, running on ruby 2.4.1 x64-mingw32)