Rubocop MutableConstant not observing frozen string literal comment

Question

I'm using RuboCop 0.46.0 and Ruby 2.3.1.

.rubocop.yml

Style/FrozenStringLiteralComment:
  EnforcedStyle: always

constant.rb

# frozen_string_literal: true

MY_CONSTANT = 'mystring'

When run, rubocop -D returns this:

Inspecting 1 file
C

Offenses:

constant.rb:3:15: C: Style/MutableConstant: Freeze mutable objects assigned to constants.
MY_CONSTANT = 'mystring'
              ^^^^^^^^^^

1 file inspected, 1 offense detected

Is there a reason MutableConstant isn't observing my frozen string literal comment?

Answer 1

Not every check makes sense for all Ruby versions. Tell RuboCop the Ruby version to check against.

Add the following to your .rubocop.yml:

AllCops:
  TargetRubyVersion: 2.3