Style/ClassEqualityComparison is overly aggressive

[gregnavis]

Expected behavior

1. Rubocop doesn't suggest using #instance_of? with an arguments whose type it doesn't know.
2. Rubocop doesn't automatically "correct" code to #instance_of? when it isn't sure the change is safe.

Actual behavior

1. Rubocop reported the following error:

test.rb:2:10: C: [Correctable] Style/ClassEqualityComparison: Use instance_of?(@klass_name) instead of comparing classes.
  object.class.name == @klass_name

The error message contains a suggestion to use #instance_of?(@klass_name), but Rubocop doesn't know the type of @klass_name. That suggestion can be incorrect in many cases.

2. Rubocop changed the code above to object.instance_of?(@klass_name), resulting in TypeError at runtime.

Additionally, when the method is in a module/class like in the example below:

class MyClass
  def check_class?(object)
    object.class.name == @klass_name
  end
end

then Rubocop converts it to:

class MyClass
  def check_class?(object)
    object.instance_of?(::@klass_name)
  end
end

This produces a syntax error in Ruby 3.1.

Steps to reproduce the problem

1. Create a file called test.rb with the following code:

class MyClass
  def check_class?(object)
    object.class.name == @klass_name
  end
end

2. Call rubocop test.rb.

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler.
If you see extension cop versions (e.g. rubocop-performance, rubocop-rspec, and others)
output by rubocop -V, include them as well. Here's an example:

% bundle3.1 exec rubocop -V
1.38.0 (using Parser 3.1.2.1, rubocop-ast 1.23.0, running on ruby 3.1.2) [arm64-darwin22]
  - rubocop-rails 2.17.2