Add Rails/FilePath auto-correct

[grosser]

test/integration/cleanliness_test.rb:9:46: C: Rails/FilePath: Please use Rails.root.join('path/to') instead.
    files -= [File.expand_path(__FILE__).sub("#{Rails.root}/", '')]
                                             ^^^^^^^^^^^^^^^^

---

Expected behavior

autocorrect

Actual behavior

no autocorrect

Steps to reproduce the problem

see code above

RuboCop version

1.9.1 (using Parser 3.0.0.0, rubocop-ast 1.4.1, running on ruby 2.6.5 x86_64-darwin19)
  - rubocop-rails 2.9.1

[koic]

C is an abbreviation for Convension, not an abbreviation for Correctable. So, C does not mention auto-correction. Also, W is an abbreviation for Warning. So, I think this is the expected behavior.
https://docs.rubocop.org/rubocop/1.9/formatters.html#progress-formatter-default

Currently RuboCop Rails (2.9) doesn't support auto-correct for Rails/FilePath.
https://docs.rubocop.org/rubocop-rails/2.9/cops_rails.html#railsfilepath

OTOH, I think it can be safely auto-corrected (rubocop -a), so it should be possible to enhance Rails/FilePath.

[grosser]

ah thx, I always thought it's correction because they usually had an auto-correct 👍

[grosser]

I updated the title/descriotion

[henrahmagix]

Autocorrection for this appears to have been added in #991

The exact example given here now autocorrects from:

File.expand_path(__FILE__).sub("#{Rails.root}/", '')

to

File.expand_path(__FILE__).sub("#{Rails.root.join('')}", '')

[henrahmagix]

@grosser sorry I forgot to say that the autocorrect actually breaks the original intention of the code (it's getting rid of the trailing slash, meaning that slash doesn't get deleted by the .sub call), so it's a bug: see #1177 =)

[grosser]

ah thx, I was like "looks sus but at least it will shut up" :D