Rails/FilePath autocorrect shouldn't remove important trailing slash in dynamic string containing Rails.root

[henrahmagix]

I'm trying to use Rails.root to remove it from an absolute filepath to result in a filepath relative to Rails.root.

my_abs_path              = "/Users/me/rails_app/config/locales/text_en.yml"
expected_relative_result = "config/locales/text_en.yml"

my_abs_path.delete_prefix("#{Rails.root}/") == expected_relative_result
# => true

Expected behavior

# this should be allowed by Rails/FilePath cop because the last / in /Users/me/rails_app/ must be deleted, not just /Users/me/rails_app
my_abs_path.delete_prefix("#{Rails.root}/")

Actual behavior

my_abs_path.delete_prefix("#{Rails.root}/")
# raises Rails/FilePath, and is autocorrected to
my_abs_path.delete_prefix("#{Rails.root.join('')}")
# which raises Style/RedundantInterpolation, so we manually correct to
my_abs_path.delete_prefix(Rails.root.join('').to_s)
# which is wrong:
actual = my_abs_path.delete_prefix(Rails.root.join('').to_s)
actual == expected_relative_result
# => false
puts actual
# => "/config/locales/text_en.yml"

# so we try giving an argument to join, but still wrong because Rails.root.join never adds a trailing slash:
actual = my_abs_path.delete_prefix(Rails.root.join('./').to_s)
actual == expected_relative_result
# => false
puts actual
# => "/config/locales/text_en.yml"

Steps to reproduce the problem

Copy the below into a file, run RuboCop with autocorrect enabled and manually fix any other cops that are raised, then assert that the result is true.
rubocop-rails-filepath-test.rb

# where Rails.root is /Users/me/rails_app
my_abs_path = "/Users/me/rails_app/config/locales/text_en.yml"
expected_relative_result = "config/locales/text_en.yml"

actual = my_abs_path.delete_prefix("#{Rails.root}/")
if actual != expected_relative_result
  raise "Invalid autocorrection: #{actual.inspect} != #{expected_relative_result.inspect}"
end

rubocop -a rubocop-rails-filepath-test.rb
rubocop -A rubocop-rails-filepath-test.rb # autofix Style/RedundantInterpolation
bin/rails c < rubocop-rails-filepath-test.rb

RuboCop version

1.57.2 (using Parser 3.2.2.4, rubocop-ast 1.30.0, running on ruby 3.0.6) [arm64-darwin21]
  - rubocop-rails 2.22.1
  - rubocop-rspec 2.18.1

[henrahmagix]

I can see autocorrection was added in #991 so is this considered a bug of that? If so, then I can submit a fix that allows "#{Rails.root}/" if that's acceptable?

I also saw #1071 which might get fixed at the same time; I can check.

Also theres #434 which includes the exact same case as this.