Exclude File.join from Rails/RootPathnameMethods target methods

Author: r7kamura

changelog/change_exclude_file_join_from_rails_root_pathname_methods.md

@@ -0,0 +1 @@
+* [#1000](https://github.com/rubocop/rubocop-rails/pull/1000): Exclude `File.join` from `Rails/RootPathnameMethods` target methods. ([@r7kamura][])

lib/rubocop/cop/rails/root_pathname_methods.rb

@@ -65,7 +65,6 @@ class RootPathnameMethods < Base
           fnmatch?
           ftype
           grpowned?
-          join
           lchmod
           lchown
           lstat

spec/rubocop/cop/rails/root_pathname_methods_spec.rb

@@ -191,4 +191,10 @@
       file = Rails.root.join('docs', 'invoice.pdf').open
     RUBY
   end
+
+  it 'does not register an offense when using `File.join(Rails.root, ...)`' do
+    expect_no_offenses(<<~RUBY)
+      File.join(Rails.root, '/foo')
+    RUBY
+  end
 end