Support ::Rails and ::File on Rails/FilePath cop

changelog/fix_support_rails_and_file_on_rails_file_path.md

@@ -0,0 +1 @@
+* [#865](https://github.com/rubocop/rubocop-rails/pull/865): Support `::Rails` and `::File` on `Rails/FilePath` cop. ([@r7kamura][])

lib/rubocop/cop/rails/file_path.rb

@@ -34,15 +34,15 @@ class FilePath < Base
         RESTRICT_ON_SEND = %i[join].freeze
 
         def_node_matcher :file_join_nodes?, <<~PATTERN
-          (send (const nil? :File) :join ...)
+          (send (const {nil? cbase} :File) :join ...)
         PATTERN
 
         def_node_search :rails_root_nodes?, <<~PATTERN
-          (send (const nil? :Rails) :root)
+          (send (const {nil? cbase} :Rails) :root)
         PATTERN
 
         def_node_matcher :rails_root_join_nodes?, <<~PATTERN
-          (send (send (const nil? :Rails) :root) :join ...)
+          (send #rails_root_nodes? :join ...)
         PATTERN
 
         def on_dstr(node)

spec/rubocop/cop/rails/file_path_spec.rb

@@ -13,6 +13,15 @@
       end
     end
 
+    context 'when using ::Rails.root.join with some path strings' do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY)
+          ::Rails.root.join('app', 'models', 'user.rb')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path/to')`.
+        RUBY
+      end
+    end
+
     context 'when using Rails.root.join in string interpolation of argument' do
       it 'registers an offense' do
         expect_offense(<<~'RUBY')
@@ -55,6 +64,15 @@
       end
     end
 
+    context 'when using ::File.join with Rails.root' do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY)
+          ::File.join(Rails.root, 'app', 'models')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path/to')`.
+        RUBY
+      end
+    end
+
     context 'when using Rails.root.join with slash separated path string' do
       it 'does not register an offense' do
         expect_no_offenses("Rails.root.join('app/models/goober')")