Fix an incorrect autocorrect for Rails/FilePath when File.join with…

… Rails.root and path starting with `/`

changelog/fix_an_incorrect_autocorrect_for_rails_file_path_when_file_join_with_start_slash.md

@@ -0,0 +1 @@
+* [#1049](https://github.com/rubocop/rubocop-rails/pull/1049): Fix an incorrect autocorrect for `Rails/FilePath` when File.join with Rails.root and path starting with `/`. ([@ydah][])

lib/rubocop/cop/rails/file_path.rb

@@ -180,6 +180,9 @@ def autocorrect_file_join(corrector, node)
               side: :right
             )
           )
+          node.arguments.filter(&:str_type?).each do |argument|
+            corrector.replace(argument, argument.value.delete_prefix('/').inspect)
+          end
           corrector.insert_after(node, '.to_s')
         end
 

spec/rubocop/cop/rails/file_path_spec.rb

@@ -17,6 +17,19 @@
       end
     end
 
+    context 'when using File.join with Rails.root and path starting with `/`' do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY)
+          File.join(Rails.root, '/app/models', '/user.rb')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path/to').to_s`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          Rails.root.join("app/models/user.rb").to_s
+        RUBY
+      end
+    end
+
     context 'when using ::Rails.root.join with some path strings' do
       it 'registers an offense' do
         expect_offense(<<~RUBY)
@@ -246,7 +259,20 @@
         RUBY
 
         expect_correction(<<~RUBY)
-          Rails.root.join('app', 'models').to_s
+          Rails.root.join("app", "models").to_s
+        RUBY
+      end
+    end
+
+    context 'when using File.join with Rails.root and path starting with `/`' do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY)
+          File.join(Rails.root, '/app/models', '/user.rb')
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path', 'to').to_s`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          Rails.root.join("app", "models", "user.rb").to_s
         RUBY
       end
     end