Fix wrong autocorrect for Rails/FilePath when passing an array to File.join

changelog/fix_wrong_autocorrect_for_rails_file_path.md

@@ -0,0 +1 @@
+* [#1326](https://github.com/rubocop/rubocop-rails/pull/1326): Fix wrong autocorrect for `Rails/FilePath` when passing an array to `File.join`. ([@earlopain][])

lib/rubocop/cop/rails/file_path.rb

@@ -97,7 +97,7 @@ def check_for_file_join_with_rails_root(node)
           return unless node.arguments.any? { |e| rails_root_nodes?(e) }
 
           register_offense(node, require_to_s: true) do |corrector|
-            autocorrect_file_join(corrector, node)
+            autocorrect_file_join(corrector, node) unless node.first_argument.array_type?
           end
         end
 

spec/rubocop/cop/rails/file_path_spec.rb

@@ -114,6 +114,26 @@
       end
     end
 
+    context 'when using File.join with an array' do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY)
+          File.join([Rails.root, 'foo'])
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path/to').to_s`.
+        RUBY
+
+        expect_no_corrections
+      end
+
+      it 'registers an offense for nested arrays' do
+        expect_offense(<<~RUBY)
+          File.join([Rails.root, 'foo', ['bar']])
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `Rails.root.join('path/to').to_s`.
+        RUBY
+
+        expect_no_corrections
+      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')")