[Fix #1389] Handle TypeError caused by passing array literals as arguments to File methods in Rails/RootPathnameMethods cop

changelog/fix_rails_root_pathname_to_handle_type_error_caused_by_an_array.md

@@ -0,0 +1 @@
+* [#1389](https://github.com/rubocop/rubocop-rails/issues/1389): Handle `TypeError` caused by passing array literals as arguments to `File` methods in `Rails/RootPathnameMethods` cop. ([@ydakuka][])

lib/rubocop/cop/rails/root_pathname_methods.rb

@@ -237,7 +237,12 @@ def build_path_replacement(path, method, args)
           end
 
           replacement = "#{path_replacement}.#{method}"
-          replacement += "(#{args.map(&:source).join(', ')})" unless args.empty?
+
+          if args.any?
+            formatted_args = args.map { |arg| arg.array_type? ? "*#{arg.source}" : arg.source }
+            replacement += "(#{formatted_args.join(', ')})"
+          end
+
           replacement
         end
 

spec/rubocop/cop/rails/root_pathname_methods_spec.rb

@@ -210,4 +210,70 @@
       file = Rails.root.join('docs', 'invoice.pdf').open
     RUBY
   end
+
+  it 'registers an offense when using only [] syntax' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, ['app', 'models'])
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join(*['app', 'models'])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join(*['app', 'models'])
+    RUBY
+  end
+
+  it 'registers an offense when using a leading string and an array using [] syntax' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, "app", ["models", "goober"])
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join("app", *["models", "goober"])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join("app", *["models", "goober"])
+    RUBY
+  end
+
+  it 'registers an offense when using an array using [] syntax and a trailing string' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, ["app", "models"], "goober")
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join(*["app", "models"], "goober")`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join(*["app", "models"], "goober")
+    RUBY
+  end
+
+  it 'registers an offense when using only %w[] syntax' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, %w[app models])
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join(*%w[app models])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join(*%w[app models])
+    RUBY
+  end
+
+  it 'registers an offense when using a leading string and an array using %w[] syntax' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, "app", %w[models goober])
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join("app", *%w[models goober])`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join("app", *%w[models goober])
+    RUBY
+  end
+
+  it 'registers an offense when using an array using %w[] syntax and a trailing string' do
+    expect_offense(<<~RUBY)
+      File.join(Rails.root, %w[app models], "goober")
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname`, so you can use `Rails.root.join(*%w[app models], "goober")`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Rails.root.join(*%w[app models], "goober")
+    RUBY
+  end
 end