Fix Rails/RootPathnameMethods autocorrection for Pathname calls without parens

changelog/fix_railsrootpathnamemethods.md

@@ -0,0 +1 @@
+* [#855](https://github.com/rubocop/rubocop-rails/pull/855): Fix Rails/RootPathnameMethods autocorrection for Pathname calls without parens. ([@gsamokovarov][])

lib/rubocop/cop/rails/root_pathname_methods.rb

@@ -163,12 +163,11 @@ class RootPathnameMethods < Base
         def on_send(node)
           evidence(node) do |method, path, args, rails_root|
             add_offense(node, message: format(MSG, method: method, rails_root: rails_root.source)) do |corrector|
-              if dir_glob?(node)
-                replacement = build_path_glob(path, method)
-              else
-                replacement = "#{path.source}.#{method}"
-                replacement += "(#{args.map(&:source).join(', ')})" unless args.empty?
-              end
+              replacement = if dir_glob?(node)
+                              build_path_glob_replacement(path, method)
+                            else
+                              build_path_replacement(path, method, args)
+                            end
 
               corrector.replace(node, replacement)
             end
@@ -184,7 +183,7 @@ def evidence(node)
           yield(method, path, args, rails_root)
         end
 
-        def build_path_glob(path, method)
+        def build_path_glob_replacement(path, method)
           receiver = range_between(path.loc.expression.begin_pos, path.children.first.loc.selector.end_pos).source
 
           argument = if path.arguments.one?
@@ -196,6 +195,18 @@ def build_path_glob(path, method)
           "#{receiver}.#{method}(#{argument})"
         end
 
+        def build_path_replacement(path, method, args)
+          path_replacement = path.source
+          if path.arguments? && !path.parenthesized_call?
+            path_replacement[' '] = '('
+            path_replacement << ')'
+          end
+
+          replacement = "#{path_replacement}.#{method}"
+          replacement += "(#{args.map(&:source).join(', ')})" unless args.empty?
+          replacement
+        end
+
         def include_interpolation?(arguments)
           arguments.any? do |argument|
             argument.children.any? { |child| child.respond_to?(:begin_type?) && child.begin_type? }

spec/rubocop/cop/rails/root_pathname_methods_spec.rb

@@ -148,4 +148,15 @@
       files.map { |file| Rails.root.join('db', file).open('wb') }
     RUBY
   end
+
+  it 'registers an offense when using `File.open Rails.root.join ...` without parens' do
+    expect_offense(<<~RUBY)
+      file = File.open Rails.root.join 'docs', 'invoice.pdf'
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname` so you can just append `#open`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      file = Rails.root.join('docs', 'invoice.pdf').open
+    RUBY
+  end
 end