[Fix #870] Fix an error for Rails/RootPathnameMethods

Fixes #870.

This PR fixes an error for `Rails/RootPathnameMethods`
when using `Rails.env` argument within `Dir.glob`.

Author: koic

changelog/fix_an_error_for_rails_root_pathname_methods.md

@@ -0,0 +1 @@
+* [#870](https://github.com/rubocop/rubocop-rails/issues/870): Fix an error for `Rails/RootPathnameMethods` when using `Rails.env` argument within `Dir.glob`. ([@koic][])

lib/rubocop/cop/rails/root_pathname_methods.rb

@@ -214,8 +214,17 @@ def include_interpolation?(arguments)
         end
 
         def join_arguments(arguments)
-          quote = include_interpolation?(arguments) ? '"' : "'"
-          joined_arguments = arguments.map(&:value).join('/')
+          use_interpolation = false
+
+          joined_arguments = arguments.map do |arg|
+            if arg.respond_to?(:value)
+              arg.value
+            else
+              use_interpolation = true
+              "\#{#{arg.source}}"
+            end
+          end.join('/')
+          quote = include_interpolation?(arguments) || use_interpolation ? '"' : "'"
 
           "#{quote}#{joined_arguments}#{quote}"
         end

spec/rubocop/cop/rails/root_pathname_methods_spec.rb

@@ -101,6 +101,21 @@
         Rails.root.glob("**/#{path}/*.rb")
       RUBY
     end
+
+    it 'registers an offense when using `Rails.env` argument within `Dir.glob`' do
+      expect_offense(<<~'RUBY')
+        Dir.glob(Rails.root.join("db", "seeds", Rails.env, "*.rb")).sort.each do |file|
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rails.root` is a `Pathname` so you can just append `#glob`.
+          load file
+        end
+      RUBY
+
+      expect_correction(<<~'RUBY')
+        Rails.root.glob("db/seeds/#{Rails.env}/*.rb").sort.each do |file|
+          load file
+        end
+      RUBY
+    end
   end
 
   # This is handled by `Rails/RootJoinChain`