[Fix rubocop#700] Fix a false positive for Rails/FilePath

CHANGELOG.md

@@ -589,3 +589,4 @@
 [@natematykiewicz]: https://github.com/natematykiewicz
 [@lulalala]: https://github.com/lulalala
 [@gmcgibbon]: https://github.com/gmcgibbon
+[@tk0miya]: https://github.com/tk0miya

changelog/fix_a_false_positive_for_rails_filepath_for_colon_separated_pathlist.md

@@ -0,0 +1 @@
+* [#700](https://github.com/rubocop/rubocop-rails/issues/700): Fix a false positive for `Rails/FilePath` when a list of paths separated by colon including Rails.root. ([@tk0miya][])

lib/rubocop/cop/rails/file_path.rb

@@ -48,6 +48,7 @@ class FilePath < Base
         def on_dstr(node)
           return unless rails_root_nodes?(node)
           return unless node.children.last.str_type?
+          return if node.children.last.source.start_with?(':')
           return unless node.children.last.source.start_with?('.') ||
                         node.children.last.source.include?(File::SEPARATOR)
 

spec/rubocop/cop/rails/file_path_spec.rb

@@ -122,6 +122,14 @@
         RUBY
       end
     end
+
+    context 'when concat Rails.root and colon using string interpoloation' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~'RUBY')
+          "#{Rails.root}:/foo/bar"
+        RUBY
+      end
+    end
   end
 
   context 'when EnforcedStyle is `arguments`' do
@@ -245,5 +253,13 @@
         RUBY
       end
     end
+
+    context 'when concat Rails.root and colon using string interpoloation' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~'RUBY')
+          "#{Rails.root}:/foo/bar"
+        RUBY
+      end
+    end
   end
 end