Fix Rails/FilePath cop error in case of extra operations in `Rails.…

…root` interpolation

Follow-up to rubocop#1392.
Previous PR didn't fix cases like this

```
"#{Rails.root || '.'}/config"
```

(it makes sense in real code since `Rails.root` [can be nil](https://github.com/rails/rails/blob/main/railties/lib/rails.rb#L65-L67))

I think it's safe to simply check if the entire expression is of `send` type.

changelog/fix_rails_file_path_cop_error_on_extra_operations_in_rails_root_interpolation.md

@@ -0,0 +1 @@
+* [#1398](https://github.com/rubocop/rubocop-rails/pull/1398): Fix `Rails/FilePath` cop error in case of extra operations in `Rails.root` interpolation. ([@viralpraxis][])

lib/rubocop/cop/rails/file_path.rb

@@ -76,7 +76,7 @@ def check_for_slash_after_rails_root_in_dstr(node)
           rails_root_index = find_rails_root_index(node)
           slash_node = node.children[rails_root_index + 1]
           return unless slash_node&.str_type? && slash_node.source.start_with?(File::SEPARATOR)
-          return if node.children[rails_root_index].each_descendant(:rescue).any?
+          return unless node.children[rails_root_index].children.first.send_type?
 
           register_offense(node, require_to_s: false) do |corrector|
             autocorrect_slash_after_rails_root_in_dstr(corrector, node, rails_root_index)

spec/rubocop/cop/rails/file_path_spec.rb

@@ -407,12 +407,20 @@
       end
     end
 
-    context 'when rescued concat Rails.root' do
+    context 'when rescued `Rails.root`' do
       it 'does not register an offense' do
         expect_no_offenses(<<~'RUBY')
           "#{Rails.root rescue '.'}/config"
         RUBY
       end
     end
+
+    context 'with addition operations inside `Rails.root` interpolation expression' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~'RUBY')
+          "#{Rails.root || '.'}/config"
+        RUBY
+      end
+    end
   end
 end