Fix route code lens when there are no classes in the stack (#407)

Author: vinistock

lib/ruby_lsp/ruby_lsp_rails/code_lens.rb

@@ -160,8 +160,10 @@ def on_class_node_leave(node)
 
       sig { returns(T.nilable(T::Boolean)) }
       def controller?
-        class_name, superclass_name = T.must(@constant_name_stack.last)
-        class_name.end_with?("Controller") && superclass_name&.end_with?("Controller")
+        class_name, superclass_name = @constant_name_stack.last
+        return false unless class_name && superclass_name
+
+        class_name.end_with?("Controller") && superclass_name.end_with?("Controller")
       end
 
       sig { params(node: Prism::DefNode).void }

test/ruby_lsp_rails/code_lens_test.rb

@@ -303,6 +303,15 @@ def index
         assert_match("config/routes.rb", path)
       end
 
+      test "doesn't break when analyzing a file without a class" do
+        response = generate_code_lens_for_source(<<~RUBY)
+          def index
+          end
+        RUBY
+
+        assert_empty(response)
+      end
+
       private
 
       attr_reader :ruby