[rack]: fix rubocop for rack error setting

lib/ddtrace/contrib/rails/middlewares.rb

@@ -24,18 +24,16 @@ def call(env)
         rescue Exception => e
           tracer = Datadog.configuration[:rails][:tracer]
           span = tracer.active_span
-          unless span.nil?
+          if !span.nil? && ActionPack::Utils.exception_is_error?(e)
             # Only set error if it's supposed to be flagged as such
             # e.g. we don't want to flag 404s.
             # You can add custom errors via `config.action_dispatch.rescue_responses`
-            if ActionPack::Utils.exception_is_error?(e)
-              span.set_error(e)
+            span.set_error(e)
 
-              # Some exception gets handled by Rails middleware before it can be set on Rack middleware
-              # The rack span is the root span of the request and should make sure it has the full exception
-              # set on it.             
-              env[:datadog_rack_request_span].set_error(e) if env[:datadog_rack_request_span]
-            end
+            # Some exception gets handled by Rails middleware before it can be set on Rack middleware
+            # The rack span is the root span of the request and should make sure it has the full exception
+            # set on it.
+            env[:datadog_rack_request_span].set_error(e) if env[:datadog_rack_request_span]
           end
           raise e
         end

test/contrib/rails/apps/controllers.rb

@@ -4,7 +4,7 @@
 class ApplicationController < ActionController::Base; end
 
 class TracingController < ActionController::Base
-  rescue_from 'ActionController::RenderError' do 
+  rescue_from 'ActionController::RenderError' do
     render 'views/tracing/index.html.erb'
   end
 

test/contrib/rails/rack_middleware_test.rb

@@ -173,10 +173,9 @@ class FullStackTest < ActionDispatch::IntegrationTest
     assert_equal(request_span.status, 0, 'rack span should not be flagged as an error')
     assert_nil(request_span.get_tag('error.type'))
     assert_nil(request_span.get_tag('error.msg'))
-    assert_nil(request_span.get_tag('error.stack'))    
+    assert_nil(request_span.get_tag('error.stack'))
   end
 
-
   test 'custom error controllers should not override trace resource names' do
     # Simulate an error being passed to the exception controller
     # (Syntax depends on Rails integration test version)