resolve: Leave a comment about name bindings for legacy derive helpers

Author: petrochenkov

compiler/rustc_resolve/src/ident.rs

@@ -432,6 +432,11 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                         }
                     }
                     Scope::DeriveHelpersCompat => {
+                        // FIXME: Try running this logic eariler, to allocate name bindings for
+                        // legacy derive helpers when creating an attribute invocation with
+                        // following derives. Legacy derive helpers are not common, so it shouldn't
+                        // affect performance. It should also allow to remove the `derives`
+                        // component from `ParentScope`.
                         let mut result = Err(Determinacy::Determined);
                         for derive in parent_scope.derives {
                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };