mbe: Add FIXME about tracking multiple macro kinds for a Def

Author: joshtriplett

compiler/rustc_resolve/src/ident.rs

@@ -629,6 +629,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         let binding_macro_kind = binding.macro_kind();
                         // If we're looking for an attribute, that might be supported by a
                         // `macro_rules!` macro.
+                        // FIXME: Replace this with tracking multiple macro kinds for one Def.
                         if !(sub_namespace_match(binding_macro_kind, macro_kind)
                             || (binding_macro_kind == Some(MacroKind::Bang)
                                 && macro_kind == Some(MacroKind::Attr)