code: WriteableScope enterScope(Env<AttrContext> env) {
          return (env.tree.hasTag(JCTree.Tag.CLASSDEF))
              ? ((JCClassDecl) env.tree).sym.members_field
              : env.info.scope;
      }
docs: The scope in which a member definition in environment env is to be entered
  This is usually the environment's scope, except for class environments,
  where the local scope is for type variables, and the this and super symbol
  only, and members go into the class member scope.