code: Env<AttrContext> topLevelEnv(JCCompilationUnit tree) {
          Env<AttrContext> localEnv = new Env<>(tree, new AttrContext());
          localEnv.toplevel = tree;
          localEnv.enclClass = predefClassDef;
          tree.toplevelScope = WriteableScope.create(tree.packge);
          tree.namedImportScope = new NamedImportScope(tree.packge, tree.toplevelScope);
          tree.starImportScope = new StarImportScope(tree.packge);
          localEnv.info.scope = tree.toplevelScope;
          localEnv.info.lint = lint;
          return localEnv;
      }
docs: Create a fresh environment for toplevels.
  @param tree     The toplevel tree.