@NotNull
  private static ASTNode findFirstGrammarNode(RncFile file) {
    final RncGrammar grammar = file.getGrammar();
    assert grammar != null;
    final ASTNode grammarNode = grammar.getNode();
    assert grammarNode != null;
    final ASTNode astNode = grammarNode.getFirstChildNode();
    assert astNode != null;
    return astNode;
  }
@NotNull
  private static ASTNode findFirstGrammarNode(RncFile file)