code: func varNameForVar(raw config.InterpolatedVariable) string {
  	switch v := raw.(type) {
  	case *config.ModuleVariable:
  		return fmt.Sprintf("module.%s.output.%s", v.Name, v.Field)
  	case *config.ResourceVariable:
  		return v.ResourceId()
  	case *config.UserVariable:
  		return fmt.Sprintf("var.%s", v.Name)
  	default:
  		return ""
  	}
  }
docs: // varNameForVar returns the VarName value for an interpolated variable.
  // This value is compared to the VarName() value for the nodes within the
  // graph to build the graph edges.