static String stringify(TypeMirror mirror) {
    String string = mirror.toString();
    // -1 + -1 both not found, special symbols for type annotations
    // where @ is normal annotation sign, but : is synthetic insert in some
    // javac versions, accompanying weird Java type_use annotations
    if (string.indexOf('@') + string.indexOf(':') == -2) {
      return string;
    }

    StringBuilder builder = new StringBuilder();
    append(builder, mirror);
    return builder.toString();
  }
overridable stringify.
@param input the input
@param context the context
@return the string
generator/src/org/immutables/generator/TypeHierarchyCollector.java