Function kind_case

common/constant.h:416–422

  }

  ConstantKindCase kind_case() const {
    static_assert(absl::variant_size_v<ConstantKind> == 10);
    if (kind_.index() <= 10) {
      return static_cast<ConstantKindCase>(kind_.index());
    }
    return ConstantKindCase::kUnspecified;
  }

 private:
  friend class Expr;