Data classes with _N field names fail with unintuitive error

[densh]

scala> @data class Foo(_1: Int,_2: Int,_3: Int,_4: Int,_5: Int,_6: Int,_7: Int,_8: Int,_9: Int,_10: Int,_11: Int,_12: Int,_13: Int,_14: Int,_15: Int,_16: Int,_17: Int,_18: Int,_19: Int,_20: Int,_21: Int,_22: Int,_23: Int,_24: Int,_25: Int,_26: Int,_27: Int,_28: Int,_29: Int,_30: Int)
<console>:11: error: overloaded method _1 needs result type

The failure is to be expected but the error message could be made much nicer.