ClassCastException during pattern match on inner classes defined in base traits

[grindvoll]

The following code crashes with a ClassCastException:

    trait Common {
      case class Data(a: String)
    }
    object O1 extends Common
    object O2 extends Common

    val data = O2.Data("test")

    // Runtime error: java.lang.ClassCastException: O2$ cannot be cast to O1$
    data match {
        case O1.Data(s) => println("O1 data")
        case O2.Data(s) => println("O2 data")
        case _ => println("Unknown")
    }

(Observed on 0.4.0-RC1)

[allanrenucci]

After pattern matcher

Dotty:

 if (x1.$isInstanceOf$[Common.this.Data].&&(x1.asInstanceOf[Common.this.Data].1_<outer>.eq(Common.this))

Scalac:

if (x1.isInstanceOf[O1.Data].&&((x1.asInstanceOf[O1.Data]: O1.Data).<outer>.eq(O1)))

Bytecode

Here Dotty emits an invalid cast that throws at runtime:

if (data2 instanceof Common.Data && (O1$)data2.Common$Data$$$outer() == O1$.MODULE$)

Scalac:

if (data2 instanceof Common.Data && data2.Common$Data$$$outer() == O1$.MODULE$)