crash on compilable code: cannot be cast to dotty.tools.dotc.core.Types$MethodType

[helloqirun]

scalac can compile but dotc crashes.

$ dotc -version

Dotty compiler version 0.5.0-bin-SNAPSHOT-git-4fefb64 -- Copyright 2002-2017, LAMP/EPFL

$ cat abc.scala

object Test {
  def main(args: Array[String]): Unit = {
    val i2s = (x: Int) => ""
    assert(asInstanceOf.asInstanceOf[AnyRef => String].apply(null) == "")
    val i2i = (x: Int) => x + 1
    assert(i2i.asInstanceOf[AnyRef => Int].apply(null) == 1)
  }
}

$ dotc abc.scala

-- Error: abc.scala:4:36 -------------------------------------------------------
4 |    assert(asInstanceOf.asInstanceOf[AnyRef => String].apply(null) == "")
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |           class Nothing in package scala does not take type parameters

exception occurred while compiling abc.scala
Exception in thread "main" java.lang.ClassCastException: dotty.tools.dotc.core.Types$$anon$9 cannot be cast to dotty.tools.dotc.core.Types$MethodType
	at dotty.tools.dotc.transform.ElimRepeated.$anonfun$1(ElimRepeated.scala:79)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.dotc.transform.ElimRepeated.transformApply(ElimRepeated.scala:79)
	at dotty.tools.dotc.transform.MegaPhase.goApply(MegaPhase.scala:576)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:250)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:365)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:211)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:364)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:248)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:365)
	at dotty.tools.dotc.transform.MegaPhase.mapValDef$1(MegaPhase.scala:217)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:221)
<snipped>

[allanrenucci]

There are two issues here:

1. We cannot compile when scalac can:

class Test {
  asInstanceOf.asInstanceOf[AnyRef => String]
}

-- Error: tests/allan/Test.scala:2:27 ------------------------------------------
2 |  asInstanceOf.asInstanceOf[AnyRef => String]
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  class Nothing in package scala does not take type parameters
one error found
java.lang.RuntimeException: Nonzero exit code returned from runner: 1

Note that if Nothing is not inferred, it compiles: asInstanceOf[Nothing].asInstanceOf[AnyRef => String]

2. Which then causes a compiler crash:

class Test {
  asInstanceOf.asInstanceOf[AnyRef => String].apply(null)
}

-- Error: tests/allan/Test.scala:2:27 ------------------------------------------
2 |  asInstanceOf.asInstanceOf[AnyRef => String].apply(null)
  |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |  class Nothing in package scala does not take type parameters
exception occurred while compiling tests/allan/Test.scala
Exception in thread "main" java.lang.ClassCastException: dotty.tools.dotc.core.Types$ErrorType$$anon$4 cannot be cast to dotty.tools.dotc.core.Types$MethodType
	at dotty.tools.dotc.transform.ElimRepeated.$anonfun$transformApply$1(ElimRepeated.scala:79)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.dotc.core.Phases.atPhase$(Phases.scala:35)
	at dotty.tools.dotc.core.Contexts$Context.atPhase(Contexts.scala:67)
	at dotty.tools.dotc.transform.ElimRepeated.transformApply(ElimRepeated.scala:78)