AssertionError in rebindSuper

[sir-wabbit]

Minimized code

// AE-ed9d1b1f2a3006febec44cbf09eca6d2226b5b0f
trait Parent {
  def name: String
}
trait Son extends Parent {
  abstract override def name = ""
  def parentName = super.name
}
class GrandSon extends Son

If I remove abstract, I get:

-- Error: test.scala:6:25 ------------------------------------------------------
6 |  def parentName = super.name
  |                   ^^^^^^^^^^
  |method name in trait Parent is accessed from super. It may not be abstract unless it is overridden by a member declared `abstract' and `override'

I think this requires further elaboration 😅 🤔

Output (click arrow to expand)

exception occurred while compiling test.scala
java.lang.AssertionError: assertion failed while compiling test.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
	at dotty.DottyPredef$.assertFail(DottyPredef.scala:16)
	at dotty.tools.dotc.transform.ResolveSuper$.rebindSuper(ResolveSuper.scala:100)
	at dotty.tools.dotc.transform.ResolveSuper.superAccessors$2$$anonfun$2(ResolveSuper.scala:51)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.transform.ResolveSuper.superAccessors$3(ResolveSuper.scala:52)
	at dotty.tools.dotc.transform.ResolveSuper.$anonfun$1(ResolveSuper.scala:54)
	at scala.collection.immutable.List.flatMap(List.scala:293)
	at dotty.tools.dotc.transform.ResolveSuper.transformTemplate(ResolveSuper.scala:54)
	at dotty.tools.dotc.transform.ResolveSuper.transformTemplate(ResolveSuper.scala:42)
	at dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:971)
	at dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:972)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:340)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:396)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:251)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:394)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$2(MegaPhase.scala:404)
	at dotty.tools.dotc.transform.MegaPhase.$anonfun$1(MegaPhase.scala:409)
	at scala.collection.immutable.List.mapConserve(List.scala:472)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:409)
	at dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:356)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:359)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:396)
	at dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:415)
	at dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:427)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:318)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:319)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:180)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:190)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:198)
	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:64)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:205)
	at dotty.tools.dotc.Run.compileSources(Run.scala:142)
	at dotty.tools.dotc.Run.compile(Run.scala:124)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:38)
	at dotty.tools.dotc.Driver.process(Driver.scala:194)
	at dotty.tools.dotc.Driver.process(Driver.scala:163)
	at dotty.tools.dotc.Driver.process(Driver.scala:175)
	at dotty.tools.dotc.Driver.main(Driver.scala:202)
	at dotty.tools.dotc.Main.main(Main.scala)

[nicolasstucki]

Related issue

trait Parent {
  def name: String
}
trait Son extends Parent {
  abstract override def name: String = ""
  // def parentName = super.name
}
class GrandSon extends Son

Compiles in dotty but fails in scalac. This error would be emitted before the crash.

[som-snytt]

The following compiles in a single package or removing protected modifier but fails in this form:

package apackage {

  abstract class A {
    protected val x: Int
  }
  abstract class A2 {
    val x: Int
  }
}

package bpackage {
  import apackage._

  trait B extends A {
    println(x)
  }
  trait B2 extends A2 {
    println(x)
  }
}

package cpackage {
  import apackage._
  import bpackage._

  case class C(override protected val x: Int) extends A with B
  case class C2(override val x: Int) extends A2 with B2
}

Reported at scala/bug#12249