Assertion error when using self-type in F-bounded type

[Sciss]

Minimized code

trait Foo[T <: Foo[T]] {
  type I <: Foo[I]
}

trait Bar[T <: Foo[T]] extends Foo[T] {
  self: T =>
}

Output

[info] assertion failure for LazyRef(...) <:< LazyRef(...), frozen = true
[info] assertion failure for de.sciss.lucre.Foo[LazyRef(...)] <:< de.sciss.lucre.Foo[LazyRef(...)], frozen = true
[info] assertion failure for  <: de.sciss.lucre.Foo[LazyRef(...)] <:<  <: de.sciss.lucre.Foo[LazyRef(...)], frozen = true
[info] assertion failure for LazyRef(...) <:< LazyRef(...), frozen = true
[info] assertion failure for de.sciss.lucre.Foo[LazyRef(...)] <:< de.sciss.lucre.Foo[LazyRef(...)], frozen = true
[info] assertion failure for  <: de.sciss.lucre.Foo[LazyRef(...)] <:<  <: de.sciss.lucre.Foo[LazyRef(...)], frozen = true
[info] exception occurred while typechecking /data/temp/DottyBasicTxnImpl/src/main/scala/de/sciss/lucre/Bar.scala
[info] exception occurred while compiling /data/temp/DottyBasicTxnImpl/src/main/scala/de/sciss/lucre/Bar.scala
java.lang.AssertionError: assertion failed while compiling /data/temp/DottyBasicTxnImpl/src/main/scala/de/sciss/lucre/Bar.scala
[error] ## Exception when compiling 1 sources to /data/temp/DottyBasicTxnImpl/target/scala-3.0.0-M1/classes
[error] java.lang.AssertionError: assertion failed
[error] dotty.DottyPredef$.assertFail(DottyPredef.scala:16)
[error] dotty.tools.dotc.core.Types$LazyRef.ref(Types.scala:2691)
[error] dotty.tools.dotc.core.Types$Type.dealias1(Types.scala:1275)
[error] dotty.tools.dotc.core.Types$Type.dealias(Types.scala:1283)
[error] dotty.tools.dotc.core.Types$Type.isSingleton(Types.scala:283)
[error] dotty.tools.dotc.core.TypeComparer.isSingletonBounds$1(TypeComparer.scala:1878)
[error] dotty.tools.dotc.core.TypeComparer.singletonInterval(TypeComparer.scala:1880)
[error] dotty.tools.dotc.core.TypeComparer.glbArgs(TypeComparer.scala:2015)
[error] dotty.tools.dotc.core.TypeComparer.distributeAnd(TypeComparer.scala:2180)
[error] dotty.tools.dotc.core.TypeComparer.andTypeGen(TypeComparer.scala:2088)
[error] dotty.tools.dotc.core.TypeComparer.andType(TypeComparer.scala:2116)
[error] dotty.tools.dotc.core.TypeComparer.glb(TypeComparer.scala:1924)
[error] dotty.tools.dotc.core.TypeComparer$.glb(TypeComparer.scala:2591)
[error] dotty.tools.dotc.core.Types$Type.$amp(Types.scala:1028)
[error] dotty.tools.dotc.core.Types$TypeBounds.$amp(Types.scala:4607)
[error] dotty.tools.dotc.core.Denotations$.infoMeet(Denotations.scala:528)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeSingleDenot$1(Denotations.scala:475)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeDenot$1(Denotations.scala:405)
[error] dotty.tools.dotc.core.Denotations$Denotation.meet(Denotations.scala:491)
[error] dotty.tools.dotc.core.Types$Type.goAnd$1(Types.scala:750)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:617)
[error] dotty.tools.dotc.core.Types$Type.goThis$1(Types.scala:706)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:600)
[error] dotty.tools.dotc.core.Types$Type.findMember(Types.scala:771)
[error] dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:566)
[error] dotty.tools.dotc.core.Types$Type.nonPrivateMember(Types.scala:556)
[error] dotty.tools.dotc.core.Types$NamedType.memberDenot(Types.scala:2115)
[error] dotty.tools.dotc.core.Types$NamedType.reload$1(Types.scala:2394)
[error] dotty.tools.dotc.core.Types$NamedType.withPrefix(Types.scala:2406)
[error] dotty.tools.dotc.core.Types$NamedType.derivedSelect(Types.scala:2347)
[error] dotty.tools.dotc.core.Types$TypeMap.derivedSelect(Types.scala:4995)
[error] dotty.tools.dotc.core.Types$ApproximatingTypeMap.derivedSelect(Types.scala:5297)
[error] dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:102)
[error] dotty.tools.dotc.core.Types$TypeMap.mapOver$$anonfun$1(Types.scala:5116)
[error] dotty.tools.dotc.core.Types$LazyRef$.apply$$anonfun$1(Types.scala:2682)
[error] dotty.tools.dotc.core.Types$LazyRef.ref(Types.scala:2695)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:306)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.isSubArg$1(TypeComparer.scala:1438)
[error] dotty.tools.dotc.core.TypeComparer.recurArgs$1(TypeComparer.scala:1443)
[error] dotty.tools.dotc.core.TypeComparer.isSubArgs(TypeComparer.scala:1446)
[error] dotty.tools.dotc.core.TypeComparer.checkSubArgs$1(TypeComparer.scala:1035)
[error] dotty.tools.dotc.core.TypeComparer.loop$3(TypeComparer.scala:1037)
[error] dotty.tools.dotc.core.TypeComparer.isMatchingApply$1(TypeComparer.scala:1052)
[error] dotty.tools.dotc.core.TypeComparer.compareAppliedType2$1(TypeComparer.scala:1111)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:549)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:476)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:363)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.compareTypeBounds$1(TypeComparer.scala:710)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:716)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:476)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:363)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.isSub(TypeComparer.scala:186)
[error] dotty.tools.dotc.core.ConstraintHandling.op$proxy1$1(ConstraintHandling.scala:220)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen(ConstraintHandling.scala:220)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen$(ConstraintHandling.scala:25)
[error] dotty.tools.dotc.core.TypeComparer.isSubTypeWhenFrozen(TypeComparer.scala:30)
[error] dotty.tools.dotc.core.TypeComparer$.isSubTypeWhenFrozen(TypeComparer.scala:2563)
[error] dotty.tools.dotc.core.Types$Type.frozen_$less$colon$less(Types.scala:937)
[error] dotty.tools.dotc.core.Types$Type.overrides(Types.scala:978)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeSingleDenot$1(Denotations.scala:472)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeDenot$1(Denotations.scala:405)
[error] dotty.tools.dotc.core.Denotations$Denotation.meet(Denotations.scala:491)
[error] dotty.tools.dotc.core.Types$Type.goAnd$1(Types.scala:750)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:617)
[error] dotty.tools.dotc.core.Types$Type.goThis$1(Types.scala:706)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:600)
[error] dotty.tools.dotc.core.Types$Type.findMember(Types.scala:771)
[error] dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:566)
[error] dotty.tools.dotc.core.Types$Type.nonPrivateMember(Types.scala:556)
[error] dotty.tools.dotc.core.Types$NamedType.memberDenot(Types.scala:2115)
[error] dotty.tools.dotc.core.Types$NamedType.reload$1(Types.scala:2394)
[error] dotty.tools.dotc.core.Types$NamedType.withPrefix(Types.scala:2406)
[error] dotty.tools.dotc.core.Types$NamedType.derivedSelect(Types.scala:2347)
[error] dotty.tools.dotc.core.Types$TypeMap.derivedSelect(Types.scala:4995)
[error] dotty.tools.dotc.core.Types$ApproximatingTypeMap.derivedSelect(Types.scala:5297)
[error] dotty.tools.dotc.core.TypeOps$AsSeenFromMap.apply(TypeOps.scala:102)
[error] dotty.tools.dotc.core.Types$TypeMap.mapOver$$anonfun$1(Types.scala:5116)
[error] dotty.tools.dotc.core.Types$LazyRef$.apply$$anonfun$1(Types.scala:2682)
[error] dotty.tools.dotc.core.Types$LazyRef.ref(Types.scala:2695)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:306)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.isSubArg$1(TypeComparer.scala:1438)
[error] dotty.tools.dotc.core.TypeComparer.recurArgs$1(TypeComparer.scala:1443)
[error] dotty.tools.dotc.core.TypeComparer.isSubArgs(TypeComparer.scala:1446)
[error] dotty.tools.dotc.core.TypeComparer.checkSubArgs$1(TypeComparer.scala:1035)
[error] dotty.tools.dotc.core.TypeComparer.loop$3(TypeComparer.scala:1037)
[error] dotty.tools.dotc.core.TypeComparer.isMatchingApply$1(TypeComparer.scala:1052)
[error] dotty.tools.dotc.core.TypeComparer.compareAppliedType2$1(TypeComparer.scala:1111)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:549)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:476)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:363)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.compareTypeBounds$1(TypeComparer.scala:710)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:716)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:476)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:363)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1227)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:174)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:184)
[error] dotty.tools.dotc.core.TypeComparer.isSub(TypeComparer.scala:186)
[error] dotty.tools.dotc.core.ConstraintHandling.op$proxy1$1(ConstraintHandling.scala:220)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen(ConstraintHandling.scala:220)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen$(ConstraintHandling.scala:25)
[error] dotty.tools.dotc.core.TypeComparer.isSubTypeWhenFrozen(TypeComparer.scala:30)
[error] dotty.tools.dotc.core.TypeComparer$.isSubTypeWhenFrozen(TypeComparer.scala:2563)
[error] dotty.tools.dotc.core.Types$Type.frozen_$less$colon$less(Types.scala:937)
[error] dotty.tools.dotc.core.Types$Type.overrides(Types.scala:978)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeSingleDenot$1(Denotations.scala:470)
[error] dotty.tools.dotc.core.Denotations$Denotation.mergeDenot$1(Denotations.scala:405)
[error] dotty.tools.dotc.core.Denotations$Denotation.meet(Denotations.scala:491)
[error] dotty.tools.dotc.core.Types$Type.goAnd$1(Types.scala:750)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:617)
[error] dotty.tools.dotc.core.Types$Type.goThis$1(Types.scala:706)
[error] dotty.tools.dotc.core.Types$Type.go$1(Types.scala:600)
[error] dotty.tools.dotc.core.Types$Type.findMember(Types.scala:771)
[error] dotty.tools.dotc.core.Types$Type.memberBasedOnFlags(Types.scala:566)
[error] dotty.tools.dotc.core.Types$Type.member(Types.scala:550)
[error] dotty.tools.dotc.typer.Checking$.liftedTree1$2(Checking.scala:410)
[error] dotty.tools.dotc.typer.Checking$.checkNonCyclicInherited$$anonfun$1(Checking.scala:422)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.typer.Checking$.checkNonCyclicInherited(Checking.scala:422)
[error] dotty.tools.dotc.typer.Checking.checkNonCyclicInherited(Checking.scala:657)
[error] dotty.tools.dotc.typer.Checking.checkNonCyclicInherited$(Checking.scala:649)
[error] dotty.tools.dotc.typer.Typer.checkNonCyclicInherited(Typer.scala:92)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2141)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$2(Typer.scala:2447)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2451)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2519)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2589)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2593)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2615)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2664)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2245)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2491)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2520)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2589)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2593)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2708)
[error] dotty.tools.dotc.typer.FrontEnd.liftedTree1$1(FrontEnd.scala:79)
[error] dotty.tools.dotc.typer.FrontEnd.typeCheck$$anonfun$1(FrontEnd.scala:84)
[error] dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:43)
[error] dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:85)
[error] dotty.tools.dotc.typer.FrontEnd.runOn$$anonfun$3(FrontEnd.scala:120)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:120)
[error] dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:185)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
[error] dotty.tools.dotc.Run.runPhases$5(Run.scala:195)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:203)
[error] dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:210)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:147)
[error] dotty.tools.dotc.Run.compile(Run.scala:129)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:38)
[error] dotty.tools.dotc.Driver.process(Driver.scala:194)
[error] dotty.tools.dotc.Main.process(Main.scala)
...

[bishabosha]

closed by #10270

[bishabosha]

@Sciss is this pattern necessary for you? I notice this works in Scala 2, but now it is just a cyclic reference error instead of a crash

[Sciss]

Yes, it's a basic element in the framework I'm developing. There is an outer system T that can make reference to a sibling system I. Why is it an error? Are you saying the code example is forbidden now? And what is the invalidity of it? What happens if Bar fixes I, like

trait Bar[T <: Foo[T]] extends Foo[T] {
  self: T =>

  type I = ???
}

But then the self-type T is probably parsed before I is fixed? The self-type T is pretty essential for using F-bounded type, otherwise it's quite useless.

Or would

trait Bar[T <: Foo[T], I1 <: Foo[I1]] extends Foo[T] {
  self: T =>

  type I = I1
}

work?

[bishabosha]

@Sciss so concretely the type of some LazyRef is requested while looking for a member called I, but before its internal type is known. The second example you give works:

trait Bar[T <: Foo[T], I1 <: Foo[I1]] extends Foo[T] {
  self: T =>

  type I = I1
}

[Sciss]

@bishabosha Ok. I can only really test this with new released milestone, as the example was pretty much isolated, but my guess is that with the second form I can find a way to make the implementation work, so I'm not too worried.