MatchError in SymDenotation.opaqueAlias on hk opaque types

[panacekcz]

Test code 1:

object O1 {
  type A[X] = X
  opaque type T = A
}

Output:

exception occurred while compiling opaque-hk-1.scala
scala.MatchError: TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any) (of class dotty.tools.dotc.core.Types$CachedTypeRef) while compiling opaque-hk-1.scala
Exception in thread "main" scala.MatchError: TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any) (of class dotty.tools.dotc.core.Types$CachedTypeRef)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.extractAlias$1(SymDenotations.scala:1085)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.opaqueAlias(SymDenotations.scala:1089)
        at dotty.tools.dotc.transform.ElimOpaque.transformSym(ElimOpaque.scala:43)
        at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform(DenotTransformers.scala:66)
        at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform$(DenotTransformers.scala:65)
        at dotty.tools.dotc.transform.ElimOpaque.transform(ElimOpaque.scala:30)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:921)
        at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:483)
        at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:478)
        at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:472)
        at dotty.tools.dotc.core.Symbols$.toDenot(Symbols.scala:824)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1$adapted(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.Scopes$Scope.filter(Scopes.scala:102)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.paramAccessors(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.Contexts$Context.superCallContext(Contexts.scala:367)
        at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:337)
        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$1(MegaPhase.scala:404)
        at dotty.tools.dotc.transform.MegaPhase.$anonfun$transformStats$2(MegaPhase.scala:409)
        at scala.collection.immutable.List.mapConserve(List.scala:179)
        at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:409)
        at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:339)
        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$1(MegaPhase.scala:404)
        at dotty.tools.dotc.transform.MegaPhase.$anonfun$transformStats$2(MegaPhase.scala:409)
        at scala.collection.immutable.List.mapConserve(List.scala:179)
        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.$anonfun$runOn$1(Phases.scala:316)
        at scala.collection.immutable.List.map(List.scala:286)
        at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:314)
        at dotty.tools.dotc.Run.$anonfun$compileUnits$3(Run.scala:158)
        at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
        at dotty.tools.dotc.util.Stats$.trackTime(Stats.scala:49)
        at dotty.tools.dotc.Run.$anonfun$compileUnits$2(Run.scala:155)
        at dotty.tools.dotc.Run.$anonfun$compileUnits$2$adapted(Run.scala:153)
        at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:36)
        at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:33)
        at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:198)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:153)
        at dotty.tools.dotc.Run.$anonfun$compileUnits$1(Run.scala:178)
        at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:102)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:133)
        at dotty.tools.dotc.Run.compileSources(Run.scala:120)
        at dotty.tools.dotc.Run.compile(Run.scala:104)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:33)
        at dotty.tools.dotc.Driver.process(Driver.scala:170)
        at dotty.tools.dotc.Driver.process(Driver.scala:139)
        at dotty.tools.dotc.Driver.process(Driver.scala:151)
        at dotty.tools.dotc.Driver.main(Driver.scala:178)
        at dotty.tools.dotc.Main.main(Main.scala)

Test code 2:

object O2 {
  opaque type A[X] = X
  object A {
    opaque type T = A
  }
}

Output:

exception occurred while compiling opaque-hk-2.scala
scala.MatchError: AppliedType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),module class O2$)),module class A$)),A),List(TypeBounds(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Nothing),TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any)))) (of class dotty.tools.dotc.core.Types$CachedAppliedType) while compiling opaque-hk-2.scala
Exception in thread "main" scala.MatchError: AppliedType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),module class O2$)),module class A$)),A),List(TypeBounds(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Nothing),TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any)))) (of class dotty.tools.dotc.core.Types$CachedAppliedType)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.extractAlias$1(SymDenotations.scala:1085)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.opaqueAlias(SymDenotations.scala:1089)
        at dotty.tools.dotc.transform.ElimOpaque.transformSym(ElimOpaque.scala:43)
        at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform(DenotTransformers.scala:66)
        at dotty.tools.dotc.core.DenotTransformers$SymTransformer.transform$(DenotTransformers.scala:65)
        at dotty.tools.dotc.transform.ElimOpaque.transform(ElimOpaque.scala:30)
        at dotty.tools.dotc.core.Denotations$SingleDenotation.current(Denotations.scala:921)
        at dotty.tools.dotc.core.Symbols$Symbol.recomputeDenot(Symbols.scala:483)
        at dotty.tools.dotc.core.Symbols$Symbol.computeDenot(Symbols.scala:478)
        at dotty.tools.dotc.core.Symbols$Symbol.denot(Symbols.scala:472)
        at dotty.tools.dotc.core.Symbols$.toDenot(Symbols.scala:824)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.$anonfun$paramAccessors$1$adapted(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.Scopes$Scope.filter(Scopes.scala:102)
        at dotty.tools.dotc.core.SymDenotations$ClassDenotation.paramAccessors(SymDenotations.scala:1927)
        at dotty.tools.dotc.core.Contexts$Context.superCallContext(Contexts.scala:367)
        at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:337)
        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$1(MegaPhase.scala:404)
        at dotty.tools.dotc.transform.MegaPhase.$anonfun$transformStats$2(MegaPhase.scala:409)
        at scala.collection.immutable.List.mapConserve(List.scala:179)
        at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:409)
        at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:339)
        (... same as test 1)

Test code 3:

object O3 {
  opaque type R[X] = R[X]
}

Output:

exception occurred while compiling opaque-hk-3.scala
scala.MatchError: AppliedType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),module class O3$)),type R),List(TypeParamRef(X0))) (of class dotty.tools.dotc.core.Types$CachedAppliedType) while compiling opaque-hk-3.scala
Exception in thread "main" scala.MatchError: AppliedType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),module class O3$)),type R),List(TypeParamRef(X0))) (of class dotty.tools.dotc.core.Types$CachedAppliedType)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.extractAlias$1(SymDenotations.scala:1085)
        at dotty.tools.dotc.core.SymDenotations$SymDenotation.extractAlias$1(SymDenotations.scala:1087)
        (... same as test 1)

[panacekcz]

Even simpler way to reproduce is to define a hk opaque alias to Any or Nothing.

object O4{
  opaque type T[X] = Any
}

object O5{
  opaque type T[X] = Nothing
}