post/Iter3.scala fails to compile. ClassCast exception in typer.

[DarkDimius]

after applying #836, #833 and #837.

dotc -bootstrapped Iter3.scala

exception occurred while compiling Iter3.scala
Exception in thread "main" java.lang.ClassCastException: dotty.tools.dotc.core.Types$PolyParam cannot be cast to dotty.tools.dotc.core.Types$TypeBounds
    at dotty.tools.dotc.core.OrderingConstraint.nonParamBounds(OrderingConstraint.scala:193)
    at dotty.tools.dotc.core.OrderingConstraint.narrowBound(OrderingConstraint.scala:356)
    at dotty.tools.dotc.core.OrderingConstraint.narrowBound(OrderingConstraint.scala:126)
    at dotty.tools.dotc.core.ConstraintHandling.addOneBound(ConstraintHandling.scala:38)
    at dotty.tools.dotc.core.ConstraintHandling.$anonfun$unify$3(ConstraintHandling.scala:105)
    at dotty.tools.dotc.core.ConstraintHandling$$Lambda$720/341748265.apply(Unknown Source)
    at scala.collection.LinearSeqOptimized$class.forall(LinearSeqOptimized.scala:83)
    at scala.collection.immutable.List.forall(List.scala:84)
    at dotty.tools.dotc.core.ConstraintHandling.unify(ConstraintHandling.scala:105)
    at dotty.tools.dotc.core.ConstraintHandling.addLess(ConstraintHandling.scala:76)
    at dotty.tools.dotc.core.TypeComparer.addLess(TypeComparer.scala:19)
    at dotty.tools.dotc.core.ConstraintHandling.liftedTree1$1(ConstraintHandling.scala:227)
    at dotty.tools.dotc.core.ConstraintHandling.addConstraint(ConstraintHandling.scala:225)
    at dotty.tools.dotc.core.TypeComparer.addConstraint(TypeComparer.scala:19)
    at dotty.tools.dotc.core.TypeComparer.comparePolyParam$1(TypeComparer.scala:255)
    at dotty.tools.dotc.core.TypeComparer.secondTry(TypeComparer.scala:258)
    at dotty.tools.dotc.core.TypeComparer.firstTry(TypeComparer.scala:177)
    at dotty.tools.dotc.core.TypeComparer.liftedTree3$1(TypeComparer.scala:100)
    at dotty.tools.dotc.core.TypeComparer.$anonfun$isSubType$3(TypeComparer.scala:97)
    at dotty.tools.dotc.core.TypeComparer$$Lambda$372/1458849419.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:91)
    at dotty.tools.dotc.core.TypeComparer.secondTry(TypeComparer.scala:272)
    at dotty.tools.dotc.core.TypeComparer.firstTry(TypeComparer.scala:177)
    at dotty.tools.dotc.core.TypeComparer.liftedTree3$1(TypeComparer.scala:100)
    at dotty.tools.dotc.core.TypeComparer.$anonfun$isSubType$3(TypeComparer.scala:97)
    at dotty.tools.dotc.core.TypeComparer$$Lambda$372/1458849419.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:91)
    at dotty.tools.dotc.core.TypeComparer.firstTry(TypeComparer.scala:179)
    at dotty.tools.dotc.core.TypeComparer.liftedTree3$1(TypeComparer.scala:100)
    at dotty.tools.dotc.core.TypeComparer.$anonfun$isSubType$3(TypeComparer.scala:97)
    at dotty.tools.dotc.core.TypeComparer$$Lambda$372/1458849419.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:91)
    at dotty.tools.dotc.core.TypeComparer.compareTypeBounds$1(TypeComparer.scala:401)
    at dotty.tools.dotc.core.TypeComparer.thirdTry(TypeComparer.scala:408)
    at dotty.tools.dotc.core.TypeComparer.secondTry(TypeComparer.scala:291)
    at dotty.tools.dotc.core.TypeComparer.firstTry(TypeComparer.scala:232)
    at dotty.tools.dotc.core.TypeComparer.liftedTree3$1(TypeComparer.scala:100)
    at dotty.tools.dotc.core.TypeComparer.$anonfun$isSubType$3(TypeComparer.scala:97)
    at dotty.tools.dotc.core.TypeComparer$$Lambda$372/1458849419.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:91)
    at dotty.tools.dotc.core.TypeComparer.isSubRefinements(TypeComparer.scala:616)
    at dotty.tools.dotc.core.TypeComparer.compareRefined$1(TypeComparer.scala:344)
    at dotty.tools.dotc.core.TypeComparer.thirdTry(TypeComparer.scala:346)
    at dotty.tools.dotc.core.TypeComparer.secondTry(TypeComparer.scala:291)
    at dotty.tools.dotc.core.TypeComparer.firstTry(TypeComparer.scala:232)
    at dotty.tools.dotc.core.TypeComparer.liftedTree3$1(TypeComparer.scala:100)
    at dotty.tools.dotc.core.TypeComparer.$anonfun$isSubType$3(TypeComparer.scala:97)
    at dotty.tools.dotc.core.TypeComparer$$Lambda$372/1458849419.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:91)
    at dotty.tools.dotc.core.TypeComparer.topLevelSubType(TypeComparer.scala:85)
    at dotty.tools.dotc.core.Types$Type.$anonfun$$less$colon$less$1(Types.scala:595)
    at dotty.tools.dotc.core.Types$Type$$Lambda$370/600746945.apply$mcZ$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcZ$sp.apply(JFunction0$mcZ$sp.java:12)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.core.Types$Type.$less$colon$less(Types.scala:594)
    at dotty.tools.dotc.typer.ProtoTypes$Compatibility.isCompatible(ProtoTypes.scala:37)
    at dotty.tools.dotc.typer.Typer.isCompatible(Typer.scala:57)
    at dotty.tools.dotc.typer.ProtoTypes$Compatibility.constrainResult(ProtoTypes.scala:61)
    at dotty.tools.dotc.typer.Typer.constrainResult(Typer.scala:57)
    at dotty.tools.dotc.typer.Applications$Application.init(Applications.scala:183)
    at dotty.tools.dotc.typer.Applications$TypedApply.<init>(Applications.scala:434)
    at dotty.tools.dotc.typer.Applications$ApplyToUntyped.<init>(Applications.scala:512)
    at dotty.tools.dotc.typer.Applications.$anonfun$$anonfun$realApply$1$2(Applications.scala:549)
    at dotty.tools.dotc.typer.Applications$$Lambda$421/94345706.apply(Unknown Source)
    at dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:1215)
    at dotty.tools.dotc.typer.Applications.$anonfun$realApply$1(Applications.scala:559)
    at dotty.tools.dotc.typer.Applications$$Lambda$419/644166178.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:530)
    at dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:596)
    at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:57)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1120)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.ProtoTypes$FunProto.typedArg(ProtoTypes.scala:201)
    at dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:513)
    at dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:511)
    at dotty.tools.dotc.typer.Applications$Application.addTyped$1(Applications.scala:316)
    at dotty.tools.dotc.typer.Applications$Application.matchArgs(Applications.scala:355)
    at dotty.tools.dotc.typer.Applications$Application.matchArgs(Applications.scala:356)
    at dotty.tools.dotc.typer.Applications$Application.init(Applications.scala:192)
    at dotty.tools.dotc.typer.Applications$TypedApply.<init>(Applications.scala:434)
    at dotty.tools.dotc.typer.Applications$ApplyToUntyped.<init>(Applications.scala:512)
    at dotty.tools.dotc.typer.Applications.$anonfun$$anonfun$realApply$1$2(Applications.scala:549)
    at dotty.tools.dotc.typer.Applications$$Lambda$421/94345706.apply(Unknown Source)
    at dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:1215)
    at dotty.tools.dotc.typer.Applications.$anonfun$realApply$1(Applications.scala:559)
    at dotty.tools.dotc.typer.Applications$$Lambda$419/644166178.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:530)
    at dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:596)
    at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:57)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1120)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedIf$1(Typer.scala:494)
    at dotty.tools.dotc.typer.Typer$$Lambda$473/1164371389.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedIf(Typer.scala:492)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1129)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1207)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedBlock$2(Typer.scala:447)
    at dotty.tools.dotc.typer.Typer$$Lambda$468/1926764753.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:444)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1128)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1207)
    at dotty.tools.dotc.typer.Typer.caseRest$1(Typer.scala:678)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedCase$3(Typer.scala:693)
    at dotty.tools.dotc.typer.Typer$$Lambda$642/90205195.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedCase(Typer.scala:667)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedCases$1(Typer.scala:661)
    at dotty.tools.dotc.typer.Typer$$Lambda$641/564742142.apply(Unknown Source)
    at dotty.tools.dotc.core.Decorators$ListDecorator$.loop$4(Decorators.scala:51)
    at dotty.tools.dotc.core.Decorators$ListDecorator$.mapconserve$extension(Decorators.scala:67)
    at dotty.tools.dotc.typer.Typer.typedCases(Typer.scala:661)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedMatch$1(Typer.scala:633)
    at dotty.tools.dotc.typer.Typer$$Lambda$638/326298949.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedMatch(Typer.scala:624)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1132)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1207)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedDefDef$2(Typer.scala:934)
    at dotty.tools.dotc.typer.Typer$$Lambda$429/1580893732.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:927)
    at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1108)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1158)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.traverse$2(Typer.scala:1192)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1203)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedClassDef$3(Typer.scala:963)
    at dotty.tools.dotc.typer.Typer$$Lambda$425/32017212.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:946)
    at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1111)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1158)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.traverse$2(Typer.scala:1192)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1203)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedClassDef$3(Typer.scala:963)
    at dotty.tools.dotc.typer.Typer$$Lambda$425/32017212.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:946)
    at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1111)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1158)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.traverse$2(Typer.scala:1192)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1203)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedPackageDef$1(Typer.scala:1051)
    at dotty.tools.dotc.typer.Typer$$Lambda$277/796684896.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1042)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1148)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.traverse$2(Typer.scala:1198)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1203)
    at dotty.tools.dotc.typer.Typer.$anonfun$typedPackageDef$1(Typer.scala:1051)
    at dotty.tools.dotc.typer.Typer$$Lambda$277/796684896.apply(Unknown Source)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:31)
    at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1042)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1148)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1160)
    at dotty.tools.dotc.typer.Typer.liftedTree12$1(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer.$anonfun$typed$2(Typer.scala:1170)
    at dotty.tools.dotc.typer.Typer$$Lambda$275/288665596.apply(Unknown Source)
    at dotty.tools.dotc.reporting.Reporting.traceIndented(Reporter.scala:148)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:53)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1168)
    at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1207)
    at dotty.tools.dotc.typer.FrontEnd.$anonfun$typeCheck$1(FrontEnd.scala:42)
    at dotty.tools.dotc.typer.FrontEnd$$Lambda$273/1513712028.apply$mcV$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
    at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:19)
    at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:46)
    at dotty.tools.dotc.typer.FrontEnd.$anonfun$runOn$7(FrontEnd.scala:53)
    at dotty.tools.dotc.typer.FrontEnd$$Lambda$272/747464370.applyVoid(Unknown Source)
    at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
    at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
    at scala.collection.immutable.List.foreach(List.scala:381)
    at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:53)
    at dotty.tools.dotc.Run.$anonfun$$anonfun$3(Run.scala:59)
    at dotty.tools.dotc.Run$$Lambda$194/611437735.applyVoid(Unknown Source)
    at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
    at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
    at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
    at dotty.tools.dotc.Run.$anonfun$compileUnits$1(Run.scala:57)
    at dotty.tools.dotc.Run$$Lambda$185/1761291320.apply$mcV$sp(Unknown Source)
    at scala.compat.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
    at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:58)
    at dotty.tools.dotc.Run.compileUnits(Run.scala:65)
    at dotty.tools.dotc.Run.compileSources(Run.scala:49)
    at dotty.tools.dotc.Run.compile(Run.scala:33)
    at dotty.tools.dotc.Driver.doCompile(Driver.scala:21)
    at dotty.tools.dotc.Driver.process(Driver.scala:44)
    at dotty.tools.dotc.Driver.main(Driver.scala:48)
    at dotty.tools.dotc.Main.main(Main.scala)

[DarkDimius]

Same error seems to happen in t2504.scala

[DarkDimius]

Same error seems to happen in t2293.scala
And typers.scala, and t8230a.scala

[DarkDimius]

dotc -bootstrapped Iter3.scala
Leads to the same error on my machine.
This is not specific to bootstrapped version.

[DarkDimius]

https://www.diffchecker.com/trmxnro9 contains diff between typecheckings

[DarkDimius]

Ok. I have progress here.

OrderingConstraint.scala:

def contains(param: PolyParam): Boolean = {
    val entries = boundsMap(param.binder)
    entries != null && entries(param.paramNum).isInstanceOf[TypeBounds]
  }

becomes

def contains(param: dotty.tools.dotc.core.Types.Types$PolyParam):
          Boolean
         = {
          val entries: dotty.tools.dotc.core.Types.Types$Type[] =
            OrderingConstraint.this.boundsMap().apply(param.binder()).
              asInstanceOf
            [dotty.tools.dotc.core.Types.Types$Type[]]
          entries.==(null).unary_!().&&(true)
        }

after erasure.

I've traced it to this line:
https://github.com/lampepfl/dotty/blob/master/src/dotty/tools/dotc/transform/TypeTestsCasts.scala#L50

where for expr = entries.apply(param.paramNum) we have type TypeRef(TermRef(NoPrefix,entries),scala$Array$$T) that is an alias to TypeAlias(WildcardType(NoType)).

[DarkDimius]

how to reproduce:

dotc ./dotty/tools/dotc/core/OrderingConstraint.scala -Xprint:eras

....
result of ./dotty/tools/dotc/core/OrderingConstraint.scala after erasure:
package dotty.tools {
  package dotty.tools.dotc {
    package dotty.tools.dotc.core {
      final lazy module val OrderingConstraint:
        dotty.tools.dotc.core.OrderingConstraint$
       = new dotty.tools.dotc.core.OrderingConstraint$()
      class OrderingConstraint(boundsMap: dotty.tools.dotc.util.SimpleMap,
        lowerMap: dotty.tools.dotc.util.SimpleMap
      , upperMap: dotty.tools.dotc.util.SimpleMap) extends
        dotty.tools.dotc.core.Constraint
      () {
        private <accessor> def boundsMap(): dotty.tools.dotc.util.SimpleMap
        private <accessor> def lowerMap(): dotty.tools.dotc.util.SimpleMap
        private <accessor> def upperMap(): dotty.tools.dotc.util.SimpleMap
        private def paramCount(entries: dotty.tools.dotc.core.Types.Type[]): Int
           =
        entries.[]length().>>(1)
        private def typeVar(entries: dotty.tools.dotc.core.Types.Type[], n: Int)
          :
        dotty.tools.dotc.core.Types.Type =
          entries.[]apply(this.paramCount(entries).+(n))
        def entry(param: dotty.tools.dotc.core.Types.PolyParam):
          dotty.tools.dotc.core.Types.Type
         = {
          val entries: dotty.tools.dotc.core.Types.Type[] =
            OrderingConstraint.this.boundsMap().apply(param.binder()).
              asInstanceOf
            [dotty.tools.dotc.core.Types.Type[]]
          if entries.==(null) then dotty.tools.dotc.core.Types.NoType else
            entries.[]apply(param.paramNum())
        }
        def contains(pt: dotty.tools.dotc.core.Types.PolyType): Boolean =
          OrderingConstraint.this.boundsMap().apply(pt).==(null).unary_!()
        def contains(param: dotty.tools.dotc.core.Types.PolyParam): Boolean = {
          val entries: dotty.tools.dotc.core.Types.Type[] =
            OrderingConstraint.this.boundsMap().apply(param.binder()).
              asInstanceOf
            [dotty.tools.dotc.core.Types.Type[]]
          entries.==(null).unary_!().&&(true)
        }

see true in the last line.

[DarkDimius]

Not a blocker anymore, as I have a workaroud