Crash when type override has wrong kind

[japgolly]

Compiler version

3.0.0

Minimized code

trait Step {
  type Self
  type Next[A]
}

trait DynamicNextStep {
  type OneOf[Self, Next[_]]
  def apply(s: Step): OneOf[s.Self, s.Next]
}

object X extends DynamicNextStep {
  override type OneOf[Self] = Self
  override def apply(s: Step) = ???
}

Output (click arrow to expand)

[error] java.util.NoSuchElementException: head of empty list
[error] scala.collection.immutable.Nil$.head(List.scala:629)
[error] scala.collection.immutable.Nil$.head(List.scala:628)
[error] dotty.tools.dotc.core.TypeComparer.recurArgs$1(TypeComparer.scala:1411)
[error] dotty.tools.dotc.core.TypeComparer.isSubArgs(TypeComparer.scala:1484)
[error] dotty.tools.dotc.core.TypeComparer.loop$3(TypeComparer.scala:1074)
[error] dotty.tools.dotc.core.TypeComparer.isMatchingApply$1(TypeComparer.scala:1092)
[error] dotty.tools.dotc.core.TypeComparer.compareAppliedType2$1(TypeComparer.scala:1151)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:556)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:487)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:369)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1267)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:180)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:190)
[error] dotty.tools.dotc.core.TypeComparer.compareMethod$1(TypeComparer.scala:687)
[error] dotty.tools.dotc.core.TypeComparer.thirdTry$1(TypeComparer.scala:690)
[error] dotty.tools.dotc.core.TypeComparer.secondTry$1(TypeComparer.scala:487)
[error] dotty.tools.dotc.core.TypeComparer.firstTry$1(TypeComparer.scala:369)
[error] dotty.tools.dotc.core.TypeComparer.recur(TypeComparer.scala:1267)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:180)
[error] dotty.tools.dotc.core.TypeComparer.isSubType(TypeComparer.scala:190)
[error] dotty.tools.dotc.core.TypeComparer.isSub(TypeComparer.scala:192)
[error] dotty.tools.dotc.core.ConstraintHandling.op$proxy1$1(ConstraintHandling.scala:221)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen(ConstraintHandling.scala:221)
[error] dotty.tools.dotc.core.ConstraintHandling.isSubTypeWhenFrozen$(ConstraintHandling.scala:26)
[error] dotty.tools.dotc.core.TypeComparer.isSubTypeWhenFrozen(TypeComparer.scala:30)
[error] dotty.tools.dotc.core.TypeComparer$.isSubTypeWhenFrozen(TypeComparer.scala:2615)
[error] dotty.tools.dotc.core.Types$Type.frozen_$less$colon$less(Types.scala:1026)
[error] dotty.tools.dotc.core.Types$Type.overrides(Types.scala:1067)
[error] dotty.tools.dotc.typer.RefChecks$.dotty$tools$dotc$typer$RefChecks$$$_$compatibleTypes$2(RefChecks.scala:284)
[error] dotty.tools.dotc.typer.RefChecks$.compatTypes$2(RefChecks.scala:322)
[error] dotty.tools.dotc.typer.RefChecks$.checkOverride$1(RefChecks.scala:472)
[error] dotty.tools.dotc.typer.RefChecks$.dotty$tools$dotc$typer$RefChecks$$$checkAllOverrides(RefChecks.scala:517)
[error] dotty.tools.dotc.typer.RefChecks.transformTemplate(RefChecks.scala:1225)
[error] dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:1004)
[error] dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:1005)
[error] dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:1005)
[error] dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:1005)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:363)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
[error] dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:256)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
[error] dotty.tools.dotc.transform.MegaPhase.transformStat$2(MegaPhase.scala:437)
[error] dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
[error] dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
[error] dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
[error] dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
[error] dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:442)
[error] dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:382)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:385)
[error] dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
[error] dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:448)
[error] dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:460)
[error] dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:303)
[error] scala.collection.immutable.List.map(List.scala:250)
[error] dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:304)
[error] dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:205)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
[error] dotty.tools.dotc.Run.runPhases$5(Run.scala:215)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:223)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:230)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:166)
[error] dotty.tools.dotc.Run.compile(Run.scala:150)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:186)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:241)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:176)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:157)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:157)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:204)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:174)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:172)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:457)
[error] sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:261)
[error] sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:412)
[error] sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:499)
[error] sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:399)
[error] sbt.internal.inc.Incremental$.apply(Incremental.scala:166)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:528)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:482)
[error] sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
[error] sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2346)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2303)
[error] sbt.internal.io.Retry$.apply(Retry.scala:46)
[error] sbt.internal.io.Retry$.apply(Retry.scala:28)
[error] sbt.internal.io.Retry$.apply(Retry.scala:23)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2299)
[error] scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
[error] sbt.std.Transform$$anon$4.work(Transform.scala:68)
[error] sbt.Execute.$anonfun$submit$2(Execute.scala:282)
[error] sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
[error] sbt.Execute.work(Execute.scala:291)
[error] sbt.Execute.$anonfun$submit$1(Execute.scala:282)
[error] sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[error] java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[error] java.base/java.lang.Thread.run(Thread.java:834)