Unhandled exception while running erasure

[abosshard]

Compiler version

3.5.0, 3.4.3

Minimized code

trait A[T]:
  type R = T ?=> Unit
  def f: R = ()

class B extends A[Int]:
  override def f: R = ()

Output (click arrow to expand)

  unhandled exception while running erasure on Bug.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/scala/scala3/issues/new/choose
  For non-enriched exceptions, compile with -Xno-enrich-error-messages.

     while compiling: Bug.scala
        during phase: erasure
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.14
    compiler version: version 3.5.0
            settings: 

Exception in thread "main" scala.MatchError: TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),class B)),type R) (of class dotty.tools.dotc.core.Types$CachedTypeRef)
	at dotty.tools.dotc.transform.ContextFunctionResults$.recur$1(ContextFunctionResults.scala:105)
	at dotty.tools.dotc.transform.ContextFunctionResults$.contextFunctionResultTypeAfter(ContextFunctionResults.scala:106)
	at dotty.tools.dotc.transform.Bridges.etaExpand$1(Bridges.scala:157)
	at dotty.tools.dotc.transform.Bridges.bridgeRhs$1(Bridges.scala:166)
	at dotty.tools.dotc.transform.Bridges.addBridge$$anonfun$2(Bridges.scala:168)
	at dotty.tools.dotc.ast.tpd$.DefDef(tpd.scala:312)
	at dotty.tools.dotc.transform.Bridges.addBridge(Bridges.scala:168)
	at dotty.tools.dotc.transform.Bridges.addBridgeIfNeeded(Bridges.scala:94)
	at dotty.tools.dotc.transform.Bridges.add(Bridges.scala:178)
	at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1078)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:3074)
	at dotty.tools.dotc.transform.Erasure$Typer.typedClassDef(Erasure.scala:1056)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3380)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3384)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3476)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3554)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3558)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3580)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3626)
	at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1080)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:3207)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3426)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3477)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3554)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3558)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3669)
	at dotty.tools.dotc.transform.Erasure.run(Erasure.scala:145)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:380)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:373)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:343)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:336)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:384)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:396)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:396)
	at dotty.tools.dotc.Run.compileSources(Run.scala:282)
	at dotty.tools.dotc.Run.compile(Run.scala:267)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.dotc.Driver.process(Driver.scala:201)
	at dotty.tools.dotc.Driver.process(Driver.scala:169)
	at dotty.tools.dotc.Driver.process(Driver.scala:181)
	at dotty.tools.dotc.Driver.main(Driver.scala:211)
	at dotty.tools.MainGenericCompiler$.run$1(MainGenericCompiler.scala:162)
	at dotty.tools.MainGenericCompiler$.main(MainGenericCompiler.scala:186)
	at dotty.tools.MainGenericCompiler.main(MainGenericCompiler.scala)