AssertionError: no TypeBounds allowed on SAM expansion with wildcard

[panacekcz]

minimized code

@FunctionalInterface
abstract class Q[A]{
  def apply(a: A): Int
}
object O{
 def m(i: Int): Int = i
 val x: Q[_] = m
}

Stack trace

exception occurred while compiling sam-wildcard.scala
java.lang.AssertionError: no TypeBounds allowed while compiling sam-wildcard.scala
Exception in thread "main" java.lang.AssertionError: no TypeBounds allowed
	at dotty.tools.dotc.core.TypeApplications$.noBounds(TypeApplications.scala:21)
	at dotty.tools.dotc.core.TypeApplications$.argTypes$extension$$anonfun$1(TypeApplications.scala:487)
	at scala.collection.immutable.List.mapConserve(List.scala:444)
	at dotty.tools.dotc.core.TypeApplications$.argTypes$extension(TypeApplications.scala:487)
	at dotty.tools.dotc.ast.tpd$.isApplicable$1$$anonfun$1(tpd.scala:275)
	at dotty.tools.dotc.core.Types$LambdaType.instantiate(Types.scala:3093)
	at dotty.tools.dotc.core.Types$MethodOrPoly.instantiate(Types.scala:3147)
	at dotty.tools.dotc.ast.tpd$.isApplicable$3(tpd.scala:275)
	at dotty.tools.dotc.ast.tpd$.$anonfun$5(tpd.scala:281)
	at dotty.tools.dotc.core.Denotations$SingleDenotation.suchThat(Denotations.scala:761)
	at dotty.tools.dotc.ast.tpd$.ClassDef(tpd.scala:281)
	at dotty.tools.dotc.ast.tpd$.AnonClass(tpd.scala:332)
	at dotty.tools.dotc.transform.ExpandSAMs.transformBlock(ExpandSAMs.scala:51)
	at dotty.tools.dotc.transform.MegaPhase.goBlock(MegaPhase.scala:701)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:288)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:396)
	at dotty.tools.dotc.transform.MegaPhase.mapValDef$1(MegaPhase.scala:234)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:238)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:394)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$2(MegaPhase.scala:404)
	at dotty.tools.dotc.transform.MegaPhase.$anonfun$1(MegaPhase.scala:409)
	at scala.collection.immutable.List.mapConserve(List.scala:444)
	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$2(MegaPhase.scala:404)
	at dotty.tools.dotc.transform.MegaPhase.$anonfun$1(MegaPhase.scala:409)
	at scala.collection.immutable.List.mapConserve(List.scala:444)
	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.runOn$$anonfun$1(Phases.scala:315)
	at scala.collection.immutable.List.map(List.scala:219)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:316)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:167)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:177)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:185)
	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:65)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:192)
	at dotty.tools.dotc.Run.compileSources(Run.scala:129)
	at dotty.tools.dotc.Run.compile(Run.scala:112)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:36)
	at dotty.tools.dotc.Driver.process(Driver.scala:189)
	at dotty.tools.dotc.Driver.process(Driver.scala:158)
	at dotty.tools.dotc.Driver.process(Driver.scala:170)
	at dotty.tools.dotc.Driver.main(Driver.scala:197)
	at dotty.tools.dotc.Main.main(Main.scala)