Assertion failed when not adding prefix to extension method in method body

[Katrix]

Compiler version

3.0.0-M4-bin-20210204-406ff9d-NIGHTLY

Minimized code

trait RepresentableK[F[_[_], _]]:
  type RepresentationK[_]

  def tabulateK[A[_], C](f: RepresentationK ~>: A): F[A, C]

  extension[A[_], C](fa: F[A, C])
    def indexK: RepresentationK ~>: A
  
    def mapK[B[_]] (f: A ~>: B): F[B, C] =
      tabulateK([Z] => (r: RepresentationK[Z]) => f(indexK(r)))

Replacing f(indexK(r)) with f(fa.indexK(r))
I honestly didn't expect it to work, but I more just expected a normal error message.

Output (click arrow to expand)

[error] ## Exception when compiling 15 sources to D:\DevProjects\Stable\perspective\dotty\perspective\target\scala-3.0.0-M4\classes
[error] java.lang.AssertionError: assertion failed
[error] scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:11)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.extensionParam(SymDenotations.scala:341)
[error] dotty.tools.dotc.typer.Typer.isLocalExtensionMethodRef$3$$anonfun$2(Typer.scala:513)
[error] dotty.tools.dotc.core.Denotations$SingleDenotation.hasAltWith(Denotations.scala:610)
[error] dotty.tools.dotc.typer.Typer.isLocalExtensionMethodRef$1(Typer.scala:513)
[error] dotty.tools.dotc.typer.Typer.typedIdent(Typer.scala:519)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2546)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2638)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:821)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:974)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:301)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:102)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2577)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.$anonfun$2(ProtoTypes.scala:414)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.cacheTypedArg(ProtoTypes.scala:370)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.typedArg(ProtoTypes.scala:415)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:789)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:789)
[error] dotty.tools.dotc.typer.Applications$Application.addTyped$1(Applications.scala:520)
[error] dotty.tools.dotc.typer.Applications$Application.matchArgs(Applications.scala:580)
[error] dotty.tools.dotc.typer.Applications$Application.init(Applications.scala:431)
[error] dotty.tools.dotc.typer.Applications$TypedApply.<init>(Applications.scala:684)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.<init>(Applications.scala:788)
[error] dotty.tools.dotc.typer.Applications.ApplyTo(Applications.scala:999)
[error] dotty.tools.dotc.typer.Applications.ApplyTo$(Applications.scala:301)
[error] dotty.tools.dotc.typer.Typer.ApplyTo(Typer.scala:102)
[error] dotty.tools.dotc.typer.Applications.simpleApply$1(Applications.scala:846)
[error] dotty.tools.dotc.typer.Applications.realApply$5$$anonfun$4(Applications.scala:925)
[error] dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:2832)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:936)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:974)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:301)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:102)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2577)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Namer.typedAheadExpr$$anonfun$1(Namer.scala:1305)
[error] dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1292)
[error] dotty.tools.dotc.typer.Namer.typedAheadExpr(Namer.scala:1305)
[error] dotty.tools.dotc.typer.Namer.rhsType$1$$anonfun$1(Namer.scala:1447)
[error] dotty.tools.dotc.typer.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:223)
[error] dotty.tools.dotc.typer.Namer.rhsType$2(Namer.scala:1447)
[error] dotty.tools.dotc.typer.Namer.cookedRhsType$1(Namer.scala:1458)
[error] dotty.tools.dotc.typer.Namer.lhsType$1(Namer.scala:1459)
[error] dotty.tools.dotc.typer.Namer.inferredType$1(Namer.scala:1470)
[error] dotty.tools.dotc.typer.Namer.valOrDefDefSig(Namer.scala:1479)
[error] dotty.tools.dotc.typer.Namer.defDefSig(Namer.scala:1562)
[error] dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:703)
[error] dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:830)
[error] dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:731)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
[error] dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
[error] dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
[error] dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:2519)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2544)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2638)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2730)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2780)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2227)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$2(Typer.scala:2565)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2569)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2638)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2730)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2780)
[error] dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:969)
[error] dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:973)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2585)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.typedNew(Typer.scala:735)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2581)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2623)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.$anonfun$2(ProtoTypes.scala:414)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.cacheTypedArg(ProtoTypes.scala:370)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.typedArg(ProtoTypes.scala:415)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:789)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.typedArg(Applications.scala:789)
[error] dotty.tools.dotc.typer.Applications$Application.addTyped$1(Applications.scala:520)
[error] dotty.tools.dotc.typer.Applications$Application.matchArgs(Applications.scala:580)
[error] dotty.tools.dotc.typer.Applications$Application.init(Applications.scala:431)
[error] dotty.tools.dotc.typer.Applications$TypedApply.<init>(Applications.scala:684)
[error] dotty.tools.dotc.typer.Applications$ApplyToUntyped.<init>(Applications.scala:788)
[error] dotty.tools.dotc.typer.Applications.ApplyTo(Applications.scala:999)
[error] dotty.tools.dotc.typer.Applications.ApplyTo$(Applications.scala:301)
[error] dotty.tools.dotc.typer.Typer.ApplyTo(Typer.scala:102)
[error] dotty.tools.dotc.typer.Applications.simpleApply$1(Applications.scala:846)
[error] dotty.tools.dotc.typer.Applications.realApply$5$$anonfun$4(Applications.scala:925)
[error] dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:2832)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:936)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:974)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:301)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:102)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2577)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Typer.$anonfun$35(Typer.scala:2081)
[error] dotty.tools.dotc.typer.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:223)
[error] dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2081)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2554)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2638)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2730)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2780)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2227)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$2(Typer.scala:2565)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2569)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2638)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2730)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2780)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2362)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2610)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2639)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2704)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2708)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2824)
[error] dotty.tools.dotc.typer.FrontEnd.liftedTree1$1(FrontEnd.scala:79)
[error] dotty.tools.dotc.typer.FrontEnd.typeCheck$$anonfun$1(FrontEnd.scala:84)
[error] dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:43)
[error] dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:85)
[error] dotty.tools.dotc.typer.FrontEnd.runOn$$anonfun$3(FrontEnd.scala:120)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:333)
[error] dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:120)
[error] dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:189)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
[error] dotty.tools.dotc.Run.runPhases$5(Run.scala:199)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:207)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:214)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:150)
[error] dotty.tools.dotc.Run.compile(Run.scala:134)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:92)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:186)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:241)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:176)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:157)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:157)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:204)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:573)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:573)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:173)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:171)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:458)
[error] sbt.internal.inc.IncrementalCommon$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$8(Incremental.scala:413)
[error] sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:498)
[error] sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:400)
[error] sbt.internal.inc.Incremental$.apply(Incremental.scala:165)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:573)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:491)
[error] sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
[error] sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2176)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2133)
[error] sbt.internal.io.Retry$.apply(Retry.scala:40)
[error] sbt.internal.io.Retry$.apply(Retry.scala:23)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2129)
[error] scala.Function1.$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$2.call(CompletionService.scala:64)
[error] java.util.concurrent.FutureTask.run(FutureTask.java:266)
[error] java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
[error] java.util.concurrent.FutureTask.run(FutureTask.java:266)
[error] java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
[error] java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
[error] java.lang.Thread.run(Thread.java:748)

[prolativ]

@Katrix as a rule when supplying minimized code to an issue please first try compiling it in separation from the codebase of your project so that missing definitions don't hide the actual error that we'll need to reproduce.
In this case ~>: is not defined although I guess it should be something like

trait ~>: [A[_], B[_]]

[Katrix]

Ahh yes, sorry about that. Guess I forgot about the arrow. Generally minimize code in Scastie, but that wasn't an option here as I used the nightly version.

type FunctionK[A[_], B[_]] = [Z] => A[Z] => B[Z]
type ~>:[A[_], B[_]] = FunctionK[A, B]

[anatoliykmetyuk]

Minimised:

extension(a: Int)
  def b: Int = ???
  def h: Unit =
    [A] => (r: Int) => b