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assertion failed: <: X[?] & Xa[?] when searching for a higher-kinded type variable with an intersection #13987

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neko-kai opened this issue Nov 21, 2021 · 1 comment · Fixed by #14068
Closed

assertion failed: <: X[?] & Xa[?] when searching for a higher-kinded type variable with an intersection #13987

neko-kai opened this issue Nov 21, 2021 · 1 comment · Fixed by #14068
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@odersky
Labels
itype:bug
Milestone
3.1.2

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@neko-kai
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Compiler version

3.1.2-RC1-bin-20211118-2b37257-NIGHTLY

Minimized code

Scastie: https://scastie.scala-lang.org/Gx3EdTaQTgSTYJQLI42dqg

sealed trait Xa[T]
sealed trait Mu[T] extends Xa[T]
object Xa {
  // bad
  implicit def convertMu[X[x] <: Xa[x], A, B](implicit t: X[A] with Xa[A]): X[B] = t.asInstanceOf[X[B]]
  // good
//  implicit def convertMu[X[x] <: Xa[x], A, B](implicit t: X[A] with Mu[A]): X[B] = t.asInstanceOf[X[B]]
}
object Mu {
  implicit def mu: Mu[Int] = new Mu[Int] {}
}

object App extends App {
  def constrain(a: Mu[Long]): Unit = println(a)
  constrain(Xa.convertMu)
}

Output

java.lang.AssertionError: assertion failed: <: X[?] & Xa[?] / TypeBounds(TypeRef(...

Stack trace 
java.lang.AssertionError: assertion failed:  <: X[?] & Xa[?] / TypeBounds(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Nothing),AppliedType(TypeParamRef(X),List(TypeBounds(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Nothing),TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any))))) & AppliedType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),trait Xa),List(TypeBounds(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Nothing),TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any))))
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.core.Types$AndType$.apply(Types.scala:3171)
	at dotty.tools.dotc.core.Types$AndType$.make(Types.scala:3206)
	at dotty.tools.dotc.core.Types$AndType.derivedAndType(Types.scala:3152)
	at dotty.tools.dotc.core.Types$TypeMap.derivedAndType(Types.scala:5376)
	at dotty.tools.dotc.core.Types$TypeMap.mapOver(Types.scala:5500)
	at dotty.tools.dotc.typer.Implicits$$anon$5.apply(Implicits.scala:476)
	at dotty.tools.dotc.typer.Implicits$NoMatchingImplicits.clarify(Implicits.scala:479)
	at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:401)
	at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:714)
	at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
	at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:35)
	at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:785)
	at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:189)
	at dotty.tools.dotc.printing.Printer.toText$$anonfun$1(Printer.scala:173)
	at scala.collection.immutable.List.map(List.scala:246)
	at scala.collection.immutable.List.map(List.scala:79)
	at dotty.tools.dotc.printing.Printer.toText(Printer.scala:173)
	at dotty.tools.dotc.printing.Printer.toTextGlobal$$anonfun$2(Printer.scala:181)
	at dotty.tools.dotc.printing.Printer.atPrec(Printer.scala:43)
	at dotty.tools.dotc.printing.Printer.toTextGlobal(Printer.scala:181)
	at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:436)
	at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:714)
	at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
	at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:35)
	at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:785)
	at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:189)
	at dotty.tools.dotc.printing.Showable.show(Showable.scala:23)
	at dotty.tools.dotc.printing.Showable.show$(Showable.scala:9)
	at dotty.tools.dotc.ast.Trees$Tree.show(Trees.scala:48)
	at dotty.tools.dotc.typer.ImplicitSearchError.formatMsg(ErrorReporting.scala:284)
	at dotty.tools.dotc.typer.ImplicitSearchError.missingArgMsg(ErrorReporting.scala:266)
	at dotty.tools.dotc.typer.Implicits.missingArgMsg(Implicits.scala:892)
	at dotty.tools.dotc.typer.Implicits.missingArgMsg$(Implicits.scala:776)
	at dotty.tools.dotc.typer.Typer.missingArgMsg(Typer.scala:113)
	at dotty.tools.dotc.typer.Typer.issueErrors$1$$anonfun$1$$anonfun$1(Typer.scala:3472)
	at dotty.tools.dotc.reporting.NoExplanation.msg(Message.scala:139)
	at dotty.tools.dotc.reporting.Message.message(Message.scala:87)
	at dotty.tools.dotc.reporting.Message.isNonSensical(Message.scala:99)
	at dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden(HideNonSensicalMessages.scala:16)
	at dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden$(HideNonSensicalMessages.scala:10)
	at dotty.tools.dotc.reporting.AbstractReporter.isHidden(AbstractReporter.scala:8)
	at dotty.tools.dotc.reporting.Reporter.issueUnconfigured(Reporter.scala:153)
	at dotty.tools.dotc.reporting.Reporter.go$1(Reporter.scala:177)
	at dotty.tools.dotc.reporting.Reporter.issueIfNotSuppressed(Reporter.scala:195)
	at dotty.tools.dotc.reporting.Reporter.report(Reporter.scala:198)
	at dotty.tools.dotc.reporting.Reporter.flush$$anonfun$1(Reporter.scala:243)
	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:333)
	at dotty.tools.dotc.reporting.Reporter.flush(Reporter.scala:243)
	at dotty.tools.dotc.core.TyperState.commit(TyperState.scala:144)
	at dotty.tools.dotc.typer.Applications.fail$1(Applications.scala:980)
	at dotty.tools.dotc.typer.Applications.realApply$1$$anonfun$4$$anonfun$1(Applications.scala:986)
	at scala.Option.getOrElse(Option.scala:201)
	at dotty.tools.dotc.typer.Applications.realApply$1$$anonfun$4(Applications.scala:987)
	at dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:3059)
	at dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:988)
	at dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1026)
	at dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:317)
	at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:113)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2784)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2847)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2912)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2916)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2965)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2988)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2429)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2772)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2776)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2846)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2912)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2916)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2938)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2988)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2556)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2817)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2847)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2912)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2916)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3032)
	at dotty.tools.dotc.typer.TyperPhase.liftedTree1$1(TyperPhase.scala:47)
	at dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:53)
	at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:411)
	at dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:54)
	at dotty.tools.dotc.typer.TyperPhase.runOn$$anonfun$3(TyperPhase.scala:88)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:88)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:261)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:272)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:280)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:289)
	at dotty.tools.dotc.Run.compileSources(Run.scala:222)
	at dotty.tools.dotc.Run.compile(Run.scala:206)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
	at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:192)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:247)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:182)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163)
	at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
	at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163)
	at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:210)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:528)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:528)
	at sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:175)
	at sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:173)
	at sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:459)
	at sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
	at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263)
	at sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:414)
	at sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:501)
	at sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:401)
	at sbt.internal.inc.Incremental$.apply(Incremental.scala:167)
	at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:528)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:482)
	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
	at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2357)
	at sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2314)
	at sbt.internal.io.Retry$.apply(Retry.scala:46)
	at sbt.internal.io.Retry$.apply(Retry.scala:28)
	at sbt.internal.io.Retry$.apply(Retry.scala:23)
	at sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
	at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2310)
	at scala.Function1.$anonfun$compose$1(Function1.scala:49)
	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
	at sbt.std.Transform$$anon$4.work(Transform.scala:68)
	at sbt.Execute.$anonfun$submit$2(Execute.scala:282)
	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
	at sbt.Execute.work(Execute.scala:291)
	at sbt.Execute.$anonfun$submit$1(Execute.scala:282)
	at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
	at sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

Expectation

Expected to work, as in Scala 2: https://scastie.scala-lang.org/qpkqt46xTDOV6unUEAs2Dg

This is related to #13986 - it's a variation of the minimized code there, were an intersection is used to try to bring the implicits in Xa/Mu into implicit scope. The variation using with Xa[A] fails to bring implicits into scope AND causes the assertion failure above. Adding with Mu[A] succeeds, but shouldn't be necessary as the type variable X[x] has sufficient bounds to bring in Mu companion object regardless of the intersection (#13986)
@neko-kai neko-kai mentioned this issue Nov 21, 2021
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@prolativ
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Interestingly the compiler won't crash internally and we'll get a different compilation error if we make convertMu non-implicit:

no implicit argument of type X[A] & Xa[A] was found for parameter t of method convertMu in object Xa
 
where:     A is a type variable
           X is a type variable with constraint <: Mu
   constrain(Xa.convertMu)
                         ^

@odersky odersky self-assigned this Dec 7, 2021
odersky added a commit to dotty-staging/dotty that referenced this issue Dec 7, 2021
@odersky
Don't generate illegal types when clarifying implicit errors
b3ed0f8 
Fixes scala#13987
@odersky odersky mentioned this issue Dec 7, 2021
Merged
olsdavis pushed a commit to olsdavis/dotty that referenced this issue Apr 4, 2022
@odersky @olsdavis
Don't generate illegal types when clarifying implicit errors
0d5a3bf 
Fixes scala#13987
@Kordyjan Kordyjan added this to the 3.1.2 milestone Aug 2, 2023
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Don't generate illegal types when clarifying implicit errors dotty-staging/dotty
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@neko-kai @odersky @prolativ @Kordyjan