Exception throw when compiling a project: java.lang.NullPointerException: tried to cast away nullability, but value is null

[OndrejSpanel]

Compiler version

3.1.3

Minimized example

I am afraid I do not have a minimized example yet, I will need some advice on how to extract it.

I am trying to port my complex project to Scala 3. I have fixed most deprecation warnings in 2.13 and upgraded almost all libraries. I am not getting much compiler errors any more, but still use both "-source:3.0-migration" and "-Xignore-scala2-macros", as not all libraries are ported and I still need to compile the project as 2.13 one.

Output

When building my project with Scala 3.1.3, I get following error:

Exception when compiling 382 sources to .......
java.lang.NullPointerException: tried to cast away nullability, but value is null

I am not told which part of the project / what particulat Scala source is the compiler working at, therefore I have no idea how could I pinpoint the problem.

The top of the callstack is:

[error] java.lang.NullPointerException: tried to cast away nullability, but value is null
[error] scala.runtime.Scala3RunTime$.nn(Scala3RunTime.scala:19)
[error] dotty.tools.dotc.core.OrderingConstraint.swapKey$1(OrderingConstraint.scala:495)
[error] dotty.tools.dotc.core.OrderingConstraint.subst(OrderingConstraint.scala:496)
[error] dotty.tools.dotc.core.OrderingConstraint.subst(OrderingConstraint.scala:494)
[error] dotty.tools.dotc.core.TyperState.ensureNotConflicting$$anonfun$1(TyperState.scala:181)
[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.core.TyperState.ensureNotConflicting(TyperState.scala:182)
[error] dotty.tools.dotc.core.TyperState.mergeConstraintWith(TyperState.scala:193)
[error] dotty.tools.dotc.core.TyperState.commit(TyperState.scala:163)
[error] dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:3111)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:1002)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1040)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:327)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:117)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2832)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3080)
[error] dotty.tools.dotc.typer.Typer.$anonfun$47(Typer.scala:2278)
[error] dotty.tools.dotc.typer.PrepareInlineable$.dropInlineIfError(PrepareInlineable.scala:248)
[error] dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2278)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2808)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2476)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2820)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2476)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:2820)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2824)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2894)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2986)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2603)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2865)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3013)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3036)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2603)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2865)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2895)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2960)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:2964)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3080)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:43)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$adapted$1(TyperPhase.scala:50)
[error] scala.Function0.apply$mcV$sp(Function0.scala:39)
[error] dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:414)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:50)
[error] dotty.tools.dotc.typer.TyperPhase.runOn$$anonfun$3(TyperPhase.scala:84)
[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.TyperPhase.runOn(TyperPhase.scala:84)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:225)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:236)```

Expectation

I think compiler can show errors, but should never throw exceptions.

[odersky]

Yes, that's clearly a compiler bug.

[odersky]

@OndrejSpanel if you run this on latest main once #15890 is merged you should hopefully get the compilation unit that caused the crash.

[OndrejSpanel]

if you run this on latest main

To clarify how to proceed: does this mean I should test the issue on 3.1.4 once it is released?

[odersky]

If you want to wait for a release it would be 3.2.1. But you could also run with the nightly before. once #15845 is merged.

…

On Sat, Aug 20, 2022 at 1:16 PM Ondřej Španěl ***@***.***> wrote: if you run this on latest main To clarify how to proceed: does this mean I should test the issue on 3.1.4 once it is released? — Reply to this email directly, view it on GitHub <#15845 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAGCKVUZZ66FY3AY5AEKAQDV2C47DANCNFSM56HDFLOA> . You are receiving this because you commented.Message ID: ***@***.***>

-- Martin Odersky Professor, Programming Methods Group (LAMP) Faculty IC, EPFL Station 14, Lausanne, Switzerland

[bishabosha]

@OndrejSpanel can you try with scalaVersion 3.2.1-RC1-bin-20220820-ead0fbc-NIGHTLY? - it should contain more debug info for this crash

[OndrejSpanel]

Thanks for pinging me. When I have tried that, I am told which file is the error in, and that the error is while typechecking:

java.lang.NullPointerException: tried to cast away nullability, but value is null while typechecking <some path>\State.scala

When I remove State.scala completely, I get a different error in a different file:

java.lang.AssertionError: NoDenotation.owner while typechecking <some path>\SomeFile.scala

[error] ## Exception when compiling 387 sources to ccccccc\target\scala-3.2.1-RC1-bin-20220820-ead0fbc-NIGHTLY\classes
[error] java.lang.AssertionError: NoDenotation.owner
[error] dotty.tools.dotc.core.SymDenotations$NoDenotation$.owner(SymDenotations.scala:2501)
[error] dotty.tools.dotc.typer.Typer.canAssign$1(Typer.scala:990)
[error] dotty.tools.dotc.typer.Typer.typedAssign(Typer.scala:1027)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2922)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2978)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3045)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3049)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.$anonfun$3$$anonfun$1(ProtoTypes.scala:437)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.cacheTypedArg(ProtoTypes.scala:406)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.$anonfun$3(ProtoTypes.scala:437)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.$anonfun$adapted$1(ProtoTypes.scala:437)
[error] dotty.tools.dotc.core.Decorators$ListDecorator$.loop$3(Decorators.scala:174)
[error] dotty.tools.dotc.core.Decorators$ListDecorator$.mapWithIndexConserve$extension(Decorators.scala:181)
[error] dotty.tools.dotc.typer.ProtoTypes$FunProto.typedArgs(ProtoTypes.scala:437)
[error] dotty.tools.dotc.typer.Applications.resolveOverloaded1(Applications.scala:1975)

I will try removing a much as possible to still get the NullPointerException and not AssertionError from State.scala, perhaps that will tell something useful.

[OndrejSpanel]

I was able to reduce the repro into two files, each of them containing only a few lines of code. Repro is available in https://github.com/OndrejSpanel/scala3-error-repro

I was not able to reproduce the issue in a single file, or without a nested state package.

This is how the files currently look like:

Config.scala:

package config
package state

case class Config(simulations: Seq[(String, Any)] = Seq.empty)

State.scala:

package config

import state._

object State {

  object Info {
    def apply(): Info = Info(Config(), Seq.empty)
  }
  case class Info(cfg: AnyRef, allTypes: Seq[AnyRef])
}

[odersky]

Thanks for minimization! I tried to reproduce it, but it works for me. Is there something unexpected on your classpath maybe?

[OndrejSpanel]

Is there something unexpected on your classpath maybe?

How can I check for that?

I get the error by just launching sbt compile in the project directory.

I use Windows 11 x64, my default Java version is 11:

welcome to sbt 1.7.1 (Oracle Corporation Java 11.0.15.1)