java.lang.NullPointerException in scalac

jimka · June 24, 2019, 9:47am

I have some code which triggers a java.lang.NullPointerException in scalac. Should I try to submit a bug report with a minimum working example (MWE). Or is this type of thing of no real interest to the compiler developers?
Or is this a bug in the jet brains plugin, better reported to IntelliJ?

I can probably easily fix my code to avoid the issue.

Error:scalac: Error: org.jetbrains.jps.incremental.scala.remote.ServerException
java.lang.NullPointerException
	at scala.reflect.internal.Types$TypeRef.computeHashCode(Types.scala:2146)
	at scala.reflect.internal.Types$UniqueType.<init>(Types.scala:1078)
	at scala.reflect.internal.Types$TypeRef.<init>(Types.scala:2108)
	at scala.reflect.internal.Types$ArgsTypeRef.<init>(Types.scala:1870)
	at scala.reflect.internal.Types$ClassArgsTypeRef.<init>(Types.scala:2437)
	at scala.reflect.internal.Types$TypeRef$.apply(Types.scala:2447)
	at scala.reflect.internal.Types.copyTypeRef(Types.scala:3673)
	at scala.reflect.internal.Types.copyTypeRef$(Types.scala:3665)
	at scala.reflect.internal.SymbolTable.copyTypeRef(SymbolTable.scala:27)
	at scala.reflect.internal.Types.appliedType(Types.scala:3749)
	at scala.reflect.internal.Types.appliedType$(Types.scala:3734)
	at scala.reflect.internal.SymbolTable.appliedType(SymbolTable.scala:27)
	at scala.reflect.internal.Types.appliedType(Types.scala:3767)
	at scala.reflect.internal.Types.appliedType$(Types.scala:3766)
	at scala.reflect.internal.SymbolTable.appliedType(SymbolTable.scala:27)
	at scala.reflect.internal.Definitions$DefinitionsClass$VarArityClass.specificType(Definitions.scala:602)
	at scala.reflect.internal.Definitions$DefinitionsClass.functionType(Definitions.scala:620)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedFunctionUndoingEtaExpansion$6(Typers.scala:3153)
	at scala.tools.nsc.typechecker.Typers$Typer.typedFunctionUndoingEtaExpansion(Typers.scala:73)
	at scala.tools.nsc.typechecker.Typers$Typer.typedFunction(Typers.scala:3049)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typed1$97(Typers.scala:5621)
	at scala.tools.nsc.typechecker.Typers$Typer.typedFunction$1(Typers.scala:500)
	at scala.tools.nsc.typechecker.Typers$Typer.typedOutsidePatternMode$1(Typers.scala:5658)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5690)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedArg$1(Typers.scala:3389)
	at scala.tools.nsc.typechecker.Typers$Typer.typedArg(Typers.scala:491)
	at scala.tools.nsc.typechecker.Typers$Typer.typedArgToPoly$1(Typers.scala:3779)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$doTypedApply$33(Typers.scala:3787)
	at scala.tools.nsc.typechecker.Typers$Typer.handlePolymorphicCall$1(Typers.scala:3787)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedApply(Typers.scala:3798)
	at scala.tools.nsc.typechecker.Typers$Typer.normalTypedApply$1(Typers.scala:4876)
	at scala.tools.nsc.typechecker.Typers$Typer.typedApply$1(Typers.scala:4885)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5680)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedFunction(Typers.scala:5801)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedFunction$2(Typers.scala:3058)
	at scala.reflect.internal.Trees$TreeContextApiImpl.orElse(Trees.scala:113)
	at scala.tools.nsc.typechecker.Typers$Typer.typedFunction(Typers.scala:3049)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typed1$97(Typers.scala:5621)
	at scala.tools.nsc.typechecker.Typers$Typer.typedFunction$1(Typers.scala:500)
	at scala.tools.nsc.typechecker.Typers$Typer.typedOutsidePatternMode$1(Typers.scala:5658)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5690)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedArg$1(Typers.scala:3389)
	at scala.tools.nsc.typechecker.Typers$Typer.typedArg(Typers.scala:491)
	at scala.tools.nsc.typechecker.Typers$Typer.typedArgToPoly$1(Typers.scala:3779)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$doTypedApply$33(Typers.scala:3787)
	at scala.tools.nsc.typechecker.Typers$Typer.handlePolymorphicCall$1(Typers.scala:3787)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedApply(Typers.scala:3798)
	at scala.tools.nsc.typechecker.Typers$Typer.normalTypedApply$1(Typers.scala:4876)
	at scala.tools.nsc.typechecker.Typers$Typer.typedApply$1(Typers.scala:4885)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5680)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.typedCase(Typers.scala:5801)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedCases$1(Typers.scala:2579)
	at scala.tools.nsc.typechecker.Typers$Typer.typedCases(Typers.scala:2578)
	at scala.tools.nsc.typechecker.Typers$Typer.typedMatch(Typers.scala:2590)
	at scala.tools.nsc.typechecker.Typers$Typer.typedVirtualizedMatch$1(Typers.scala:4585)
	at scala.tools.nsc.typechecker.Typers$Typer.typedOutsidePatternMode$1(Typers.scala:5659)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5690)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.typedBlock(Typers.scala:2504)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typed1$98(Typers.scala:5655)
	at scala.tools.nsc.typechecker.Typers$Typer.typedOutsidePatternMode$1(Typers.scala:500)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5690)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.typedDefDef(Typers.scala:5942)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5645)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.typedStat$1(Typers.scala:5790)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedStats$10(Typers.scala:3373)
	at scala.tools.nsc.typechecker.Typers$Typer.typedStats(Typers.scala:3373)
	at scala.tools.nsc.typechecker.Typers$Typer.typedTemplate(Typers.scala:2030)
	at scala.tools.nsc.typechecker.Typers$Typer.typedClassDef(Typers.scala:1843)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5646)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Typers$Typer.typedStat$1(Typers.scala:5790)
	at scala.tools.nsc.typechecker.Typers$Typer.$anonfun$typedStats$10(Typers.scala:3373)
	at scala.tools.nsc.typechecker.Typers$Typer.typedStats(Typers.scala:3373)
	at scala.tools.nsc.typechecker.Typers$Typer.typedPackageDef$1(Typers.scala:5356)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5649)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5726)
	at scala.tools.nsc.typechecker.Analyzer$typerFactory$TyperPhase.apply(Analyzer.scala:114)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:448)
	at scala.tools.nsc.typechecker.Analyzer$typerFactory$TyperPhase.run(Analyzer.scala:103)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1498)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1482)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1475)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1598)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:130)
	at xsbt.CachedCompiler0.run(CompilerInterface.scala:105)
	at xsbt.CompilerInterface.run(CompilerInterface.scala:31)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sbt.internal.inc.AnalyzingCompiler.call(AnalyzingCompiler.scala:237)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:111)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:90)
	at org.jetbrains.jps.incremental.scala.local.IdeaIncrementalCompiler.compile(IdeaIncrementalCompiler.scala:40)
	at org.jetbrains.jps.incremental.scala.local.LocalServer.compile(LocalServer.scala:35)
	at org.jetbrains.jps.incremental.scala.remote.Main$.make(Main.scala:83)
	at org.jetbrains.jps.incremental.scala.remote.Main$.nailMain(Main.scala:26)
	at org.jetbrains.jps.incremental.scala.remote.Main.nailMain(Main.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.martiansoftware.nailgun.NGSession.run(NGSession.java:319)```

jimka · June 24, 2019, 10:30am

This could of course be something in my IntelliJ environment, not ruling that out, but now when i compile, I no longer get the scalac stacktrace, but just the NullPointException error message. Is this normal?

jimka · June 24, 2019, 10:34am

When I paste a reduced version of the code onto Scastie, it tersely reports the error, but doesn’t seem to crash the compiler. https://scastie.scala-lang.org/jimka2001/RE5h9qDnQD6I1frr23XVVw/3

jducoeur · June 24, 2019, 11:59am

Seems likely worth minimizing and reporting the bug, but where to report depends on the recipe. If it repros in sbt, then it’s a Scala bug and should be reported in scala/scala. If it only repros in IntelliJ, then it’s probably an IDEA bug and should be reported to JetBrains. (I suspect the latter, given the exception, but can’t say for certain.)

jimka · June 24, 2019, 12:19pm

The problems is somewhat reproducible on Scastie. @martijnhoekstra reports seeing the stacktrace, but i don’t see it myself.

martijnhoekstra · June 24, 2019, 12:20pm

I do!

jimka · June 24, 2019, 12:21pm

Yes, I see it there as well. Thanks.

jimka · June 24, 2019, 12:24pm

Adding the type annotations as the compiler suggests fixes the problem and avoids the null exception. So I’m off and running. Not sure what my responsibility as a good Scala citizen is in this cased.

  def reduceOne(posCount: Int, addFunction: HashUpdateFunction, removeFunction: HashUpdateFunction): Unit = {
    val posCountDec = posCount - 1
    (hash.get(posCount), hash.get(posCountDec)) match {
      case (None, _) => Unit
      case (_, None) => Unit
      case (Some(lengthHashA), Some(lengthHashB)) =>
       type B = HashMap[Clause,Set[Clause]]
        mapCommon(lengthHashA, lengthHashB, (length:Int, rectHashA:B, rectHashB:B) =>
          mapCommon(rectHashA, rectHashB, (rectified:Clause, cla:Set[Clause], clb:Set[Clause]) =>
            crossCompatiblize(cla, clb, posCount, length, rectified, removeFunction, addFunction)))
    }
  }