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Compiler throws NullPointerException when inferring type #9291

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scabug opened this issue Apr 30, 2015 · 3 comments
Closed

Compiler throws NullPointerException when inferring type #9291

scabug opened this issue Apr 30, 2015 · 3 comments
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@lrytz
Labels
backend compiler crash infer minimized named/default args regression
Milestone
2.13.0-M3

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@scabug
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scabug commented Apr 30, 2015

The following test case causes the compiler to throw a NullPointerException:

// more than one field is required to trigger crash
// there must be a default value for one of the parameters
case class OuterObject(field: Int = 1, anotherField: Int = 2)
	
object Test {
	OuterObject().copy(field = OuterObject().field)

	// declaring something without explicit type, with the same name as OuterObject.field
	def field = "anything"
}

Some things to note:

  • the name of the def Test.field is important, if it is not the same as the parameter name in OuterObject, the crash does not occur.
  • if OuterObject.field is the only parameter, the crash does not occur (any number of additional parameter are needed)
  • using the default values is important, i.e. changing the test case to have both parameters specified within the copy call avoids the bug: {code}
    OuterObject().copy(field = OuterObject(1, 2).field) {code}

The exception does not occur on 2.10.4 (we are upgrading from that version). Since this bug seems so bizarrely specific, a workaround should be available by changing pretty much anything about the code, e.g. explicitly defining type information.

Compiling with -Ydebug gives the following additional output:

warning: !!! exception when typing OuterObject().copy(field = OuterObject().field), pt=?
warning: !!! exception when typing <module> object Test extends scala.AnyRef {
  <method> def <init>(): <empty>.this.Test.type = {
    super.<init>();
    ()
  };
  OuterObject().copy(field = OuterObject().field);
  <method> <triedcooking> def field: lang.this.String = "anything"
}, pt=?
warning: !!! exception when typing package <empty> {
  case class OuterObject extends scala.Product with scala.Serializable {
    <caseaccessor> <paramaccessor> <triedcooking> private[this] val field : scala.this.Int = _;
    <caseaccessor> <paramaccessor> <triedcooking> private[this] val anotherField : scala.this.Int = _;
    <method> <triedcooking> def <init>(field: Int = 1, anotherField: Int = 2): <empty>.this.OuterObject = {
      super.<init>();
      ()
    }
  };
  <module> object Test extends scala.AnyRef {
    <method> def <init>(): <empty>.this.Test.type = {
      super.<init>();
      ()
    };
    OuterObject().copy(field = OuterObject().field);
    <method> <triedcooking> def field: lang.this.String = "anything"
  }
}, pt=?

Partial stack trace:

error: java.lang.NullPointerException
	at scala.tools.nsc.typechecker.Typers$Typer.noExpectedType$1(Typers.scala:3378)
	at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$handleMonomorphicCall$1(Typers.scala:3381)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedApply(Typers.scala:3409)
	at scala.tools.nsc.typechecker.Typers$Typer.tryNamesDefaults$1(Typers.scala:3295)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedApply(Typers.scala:3367)
	at scala.tools.nsc.typechecker.Typers$Typer.tryNamesDefaults$1(Typers.scala:3353)
	at scala.tools.nsc.typechecker.Typers$Typer.doTypedApply(Typers.scala:3367)
	at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$tryTypedApply$1$1.apply(Typers.scala:4404)
	at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$tryTypedApply$1$1.apply(Typers.scala:4404)
	at scala.tools.nsc.typechecker.Typers$Typer.silent(Typers.scala:676)
	at scala.tools.nsc.typechecker.Typers$Typer.tryTypedApply$1(Typers.scala:4404)
	at scala.tools.nsc.typechecker.Typers$Typer.normalTypedApply$1(Typers.scala:4449)
	at scala.tools.nsc.typechecker.Typers$Typer.typedApply$1(Typers.scala:4484)
	at scala.tools.nsc.typechecker.Typers$Typer.typedInAnyMode$1(Typers.scala:5242)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5259)
	at scala.tools.nsc.typechecker.Typers$Typer.runTyper$1(Typers.scala:5295)
	at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$typedInternal(Typers.scala:5322)
	at scala.tools.nsc.typechecker.Typers$Typer.body$2(Typers.scala:5269)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5273)
	at scala.tools.nsc.typechecker.Typers$Typer.typedByValueExpr(Typers.scala:5351)
	at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$typedStat$1(Typers.scala:2977)
	at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$60.apply(Typers.scala:3081)
	at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$60.apply(Typers.scala:3081)
	at scala.collection.immutable.List.loop$1(List.scala:172)
	at scala.collection.immutable.List.mapConserve(List.scala:188)
	at scala.tools.nsc.typechecker.Typers$Typer.typedStats(Typers.scala:3081)
	at scala.tools.nsc.typechecker.Typers$Typer.typedTemplate(Typers.scala:1880)
	at scala.tools.nsc.typechecker.Typers$Typer.typedModuleDef(Typers.scala:1767)
	at scala.tools.nsc.typechecker.Typers$Typer.typedMemberDef$1(Typers.scala:5209)
	at scala.tools.nsc.typechecker.Typers$Typer.typed1(Typers.scala:5258)
	at scala.tools.nsc.typechecker.Typers$Typer.runTyper$1(Typers.scala:5295)
	at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$typedInternal(Typers.scala:5322)
	at scala.tools.nsc.typechecker.Typers$Typer.body$2(Typers.scala:5269)
	at scala.tools.nsc.typechecker.Typers$Typer.typed(Typers.scala:5273)
	at scala.tools.nsc.typechecker.Typers$Typer.typedByValueExpr(Typers.scala:5351)
	at ...
Exception in thread "main" java.lang.NullPointerException
	at scala.tools.nsc.typechecker.Typers$Typer.noExpectedType$1(Typers.scala:3378)
	at ...
@scabug
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scabug commented Apr 30, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9291?orig=1
Reporter: Frej Bjon (fbjon)
Affected Versions: 2.11.6, 2.11.7
See #5091, #8342

@scabug
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scabug commented Oct 9, 2015

Frej Bjon (fbjon) said:
Bumped into this again in a different piece of code, but in narrowing down the issue, it changed from a crash to an erroneous "recursive type needs value" exception. It looks like this is related to #5091 and so might be related to #8342.

@scabug scabug added this to the Backlog milestone Apr 7, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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@hrhino
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hrhino commented Jan 16, 2018

This is fixed in 2.13.0-M3 by (I presume) scala/scala#6092.

@hrhino hrhino modified the milestones: Backlog, 2.13.0-M3 Jan 16, 2018
hrhino added a commit to hrhino/scala that referenced this issue Jan 16, 2018
@hrhino
Test cases for a few accidentally-fixed bugs.
eee8097 
- scala/bug#5638 was fixed by something farther back than I can build.
- scala/bug#8348 was fixed by scala#5251.
- scala/bug#9291 was fixed by scala#6092.
@hrhino hrhino mentioned this issue Jan 16, 2018
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backend compiler crash infer minimized named/default args regression
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@lrytz @SethTisue @scabug @hrhino