NPE in when completing default getters

[scabug]

I get the following exception in the IDE when opening certain files. I couldn't nail it down to a specific file yet, but git archeology suggests an existing workaround was removed with the belief that the NPE can't happen anymore:

module.attachments.get[ConstructorDefaultsAttachment] match {
  // by martin: the null case can happen in IDE; this is really an ugly hack on top of an ugly hack but it seems to work
  // later by lukas: disabled when fixing SI-5975, i think it cannot happen anymore
  case Some(cda) /*if cma.companionModuleClassNamer == null*/ =>
    val p = (cda.classWithDefault, cda.companionModuleClassNamer)
    moduleNamer = Some(p)
    p

java.lang.NullPointerException
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2$$anonfun$apply$14.apply(Namers.scala:1169)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2.apply(Namers.scala:1102)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2.apply(Namers.scala:1099)
	at scala.collection.LinearSeqOptimized$class.foldLeft(LinearSeqOptimized.scala:110)
	at scala.collection.immutable.List.foldLeft(List.scala:78)
	at scala.tools.nsc.typechecker.Namers$Namer.addDefaultGetters(Namers.scala:1099)
	at scala.tools.nsc.typechecker.Namers$Namer.methodSig(Namers.scala:1027)
	at scala.tools.nsc.typechecker.Namers$Namer.getSig$1(Namers.scala:1305)
	at scala.tools.nsc.typechecker.Namers$Namer.typeSig(Namers.scala:1347)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply$mcV$sp(Namers.scala:709)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:708)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:708)
	at scala.tools.nsc.typechecker.Namers$Namer.scala$tools$nsc$typechecker$Namers$Namer$$logAndValidate(Namers.scala:1385)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:708)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:707)
	at scala.tools.nsc.typechecker.Namers$$anon$1.completeImpl(Namers.scala:1496)
	at scala.tools.nsc.typechecker.Namers$LockingTypeCompleter$class.complete(Namers.scala:1504)
	at scala.tools.nsc.typechecker.Namers$$anon$1.complete(Namers.scala:1494)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1217)
	at scala.reflect.internal.Symbols$Symbol.paramss(Symbols.scala:1473)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$DefOwner$class.addDef(ScalaStructureBuilder.scala:668)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$Builder.addDef(ScalaStructureBuilder.scala:871)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$DefOwner$class.addDef(ScalaStructureBuilder.scala:658)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$Builder.addDef(ScalaStructureBuilder.scala:871)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser.traverse(ScalaStructureBuilder.scala:943)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser.traverse(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser.traverse(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser$$anonfun$traverse$1.apply(ScalaStructureBuilder.scala:950)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser$TreeTraverser.traverse(ScalaStructureBuilder.scala:950)
	at scala.tools.eclipse.javaelements.ScalaStructureBuilder$StructureBuilderTraverser.traverse(ScalaStructureBuilder.scala:903)
	at scala.tools.eclipse.javaelements.ScalaCompilationUnit$$anonfun$buildStructure$2$$anonfun$apply$5$$anonfun$apply$1.apply$mcV$sp(ScalaCompilationUnit.scala:74)
	at scala.tools.eclipse.javaelements.ScalaCompilationUnit$$anonfun$buildStructure$2$$anonfun$apply$5$$anonfun$apply$1.apply(ScalaCompilationUnit.scala:73)
	at scala.tools.eclipse.javaelements.ScalaCompilationUnit$$anonfun$buildStructure$2$$anonfun$apply$5$$anonfun$apply$1.apply(ScalaCompilationUnit.scala:73)
	at scala.tools.nsc.util.InterruptReq.execute(InterruptReq.scala:26)
	at scala.tools.nsc.interactive.Global.pollForWork(Global.scala:331)
	at scala.tools.nsc.interactive.PresentationCompilerThread.run(PresentationCompilerThread.scala:22)

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6576?orig=1
Reporter: @dragos
Affected Versions: 2.10.1-RC1

[scabug]

@dragos said (edited on Oct 28, 2012 2:49:02 PM UTC):
I noticed that this error seems to be related to annotations. For instance, code in ProductN.scala (where I see this exception thrown quite often) has the following declaration:

  @throws(classOf[IndexOutOfBoundsException])
  override def productElement(n: Int) = n match { 
..

and throws takes a default argument:

class throws[T <: Throwable](cause: String = "") extends scala.annotation.StaticAnnotation {

[scabug]

@lrytz said:
this could be helpful; on the other hand, it might also just be due to the fact that we don't have many constructors with default arguments in our codebase; (case classes that are created through companion-apply would not count here, since they're not constructor calls).

[scabug]

@dragos said:
What could be helpful? :)

[scabug]

@lrytz said:
knowing that it happens when there are annotations..

[scabug]

@dragos said:
Ah, right. Yes, the compiler reports in the log the position in the tree where the exception occurred, and it is exactly the throws annotation. So it's not just a hunch, it's fact :) I still don't know what's the sequence of actions that gets it there..

[scabug]

@dragos said:
I'm seeing this quite often. Could we roll this into the compiler, either 2.10.x or next RC? It's simply reverting a commit that commented out a null check.

[scabug]

@paulp said:
I think this will be fixed (somewhat indirectly) by scala/scala#1801 . It was possible for erroneous annotations to cause typed to return a tree with a null type and without marking the tree erroneous, invariably leading to failure at some later and most likely surprising point.

[scabug]

@dragos said:
I'll assume this is fixed, and reopen if it happens again.

[scabug]

@adriaanm said:
still happens on 2.10.1-RC1:

(when switching branches, apparently)

eclipse.buildId=I20110613-1736
java.version=1.6.0_37
java.vendor=Apple Inc.
BootLoader constants: OS=macosx, ARCH=x86_64, WS=cocoa, NL=en_US
Framework arguments:  -product org.eclipse.epp.package.java.product
Command-line arguments:  -os macosx -ws cocoa -arch x86_64 -product org.eclipse.epp.package.java.product -clean -data /Users/patrik/workspace-akka

Error
Wed Feb 13 13:43:24 CET 2013
Error during askOption

java.lang.NullPointerException
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2$$anonfun$apply$15.apply(Namers.scala:1274)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2.apply(Namers.scala:1207)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$addDefaultGetters$2.apply(Namers.scala:1204)

[scabug]

@adriaanm said:
this seems to break a common scenario in the IDE, so I would consider fixing in the next RC, especially since we assumed it was fixed for 2.10.1

[scabug]

@lrytz said:
what does it mean "when switching branches"? do you know how to reproduce the error?

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Patrik Nordwall (patriknw) said:
I don't know how to reproduce it but I mentioned that I often switch git branches, from command line, which triggers refresh in Eclipse. I could have done that when this happend, but I'm not sure.

[scabug]

@dragos said:
I don't think switching branches causes it, but it could play a role in timing. The scenario where this happens is roughly this sequence:

• get tree right after namers (symbols are in the tree, but the tree is not yet typechecked)
• traverse the tree and call sym.info along the way. This triggers lazy type completers, and one of them seems to assume a certain order of events

I couldn't reproduce this (yet) in a controlled environment, but I will try again.

[scabug]

@huitseeker said:
Had it this afternoon on 2.10.x 20ae01f4d86df1e33abaad76be171b596c8f39f3 (ping me for stacktrace).
No branch switch this time, but massive re-opening of editors by switching to a different Mylyn context.