Compiler crash for a package object containing a class and companion

[scabug]

When I compile the following compilation unit, the compiler crashes upon the third compilation. I do not delete the generated class files between the compiler runs.

package p {
  package object base {
    case class B()
  }
}

The first compiler run is fine, the second generates a message regarding a suppressed failed assert, and on the third run the compiler crashes.

% scalac -version
Scala compiler version 2.9.2 -- Copyright 2002-2011, LAMP/EPFL

% rm -r p
% scalac Test.scala
% scalac Test.scala
Suppressing failed assert: java.lang.AssertionError: assertion failed: List(obje
ct package$B, object package$B)

% scalac Test.scala
Suppressing failed assert: java.lang.AssertionError: assertion failed: List(obje
ct package$B, object package$B)
error: java.lang.AssertionError: assertion failed: List(object package$B, object
 package$B)
        at scala.tools.nsc.symtab.Symbols$Symbol.suchThat(Symbols.scala:1055)
        at scala.tools.nsc.symtab.Symbols$Symbol.companionModule0(Symbols.scala:
1317)
        at scala.tools.nsc.symtab.Symbols$Symbol.companionSymbol(Symbols.scala:1
338)
        at scala.tools.nsc.backend.jvm.GenJVM$BytecodeGenerator.scalaSignatureAd
dingMarker(GenJVM.scala:236)
        at scala.tools.nsc.backend.jvm.GenJVM$BytecodeGenerator.genClass(GenJVM.
scala:350)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase$$anonfun$run$4.apply(GenJ
VM.scala:86)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase$$anonfun$run$4.apply(GenJ
VM.scala:86)
        at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(Has
hMap.scala:104)
        at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(Has
hMap.scala:104)
        at scala.collection.Iterator$class.foreach(Iterator.scala:772)
        at scala.collection.mutable.HashTable$$anon$1.foreach(HashTable.scala:15
7)
        at scala.collection.mutable.HashTable$class.foreachEntry(HashTable.scala
:190)
        at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:45)
        at scala.collection.mutable.HashMap$$anon$2.foreach(HashMap.scala:104)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase.run(GenJVM.scala:86)
        at scala.tools.nsc.Global$Run.compileSources(Global.scala:953)
        at scala.tools.nsc.Global$Run.compile(Global.scala:1041)
        at scala.tools.nsc.Main$.process(Main.scala:106)
        at scala.tools.nsc.Main$.main(Main.scala:123)
        at scala.tools.nsc.Main.main(Main.scala)

Exception in thread "main" java.lang.AssertionError: assertion failed: List(obje
ct package$B, object package$B)
        at scala.tools.nsc.symtab.Symbols$Symbol.suchThat(Symbols.scala:1055)
        at scala.tools.nsc.symtab.Symbols$Symbol.companionModule0(Symbols.scala:
1317)
        at scala.tools.nsc.symtab.Symbols$Symbol.companionSymbol(Symbols.scala:1
338)
        at scala.tools.nsc.backend.jvm.GenJVM$BytecodeGenerator.scalaSignatureAd
dingMarker(GenJVM.scala:236)
        at scala.tools.nsc.backend.jvm.GenJVM$BytecodeGenerator.genClass(GenJVM.
scala:350)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase$$anonfun$run$4.apply(GenJ
VM.scala:86)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase$$anonfun$run$4.apply(GenJ
VM.scala:86)
        at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(Has
hMap.scala:104)
        at scala.collection.mutable.HashMap$$anon$2$$anonfun$foreach$3.apply(Has
hMap.scala:104)
        at scala.collection.Iterator$class.foreach(Iterator.scala:772)
        at scala.collection.mutable.HashTable$$anon$1.foreach(HashTable.scala:15
7)
        at scala.collection.mutable.HashTable$class.foreachEntry(HashTable.scala
:190)
        at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:45)
        at scala.collection.mutable.HashMap$$anon$2.foreach(HashMap.scala:104)
        at scala.tools.nsc.backend.jvm.GenJVM$JvmPhase.run(GenJVM.scala:86)
        at scala.tools.nsc.Global$Run.compileSources(Global.scala:953)
        at scala.tools.nsc.Global$Run.compile(Global.scala:1041)
        at scala.tools.nsc.Main$.process(Main.scala:106)
        at scala.tools.nsc.Main$.main(Main.scala:123)
        at scala.tools.nsc.Main.main(Main.scala)

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-5954?orig=1
Reporter: @dgruntz
Affected Versions: 2.9.2, 2.10.0-M3, 2.10.0-M4
See #2130, #3437, #4695, #7195

[scabug]

@JamesIry said:
Under 2.10.0 RC3 the crash happens on the second compile but is otherwise identical to the bug reported here.

[scabug]

@retronym said:
(possibly) related: #4695

[scabug]

@JamesIry said:
Minimized the crasher a bit more.

[scabug]

@JamesIry said (edited on Dec 11, 2012 7:20:57 PM UTC):
Also looks related #5957

[scabug]

@JamesIry said:
Historical notes of things somewhat related #2130,#3437. At some point case classes in package objects did not work at all. So they got disabled. But now they work. So they've been reenabled. Except they don't work on the second compile because we're getting this duplicated symbol nonsense.

[scabug]

@JamesIry said (edited on Jan 9, 2013 10:32:35 PM UTC):
Here's the simplest reproducer

package object base {
  class B
  object B
}

[scabug]

@JamesIry said:
Some in progress notes. I've renamed class and object 'B' to 'buhB' to make it easier to do a search using contains. That's important because some names change along the way. All the following results come from the same run, which is important as ids aren't stable from one run to the next.

On the second and subsequent compiles, early in the process, we get symbol package$buhB from its class file. Here it has id 6946

*** package$buhB#6946
java.lang.Exception: Stack trace
  at java.lang.Thread.dumpStack(Thread.java:1273)
  at scala.reflect.internal.Symbols$Symbol.<init>(Symbols.scala:144)
  at scala.reflect.internal.Symbols$TermSymbol.<init>(Symbols.scala:2380)
  at scala.reflect.internal.Symbols$ModuleSymbol.<init>(Symbols.scala:2550)
  at scala.reflect.internal.Symbols$Symbol.createModuleSymbol(Symbols.scala:1089)
  at scala.reflect.internal.Symbols$Symbol.newTermSymbol(Symbols.scala:1106)
  at scala.reflect.internal.Symbols$Symbol.newModuleSymbol(Symbols.scala:252)
  at scala.reflect.internal.Symbols$Symbol.newModule(Symbols.scala:235)
  at scala.tools.nsc.symtab.SymbolLoaders.enterModule(SymbolLoaders.scala:47)
  at scala.tools.nsc.symtab.SymbolLoaders.enterClassAndModule(SymbolLoaders.scala:98)
  at scala.tools.nsc.symtab.SymbolLoaders.initializeFromClassPath(SymbolLoaders.scala:138)
  at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader$$anonfun$doComplete$3.apply(SymbolLoaders.scala:231)
  at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader$$anonfun$doComplete$3.apply(SymbolLoaders.scala:230)
  at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:772)
  at scala.collection.Iterator$class.foreach(Iterator.scala:727)
  at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
  at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
  at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
  at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:771)
  at scala.tools.nsc.symtab.SymbolLoaders$PackageLoader.doComplete(SymbolLoaders.scala:230)
  at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:187)
  at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1224)
  at scala.reflect.internal.Types$TypeRef.decls(Types.scala:2406)
  at scala.tools.nsc.typechecker.Namers$Namer.enterPackage(Namers.scala:612)
  at scala.tools.nsc.typechecker.Namers$Namer.dispatch$1(Namers.scala:219)
  at scala.tools.nsc.typechecker.Namers$Namer.liftedTree1$1(Namers.scala:234)
  at scala.tools.nsc.typechecker.Namers$Namer.enterSym(Namers.scala:234)
  at scala.tools.nsc.typechecker.Analyzer$namerFactory$$anon$1.apply(Analyzer.scala:42)
  at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:463)
  at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:430)
  at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:430)
  at scala.collection.Iterator$class.foreach(Iterator.scala:727)
  at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
  at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:430)
  ...

Somewhat later we get symbol buhB from Namer, here with id 7260.

*** buhB#7260
java.lang.Exception: Stack trace
	at java.lang.Thread.dumpStack(Thread.java:1273)
	at scala.reflect.internal.Symbols$Symbol.<init>(Symbols.scala:144)
	at scala.reflect.internal.Symbols$TermSymbol.<init>(Symbols.scala:2380)
	at scala.reflect.internal.Symbols$ModuleSymbol.<init>(Symbols.scala:2550)
	at scala.reflect.internal.Symbols$Symbol.createModuleSymbol(Symbols.scala:1089)
	at scala.reflect.internal.Symbols$Symbol.newTermSymbol(Symbols.scala:1106)
	at scala.reflect.internal.Symbols$Symbol.newModuleSymbol(Symbols.scala:252)
	at scala.reflect.internal.Symbols$Symbol.newModule(Symbols.scala:235)
	at scala.tools.nsc.typechecker.Namers$Namer.createMemberSymbol(Namers.scala:289)
	at scala.tools.nsc.typechecker.Namers$Namer.assignSymbol(Namers.scala:249)
	at scala.tools.nsc.typechecker.Namers$Namer.assignAndEnterSymbol(Namers.scala:252)
	at scala.tools.nsc.typechecker.Namers$Namer.enterModuleSymbol(Namers.scala:411)
	at scala.tools.nsc.typechecker.Namers$Namer.enterModuleDef(Namers.scala:390)
	at scala.tools.nsc.typechecker.Namers$Namer.dispatch$1(Namers.scala:221)
	at scala.tools.nsc.typechecker.Namers$Namer.liftedTree1$1(Namers.scala:234)
	at scala.tools.nsc.typechecker.Namers$Namer.enterSym(Namers.scala:234)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$enterSyms$1.apply(Namers.scala:425)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$enterSyms$1.apply(Namers.scala:424)
	at scala.collection.LinearSeqOptimized$class.foldLeft(LinearSeqOptimized.scala:111)
	at scala.collection.immutable.List.foldLeft(List.scala:78)
	at scala.tools.nsc.typechecker.Namers$Namer.enterSyms(Namers.scala:424)
	at scala.tools.nsc.typechecker.Namers$Namer.templateSig(Namers.scala:860)
	at scala.tools.nsc.typechecker.Namers$Namer.getSig$1(Namers.scala:1298)
	at scala.tools.nsc.typechecker.Namers$Namer.typeSig(Namers.scala:1345)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply$mcV$sp(Namers.scala:707)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:706)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1$$anonfun$apply$1.apply(Namers.scala:706)
	at scala.tools.nsc.typechecker.Namers$Namer$LogTransitions.apply(Namers.scala:1374)
	at scala.tools.nsc.typechecker.Namers$Namer.scala$tools$nsc$typechecker$Namers$Namer$$logAndValidate(Namers.scala:1383)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:706)
	at scala.tools.nsc.typechecker.Namers$Namer$$anonfun$monoTypeCompleter$1.apply(Namers.scala:705)
	at scala.tools.nsc.typechecker.Namers$$anon$1.completeImpl(Namers.scala:1498)
	at scala.tools.nsc.typechecker.Namers$LockingTypeCompleter$class.complete(Namers.scala:1506)
	at scala.tools.nsc.typechecker.Namers$$anon$1.complete(Namers.scala:1496)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1224)
	at scala.reflect.internal.SymbolTable.openPackageModule(SymbolTable.scala:244)
	at scala.tools.nsc.typechecker.Analyzer$packageObjects$$anon$2$$anon$4.traverse(Analyzer.scala:61)
	at scala.tools.nsc.typechecker.Analyzer$packageObjects$$anon$2$$anon$4.traverse(Analyzer.scala:57)
	at scala.reflect.api.Trees$Traverser$$anonfun$traverseTrees$1.apply(Trees.scala:2853)
	at scala.reflect.api.Trees$Traverser$$anonfun$traverseTrees$1.apply(Trees.scala:2853)
	at scala.collection.immutable.List.foreach(List.scala:309)
	at scala.reflect.api.Trees$Traverser.traverseTrees(Trees.scala:2853)
	at scala.reflect.internal.Trees$$anonfun$itraverse$1.apply$mcV$sp(Trees.scala:1095)
	at scala.reflect.api.Trees$Traverser.atOwner(Trees.scala:2873)
	at scala.reflect.internal.Trees$class.itraverse(Trees.scala:1094)
	at scala.reflect.internal.SymbolTable.itraverse(SymbolTable.scala:13)
	at scala.reflect.internal.SymbolTable.itraverse(SymbolTable.scala:13)
	at scala.reflect.api.Trees$Traverser.traverse(Trees.scala:2849)
	at scala.tools.nsc.typechecker.Analyzer$packageObjects$$anon$2$$anon$4.traverse(Analyzer.scala:64)
	at scala.tools.nsc.typechecker.Analyzer$packageObjects$$anon$2$$anon$4.traverse(Analyzer.scala:57)
	at scala.reflect.api.Trees$Traverser.apply(Trees.scala:2879)
	at scala.tools.nsc.typechecker.Analyzer$packageObjects$$anon$2.apply(Analyzer.scala:69)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:463)
	at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:430)
	at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:430)
	at scala.collection.Iterator$class.foreach(Iterator.scala:727)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:430)
        ...

Finally, during code gen we get our assert saying that symbols 6946 and 7260 are overloaded alternatives. Same name, same type, same owner.

assertion failed: Symbol is unexpectedly overloaded with alternatives 'object package$buhB#6946#MOD (object package$buhB#6946#MOD->package buhbase#29#PK->package <root>#2#PK)'and'object package$buhB#7260#MOD (object package$buhB#7260#MOD->package buhbase#29#PK->package <root>#2#PK)'.
	at scala.Predef$.assert(Predef.scala:179)
	at scala.reflect.internal.Symbols$Symbol.suchThat(Symbols.scala:1651)
	at scala.reflect.internal.Symbols$ClassSymbol.companionModule0(Symbols.scala:2937)
	at scala.reflect.internal.Symbols$ClassSymbol.companionModule(Symbols.scala:2940)
	at scala.tools.nsc.backend.jvm.GenASM$JPlainBuilder.genClass(GenASM.scala:1369)
	at scala.tools.nsc.backend.jvm.GenASM$AsmPhase.run(GenASM.scala:119)
        ...
}

So, Namer tried to look up buhB, didn't find it, created #7260. Later #7260 was renamed to package$buhB and by then the damage was done. I don't yet know where the name gets changed.

Some investigation I need to do: do all inner classes get loaded with mangled name symbols? Or is that something special about objects inside package objects? If the later, is that deliberate or a mistake? If the former, then shouldn't Namer be figuring out the mangling in order to do the lookup properly?

[scabug]

@adriaanm said (edited by @JamesIry on Jan 14, 2013 7:30:08 PM UTC):
scala/scala#1882 adds an implementation restriction preventing this problem from occurring, but the bug is being left open as the core problem isn't solved.

[scabug]

@JamesIry said:
Jason suggest this might be a related issue/fix #6976 scala/scala#1910. On the surface I don't think it is. With this issue we've got a problem with some names that start different (making lookup fail) and then at a later phase become the same. 6976 is our old friend lazy initialization.

[scabug]

@JamesIry said:
It turns out this works fine on second+ compile in sbt.

[scabug]

@JamesIry said:
The implementation restriction is being turned into a warning in scala/scala#2079

[scabug]

@JamesIry said:
Disabling the assert is not an option. With it disabled and separate compilation of a simple test driver you can end up with

how can getCommonSuperclass() do its job if different class symbols get the same bytecode-level internal name: Foo/package$Bar
	at scala.Predef$.assert(Predef.scala:179)
	at scala.tools.nsc.Global.assert(Global.scala:238)
	at scala.tools.nsc.backend.jvm.GenASM$JBuilder.javaName(GenASM.scala:547)
	at scala.tools.nsc.backend.jvm.GenASM$JPlainBuilder.genObjsInstr$1(GenASM.scala:2439)

Which is one of the things mentioned in the notes for #4695.

[scabug]

@adriaanm said:
I think Rex Kerr has a point when he says that we should be able to suppress warnings (especially new ones):

Note that the change in behavior in 2.10.1 to throw warnings for stuff like

maths/package.scala:1281: warning: class OutlierDist should be placed directly in
package maths instead of package object maths. Under some circumstances companion
objects and case classes in package objects can fail to recompile. See
https://issues.scala-lang.org/browse/SI-5954.

and also

mwt/MultiSensed.scala:143: warning: The outer reference in this type test cannot be
checked at run time. final case class NotValid(val i0: Int, val i1: Int) extends
Chunk {}

means that I can no longer run with -Xfatal-warnings, which was how I found all the
places I needed to import language.whatever; now any new instances will be lost in
the screensfull of warnings.

Incidentally, is there a way to make the latter warning go away? I don't want to
push the trait and case classes out of the enclosing class since they don't make
any logical sense elsewhere and they _are_ class-relative information (despite not
linking back to the superclass). But I would like to be able to declare that I
don't intend to check that aspect of the type at runtime; compile time is
sufficient. (I realize that I could just refer to the enclosing class, but I'd
rather avoid the extra field since there will be millions of these things.) If the
underlying bug for 5954 is fixed, I'd want to fix these also so I can
-Xfatal-warnings again.

[scabug]

@paulp said:
"I think Rex Kerr has a point when he says that we should be able to suppress warnings (especially new ones):"

This guy probably has a point as well.

#1781