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maemre opened this issue Aug 19, 2017 · 4 comments
Closed

Possibly ill-formed pattern match involving method name crashes the compiler with NPE #10474

maemre opened this issue Aug 19, 2017 · 4 comments
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@hrhino
Milestone
2.12.5

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@maemre
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maemre commented Aug 19, 2017

I accidentally created a path-dependent pattern match clause involving a method and it crashed the compiler. I minimized it to the code snippet below. I tried it with Scala 2.12.3 and OpenJDK 1.8.0_131 on Ubuntu 16.04.

object Test {
  def Foo(a: Int): Char = ???

  object Bar

  def crash[A](): Boolean = Bar match {
    case Foo.Bar ⇒ true
    case _ ⇒ false
  }
}

This is the resulting stack trace:

$ scalac parser.scala
error: java.lang.NullPointerException
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.$anonfun$valueUnbox$1(TreeInfo.scala:45)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.valueUnbox(TreeInfo.scala:45)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$Unbox$.unapply(TreeInfo.scala:50)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$BoxAndUnbox$.unapply(TreeInfo.scala:64)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:37)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1379)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1432)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1377)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.$anonfun$itransform$2(Trees.scala:1374)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1372)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1415)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.super$transform(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.$anonfun$transform$1(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:25)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.transformTemplate(Trees.scala:2563)
	at scala.reflect.internal.Trees.$anonfun$itransform$4(Trees.scala:1419)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1418)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.$anonfun$itransform$7(Trees.scala:1437)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1437)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.super$transform(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.$anonfun$transform$2(TypingTransformers.scala:42)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:25)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:140)
	at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:30)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:426)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:419)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:390)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:390)
	at scala.collection.Iterator.foreach(Iterator.scala:929)
	at scala.collection.Iterator.foreach$(Iterator.scala:929)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:390)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1431)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1416)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1412)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1515)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:35)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:24)
	at scala.tools.nsc.Driver.process(Driver.scala:55)
	at scala.tools.nsc.Driver.main(Driver.scala:68)
	at scala.tools.nsc.Main.main(Main.scala)
Exception in thread "main" java.lang.NullPointerException
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.$anonfun$valueUnbox$1(TreeInfo.scala:45)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.valueUnbox(TreeInfo.scala:45)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$Unbox$.unapply(TreeInfo.scala:50)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$BoxAndUnbox$.unapply(TreeInfo.scala:64)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:37)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1379)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1432)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1377)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.internal.Trees.$anonfun$itransform$2(Trees.scala:1374)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1372)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1415)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.super$transform(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.$anonfun$transform$1(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:25)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.transformTemplate(Trees.scala:2563)
	at scala.reflect.internal.Trees.$anonfun$itransform$4(Trees.scala:1419)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1418)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:44)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.$anonfun$itransform$7(Trees.scala:1437)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1437)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1347)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.super$transform(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.$anonfun$transform$2(TypingTransformers.scala:42)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:25)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:35)
	at scala.tools.nsc.transform.PostErasure$PostErasureTransformer.transform(PostErasure.scala:22)
	at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:140)
	at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:30)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:426)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:419)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:390)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:390)
	at scala.collection.Iterator.foreach(Iterator.scala:929)
	at scala.collection.Iterator.foreach$(Iterator.scala:929)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:390)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1431)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1416)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1412)
	at scala.tools.nsc.Global$Run.compile(Global.scala:1515)
	at scala.tools.nsc.Driver.doCompile(Driver.scala:35)
	at scala.tools.nsc.MainClass.doCompile(Main.scala:24)
	at scala.tools.nsc.Driver.process(Driver.scala:55)
	at scala.tools.nsc.Driver.main(Driver.scala:68)
	at scala.tools.nsc.Main.main(Main.scala)
@hrhino
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hrhino commented Aug 19, 2017 •
edited
Loading

Even smaller:

scala> def Foo(i: Int) = i
Foo: (i: Int)Int

scala> val Foo.Crash = ???
java.lang.NullPointerException
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.$anonfun$valueUnbox$1(TreeInfo.scala:45)
	at scala.tools.nsc.ast.TreeInfo$ValueClass$.valueUnbox(TreeInfo.scala:45)

We are failing to adapt Foo's type (i: Int)Char to a non-method type, duly marking it as error-typed, and then, in a magnificent gesture of clemency, allow the tree to pass unpunished all the way down to posterasure, where it becomes yet another statistic in the shockingly high erroneous tree recidivism rate.

EDIT:

scala> type Q = Foo.type
<console>:12: error: erroneous or inaccessible type
       type Q = Foo.type

I forget... is that better or worse than a compiler crash?

hrhino added a commit to hrhino/scala that referenced this issue Aug 19, 2017
@hrhino
Issue an error when trying to use a method as a qualifier.
eec1562 
The check for `implicitsEnabled` here seems older even than
that method; it appears to originally have looked at a flag
`reportGeneralErrors`, which seems a reasonable flag if you
want to check whether to report an error. An erroneous tree
that we do not error on, however, can be use as a qualifier
which will not necessarily cause an error until past typer,
when something finally notices the mistake and blows up.

Fixes scala/bug#10474.
@hrhino hrhino mentioned this issue Aug 19, 2017
Closed
@hrhino hrhino self-assigned this Aug 19, 2017
@adriaanm
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Thanks for the report, @maemre, and the fix, @hrhino! Pretty amazing that that loophole's been open-ish

@hrhino hrhino mentioned this issue Feb 17, 2018
Closed
@hrhino hrhino added this to the 2.12.5 milestone Feb 21, 2018
som-snytt added a commit to som-snytt/scala that referenced this issue Feb 21, 2018
@som-snytt
Tests from scala/bug#10474
8064c40
@som-snytt
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Both tests added to the other PR.

@hrhino came so close to the shortest crasher, that it's a shame to mark this as

Duplicates #10731

adriaanm pushed a commit to som-snytt/scala that referenced this issue Mar 9, 2018
@som-snytt @adriaanm
When in QUAL mode, do not eta-expand or apply to args
e694efc 
The result could never be stable...

TODO: better error message

Tests for scala/bug#10474, scala/bug#10731
adriaanm pushed a commit to som-snytt/scala that referenced this issue Mar 9, 2018
@som-snytt @adriaanm
Improve error messages for method references
aaaf9e4 
A method is not a value, and thus must somehow be converted
to an expression -- unless we're specifically looking for a method.

We can either insert an application (to implicit args or empty arg list),
or lift to a function by eta-expansion. If those are not possible,
we report an error (unstable tree -- could be refined further).

Tests for scala/bug#10474, scala/bug#10731
@lrytz
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lrytz commented Mar 12, 2018

Fixed in scala/scala#6273

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