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java.lang.VerifyError when defining extractors for traits which are subtypes #3702

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scabug opened this issue Jul 25, 2010 · 4 comments
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@scabug scabug commented Jul 25, 2010

When I have two traits, Test1 and Test2, and Test2 is a subtype of Test1, and I define two extractors for these traits, a java.lang.VerifyError is thrown at runtime when I try to use the extractors in a pattern match statement. Consider the REPL output:

$$ scala
Welcome to Scala version 2.8.0.r0-b20100714201327 (Java HotSpot(TM) Server VM, Java 1.6.0_20).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait Test1 {
     | def f1: Int
     | }
defined trait Test1

scala> trait Test2 extends Test1 {
     | def f2: Int
     | }
defined trait Test2

scala> object Test1 {
     | def unapply(t1: Test1): Option[(Int)] = Some(t1.f1)
     | }
defined module Test1

scala> object Test2 {
     | def unapply(t2: Test2): Option[(Int,Int)] = Some(t2.f1, t2.f2)
     | }
defined module Test2

scala> case class Test2Impl() extends Test2{
     | def f1 = 1
     | def f2 = 2
     | }
defined class Test2Impl

scala> val a: AnyRef = Test2Impl()
a: AnyRef = Test2Impl()

scala> a match {
     | case Test2(a,b) => println("a: " + a)    
     | case Test1(a) => println(a)
     | }
java.lang.VerifyError: (class: , method: <init> signature: ()V) Accessing value from uninitialized register 4
    at RequestResult$$.<init>(<console>:9)
    at RequestResult$$.<clinit>(<console>)
    at RequestResult$$scala_repl_result(<console>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at scala.tools.nsc.Interpreter$$Request$$$$anonfun$$loadAndRun$$1$$$$anonfun$$apply$$18.apply(Interpreter.scala:981)
    at scala.tools.nsc.Interpreter$$Request$$$$anonfun$$loadAndRun$$1$$$$anonfun$$apply$$18.apply(Interpreter.scala:981)
    at scala.util.control.Exception$$Catch.apply(Exception....
scala> 

This problem isn't just limited to the REPL, but also for compiled code. See the attached file (which is just this REPL session in a file)

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@scabug scabug commented Jul 25, 2010

Imported From: https://issues.scala-lang.org/browse/SI-3702?orig=1
Reporter: Stephen Tu (stephentu)
Attachments:

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@scabug scabug commented Aug 18, 2010

Margus Freudenthal (margus) said:
I stumbled on a similar problem when trying to match parse tree produced by ANTLR treebuilder. The code runs under Scala 2.7 and fails under 2.8 (VerifyError). Interesting point: if I delete the line "g = " " from + ".." + to", then the program runs correctly under Scala 2.8.

See attachment test_match2.scala

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@scabug scabug commented Feb 28, 2011

@paulp said:
The test_match attachment minimized is:

  def foo(h: Any, t: List[Any]) = h match {
    case 5 :: _ => ()
    case List(from) => from
  }

This one is a buzzkill because it looks to arise from the pattern matcher cheating on case List(...) in a way it doesn't with anything else so as to offer the same performance (i.e. not use unapplySeq.) Thus there is special code for treating List like it's a series of :: and someone, me we can presume, has broken that code.

I'm not sure it's the same issue as the reporter's, except that the pattern matcher can legitimately be viewed as one giant issue.

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@scabug scabug commented May 11, 2012

@soc said:
Fixed in scala/scala@4c04213

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