return inside try + pattern-match inside finally causes VerifyError

[scabug]

When upgrading to 2.9.2. to 2.10.1, ran into this.
Minimal test case:

def foo: String = try return "Hello" finally 10 match {case x => ()}

throws

java.lang.VerifyError: (class: , method: foo signature: ()Ljava/lang/String;) Inconsistent stack height 0 != 1

when accessed.

Seems to be the combination of return in the try and the pattern match in the finally that does it.

Looks like James Iry blogged about something related, recently:
http://james-iry.blogspot.com/2013/01/scala-trycatch-lifting-proposal.html

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7407?orig=1
Reporter: Leif Warner (pdxleif)
Affected Versions: 2.10.1

[scabug]

@magarciaEPFL said:
A variation of the minimized snippet, which also exercises the "non-early-return" control-flow path:

object Test {

  def main(args: Array[String]) {
    println(foo(true))
    println(foo(false))
  }

  def foo(b: Boolean): String = {
    try {
      if(b)
        return "Hello"
      else
        "abc"
    } finally {
      10 match {case x => ()}
    }
  }

}

The problem does not surface in the new backend (ok, after fixing a typo) because a more structured approach is followed to emit try-catch-finally,

magarciaEPFL/scala@master...GenRefactored27

[scabug]

Leif Warner (pdxleif) said:
OpenJDK7u40 seems to give more detailed info on these VerifyErrors, a la:

java.lang.VerifyError: Instruction type does not match stack map
Exception Details:
  Location:
    .foo()Ljava/lang/String; @20: aload_1
  Reason:
    Current frame's stack size doesn't match stackmap.
  Current Frame:
    bci: @20
    flags: { }
    locals: { '', 'java/lang/Throwable', integer, 'scala/runtime/BoxedUnit' }
    stack: { }
  Stackmap Frame:
    bci: @20
    flags: { }
    locals: { '', top, integer, 'scala/runtime/BoxedUnit' }
    stack: { 'java/lang/String' }
  Bytecode:
    0000000: 1210 100a 3db2 0016 4ea7 000b 4c10 0a3d
    0000010: b200 164e 2bbf                         
  Exception Handler Table:
    bci [0, 2] => handler: 12
  Stackmap Table:
    same_locals_1_stack_item_frame(@12,Object[#25])
    full_frame(@20,{Object[#2],Top,Integer,Object[#18]},{Object[#27]})

	at .<init>(<console>:7)
	at .<clinit>(<console>)
	at $print(<console>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)

[scabug]

@lrytz said:
As Miguel says, works in the new backend.

Test case was added in 2a659cf0, updated in scala/scala#4068

[scabug]

@retronym said:
Fixed in 2.11.5 under -Ybackend:GenBCode, which will be non-experimental and enabled by default in the 2.12 series soon.