I seem to have found some kind of bug in the JVM bytecode generator.

Here's a class that reproduces the issue if I run it:

class TestBug
{

**
** Split a string in the format hostname:port into
** its parts and pass them to the given closure.
** 
** Typically that closure will store them into
** local variables for later use in the calling
** method.
** 
static Bool splitHostPort(Str hostname, |Str,Int| func)
{
  parts := hostname.split(':')
  if(parts.size > 1)
  {
    port := Int.fromStr(parts.removeAt(-1))
    hostname = parts.join(":")
    func(hostname, port)
    return true
  }
  return false
}


new make(Str host)
{
  Int port := 0
  Str hostname := host
  if(splitHostPort(host, |h,p|{port = p ; hostname = h}))
  {
    echo("Yay")
  }
}

static Void main()
{
  t := TestBug("localhost:80")
  echo("$t")
}
}

The error I get is:

java.lang.VerifyError: (class: fan/bug/TestBug, method: splitHostPort signature:
(Ljava/lang/String;Lfan/sys/Func;)Z) Expecting to find long on stack
  at java.lang.Class.getDeclaredFields0(Native Method)
  at java.lang.Class.privateGetDeclaredFields(Class.java:2308)
  at java.lang.Class.getDeclaredFields(Class.java:1760)
  at fan.sys.ClassType.finishSlots(ClassType.java:588)
  at fan.sys.ClassType.finish(ClassType.java:550)
  at fan.sys.Method$MethodFunc.isStatic(Method.java:475)
  at fan.sys.Method$MethodFunc.callList(Method.java:191)
  at fan.sys.Method.callList(Method.java:138)
  at fanx.tools.Fan.callMain(Fan.java:173)
  at fanx.tools.Fan.executeType(Fan.java:140)
  at fanx.tools.Fan.execute(Fan.java:41)
  at fanx.tools.Fan.run(Fan.java:298)
  at fanx.tools.Fan.main(Fan.java:336)
sys::Err: Method not mapped to java.lang.reflect correctly bug::TestBug.main
fan.sys.Method$MethodFunc.isStatic (Method.java:482)
fan.sys.Method$MethodFunc.callList (Method.java:191)
fan.sys.Method.callList (Method.java:138)
fanx.tools.Fan.callMain (Fan.java:173)
fanx.tools.Fan.executeType (Fan.java:140)
fanx.tools.Fan.execute (Fan.java:41)
fanx.tools.Fan.run (Fan.java:298)
fanx.tools.Fan.main (Fan.java:336)

Workaround: if I use Str.toInt() instead of Int.fromStr() then it works.

i.e.:

port := parts.removeAt(-1).toInt(10, true)

What version of Fantom and JRE are you running? Because that program works in my environment (which would be unusual for verification bug).

Can anyone else reproduce that?

Can't reproduce here... fan.version 1.0.62, java version "1.6.0_26" (x64)

Hmmm on further investigation the error only shows up if the code is compiled and run from the F4 IDE. If I run it from the command line I cannot reproduce the problem either, how peculiar.

There must be something the F4 IDE is doing differently when it runs Fantom but I can't quite tell what that is.

F4 (unless you've configured it differently) uses an older Fantom 1.0.60.

Well I did configure it to use my latest installation of Fantom but maybe internally it is still using that older 1.0.60 to compile.