Imported From: https://issues.scala-lang.org/browse/SI-5776?orig=1
Reporter: Alan Burlison (alanbur)
Assignee: @magarciaEPFL
Affected Versions: 2.10.0-M3
See #5789

@lrytz said:
could you please provide us a self-contained example to reproduce the error. thanks

Alan Burlison (alanbur) said:
Here's the code:

object Main {
def main(args: Array[String]) {
var l = List(1,2,3,4)
l.sliding(2).foreach { case List(a, b) => printf("%d\n", a + b) }
}
}

I've managed to reproduce it:

$ /pool1/rootdisk/opt/scala/scala-2.10.0-M3/bin/fsc -Xlint -optimize neme.scala
neme.scala:4: warning: dead code following this construct
l.sliding(2).foreach { case List(a, b) => printf("%d\n", a + b) }
^
one warning found
$ fsc -Xlint -optimize neme.scala
neme.scala:4: warning: dead code following this construct
l.sliding(2).foreach { case List(a, b) => printf("%d\n", a + b) }
^
error:
while compiling: neme.scala
current phase: mixin
library version: version 2.10.0-M3
compiler version: version 2.10.0-M3
reconstructed args: -Ydead-code -Ywarn-nullary-unit -optimise -Xlint -Ywarn-inaccessible -Yinline -Ywarn-nullary-override -Yclosure-elim -Ywarn-dead-code -Yinline-handlers -Ywarn-adapted-args

uncaught exception during compilation: java.lang.AssertionError
$ fsc -version
Fast Scala compiler version 2.10.0-M2 -- Copyright 2002-2011, LAMP/EPFL

What's really odd is that when it fails above I'm getting a message from the M3 fsc but I'm (apparently) using the M2 version, I assume because the M3 fsc process is still active - when I originally saw this error I'd just installed M3. I'm wondering if this isn't some sort of malign interaction of the M2 & M3 versions of fsc, is that possible? Does the fsc driver check it is talking to a matching version of the fsc server? If not, perhaps it should?

Alan Burlison (alanbur) said:
Added more detail - may be a fsc versioning problem?

Alan Burlison (alanbur) said:
Thanks for narrowing this down Lukas, I couldn't quite figure out what was going on.

@magarciaEPFL said (edited on Jul 11, 2012 11:03:02 AM UTC):
Perhaps related to #5789.

The AssertionError occurs during the mixin phase. This can be confirmed by running

fsc test.scala -optimize -Ystop-after:constructors

multiple times, no AssertionError ensues.

In contrast, running

fsc test.scala -optimize -Ystop-after:mixin

results in AssertionError every other time.

Alan Burlison (alanbur) said:
This does indeed seem to be the same issue as reported in #5789