valueOfTerm method of scala.tools.nsc.interpreter.IMain broken in 2.9.1 RC2

[scabug]

The valueOfTerm method of scala.tools.nsc.interpreter.IMain seems to be broken in 2.9.1 RC2, whereas it works as expected in 2.9.0.1. See transcripts from both versions below.

      - 2.9.1.RC2 ##############

Welcome to Scala version 2.9.1.RC2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_26).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val n = new scala.tools.nsc.interpreter.IMain()
n: scala.tools.nsc.interpreter.IMain = scala.tools.nsc.interpreter.IMain@f4f7a86

scala> n.interpret("val a = 2+3")
a: Int = 5
res0: scala.tools.nsc.interpreter.package.IR.Result = Success

scala> n.valueOfTerm("a") == Some(5) // Should be true!
res1: Boolean = false

      - 2.9.0.1 ##############

Welcome to Scala version 2.9.0.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_26).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val n = new scala.tools.nsc.interpreter.IMain()
n: scala.tools.nsc.interpreter.IMain = scala.tools.nsc.interpreter.IMain@34ae19a

scala> n.interpret("val a = 2+3")
a: Int = 5
res0: scala.tools.nsc.interpreter.Results.Result = Success

scala> n.valueOfTerm("a") == Some(5) // Is true, as it should be
res1: Boolean = true

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-4899?orig=1
Reporter: David B. Dahl (dahl)
Affected Versions: 2.9.1

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Eugene Yokota (eed3si9n) said:
I'm still seeing this with 2.9.1.final. Why is the Fix Version/s set to Scala 2.9.0-1?

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Sebastien Riou (acapola) said:
Similar thing here, with 2.9.1.final:
Welcome to Scala version 2.9.1.final (Java HotSpot(TM) Server VM, Java 1.6.0_24).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val n = new scala.tools.nsc.interpreter.IMain()
n: scala.tools.nsc.interpreter.IMain = scala.tools.nsc.interpreter.IMain@5c18ff

scala> n.interpret("val r=1")
r: Int = 1
res0: scala.tools.nsc.interpreter.package.IR.Result = Success

scala> n.valueOfTerm("r")
res1: Option[AnyRef] = None

How to get the value of r then ???

[scabug]

Zach Cox (zcox) said:
I see this too with 2.9.1.final:

Welcome to Scala version 2.9.1.final (OpenJDK 64-Bit Server VM, Java 1.6.0_20).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val n = new scala.tools.nsc.interpreter.IMain()
n: scala.tools.nsc.interpreter.IMain = scala.tools.nsc.interpreter.IMain@3f6a5d72

scala>  n.interpret("val r=1")
r: Int = 1
res0: scala.tools.nsc.interpreter.package.IR.Result = Success

scala> n.valueOfTerm("r")
res1: Option[AnyRef] = None

The underlying cause of this is that ReadEvalPrint.call throws an exception if you try to access the evaluated value:

Welcome to Scala version 2.9.1.final (OpenJDK 64-Bit Server VM, Java 1.6.0_20).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import scala.tools.nsc.interpreter._
import scala.tools.nsc.interpreter._

scala> class MyIMain extends IMain {
     | def lastRequest = prevRequestList.last
     | }
defined class MyIMain

scala> val n = new MyIMain()
n: MyIMain = MyIMain@1483ce25

scala> n.interpret("val a = 1")
import scala.tools.nsc.interpreter._
res0: scala.tools.nsc.interpreter.package.IR.Result = Success

scala> val r = n.lastRequest
r: n.Request = Request(line=val a = 1, 1 trees)

scala> r.lineRep.call(r.lineRep.evalName)
java.lang.RuntimeException: Internal error: eval object class $line1.$eval, 

	at scala.sys.package$.error(package.scala:27)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.evalMethod(IMain.scala:750)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
	at .<init>(<console>:14)
	at .<clinit>(<console>)
	at .<init>(<console>:11)
	at .<clinit>(<console>)
	at $print(<console>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:616)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
	at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920)
	at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43)
	at scala.tools.nsc.io.package$$anon$2.run(package.scala:25)
	at java.lang.Thread.run(Thread.java:636)

IMain.valueOfTerm ultimately calls ReadEvalPrint.callEither which swallows that exception and eventually a None bubbles up and gets returned. I haven't done any more digging as to why that exception is thrown, will report more details if I find them.

Are there any known workarounds for this? We're embedding the Scala REPL and trying to customize the Print stage to dump the contents of any eval'ed collection or iterator in Gremlin and this bug is impeding progress.

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Sebastien Riou (acapola) said:
In my case, I reverted to 2.9.0.1 to get things going...

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Wiktor Macura (wmacura) said (edited on Oct 17, 2011 7:27:07 PM UTC):
Hi!

It seems that the problem is that r.lineRep.evalName returns $eval. If we call r.lineRep.call("$result") directly we get the results as expected:

object IMainSpecs extends Specification {
  "IMain" should {
    "give term value" in {
      System.setProperty("settings.usejavacp.value", "true")
      val settings = new Settings()
      settings.embeddedDefaults[UXPad]
      settings.processArgumentString("-usejavacp")

      class MyIMain extends IMain(settings) {
        def lastRequest = prevRequestList.last
      }

      val n = new MyIMain()
      n.interpret("val a = 1")

      val r = n.lastRequest
      r.lineRep.call("$result").must_== (1)
    }
  }
}

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Zach Cox (zcox) said:
Wiktor - are you using Scala 2.9.1? What exactly is UXPad?

If I run your code (excluding the UXPad line) in the REPL I end up with null instead of 1:

scala> r.lineRep.call("$result")
res4: AnyRef = null

If I run your Specification using sbt test then I get this exception on the n.interpret() line:

Exception in thread "Thread-10" java.lang.Error: typeConstructor inapplicable for <none>
	at scala.tools.nsc.symtab.SymbolTable.abort(SymbolTable.scala:34)
	at scala.tools.nsc.symtab.Symbols$Symbol.typeConstructor(Symbols.scala:877)
	at scala.tools.nsc.symtab.Definitions$definitions$.scala$tools$nsc$symtab$Definitions$definitions$$booltype(Definitions.scala:157)
	at scala.tools.nsc.symtab.Definitions$definitions$.init(Definitions.scala:814)
	at scala.tools.nsc.Global$Run.<init>(Global.scala:697)
	at scala.tools.nsc.interpreter.IMain.scala$tools$nsc$interpreter$IMain$$_initialize(IMain.scala:114)
	at scala.tools.nsc.interpreter.IMain$$anonfun$initialize$1.apply$mcZ$sp(IMain.scala:127)
	at scala.tools.nsc.interpreter.IMain$$anonfun$initialize$2.apply(IMain.scala:126)
	at scala.tools.nsc.interpreter.IMain$$anonfun$initialize$2.apply(IMain.scala:126)
	at scala.concurrent.ThreadRunner$$anon$2$$anonfun$run$2.apply(ThreadRunner.scala:45)
	at scala.concurrent.ThreadRunner.scala$concurrent$ThreadRunner$$tryCatch(ThreadRunner.scala:31)
	at scala.concurrent.ThreadRunner$$anon$2.run(ThreadRunner.scala:45)
	at java.lang.Thread.run(Thread.java:636)

Could you please provide more details about the environment in which that test passes for you?

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Wiktor Macura (wmacura) said (edited on Oct 18, 2011 3:08:17 AM UTC):
((I finally found the preview button; my apologies.))

Yes, sorry. I should have extracted the minimal test case:

import tools.nsc.interpreter.IMain
import tools.nsc.Settings

val settings = new Settings()

class MyIMain extends IMain() {
  def lastRequest = prevRequestList.last
}

val n = new MyIMain()
n.interpret("val a = 123")

val r = n.lastRequest
println(r.lineRep.call("$result"))

Running:

[wiktor@wiktorair1 Documents]# scala -version
Scala code runner version 2.9.1.final -- Copyright 2002-2011, LAMP/EPFL

[wiktor@wiktorair1 Documents]# scala Test.scala 
a: Int = 123
123

This is on OS X, if it matters.

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Zach Cox (zcox) said:
Thanks Wiktor! I did get that to work in a standalone source file (but not on the REPL - maybe some problem using an interpreter inside an interpreter...). And I'm on Ubuntu.

I made it even a bit more minimal:

class MyIMain extends tools.nsc.interpreter.IMain {
  def lastRequest = prevRequestList.last
}

val n = new MyIMain()
n.interpret("val a = 123")

println(n.lastRequest.lineRep.call("$result"))

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Commit Message Bot (anonymous) said:
(extempore in r25848) Fixing valueOfTerm in the repl.

Impressed at the amount of ticket traffic for an unadvertised internal
method. All the more reason to work toward that support repl API.
Don't worry, it'll come. Closes #4899, no review.