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-Ydelambdafy:method + lambda taking/returning a value class = kaboom #8017

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scabug opened this issue Nov 28, 2013 · 3 comments

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@scabug
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commented Nov 28, 2013

Under -Ydelambdafy:method, an anonymous function returning a value class will erroneously be translated to an anonymous function returning the underlying type of that value class, instead of its boxed representation, resulting in ClassCastException at runtime.

// DelambdafyBug.scala
object DelambdafyBug {
  def main(args: Array[String]): Unit = {
    val f = (s: String) => new scala.collection.immutable.StringOps(s)
    f("Hello") foreach println
  }
}
// build.sbt
scalaVersion := "2.11.0-M7"

scalacOptions += "-Ydelambdafy:method"

During posterasure, the knowledge that the result type was a value class, here StringOps (and not a String) is lost. I think posterasure should perform a boxing operation, here (or erasure itself).

After erasure:

package <empty>{type} {
  object DelambdafyBug extends Object {
    def <init>(): DelambdafyBug.type = {
      DelambdafyBug.super{Object}.<init>{()Object}(){Object};
      (){Unit}
    }{Unit};
    def main(args: Array[String]): Unit = {
      val f: Function1 = {
        final <artifact> def $anonfun(s: String): ErasedValueType(class StringOps, String) = s{ErasedValueType(class StringOps, String)};
        ((s: String) => $anonfun{(s: String)ErasedValueType(class StringOps, String)}(s{String}){ErasedValueType(class StringOps, String)}){String => ErasedValu
eType(class StringOps, String)}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      f.apply{(v1: Object)Object}("Hello"{String("Hello")}){Object}.$asInstanceOf{[T0]()T0}[collection.IndexedSeqOptimized]{()collection.IndexedSeqOptimized}(){
collection.IndexedSeqOptimized}.foreach{(f: Function1)Unit}({
        {
          final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
          ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
        }{Function1}
      }{Function1}){Unit}
    }{Unit}
  }
}

After posterasure:

package <empty>{type} {
  object DelambdafyBug extends Object {
    def <init>(): DelambdafyBug.type = {
      DelambdafyBug.super{Object}.<init>{()Object}(){Object};
      (){Unit}
    }{Unit};
    def main(args: Array[String]): Unit = {
      val f: Function1 = {
        final <artifact> def $anonfun(s: String): String = s{String};
        ((s: String) => $anonfun{(s: String)String}(s{String}){String}){String => String}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      f.apply{(v1: Object)Object}("Hello"{String("Hello")}){Object}.$asInstanceOf{[T0]()T0}[collection.IndexedSeqOptimized]{()collection.IndexedSeqOptimized}(){
collection.IndexedSeqOptimized}.foreach{(f: Function1)Unit}({
        {
          final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
          ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
        }{Function1}
      }{Function1}){Unit}
    }{Unit}
  }
}

If the lambda takes a value class instead instead, then the compiler crashes during icode because some ErasedValueType(class StringOps, String) survive until then.

DelambdafyBug.scala
object DelambdafyBug {
  def main(args: Array[String]): Unit = {
    val g = (s: scala.collection.immutable.StringOps) => s foreach println
    g("Hello")
  }
}

After erasure:

package <empty>{type} {
  object DelambdafyBug extends Object {
    def <init>(): DelambdafyBug.type = {
      DelambdafyBug.super{Object}.<init>{()Object}(){Object};
      (){Unit}
    }{Unit};
    def main(args: Array[String]): Unit = {
      val g: Function1 = {
        final <artifact> def $anonfun(s: ErasedValueType(class StringOps, String)): Unit = new collection.immutable.StringOps{collection.immutable.StringOps}{(r
epr: String)scala.collection.immutable.StringOps}(s.$asInstanceOf{[T0]()T0}[String]{()String}(){String}){scala.collection.immutable.StringOps}.foreach{(f: Funct
ion1)Unit}({
          {
            final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
            ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
          }{Function1}
        }{Function1}){Unit};
        ((s: ErasedValueType(class StringOps, String)) => $anonfun{(s: ErasedValueType(class StringOps, String))Unit}(s{ErasedValueType(class StringOps, String)
}){Unit}){ErasedValueType(class StringOps, String) => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      g.apply{(v1: Object)Object}(new collection.immutable.StringOps{collection.immutable.StringOps}{(repr: String)scala.collection.immutable.StringOps}(scala.t
his{type}.Predef.augmentString{(x: String)ErasedValueType(class StringOps, String)}("Hello"{String("Hello")}){ErasedValueType(class StringOps, String)}.$asInsta
nceOf{[T0]()T0}[String]{()String}(){String}){scala.collection.immutable.StringOps}){Object};
      val f: Function1 = {
        final <artifact> def $anonfun(s: String): ErasedValueType(class StringOps, String) = s{ErasedValueType(class StringOps, String)};
        ((s: String) => $anonfun{(s: String)ErasedValueType(class StringOps, String)}(s{String}){ErasedValueType(class StringOps, String)}){String => ErasedValu
eType(class StringOps, String)}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      f.apply{(v1: Object)Object}("Hello"{String("Hello")}){Object}.$asInstanceOf{[T0]()T0}[collection.IndexedSeqOptimized]{()collection.IndexedSeqOptimized}(){
collection.IndexedSeqOptimized}.foreach{(f: Function1)Unit}({
        {
          final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
          ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
        }{Function1}
      }{Function1}){Unit}
    }{Unit}
  }
}

After posterasure:

package <empty>{type} {
  object DelambdafyBug extends Object {
    def <init>(): DelambdafyBug.type = {
      DelambdafyBug.super{Object}.<init>{()Object}(){Object};
      (){Unit}
    }{Unit};
    def main(args: Array[String]): Unit = {
      val g: Function1 = {
        final <artifact> def $anonfun(s: String): Unit = new collection.immutable.StringOps{collection.immutable.StringOps}{(repr: String)scala.collection.immut
able.StringOps}(s{String}){scala.collection.immutable.StringOps}.foreach{(f: Function1)Unit}({
          {
            final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
            ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
          }{Function1}
        }{Function1}){Unit};
        ((s: String) => $anonfun{(s: String)Unit}(s{String}){Unit}){String => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      g.apply{(v1: Object)Object}(new collection.immutable.StringOps{collection.immutable.StringOps}{(repr: String)scala.collection.immutable.StringOps}(scala.t
his{type}.Predef.augmentString{(x: String)String}("Hello"{String("Hello")}){String}){scala.collection.immutable.StringOps}){Object};
      val f: Function1 = {
        final <artifact> def $anonfun(s: String): String = s{String};
        ((s: String) => $anonfun{(s: String)String}(s{String}){String}){String => String}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
      }{Function1};
      f.apply{(v1: Object)Object}("Hello"{String("Hello")}){Object}.$asInstanceOf{[T0]()T0}[collection.IndexedSeqOptimized]{()collection.IndexedSeqOptimized}(){
collection.IndexedSeqOptimized}.foreach{(f: Function1)Unit}({
        {
          final <artifact> def $anonfun(x: Object): Unit = scala.this{type}.Predef.println{(x: Object)Unit}(x{Object}){Unit};
          ((x: Object) => $anonfun{(x: Object)Unit}(x{Object}){Unit}){Object => Unit}.$asInstanceOf{[T0]()T0}[Function1]{()Function1}(){Function1}
        }{Function1}
      }{Function1}){Unit}
    }{Unit}
  }
}

I suspect that both errors have the same cause, namely that posterasure fails to deal with value classes in Function nodes. Hence I report the two in only one issue.

Note that both snippets work perfectly fine with -Ydelambdafy:inline (the default).

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commented Nov 28, 2013

Imported From: https://issues.scala-lang.org/browse/SI-8017?orig=1
Reporter: @sjrd
Affected Versions: 2.11.0-M7

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commented Dec 13, 2013

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commented Dec 15, 2013

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