bad explicitouter/erasure interaction regarding transform of isInstanceOf[Outer.this.Module.type] to eq(Outer.this.Module)

[scabug]

package com.middlewareman

trait Component

case class Event(component: Component)

class Owner {

  object Timestamp extends Component {
    val state = System.currentTimeMillis()
    def unapply(name: Timestamp.type) = Some(name.state)
  }

  val handler: PartialFunction[Event, Unit] = {
    case Event(Timestamp(time)) => println(time)
  }

}

I have not tried compiling outside Eclipse.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7598?orig=1
Reporter: Andreas Nyberg (middlewareman)
Affected Versions: 2.10.1, 2.10.2
Attachments:

• SI-7598.log (created on Jun 20, 2013 3:06:59 PM UTC, 28417 bytes)

[scabug]

Andreas Nyberg (middlewareman) said:
Eclipse event details attached.

[scabug]

@retronym said:
Minimized:

class Outer {
  object X

  class Inner {
    null.isInstanceOf[X.type]
  }
}

Erasure converts instanceOf tests against singleton types to eq.

              targ.tpe match {
                case SingleType(_, _) | ThisType(_) | SuperType(_, _) =>
                  val cmpOp = if (targ.tpe <:< AnyValTpe) Any_equals else Object_eq
                  atPos(tree.pos) {
                    Apply(Select(qual, cmpOp), List(gen.mkAttributedQualifier(targ.tpe)))
                  }

After erasure:

  class Outer$Inner#8101 extends Object#145 {
    <synthetic> <paramaccessor> <artifact> protected val $outer#15239: Outer#7816 = _;
    <synthetic> <stable> <artifact> def $outer#15238(): Outer#7816 = Outer$Inner#8101.this.$outer#15239;
    def <init>#13449($outer#15240: Outer#7816): Outer$Inner#8101 = {
      if ($outer#15240.eq#5861(null))
        throw null
      else
        Outer$Inner#8101.this.$outer#15239 = $outer#15240;
      Outer$Inner#8101.super.<init>#3011();
      null.eq#5861(Outer#7816.this.X#8099());
      ()
    }

We either need explicit outer to transform TypeTrees to subsitute Outer.this with $outer.type, or change erasure to make the reference to the term Outer.this.xexplicitly pass through$outer`.

[scabug]

@retronym said:
scala/scala#3066

[scabug]

@adriaanm said:
Ping – looks like this will go to 2.11.1-RC1?

[scabug]

@retronym said:
Yep. My principled fix was almost there but had some undiagnosed infinite recursions in the wild. My less principled fix (have erasure selectively call the explicitouter transformer) was a bit too much of a hack.

[scabug]

@adriaanm said:
This reminds me -- the spec defines isInstanceOf in terms of matching on type patterns, but that would entail y.isInstanceOf[x.type] should compile to y eq x, which actually breaks the compiler ("someone" cast a global to another global...)

[SethTisue]

Somehow, some way, got fixed in 2.13.6 – no compiler crash. Remains fixed in 3.2.2.

[som-snytt]

scala/scala#9504 perchance

but the retronym minimization waited for scala/scala#9581 fixing #12312 which I must have hit while typing idly into REPL during pandemic?