$delayedInit$body.$outer is missing synthetic flag

[scabug]

When extending DelayedInit trait the field referencing to an outer class "$outer" in the generated "$delayedInit$body" is not marked as synthetic. At the same time for any normal usage of inner classes generated "$outer" field is marked as synthetic.

See: https://gist.github.com/pbadenski/982dc47e8636a0f706c7bf46d610574f

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9858?orig=1
Reporter: pbadenski
Affected Versions: 2.11.8, 2.12.0-M5

[scabug]

Ausmarton Fernandes (ausmarton-at-gmail.com) said:
From Constructors.scala#L269 it looks like outerField is never given a SYNTHETIC flag. Also, looking a bit through the history of this Transformer, it doesn't seem to have ever been applying SYNTHETIC on that field unlike what you'd find in ExplicitOuter.

However, the syntax tree for the example provided seems to generate a <synthetic> Outer$delayedInit$body, which in turn contains the $outer which is not marked <synthetic> as shown below:

package <empty> {
  class Outer extends Object with DelayedInit {
    private[this] val code: scala.collection.mutable.ListBuffer = _;
    <stable> <accessor> private def code(): scala.collection.mutable.ListBuffer = Outer.this.code;
    override def delayedInit(body: Function0): Unit = {
      Outer.this.code().+=(body);
      ()
    };
    final <synthetic> def delayedEndpoint$Outer$1: Unit = {
      Outer.this.code = new scala.collection.mutable.ListBuffer();
      ()
    };
    def <init>(): Outer = {
      Outer.super.<init>();
      Outer.this.delayedInit(new Outer$delayedInit$body(Outer.this));
      ()
    }
  };
  final <synthetic> class Outer$delayedInit$body extends runtime.AbstractFunction0 {
    <paramaccessor> private[this] val $outer: Outer = _;
    final def apply(): Object = {
      Outer$delayedInit$body.this.$outer.delayedEndpoint$Outer$1();
      scala.runtime.BoxedUnit.UNIT
    };
    def <init>($outer: Outer): Outer$delayedInit$body = {
      if ($outer.eq(null))
        throw null
      else
        Outer$delayedInit$body.this.$outer = $outer;
      Outer$delayedInit$body.super.<init>();
      ()
    }
  }
}

[scabug]

@SethTisue said:
does the issue exist in 2.12.0-M5 as well?

[scabug]

Ausmarton Fernandes (ausmarton-at-gmail.com) said:
Yup, 2.12.0-M5 seems to produce a similar tree. From the git history, it looks like it's been this way at least since 2006-2007 (that's the farthest I looked).

Also, I tried adding a SYNTHETIC flag to the field in the transformer, which generates a tree like this one:

package <empty> {
  class Outer extends Object with DelayedInit {
    private[this] val code: scala.collection.mutable.ListBuffer = _;
    <stable> <accessor> private def code(): scala.collection.mutable.ListBuffer = Outer.this.code;
    override def delayedInit(body: Function0): Unit = {
      Outer.this.code().+=(body);
      ()
    };
    final <synthetic> def delayedEndpoint$Outer$1: Unit = {
      Outer.this.code = new scala.collection.mutable.ListBuffer();
      ()
    };
    def <init>(): Outer = {
      Outer.super.<init>();
      Outer.this.delayedInit(new Outer$delayedInit$body(Outer.this));
      ()
    }
  };
  final <synthetic> class Outer$delayedInit$body extends runtime.AbstractFunction0 {
    <synthetic> <paramaccessor> private[this] val $outer: Outer = _;
    final def apply(): Object = {
      Outer$delayedInit$body.this.$outer.delayedEndpoint$Outer$1();
      scala.runtime.BoxedUnit.UNIT
    };
    def <init>($outer: Outer): Outer$delayedInit$body = {
      if ($outer.eq(null))
        throw null
      else
        Outer$delayedInit$body.this.$outer = $outer;
      Outer$delayedInit$body.super.<init>();
      ()
    }
  }
}

However, I'm not sure having a <synthetic> inside a <synthetic> is valid/correct.