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Strange error when destructuring into a val or lazy val #7507

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scabug opened this issue May 22, 2013 · 6 comments
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Strange error when destructuring into a val or lazy val #7507

scabug opened this issue May 22, 2013 · 6 comments
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2.10.3-RC1

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@scabug
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scabug commented May 22, 2013 

class Bar

abstract class Cake extends Slice {
  val bar: Bar
}

trait Slice { self: Cake =>
  import bar._
  lazy val Foo(x, y) = foo
  private case class Foo(x: Int, y: Int)
  private lazy val foo: Foo = ???
}
20:50 ~/Projects/210x/sandbox (2.10.x)$ s
Test.scala:9: error: not found: value x$1
  lazy val Foo(x, y) = foo
               ^
Test.scala:9: error: not found: value x$1
  lazy val Foo(x, y) = foo
                  ^
two errors found
@scabug
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scabug commented May 22, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7507?orig=1
Reporter: @xeno-by
Affected Versions: 2.10.1

@scabug
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scabug commented May 22, 2013

@paulp said (edited on May 22, 2013 10:19:17 PM UTC):
Minimized.

abstract class Cake extends Slice { }

trait Slice { self: Cake =>
  import java.lang.String // any import will do!
  val Tuple2(x, y) = ((1, 2))
}

@scabug
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scabug commented May 23, 2013

@retronym said (edited on May 23, 2013 6:54:11 AM UTC):
After a little more whittling, it turns out to be a name lookup/access problem, unrelated to the pattern matcher.

trait Cake extends Slice

trait Slice { self: Cake =>    // must have self type that extends `Slice`
  private[this] val bippy = () // must be private[this]
  bippy
}

@scabug
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scabug commented May 23, 2013

@retronym said (edited on May 23, 2013 7:07:49 AM UTC):
It hinges on the following condition in findMember:

if (excl == 0L &&
      (// omit PRIVATE LOCALS unless selector class is contained in class owning the def.
    (bcs eq bcs0) ||
    (flags & PrivateLocal) != PrivateLocal ||
    (bcs0.head.hasTransOwner(bcs.head)))) {

    // this = Slice.this.type
    // bcs  = List(trait Cake, trait Slice, class Object, class Any)
    // bcs0 = List(trait Slice, class Object, class Any)
    // <Cake>.hasTransOwner(<Slice) == false

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scabug commented May 23, 2013

@retronym said:
Here's my proposed fix: retronym/scala@scala:2.10.x...ticket/7507

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scabug commented May 30, 2013

@retronym said:
scala/scala#2609

@scabug scabug closed this as completed Jun 4, 2013
@scabug scabug added this to the 2.10.3-RC1 milestone Apr 7, 2017
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