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Inappropriate type is inferred for an extracted value #8045

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scabug opened this issue Dec 7, 2013 · 7 comments
Closed

Inappropriate type is inferred for an extracted value #8045

scabug opened this issue Dec 7, 2013 · 7 comments

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@scabug
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@scabug scabug commented Dec 7, 2013

object Test extends App {
  case class Number(i: Int)

  object UnliftNumber {
    def unapply(t: Any): Option[Number] = t match {
      case i: Int => Some(Number(i))
      case _ => None
    }
  }

  def eval(expr: Any): Option[Number] = expr match {
    case UnliftNumber(n) => Some(n)
    case _ => None
  }

  println(eval(1))
}
Test.scala:15: error: type mismatch;
 found   : Int
 required: Test.Number
    case UnliftNumber(n) => Some(n)
                                 ^
one error found

If we the return type of eval is ommited the code compiles and runs just fine:

$ quickc -d sandbox Test.scala

$ quick -cp sandbox Test
Some(Number(1))
@scabug
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@scabug scabug commented Dec 7, 2013

Imported From: https://issues.scala-lang.org/browse/SI-8045?orig=1
Reporter: @densh
Affected Versions: 2.11.0-M7

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@scabug
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@scabug scabug commented Dec 9, 2013

@densh said:
Might be related to #7850

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@scabug
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@scabug scabug commented Dec 9, 2013

@retronym said:
Yep, regressed in scala/scala#2848

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@scabug
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@scabug scabug commented Dec 9, 2013

@retronym said:
Diffing the -Ytyper-debug before/after the regression: https://gist.github.com/retronym/7876473

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@scabug
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@scabug scabug commented Dec 9, 2013

@retronym said:
Changing Number to a non-case class works:

object Test extends App {
  class Number(i: Int)
 
  object UnliftNumber {
    def unapply(t: Any): Option[Number] = t match {
      case i: Int => Some(new Number(i))
      case _ => None
    }
  }
 
  def eval(expr: Any): Option[Number] = expr match {
    case UnliftNumber(n) => Some(n)
    case _ => None
  }
 
  println(eval(1))
}

This code seems culpable:

    /** If this is a case class, the case field accessors (which may be an empty list.)
     *  Otherwise, if there are any product selectors, that list.
     *  Otherwise, a list containing only the type itself.
     */
    def typesOfSelectorsOrSelf(tp: Type): List[Type] = (
      if (tp.typeSymbol.isCase)
        typesOfCaseAccessors(tp)
      else typesOfSelectors(tp) match {
        case Nil => tp :: Nil
        case tps => tps
      }
    )

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@scabug
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@scabug scabug commented Dec 9, 2013

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@scabug scabug commented Dec 23, 2013

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