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Pattern-matcher emits spurious exhaustiveness warning #9399

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scabug opened this issue Jul 14, 2015 · 4 comments
Closed

Pattern-matcher emits spurious exhaustiveness warning #9399

scabug opened this issue Jul 14, 2015 · 4 comments
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@retronym
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patmat
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2.12.0-M4

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@scabug
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scabug commented Jul 14, 2015

Using a similar type hierarchy to #9398, the following code produces a spurious exhaustiveness warning.

  sealed abstract class TA
  sealed abstract class TB extends TA
  case object A extends TA
  case object B extends TB

  sealed trait C
  case class CTA(id: Int, da: TA) extends C
  case class CTB(id: Int, da: TB) extends C

  val test: C => Unit = {
    case CTA(_, A) =>
    case CTA(_, B) =>
    case CTB(_, B) =>
  }

produces

match may not be exhaustive.
It would fail on the following input: CTB(_, _)
    val test: C => Unit = {
@scabug
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scabug commented Jul 14, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9399?orig=1
Reporter: David Barri (japgolly)
Affected Versions: 2.11.7
See #9398, #9630

@scabug
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scabug commented Jul 14, 2015

David Barri (japgolly) said:
Interestingly, it goes away if you change the order of cases. This produces no warning:

  val test: C => Unit = {
    case CTB(_, B) =>
    case CTA(_, B) =>
    case CTA(_, A) =>
  }

@scabug
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scabug commented Jan 25, 2016

@retronym said:
My prototype fix for #9630 (linked from that ticket) also fixes this one. I'll update this ticket when we get that polished and merged.

A workaround is to avoid using the same name for the case class fields in sibling case classes.

sealed trait C
case class CTA(id: Int, da: TA) extends C
case class CTB(id1: Int, da1: TB) extends C

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scabug commented Jan 27, 2016

@retronym said:
scala/scala#4919

@scabug scabug closed this as completed Jan 29, 2016
@scabug scabug added the patmat label Apr 7, 2017
@scabug scabug added this to the 2.12.0-M4 milestone Apr 7, 2017
@scabug scabug mentioned this issue Apr 7, 2017
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