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False positive exhaustivity warning on parameterised prefix #8068

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scabug opened this issue Dec 11, 2013 · 7 comments
Closed

False positive exhaustivity warning on parameterised prefix #8068

scabug opened this issue Dec 11, 2013 · 7 comments
Labels
fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) patmat
Milestone
2.13.8

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@scabug
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scabug commented Dec 11, 2013

This code prints false warning "match may not be exhaustive. It would fail on the following input: O"

trait K[A] {
  sealed trait T
  case class  C(x: Int) extends T
  case object O         extends T
}

object Hello {
  def f[A](k: K[A])(t: k.T) = {
    t match {
      case k.C(x) => ???
      case k.O    => ???
    }
  }
  def main(args: Array[String]) {
  }
}
@scabug
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scabug commented Dec 11, 2013

Imported From: https://issues.scala-lang.org/browse/SI-8068?orig=1
Reporter: Denis Petrov (denis)
Affected Versions: 2.10.3, 2.11.0-M7, 2.11.0

@scabug
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scabug commented Dec 11, 2013

@paulp said:
Foo1, no warning, Foo2, warning.

trait Foo1 {
  sealed trait T
  object O extends T
  def f(t: T) = t match { case O => 1 }
}
trait Foo2[UnusedTypeParameter] {
  sealed trait T
  object O extends T
  def f(t: T) = t match { case O => 1 }
}

@scabug
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scabug commented May 21, 2014

balefrost said:
When the container is a generic class instead of a generic trait, the warning still occurs.

class Foo3[UnusedTypeParameter] {
  sealed trait T
  object O extends T
  def f(t: T) = t match { case O => 1 }
}

It also occurs if the type parameter is referenced

class Foo4[A] {
  sealed trait T
  object O extends T
  def f[A](t: T, v: A) = t match { case O => v }
}

@scabug
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scabug commented May 24, 2014

balefrost said:
Appears to be fixed in 2.11.1!

@scabug
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scabug commented Jan 3, 2015

@gbasler said (edited on Jan 3, 2015 6:49:24 PM UTC):
@adriaanm this seems to be fixed in 2.11.5-SNAPSHOT... should I can create a pr with a regression test for this?

@scabug scabug added the patmat label Apr 7, 2017
@adriaanm adriaanm removed their assignment Sep 28, 2018
@SethTisue SethTisue changed the title false warning "match may not be exhaustive false warning "match may not be exhaustive" Jul 3, 2019
@SethTisue
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In 2.13.0, only the original code still warns.

@dwijnand dwijnand self-assigned this Feb 4, 2021
@dwijnand dwijnand changed the title false warning "match may not be exhaustive" False positive exhaustivity warning on parameterised prefix Nov 11, 2021
@dwijnand dwijnand removed their assignment Nov 11, 2021
@SethTisue SethTisue added the fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) label Aug 25, 2022
@SethTisue SethTisue added this to the 2.13.8 milestone Aug 25, 2022
@SethTisue
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Doesn't warn on 2.13.8.

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fixed in Scala 3 This issue does not exist in the Scala 3 compiler (https://github.com/lampepfl/dotty/) patmat
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Milestone
2.13.8
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