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Spurious "unreachable code" warning with confused prefixes #9220

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scabug opened this issue Mar 12, 2015 · 8 comments
Closed

Spurious "unreachable code" warning with confused prefixes #9220

scabug opened this issue Mar 12, 2015 · 8 comments
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patmat
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2.12.0

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@scabug
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scabug commented Mar 12, 2015

The following,

trait Command
object Command {
  sealed trait Execution extends Command
}

case class Buzz() extends Command.Execution
case class Door() extends Command.Execution

def foo(cmd: Command.Execution) = cmd match {
  case x @ (_: Buzz) => ???
  case x @ (_: Door) => ???
}

results in the following spurious unreachable code warning,

[error]  bug.scala:11: unreachable code
[error]       case x @ (_: Door) => ???
[error]                             ^

Unnesting the Execution trait from the Command companion object results in compilation without the complaint.
@scabug
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scabug commented Mar 12, 2015

Imported From: https://issues.scala-lang.org/browse/SI-9220?orig=1
Reporter: @milessabin
Affected Versions: 2.11.6

@scabug
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scabug commented Mar 13, 2015

@retronym said:

object Test {
  trait Command
  object Command {
    sealed trait Execution extends Command
  }
   
  case class Buzz() extends Command.Execution
  case class Door() extends Command.Execution

  def foo(cmd: Command.Execution) = cmd match {
    case x @ (_: Buzz) => ???
    case x @ (_: Door) => ???
  }
}

@scabug
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scabug commented Mar 13, 2015

@retronym said:
WIP: https://github.com/retronym/scala/tree/ticket/9220

@scabug scabug added the patmat label Apr 7, 2017
@scabug scabug added this to the Backlog milestone Apr 7, 2017
@OlivierBlanvillain
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This issue seams to be fixed in 2.12.

@SethTisue
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I'm unable to reproduce it in 2.10 or 2.11 either, though. That has me wondering if some special compiler flag is required, or what. (I do have -Xlint enabled.)

@Jasper-M
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@SethTisue Strange, I can reproduce it without any special flags in every version I tried except for 2.12.x

@SethTisue
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oh, never mind, I can reproduce it with Jason's version of the code.

@SethTisue
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and yup, fixed in 2.12

@SethTisue SethTisue modified the milestones: Backlog, 2.12.0 Nov 23, 2017
Jasper-M added a commit to Jasper-M/scala that referenced this issue Nov 23, 2017
@Jasper-M
Add regression test for scala/bug#9220
3a9b845
Jasper-M added a commit to Jasper-M/scala that referenced this issue Nov 23, 2017
@Jasper-M
Add regression test for scala/bug#9220
9bc6baa
lrytz added a commit to scala/scala that referenced this issue Nov 24, 2017
@lrytz
Merge pull request #6192 from Jasper-M/topic/SI-9220
dcc0780 
Add regression test for scala/bug#9220
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@retronym @SethTisue @OlivierBlanvillain @Jasper-M @scabug