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Pattern matcher exhaustivity check incomplete and non-determistic #8430

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scabug opened this issue Mar 19, 2014 · 7 comments
Closed

Pattern matcher exhaustivity check incomplete and non-determistic #8430

scabug opened this issue Mar 19, 2014 · 7 comments
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@retronym
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patmat
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2.11.1

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@scabug
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scabug commented Mar 19, 2014 •
edited by retronym 

$ cat Test.scala
package test

sealed trait CL3Literal
case object IntLit extends CL3Literal
case object CharLit extends CL3Literal
case object BooleanLit extends CL3Literal
case object UnitLit extends CL3Literal


sealed trait Tree
case class LetL(value: CL3Literal) extends Tree
case object LetP extends Tree
case object LetC extends Tree
case object LetF extends Tree

object Test {
  def transform(tree: Tree) : Any = tree match {
    case LetL(CharLit) =>
      ???
  }
}
$ scalac Test.scala
Test.scala:17: warning: match may not be exhaustive.
It would fail on the following inputs: ??, LetC, LetF, LetL(IntLit), LetP
  def transform(tree: Tree) : Any = tree match {
                                    ^
one warning found
$ scalac Test.scala
Test.scala:17: warning: match may not be exhaustive.
It would fail on the following inputs: ??, LetC, LetF, LetL(BooleanLit), LetL(IntLit), LetP
  def transform(tree: Tree) : Any = tree match {
                                    ^
one warning found

Running "scalac Test.scala" will output randomly one of the two warning messages above. One of them is more complete than the other, but is still missing the LetL(UnitLit) case.
@scabug
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scabug commented Mar 19, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8430?orig=1
Reporter: Guillaume Martres (Smarter)
Affected Versions: 2.11.0-RC1

@scabug
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scabug commented Mar 19, 2014

@VladUreche said:
Thanks a lot for the report Guillaume, it's very good that you isolated the problem!
Adriaan, I marked it as critical since it's non-deterministic, but feel free to bump it back to major.

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scabug commented Mar 19, 2014

@VladUreche said:
This bug also affects RC3:

> clean
[success] Total time: 0 s, completed Mar 20, 2014 12:25:59 AM
> compile
[info] Updating {file:/mnt/data-local/Work/Workspace/dev/test/}default-827862...
[info] Resolving org.scala-lang#scala-library;2.11.0-RC3 ...
[info] Done updating.
[info] Compiling 1 Scala source to /mnt/data-local/Work/Workspace/dev/test/target/scala-2.11.0-RC3/classes...
[warn] /mnt/data-local/Work/Workspace/dev/test/src/main/scala/test.scala:17: match may not be exhaustive.
[warn] It would fail on the following inputs: ??, LetC, LetF, LetL(BooleanLit), LetL(IntLit), LetP
[warn]   def transform(tree: Tree) : Any = tree match {
[warn]                                     ^
[warn] one warning found
[success] Total time: 2 s, completed Mar 20, 2014 12:26:01 AM
> clean  
[success] Total time: 0 s, completed Mar 20, 2014 12:26:04 AM
> compile
[info] Updating {file:/mnt/data-local/Work/Workspace/dev/test/}default-827862...
[info] Resolving org.scala-lang#scala-library;2.11.0-RC3 ...
[info] Done updating.
[info] Compiling 1 Scala source to /mnt/data-local/Work/Workspace/dev/test/target/scala-2.11.0-RC3/classes...
[warn] /mnt/data-local/Work/Workspace/dev/test/src/main/scala/test.scala:17: match may not be exhaustive.
[warn] It would fail on the following inputs: ??, LetC, LetF, LetL(IntLit), LetP
[warn]   def transform(tree: Tree) : Any = tree match {
[warn]                                     ^
[warn] one warning found
[success] Total time: 1 s, completed Mar 20, 2014 12:26:06 AM

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scabug commented Mar 19, 2014

@adriaanm said:
Thanks! This is not a blocker bug, though. We'll fix it in 2.11.1.

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scabug commented Mar 21, 2014

@retronym said:
Here's a bashy way to test this:

% (f=test/files/neg/t8430.scala; (for i in {1..20}; do echo $f; done; printf "\n") | qbin/scalac -Xresident) 2>&1 | grep "fail" | sort | uniq | wc -l
       2

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scabug commented Mar 21, 2014

@retronym said:
https://github.com/scala/scala/pull/3645/files

@scabug scabug closed this as completed Apr 21, 2014
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scabug commented Apr 21, 2014

@retronym said:
From the fix comment:

The counter-examples are still a bit off; I'm going to merge
that aspect of this ticket with SI-7746, in which we've
pinpointed the culpable part of the implementation, but haven't
had success in fixing the bug.

@scabug scabug added this to the 2.11.1 milestone Apr 7, 2017
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