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regression in extractors with existential-returning unapply/unapplySeq #8128

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scabug opened this issue Jan 9, 2014 · 5 comments
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regression in extractors with existential-returning unapply/unapplySeq #8128

scabug opened this issue Jan 9, 2014 · 5 comments

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@scabug
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@scabug scabug commented Jan 9, 2014

cat test/files/pos/patmat-existential.scala
object G {
  def unapply(m: Any): Option[_] = Some("")
}

object H {
  def unapplySeq(m: Any): Option[Seq[_]] = None
}

object Test {
  (0: Any) match {
    case G(v) => v
    case H(v) => v
    case _ =>
  }
}

The two patterns above result in:

qbin/scalac test/files/pos/patmat-existential.scala
test/files/pos/patmat-existential.scala:10: error: error during expansion of this match (this is a scalac bug).
The underlying error was: type mismatch;
 found   : _$2(in value <local Test>) where type _$2(in value <local Test>)
 required: _$2(in method unapplySeq)
  (0: Any) match {
           ^
one error found
pr/3275 /code/scala qbin/scalac test/files/pos/patmat-existential.scala
test/files/pos/patmat-existential.scala:10: error: error during expansion of this match (this is a scalac bug).
The underlying error was: type mismatch;
 found   : _$1(in value <local Test>) where type _$1(in value <local Test>)
 required: _$1(in method unapply)
  (0: Any) match {
           ^
@scabug
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@scabug scabug commented Jan 9, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8128?orig=1
Reporter: @retronym
Affected Versions: 2.11.0-M7

@scabug
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@scabug scabug commented Jan 9, 2014

@retronym said (edited on Jan 9, 2014 8:57:40 AM UTC):
The regression boils down to:

scala> class F[_]
defined class F

scala> val tp = typeOf[Some[F[X]] forSome { type X }]
warning: there were 1 feature warning(s); re-run with -feature for details
tp: $r.intp.global.Type = scala.this.Some[F[X]] forSome { type X }

scala> tp.baseType(typeOf[Option[_]].typeSymbol).typeArgs.head
res10: $r.intp.global.Type = F[X] forSome { type X }

scala> tp.memberType(tp.member(nme.get)).finalResultType
res11: $r.intp.global.Type = F[X]

The last line is what happens now in resultOfMatchingMethod.

This is support ticket #3045

@scabug
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@scabug scabug commented Jan 9, 2014

@retronym said:
This fixed the regression, but existentials in name-based extractors will still cause problems.

https://github.com/paulp/scala/pull/13

@scabug
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@scabug scabug commented Jan 14, 2014

@scabug scabug closed this Jan 14, 2014
@scabug
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@scabug scabug commented Jan 14, 2014

@retronym said:
The residual issue is now tracked as #8149

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