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Fix #16899 #17068

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Fix #16899 #17068

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931efb8
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Decel Mar 8, 2023
ce05ee8
Update TypeTestsCasts.scala
Decel Mar 8, 2023
854512a
Merge branch 'lampepfl:main' into main
Decel Mar 9, 2023
e9b4975
Add a regression test for #10369
Decel Mar 15, 2023
b94ec9b
Delete i10369.scala
Decel Mar 15, 2023
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1 change: 1 addition & 0 deletions compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,7 @@ object TypeTestsCasts {
// always false test warnings are emitted elsewhere
X.classSymbol.exists && P.classSymbol.exists &&
!X.classSymbol.asClass.mayHaveCommonChild(P.classSymbol.asClass)
|| X.classSymbol.isOneOf(FinalOrSealed)
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Option being sealed doesn't mean that isInstanceOf[Option[Int]] isn't unchecked. Except of course that Unset | Option[Int] without sealed Unset means the scrutinee after case 1 is Option[Int], but I don't think we calculate that in type tests cast, and in a way we can't, because the match tree has been transformed. There's three places (that I'm aware of) where we look at the match trees: typing, pattern match translation, and space engine analysis. Perhaps in one of those we can find a way to annotate that the Option[Int] test is fully checked. Even in the case that isn't not the type of the scrutinee, like:

(v: Unset | Option[Int] | List[Long]) match
  case v: Unset =>
  case v: Option[Int] =>
  case v: List[Long] =>

|| typeArgsTrivial(X, tpe)
||| i"its type arguments can't be determined from $X"
}
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5 changes: 5 additions & 0 deletions tests/pos/16899.scala
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@@ -0,0 +1,5 @@
sealed trait Unset

def foo(v: Unset|Option[Int]): Unit = v match
case v: Unset => ()
case v: Option[Int] => ()