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Emit unchecked warnings for trait patterns #24962

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Emit unchecked warnings for trait patterns #24962

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5 changes: 3 additions & 2 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 @@ -108,9 +108,10 @@ object TypeTestsCasts {
//
// If we perform widening, we will get X = Nothing, and we don't have
// Ident[X] <:< Ident[Int] any more.
TypeComparer.constrainPatternType(P1, X, forceInvariantRefinement = true)
val forceInvariantRefinement = !tycon.classSymbol.is(Trait)
TypeComparer.constrainPatternType(P1, X, forceInvariantRefinement = forceInvariantRefinement)
debug.println(
TypeComparer.explained(_.constrainPatternType(P1, X, forceInvariantRefinement = true))
TypeComparer.explained(_.constrainPatternType(P1, X, forceInvariantRefinement = forceInvariantRefinement))
)
}

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13 changes: 13 additions & 0 deletions tests/warn/i24322.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
trait A[+T]:
def x: T
trait B[+T] extends A[T]:
def y: T

object Troll extends A[Int] with B[Any]:
def x: Int = 0
def y: Any = ""

def f[T](a: A[T]): T = a match {
case b: B[T] => b.y // warn
case _ => a.x
}
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