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Refine parameter adaptation logic for arrays #23591

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Refine parameter adaptation logic for arrays #23591

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9 changes: 7 additions & 2 deletions compiler/src/dotty/tools/dotc/transform/Erasure.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -483,8 +483,13 @@ object Erasure {
def sameClass(tp1: Type, tp2: Type) = tp1.classSymbol == tp2.classSymbol

val paramAdaptationNeeded =
implParamTypes.lazyZip(samParamTypes).exists((implType, samType) =>
!sameClass(implType, samType) && !autoAdaptedParam(implType))
implParamTypes.lazyZip(samParamTypes).exists: (implType, samType) =>
!sameClass(implType, samType) && !autoAdaptedParam(implType)
|| (samType, implType).match {
case (defn.ArrayOf(_), defn.ArrayOf(_)) => false
case (defn.ArrayOf(_), _) => true // see #23179
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Shouldn't there be the reverse order as well ((_, defn.ArrayOf(_)))? Like if the SAM takes an Array[T] where T <: AnyRef but the lambda is specialized to T = String, for example?

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I'm unable to construct such a reversed example that will be accepted by the compiler.

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Do we need something similar for the result type (resultAdaptationNeeded)?

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Not sure, I also fail here to construct an example that would cause a run time crash (which is of course weak evidence).

case _ => false
}
val resultAdaptationNeeded =
!sameClass(implResultType, samResultType) && !autoAdaptedResult

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8 changes: 8 additions & 0 deletions tests/run/i23179.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
object Test {
trait A { def f(a: Array[AnyRef]): Any }
def g(a: A) = a.f(Array.empty[AnyRef])

def main(args: Array[String]): Unit = {
g((x: Array[? >: AnyRef]) => x.headOption)
}
}
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