Refine parameter adaptation logic for arrays

Fixes #23179

Since JDK 9, argument checks for LambdaMetaFactory have become stricter.
Which is to say that its JDK 8 version was too lax.

We apply adaptation now in case the samType is an array,
but the implType is not.

Author: bracevac

compiler/src/dotty/tools/dotc/transform/Erasure.scala

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

tests/run/i23179.scala

@@ -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)
+  }
+}