Handle opaque aliases of arrays in Space erase

Author: dwijnand

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -449,6 +449,7 @@ object SpaceEngine {
    *
    *  @param inArray whether `tp` is a type argument to `Array`
    *  @param isValue whether `tp` is the type which match against values
+   *  @param isTyped whether `tp` is the type from a `Typed` tree
    *
    *  If `isValue` is true, then pattern-bound symbols are erased to its upper bound.
    *  This is needed to avoid spurious unreachable warnings. See tests/patmat/i6197.scala.
@@ -459,7 +460,7 @@ object SpaceEngine {
         WildcardType
 
       case tp @ AppliedType(tycon, args) =>
-        val inArray = tycon.isRef(defn.ArrayClass)
+        val inArray = tycon.isRef(defn.ArrayClass) || tp.translucentSuperType.isRef(defn.ArrayClass)
         val args2 =
           if isTyped && !inArray then args.map(_ => WildcardType)
           else args.map(arg => erase(arg, inArray = inArray, isValue = false))

tests/pos/i18364.Tup.scala

@@ -0,0 +1,10 @@
+// Capturing the regression will implementing the fix for i18364
+// That broke in CI, "case _" "Unreachable case except for null"
+// Because IArray is an opaque alias of Array
+object Tup:
+  /** Convert an immutable array into a tuple of unknown arity and types */
+  def fromIArray[T](xs: IArray[T]): Tuple =
+    val xs2: IArray[Object] = xs match
+      case xs: IArray[Object] @unchecked => xs
+      case _ => xs.map(_.asInstanceOf[Object])
+    runtime.Tuples.fromIArray(xs2)