fix false positive warning

Author: zielinsky

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

@@ -362,7 +362,7 @@ object SpaceEngine {
       val funRef = fun1.tpe.asInstanceOf[TermRef]
       if (fun.symbol.name == nme.unapplySeq)
         val (arity, elemTp, resultTp) = unapplySeqInfo(fun.tpe.widen.finalResultType, fun.srcPos)
-        if fun.symbol.owner == defn.SeqFactoryClass && pat.tpe.hasClassSymbol(defn.ListClass) then
+        if fun.symbol.owner == defn.SeqFactoryClass && toUnderlying(pat.tpe).dealias.derivesFrom(defn.ListClass) then
           // The exhaustivity and reachability logic already handles decomposing sum types (into its subclasses)
           // and product types (into its components).  To get better counter-examples for patterns that are of type
           // List (or a super-type of list, like LinearSeq) we project them into spaces that use `::` and Nil.

tests/pos/i23928.scala

@@ -0,0 +1,5 @@
+object Test {
+  Nil match {
+    case Seq(xs*) => 42
+  }
+}