Fix typo leading to incorrect unreachable case warning

Author: smarter

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

@@ -187,7 +187,7 @@ trait SpaceLogic {
       case (Typ(tp1, _), Prod(tp2, fun, ss)) =>
         isSubType(tp1, tp2)
         && covers(fun, tp1, ss.length)
-        && isSubspace(Prod(tp2, fun, signature(fun, tp2, ss.length).map(Typ(_, false))), b)
+        && isSubspace(Prod(tp2, fun, signature(fun, tp1, ss.length).map(Typ(_, false))), b)
       case (Prod(_, fun1, ss1), Prod(_, fun2, ss2)) =>
         isSameUnapply(fun1, fun2) && ss1.zip(ss2).forall((isSubspace _).tupled)
     }

tests/patmat/isSubspace-Typ-Prod.scala

@@ -0,0 +1,7 @@
+case class Foo[T](x: T)
+class Bar extends Foo[String]("")
+
+def test(x: Any) = x match
+  case Foo(1) =>
+  case _: Bar => // used to warn about unreachable case
+  // case _: Foo[_] => // still warns, something else is wrong