Merge pull request #10019 from dotty-staging/fix-8344

fix #8344: add regression tests

Author: bishabosha

tests/pos/i8344-1.scala

@@ -0,0 +1,11 @@
+import scala.{Tuple => STuple}
+
+enum Datatype[T] {
+  case Tuple[T <: STuple](elems: STuple.Map[T, Datatype]) extends Datatype[T]
+}
+
+object Datatype {
+  given [H, T <: STuple](using ht: Datatype[H], tt: Datatype[T]) as Datatype[H *: T] = tt match {
+    case Datatype.Tuple(elems) => Datatype.Tuple(ht *: elems)
+  }
+}

tests/pos/i8344-2.scala

@@ -0,0 +1,8 @@
+sealed trait Datatype[T]
+case class Foo[T <: Tuple](elems: Tuple.Map[T, Datatype]) extends Datatype[T]
+
+def g =
+  val tt: Datatype[_] = ???
+  tt match {
+    case Foo(_) => ???
+  }