test: add in a regression test for #10242 (#17488)

Closes #10242

Author: nicolasstucki

tests/pos/i10242.scala

@@ -0,0 +1,32 @@
+// https://github.com/lampepfl/dotty/issues/10242  
+type Foo[A, B <: A] = A
+
+type Bar[A] = A match {
+  case Foo[String, x] => Unit
+}
+
+import scala.compiletime.ops.int.*
+
+sealed trait HList
+final case class HCons[H <: Int & Singleton, T <: HList](head: H, tail: T)
+    extends HList
+sealed trait HNil extends HList
+case object HNil extends HNil
+
+sealed trait Tensor[T, S <: HList]
+
+object tf:
+  def zeros[S <: HList](shape: S): Tensor[Float, S] = ???
+
+  type NumElements[X <: HList] <: Int = X match
+    case HNil              => 1
+    case HCons[head, tail] => head * NumElements[tail]
+
+  def reshape[T, From <: HList, To <: HList](
+      tensor: Tensor[T, From],
+      shape: To
+  )(using NumElements[From] =:= NumElements[To]): Tensor[T, To] = ???
+
+object test:
+  val x = HCons(1, HCons(2, HNil))
+  val y = tf.reshape(tf.zeros(x), HCons(2, HCons(1, HNil)))