Fix scala#13469: Add regression test

tests/pos/13469.scala

@@ -0,0 +1,47 @@
+object Meta:
+  type Shape = String | Tuple
+
+  type Demote[S <: Tuple]<: Shape = S match
+    case Tuple1[t] => t & Shape
+    case Tuple => S
+
+  type If[T <: Boolean, R1, R2] <: R1 | R2 = T match
+    case true => R1
+    case false => R2
+
+  type Contains[T <: Tuple, X] <: Boolean = T match
+    case X *: r => true
+    case _ *: r => Contains[r, X]
+    case _ => false
+
+  type RemoveStrict[T <: Tuple, X] <: Tuple = T match
+    case head *: tail => head match
+      case X => tail
+      case _ => head *: RemoveStrict[tail, X]
+
+  type WithoutStrict[T <: Tuple, T2 <: Tuple] <: Tuple = T2 match
+    case head *: tail => WithoutStrict[RemoveStrict[T, head], tail]
+    case EmptyTuple => T
+
+  /** Removes all elems from ToReplace and replaces the first replaced elem with replacement */
+  type ReplaceAllStrict[T <: Tuple, ToReplace <: Tuple, Replacement] <: Tuple = T match
+    case head *: tail =>
+      If[Contains[ToReplace, head],
+          Replacement *: WithoutStrict[tail, RemoveStrict[ToReplace, head]],
+          head *: ReplaceAllStrict[tail, ToReplace, Replacement]]
+    case EmptyTuple => T
+
+  type Sub[S <: Tuple, ToReplace <: Tuple, Replacement <: String] =
+    Demote[ReplaceAllStrict[S, ToReplace, Replacement]]
+
+object Foo:
+  import Meta._
+  val _0: Sub["batch" *: EmptyTuple, Int *: EmptyTuple, "batch"] = "batch"
+  val _1: Sub[("batch", "len"), ("batch", "len"), "batch"] = "batch"
+  val _2a: ReplaceAllStrict[("batch", "len", "embed"), "batch" *: EmptyTuple, "b"] = ("b", "len", "embed")
+  type S = ("batch", "len")
+  type ToReplace = "batch" *: EmptyTuple
+  type Replacement = "b"
+  val _2b: ReplaceAllStrict[S, ToReplace, Replacement] = ("b", "len") // ok
+  val _2c: Demote[ReplaceAllStrict[S, ToReplace, Replacement]] = ("b", "len") // ok
+  val _2d: Sub[S, ToReplace, Replacement] = ("b", "len") // error, see below