Fix #18211: Add regression test.

This is also fixed by the parent commit.

Author: sjrd

compiler/test/dotc/pos-test-pickling.blacklist

@@ -56,6 +56,7 @@ i15827.scala
 i17149.scala
 tuple-fold.scala
 mt-redux-norm.perspective.scala
+i18211.scala
 
 # Opaque type
 i5720.scala

tests/pos/i18211.scala

@@ -0,0 +1,39 @@
+import scala.compiletime.ops.int.*
+
+type AnyInt[A <: Int] <: Int = A match {
+  case _ => A
+}
+
+type IndexOf[A, T <: Tuple] <: Int = T match {
+  case EmptyTuple => -1
+  case A *: t     => 0
+  case _ *: t =>
+    IndexOf[A, t] match {
+      case -1        => -1
+      case AnyInt[a] => S[a]
+    }
+}
+
+type Indexes[A, T <: Tuple]
+object Indexes {
+  given of[A, T <: Tuple](using IndexOf[A, T] >= 0 =:= true)(using
+      index: ValueOf[IndexOf[A, T]],
+      next: Indexes[A, Tuple.Drop[T, S[IndexOf[A, T]]]]
+  ): Indexes[A, T] = ???
+
+  given empty[A, T <: Tuple](using IndexOf[A, T] =:= -1): Indexes[A, T] = ???
+}
+
+class GetAll[A]:
+  def apply[T <: Tuple](t: T)(using indexes: Indexes[A, T]): List[A] = ???
+
+def getAll[A]: GetAll[A] = new GetAll[A]
+
+def test =
+  // the code here is trying to get all values from a tuple that has type [X] as a list
+
+  // this works if there are only two strings in the tuple
+  getAll[String](("str1", 1, "str2", false))
+
+  //but this not compiles if there are more than two strings in the tuple
+  getAll[String](("str1", 1, "str2", false, "str3"))