ch join builder from homegrown ast

DisplacementJoin.scala

def join(queries: NonEmptyList[TopLevelQuery]): TopLevelQuery = {
    val size: Int = queries.size

    if (size == 1) {
      queries.head
    } else {
      queries
        .reduceRight { case (q, acc) =>
          acc.map { acc =>
            val fiels: List[String] =
              acc.select.fields

            TopLevelQuery(
              Select(fiels),
              Some(From.Subquery(
                q.copy(join = Some(Join(acc, fiels)))
              ))
            )
          }
        }
        .value
      // Can be a minor optimization
      // but i don't feel like it now:
      //
      // tlq.from match {
      //   case Some(x) => x match {
      //     case From.Table(_) =>
      //       throw new IllegalStateException(s"From=Table, this can't happen [$tlq]. @rt")
      //     case From.Subquery(tree) =>
      //       tree
      //   }
      //   case None =>
      //     throw new IllegalStateException(s"From=None, this can't happen [$tlq]. @rt")
      // }
    }
  }