src/Pure/PIDE/headless.scala

       def make_pending(maximals: List[Document.Node.Name]): List[Document.Node.Name] =
       {
         val pending = maximals.filterNot(finished)
         if (pending.isEmpty || pending.tail.isEmpty) pending
         else {
-          val depth = dep_graph.node_depth
+          val depth = dep_graph.node_depth(_ => 1)
           pending.sortBy(node => - depth(node))
         }
       }
 
       def load_checkpoints(checkpoints: List[Document.Node.Name]): (Load, Load_State) =

         else if (limit == 0) {
           val requirements = dep_graph.all_preds(pending).reverse
           ((requirements, share_common_data), Load_Bulk(pending, Nil, checkpoints))
         }
         else {
-          def count(node: Document.Node.Name): Boolean = !finished(node)
+          def count(node: Document.Node.Name): Int = if (finished(node)) 0 else 1
           val reachable = dep_graph.reachable_limit(limit, count _, dep_graph.imm_preds, pending)
           val (pending1, pending2) = pending.partition(reachable)
           val requirements = dep_graph.all_preds(pending1).reverse
           ((requirements, share_common_data), Load_Bulk(pending1, pending2, checkpoints))
         }