src/Pure/Thy/document_build.scala

     db_context: Sessions.Database_Context,
     progress: Progress = new Progress): Context =
   {
     val info = deps.sessions_structure(session)
     val base = deps(session)
-    val hierarchy = deps.sessions_structure.hierarchy(session)
+    val hierarchy = deps.sessions_structure.build_hierarchy(session)
     new Context(info, base, hierarchy, db_context, progress)
   }
 
   final class Context private[Document_Build](
     info: Sessions.Info,