src/Pure/PIDE/headless.scala

   class Resources private[Headless](
       val options: Options,
       val session_base_info: Sessions.Base_Info,
       log: Logger = No_Logger)
     extends isabelle.Resources(
-      session_base_info.sessions_structure, session_base_info.check_base, log = log)
+      session_base_info.sessions_structure, session_base_info.check.base, log = log)
   {
     resources =>
 
     val store: Sessions.Store = Sessions.store(options)