src/Pure/PIDE/headless.scala

         resources.dependencies(import_names, progress = progress).check_errors
       }
       val dep_theories = dependencies.theories
       val dep_theories_set = dep_theories.toSet
       val dep_files =
-        dependencies.loaded_files.flatMap(_._2).
-          map(path => Document.Node.Name(resources.append("", path)))
+        for (path <- dependencies.loaded_files)
+          yield Document.Node.Name(resources.append("", path))
 
       val use_theories_state =
       {
         val dep_graph = dependencies.theory_graph