src/Pure/Tools/build.scala

           case errs => result0.errors(errs).error_rc
         }
 
       if (result1.ok) {
         for (document_output <- proper_string(options.string("document_output"))) {
-          val document_output_dir = info.dir + Path.explode(document_output)
-          Isabelle_System.make_directory(document_output_dir)
-
+          val document_output_dir =
+            Isabelle_System.make_directory(info.dir + Path.explode(document_output))
           val base = deps(session_name)
           File.write(document_output_dir + Path.explode("session.tex"),
             base.session_theories.map(name => "\\input{" + name.theory_base_name + ".tex}\n\n").mkString)
         }
         Present.finish(progress, store.browser_info, graph_file, info, session_name)