src/Pure/Tools/doc.scala

 
   /* command line entry point */
 
   def main(args: Array[String])
   {
-    Command_Line.tool {
+    Command_Line.tool0 {
       val entries = contents()
       if (args.isEmpty) Console.println(cat_lines(contents_lines().map(_._2)))
       else {
         args.foreach(arg =>
           entries.collectFirst { case Doc(name, _, path) if arg == name => path } match {
             case Some(path) => view(path)
             case None => error("No Isabelle documentation entry: " + quote(arg))
           }
         )
       }
-      0
     }
   }
 }