src/Pure/General/position.ML

     val props = properties_of pos;
     val s =
       (case (line_of pos, file_of pos) of
         (SOME i, NONE) => "(line " ^ string_of_int i ^ ")"
       | (SOME i, SOME name) => "(line " ^ string_of_int i ^ " of " ^ quote name ^ ")"
-      | (NONE, SOME name) => "(" ^ quote name ^ ")"
+      | (NONE, SOME name) => "(file " ^ quote name ^ ")"
       | _ => "");
   in
     if null props then ""
     else (if s = "" then "" else " ") ^ Markup.markup (Markup.properties props Markup.position) s
   end;