anchor.diff:                    let msg = BU.format2 "checked file %s is stale (digest mismatch for %s)" checked_fn fn in
                     BU.smap_add mcache checked_fn (Invalid msg, Inl msg)
                   end
  -                else BU.smap_add mcache checked_fn (Unknown (deps_dig, dig, tc_result), Inr parsing_data)
  +                else BU.smap_add mcache checked_fn (Unknown (deps_dig, tc_result), Inr parsing_data)
   
   (*
    * Second step for loading checked files, validates the tc data
  
positive.code:       if deps_dig = deps_dig'
        then begin
          //mark the tc data of the file as valid
          BU.smap_add mcache checked_fn (Valid (dig, tc_result), parsing_data);
          //if there exists an interface for it, mark that too as valid
          //validity of implementaton tc data implies validity of iface tc data
          let validate_iface_cache () =
  
negative.code:  *  At that point, the cache is updated to either Valid or Invalid w.r.t. the tc data
   *)
  type tc_result_t =
    | Unknown of (list<(string * string)>) * tc_result  //deps as in the checked_file_entry, tc_result
    | Invalid of string  //reason why this is invalid
    | Valid   of string * tc_result  //digest of the checked file, tc_result
  
  (*
   * The cache of checked files
  