backtrace_slots.ml

(* TEST_BELOW
(* Blank lines added here to preserve locations. *)

*)

(* A test for stack backtraces *)

let get_backtrace () =
  let raw_backtrace = Printexc.get_raw_backtrace () in
  let raw_slots =
    Array.init (Printexc.raw_backtrace_length raw_backtrace)
               (Printexc.get_raw_backtrace_slot raw_backtrace) in
  let convert = Printexc.convert_raw_backtrace_slot in
  let backtrace = Array.map convert raw_slots in
  (* we'll play with raw slots a bit to check that hashing and comparison work:
     - create a hashtable that maps slots to their index in the raw backtrace
     - create a balanced set of all slots
  *)
  let table = Hashtbl.create 100 in
  Array.iteri (fun i slot -> Hashtbl.add table slot i) raw_slots;
  let module S = Set.Make(struct
    type t = Printexc.raw_backtrace_slot
    let compare = Stdlib.compare
  end) in
  let slots = Array.fold_right S.add raw_slots S.empty in
  Array.iteri (fun i slot ->
    assert (S.mem slot slots);
    assert (Hashtbl.mem table slot);
    let j =
      (* position in the table of the last slot equal to [slot] *)
      Hashtbl.find table slot in
    assert (slot = raw_slots.(j));
    assert (backtrace.(i) = backtrace.(j));
  ) raw_slots;
  backtrace

exception Error of string

let rec f msg n =
  if n = 0 then raise(Error msg) else 1 + f msg (n-1)

let g msg =
  try
    f msg 5
  with Error "a" -> print_string "a"; print_newline(); 0
     | Error "b" as exn -> print_string "b"; print_newline(); raise exn
     | Error "c" -> raise (Error "c")

let run args =
  try
    ignore (g args.(0)); print_string "No exception\n"
  with exn ->
    Printf.printf "Uncaught exception %s\n" (Printexc.to_string exn);
    get_backtrace () |> Array.iteri
        (fun i slot -> match Printexc.Slot.format i slot with
          | None -> ()
          | Some line -> print_endline line)

let _ =
  run [| "a" |];
  run [| "b" |];
  run [| "c" |];
  run [| "d" |];
  run [| |]

(* TEST
 flags = "-g";
 ocamlrunparam += ",b=1";
*)