Added backtrace primitives.

Using OCaml 3.11+ builtin facilities to record stack frames during
exception raising, we can now recover at runtime the backtrace of
an uncaught toplevel exception and display it to the user, without
the infamous OCaml debugger. The backtrace is displayed when using
the [-debug] flag.

This requires a bit of discipline, as each time we reraise an
exception we need to keep track of those frames we discarded
between the previous raise and the current [try-with] branch.

Currently, only [Anomaly] is handled, but this can be ported to any
exception as long as we add the backtrace info into the exception,
and we provide the corresponding handler to
[Backtracke.register_backtrace_handler].

Hopefully this should not be to costly, as we only do little work
when reraising, and only with the [-debug] flag set.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16166 85f007b7-540e-0410-9357-904b9bb8a0f7

1 files changed, 89 insertions, 0 deletions

diff --git a/lib/backtrace.ml b/lib/backtrace.ml
new file mode 100644
index 0000000000..84f208c9ef
--- /dev/null
+++ b/lib/backtrace.ml
@@ -0,0 +1,89 @@
+(***********************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team    *)
+(* <O___,, *        INRIA-Rocquencourt  &  LRI-CNRS-Orsay              *)
+(*   \VV/  *************************************************************)
+(*    //   *      This file is distributed under the terms of the      *)
+(*         *       GNU Lesser General Public License Version 2.1       *)
+(***********************************************************************)
+
+type raw_frame =
+| Known_location of bool   (* is_raise *)
+  * string (* filename *)
+  * int    (* line number *)
+  * int    (* start char *)
+  * int    (* end char *)
+| Unknown_location of bool (*is_raise*)
+
+type location = {
+  loc_filename : string;
+  loc_line : int;
+  loc_start : int;
+  loc_end : int;
+}
+
+type frame = { frame_location : location option; frame_raised : bool; }
+
+external get_exception_backtrace: unit -> raw_frame array option
+  = "caml_get_exception_backtrace"
+
+type t = frame list option
+
+let empty = Some []
+
+let none = None
+
+let of_raw = function
+| Unknown_location r ->
+  { frame_location = None; frame_raised = r; }
+| Known_location (r, file, line, st, en) ->
+  let loc = {
+    loc_filename = file;
+    loc_line = line;
+    loc_start = st;
+    loc_end = en;
+  } in
+  { frame_location = Some loc; frame_raised = r; }
+
+let push bt = match bt with
+| None -> None
+| Some stack ->
+  match get_exception_backtrace () with
+  | None -> bt
+  | Some frames ->
+    let len = Array.length frames in
+    let rec append accu i =
+      if i = len then accu
+      else append (of_raw frames.(i) :: accu) (succ i)
+    in
+    Some (append stack 0)
+
+(** Utilities *)
+
+let print_frame frame =
+  let raise = if frame.frame_raised then "raise" else "frame" in
+  match frame.frame_location with
+  | None -> Printf.sprintf "%s @ unknown" raise
+  | Some loc ->
+    Printf.sprintf "%s @ file \"%s\", line %d, characters %d-%d"
+      raise loc.loc_filename loc.loc_line loc.loc_start loc.loc_end
+
+(** Exception manipulation *)
+
+let handlers = ref []
+
+let register_backtrace_handler h =
+  handlers := h :: !handlers
+
+let rec push_exn_aux e = function
+| [] -> e
+| f :: l ->
+  match f e with
+  | None -> push_exn_aux e l
+  | Some e -> e
+
+let push_exn e =
+  push_exn_aux e !handlers
+
+let reraise e =
+  let e = push_exn e in
+  raise e