Custom exception printers ignored by ocaml toplevel

[vicuna]

Original bug ID: 7156
Reporter: @mjambon
Assigned to: @diml
Status: assigned (set by @mshinwell on 2016-12-08T14:08:42Z)
Resolution: open
Priority: normal
Severity: minor
Version: 4.02.3
Category: toplevel
Tags: junior_job
Monitored by: mfp @diml @hcarty

Bug description

Uncaught exceptions reported by the ocaml toplevel are printed as if no custom printer was registered. Programs compiled with ocamlc or ocamlopt behave as desired and consult the custom printers to print uncaught exceptions.

martin@mj2 ~/tmp $ echo > .ocamlinit
martin@mj2 ~/tmp $ ocaml
        OCaml version 4.02.3

# Printexc.register_printer (fun e -> Some "yo");;
- : unit = ()
# raise Exit;;
Exception: Pervasives.Exit.
# 

When compiled with ocamlc or ocamlopt however, the exception is printed using the custom printers:

martin@mj2 ~/tmp $ cat toto.ml
Printexc.register_printer (fun e -> Some "yo");;
raise Exit;;
martin@mj2 ~/tmp $ ocamlc -c toto.ml
martin@mj2 ~/tmp $ ./toto
Fatal error: exception yo

[vicuna]

Comment author: @diml

Indeed. Although I don't think we can just use [Printexc.to_string directly] as it won't print things as good when no printer is registered. Maybe we need a [Printexc.to_string_opt] function.