Better error messages on uncaught exceptions

[JasonGross]

I see things like

Error: Unhandled exception: (Invalid_argument Str.matched_group)

and similar messages for stack overflow (on logentries), and it would be nice to get a backtrace instead, so I can Can this be done?

[Zimmi48]

This message is generated here:

bot/src/bot.ml

Lines 506 to 511 in 3deea7d

	let () =
	Lwt.async_exception_hook :=
	fun exn ->
	(fun () ->
	Lwt_io.printlf "Error: Unhandled exception: %s" (Exn.to_string exn) )
	|> Lwt.async

Since we are not in a catch clause, I'm not sure that a backtrace would still be available. We could experiment with inserting Printexc.print_backtrace (and turning exception backtrace recording on, with Printexc.record_backtrace).

[Alizter]

We should record backtraces since we are not performance critical anyway. Debugging coq bot is hard enough on its own, we should help any way we can.

[Zimmi48]

Since we do not use exception-based workflows in the bot codebase (except maybe catching a few Not_found here and there coming from external libraries), would this have any actual performance impact anyway?

[Alizter]

@Zimmi48 Not for coqbot.