feat(riot): add run_with_status function where main can return a status code/error

riot/riot.ml

@@ -40,6 +40,22 @@ let run ?(rnd = Random.State.make_self_init ()) ?workers main =
   Log.debug (fun f -> f "Riot runtime shutdown");
   Stdlib.exit pool.status
 
+let on_error (error : [ `Msg of string ]) =
+  let backtrace = Printexc.get_backtrace () in
+  let error_string =
+    match error with `Msg reason -> Printf.sprintf "%s\n%s" reason backtrace
+  in
+  Log.error (fun f -> f "Riot raised an error: %s\n" error_string);
+  1
+
+let run_with_status ?(rnd = Random.State.make_self_init ()) ?workers ~on_error
+    main =
+  run ~rnd ?workers (fun _ ->
+      let status =
+        match main () with Ok code -> code | Error reason -> on_error reason
+      in
+      shutdown ~status ())
+
 let start ?rnd ?workers ~apps () =
   run ?rnd ?workers @@ fun () ->
   let child_specs =

riot/riot.mli

@@ -304,6 +304,21 @@ val shutdown : ?status:int -> unit -> unit
 val run : ?rnd:Random.State.t -> ?workers:int -> (unit -> unit) -> unit
 (** Start the Riot runtime using function [main] to boot the system *)
 
+val on_error : [ `Msg of string ] -> int
+
+val run_with_status :
+  ?rnd:Random.State.t ->
+  ?workers:int ->
+  on_error:('error -> int) ->
+  (unit -> (int, 'error) result) ->
+  unit
+(** [run_with_status ~on_error main] starts the Riot runtime using function
+    [main] to boot the system and handling errors with [on_error].
+
+    [main] should return a result of either an exit code or an error.
+    [on_error] should handle an error code appropriately, then return a status code.
+*)
+
 val start :
   ?rnd:Random.State.t ->
   ?workers:int ->