invert condition and update output

src/mo_frontend/typing.ml

@@ -2975,7 +2975,7 @@ let is_actor_dec d =
   | _ -> false
 
 let check_actors ?(viper_mode=false) ?(check_actors=false) scope progs : unit Diag.result =
-  if check_actors then Diag.return () else
+  if not check_actors then Diag.return () else
   Diag.with_message_store
     (fun msgs ->
       recover_opt (fun progs ->

src/pipeline/pipeline.ml

@@ -421,7 +421,7 @@ let chase_imports parsefn senv0 imports : (Syntax.lib list * Scope.scope) Diag.r
   in
   Diag.map (fun () -> (List.rev !libs, !senv)) (go_set None imports)
 
-let load_progs ?(viper_mode=false) ?(check_actors = false) parsefn files senv : load_result =
+let load_progs ?(viper_mode=false) ?(check_actors=false) parsefn files senv : load_result =
   let open Diag.Syntax in
   let* parsed = Diag.traverse (parsefn Source.no_region) files in
   let* rs = resolve_progs parsed in

test/run-drun/ok/bad-actor.comp-ref.ok

@@ -1,2 +1,2 @@
-bad-actor.mo:2.1-4.2: type error [M0038], misplaced await
-bad-actor.mo:2.1-4.2: type error [M0037], misplaced async expression; try enclosing in an async function
+bad-actor.mo:2.1-4.2: type error [M0141], an actor or actor class must be the only non-imported declaration in a program
+  (This is a limitation of the current version and flag -ref-system-api.)

test/run-drun/ok/bad-actor.comp.ok

@@ -1,2 +1,2 @@
-bad-actor.mo:2.1-4.2: type error [M0038], misplaced await
-bad-actor.mo:2.1-4.2: type error [M0037], misplaced async expression; try enclosing in an async function
+bad-actor.mo:2.1-4.2: type error [M0141], an actor or actor class must be the only non-imported declaration in a program
+  (This is a limitation of the current version.)