feat: check restriction on main actor before type checking (#4714)

Improve the error message for compiled code that contains illegal top-level declarations in the main program.

c.f. https://forum.dfinity.org/t/misplaced-await-and-misplaced-async/34479

src/lang_utils/error_codes.ml

@@ -144,7 +144,7 @@ let error_codes : (string * string option) list =
     "M0138", None; (* Actor classes are not supported *)
     "M0139", None; (* Inner actor classes are not supported *)
     "M0140", None; (* Actor classes with type parameters are not supported *)
-    "M0141", None; (* Forbidden declaration in program *)
+    "M0141", Some([%blob "lang_utils/error_codes/M0141.md"]); (* An actor or actor class must be the only non-imported declaration in a program *)
     "M0142", None; (* An imported library should be a module or named actor class *)
     "M0143", None; (* Imported actor class cannot be anonymous *)
     "M0144", None; (* Expected a module or actor class *)

src/lang_utils/error_codes/M0141.md

@@ -0,0 +1,38 @@
+# M0141
+
+This error indicates that the main actor or actor class has some leading or trailing declarations that are not just `import` declarations.
+
+The offending declarations should be moved into the body of the main actor or actor class.
+
+Here's an offending code example:
+
+```motoko
+import Int "mo:base/Int";
+
+// illegal leading declarations before main actor
+type Point = (Int, Int);
+let origin : Point = (0, 0);
+
+actor {
+
+  public func getOrigin() : async Point { origin };
+
+}
+```
+
+This is a possible correction of the code:
+
+```motoko
+import Int "mo:base/Int";
+
+actor {
+
+  // legal leading declarations within main actor
+  type Point = (Int, Int);
+  let origin : Point = (0, 0);
+
+  public func getOrigin() : async Point { origin };
+
+}
+```
+

src/mo_frontend/typing.ml

@@ -2974,18 +2974,29 @@ let is_actor_dec d =
     obj_sort.it = T.Actor
   | _ -> false
 
-let check_actors ?(viper_mode=false) scope progs : unit Diag.result =
+let check_actors ?(viper_mode=false) ?(check_actors=false) scope progs : unit Diag.result =
+  if not check_actors then Diag.return () else
   Diag.with_message_store
     (fun msgs ->
       recover_opt (fun progs ->
         let prog = (CompUnit.combine_progs progs).it in
         let env = env_of_scope ~viper_mode msgs scope in
+        let report ds =
+          match ds with
+            [] -> ()
+          | d :: _ ->
+            let r = { d.at with right = (Lib.List.last ds).at.right } in
+            local_error env r "M0141" "move these declarations into the body of the main actor or actor class"
+        in
         let rec go ds = function
           | [] -> ()
           | (d::ds') when is_actor_dec d ->
-            if ds <> [] || ds' <> []  then
+            if ds <> [] || ds' <> [] then begin
+              report (List.rev ds);
+              report ds';
               error_in [Flags.ICMode; Flags.RefMode] env d.at "M0141"
                 "an actor or actor class must be the only non-imported declaration in a program"
+            end
           | (d::ds') when is_import d -> go ds ds'
           | (d::ds') -> go (d::ds) ds'
         in

src/mo_frontend/typing.mli

@@ -9,7 +9,7 @@ val initial_scope : scope
 val infer_prog : ?viper_mode:bool -> scope -> string option -> Async_cap.async_cap -> Syntax.prog -> (typ * scope) Diag.result
 
 val check_lib : scope -> string option -> Syntax.lib -> scope Diag.result
-val check_actors : ?viper_mode:bool -> scope -> Syntax.prog list -> unit Diag.result
+val check_actors : ?viper_mode:bool -> ?check_actors:bool -> scope -> Syntax.prog list -> unit Diag.result
 val check_stab_sig : scope -> Syntax.stab_sig -> (field list) Diag.result
 
 val heartbeat_type : typ

src/pipeline/pipeline.ml

@@ -421,13 +421,14 @@ 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) 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
   let progs' = List.map fst rs in
   let libs = List.concat_map snd rs in
   let* libs, senv' = chase_imports parsefn senv libs in
+  let* () = Typing.check_actors ~viper_mode ~check_actors senv' progs' in
   let* senv'' = check_progs ~viper_mode senv' progs' in
   Diag.return (libs, progs', senv'')
 
@@ -510,7 +511,7 @@ type viper_result = (string * (Source.region -> Source.region option)) Diag.resu
 let viper_files' parsefn files : viper_result =
   let open Diag.Syntax in
   let* libs, progs, senv = load_progs ~viper_mode:true parsefn files initial_stat_env in
-  let* () = Typing.check_actors ~viper_mode:true senv progs in
+  let* () = Typing.check_actors ~viper_mode:true ~check_actors:true senv progs in
   let prog = CompUnit.combine_progs progs in
   let u = CompUnit.comp_unit_of_prog false prog in
   let reqs = Viper.Common.init_reqs () in
@@ -525,8 +526,7 @@ let viper_files files : viper_result =
 
 let generate_idl files : Idllib.Syntax.prog Diag.result =
   let open Diag.Syntax in
-  let* libs, progs, senv = load_progs parse_file files initial_stat_env in
-  let* () = Typing.check_actors senv progs in
+  let* libs, progs, senv = load_progs ~check_actors:true parse_file files initial_stat_env in
   Diag.return (Mo_idl.Mo_to_idl.prog (progs, senv))
 
 (* Running *)
@@ -760,8 +760,7 @@ and compile_progs mode do_link libs progs : Wasm_exts.CustomModule.extended_modu
 
 let compile_files mode do_link files : compile_result =
   let open Diag.Syntax in
-  let* libs, progs, senv = load_progs parse_file files initial_stat_env in
-  let* () = Typing.check_actors senv progs in
+  let* libs, progs, senv = load_progs ~check_actors:true parse_file files initial_stat_env in
   let idl = Mo_idl.Mo_to_idl.prog (progs, senv) in
   let ext_module = compile_progs mode do_link libs progs in
   (* validate any stable type signature *)

src/pipeline/pipeline.mli

@@ -38,4 +38,4 @@ val compile_files : Flags.compile_mode -> bool -> string list -> compile_result
 (* For use in the IDE server *)
 type load_result =
   (Syntax.lib list * Syntax.prog list * Scope.scope) Diag.result
-val load_progs : ?viper_mode:bool -> parse_fn -> string list -> Scope.scope -> load_result
+val load_progs : ?viper_mode:bool -> ?check_actors:bool -> parse_fn -> string list -> Scope.scope -> load_result

test/run-drun/bad-actor.mo

@@ -0,0 +1,12 @@
+
+// bad leading decs
+type T1 = {};
+type T2 = {};
+
+actor Self {
+
+};
+
+// bad trailing decs
+type U1 = {};
+type U2 = {};

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

@@ -0,0 +1,4 @@
+bad-actor.mo:3.1-4.13: type error [M0141], move these declarations into the body of the main actor or actor class
+bad-actor.mo:11.1-12.13: type error [M0141], move these declarations into the body of the main actor or actor class
+bad-actor.mo:6.1-8.2: 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-ref.ret.ok

@@ -0,0 +1 @@
+Return code 1

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

@@ -0,0 +1,4 @@
+bad-actor.mo:3.1-4.13: type error [M0141], move these declarations into the body of the main actor or actor class
+bad-actor.mo:11.1-12.13: type error [M0141], move these declarations into the body of the main actor or actor class
+bad-actor.mo:6.1-8.2: 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.)

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

@@ -0,0 +1 @@
+Return code 1

test/run-drun/ok/issue-1938-b.comp-ref.ok

@@ -1,2 +1,3 @@
-issue-1938-b.mo:2.1-2.9: type error [M0038], misplaced await
-issue-1938-b.mo:2.1-2.9: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938-b.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938-b.mo:2.1-2.9: 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/issue-1938-b.comp.ok

@@ -1,2 +1,3 @@
-issue-1938-b.mo:2.1-2.9: type error [M0038], misplaced await
-issue-1938-b.mo:2.1-2.9: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938-b.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938-b.mo:2.1-2.9: 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.)

test/run-drun/ok/issue-1938-c.comp-ref.ok

@@ -1,2 +1,3 @@
-issue-1938-c.mo:2.1-2.11: type error [M0038], misplaced await
-issue-1938-c.mo:2.1-2.11: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938-c.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938-c.mo:2.1-2.11: 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/issue-1938-c.comp.ok

@@ -1,2 +1,3 @@
-issue-1938-c.mo:2.1-2.11: type error [M0038], misplaced await
-issue-1938-c.mo:2.1-2.11: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938-c.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938-c.mo:2.1-2.11: 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.)

test/run-drun/ok/issue-1938-d.comp-ref.ok

@@ -1,2 +1,3 @@
+issue-1938-d.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
 issue-1938-d.mo:2.1-2.19: 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/issue-1938-d.comp.ok

@@ -1,2 +1,3 @@
+issue-1938-d.mo:1.1-1.3: type error [M0141], move these declarations into the body of the main actor or actor class
 issue-1938-d.mo:2.1-2.19: 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.)

test/run-drun/ok/issue-1938.comp-ref.ok

@@ -1,2 +1,3 @@
-issue-1938.mo:2.1-2.11: type error [M0038], misplaced await
-issue-1938.mo:2.1-2.11: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938.mo:1.1-1.13: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938.mo:2.1-2.11: 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/issue-1938.comp.ok

@@ -1,2 +1,3 @@
-issue-1938.mo:2.1-2.11: type error [M0038], misplaced await
-issue-1938.mo:2.1-2.11: type error [M0037], misplaced async expression; try enclosing in an async function
+issue-1938.mo:1.1-1.13: type error [M0141], move these declarations into the body of the main actor or actor class
+issue-1938.mo:2.1-2.11: 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.)

test/run-drun/ok/unavailable-constructor.comp-ref.ok

@@ -1,3 +1,2 @@
-unavailable-constructor.mo:1.36-1.37: type error [M0056], variable C is in scope but not available in compiled code
-unavailable-constructor.mo:5.17-5.18: type error [M0056], variable C is in scope but not available in compiled code
-unavailable-constructor.mo:8.31-8.32: type error [M0056], variable C is in scope but not available in compiled code
+unavailable-constructor.mo:3.17-3.18: type error [M0056], variable C is in scope but not available in compiled code
+unavailable-constructor.mo:6.31-6.32: type error [M0056], variable C is in scope but not available in compiled code

test/run-drun/ok/unavailable-constructor.comp.ok

@@ -1,3 +1,2 @@
-unavailable-constructor.mo:1.36-1.37: type error [M0056], variable C is in scope but not available in compiled code
-unavailable-constructor.mo:5.17-5.18: type error [M0056], variable C is in scope but not available in compiled code
-unavailable-constructor.mo:8.31-8.32: type error [M0056], variable C is in scope but not available in compiled code
+unavailable-constructor.mo:3.17-3.18: type error [M0056], variable C is in scope but not available in compiled code
+unavailable-constructor.mo:6.31-6.32: type error [M0056], variable C is in scope but not available in compiled code

test/run-drun/ok/unavailable-constructor.tc.ok

@@ -1,2 +1 @@
-unavailable-constructor.mo:1.6-1.7: warning [M0194], unused identifier f (delete or rename to wildcard `_` or `_f`)
-unavailable-constructor.mo:7.17-7.21: warning [M0194], unused identifier ctxt (delete or rename to wildcard `_` or `_ctxt`)
+unavailable-constructor.mo:5.17-5.21: warning [M0194], unused identifier ctxt (delete or rename to wildcard `_` or `_ctxt`)

test/run-drun/ok/unsupported-more.comp-ref.ok

@@ -1,4 +1,3 @@
-unsupported-more.mo:2.1-5.2: type error [M0038], misplaced await
-unsupported-more.mo:2.1-5.2: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported-more.mo:8.1-8.25: type error [M0038], misplaced await
-unsupported-more.mo:8.1-8.25: type error [M0037], misplaced async expression; try enclosing in an async function
+unsupported-more.mo:8.1-8.25: type error [M0141], move these declarations into the body of the main actor or actor class
+unsupported-more.mo:2.1-5.2: 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/unsupported-more.comp.ok

@@ -1,4 +1,3 @@
-unsupported-more.mo:2.1-5.2: type error [M0038], misplaced await
-unsupported-more.mo:2.1-5.2: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported-more.mo:8.1-8.25: type error [M0038], misplaced await
-unsupported-more.mo:8.1-8.25: type error [M0037], misplaced async expression; try enclosing in an async function
+unsupported-more.mo:8.1-8.25: type error [M0141], move these declarations into the body of the main actor or actor class
+unsupported-more.mo:2.1-5.2: 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.)

test/run-drun/ok/unsupported.comp-ref.ok

@@ -1,24 +1,16 @@
-unsupported.mo:2.1-33.2: type error [M0038], misplaced await
-unsupported.mo:2.1-33.2: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:4.14-4.50: type error [M0126], a shared function cannot be private
+unsupported.mo:36.36-36.39: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:36.26-36.29: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:50.11-50.43: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:50.3-50.35: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
+unsupported.mo:54.11-54.50: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:54.3-54.42: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
+unsupported.mo:58.53-58.61: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:58.45-58.53: type error [M0038], misplaced await
-unsupported.mo:58.45-58.53: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:58.45-58.53: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
+unsupported.mo:62.47-62.55: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:62.39-62.47: type error [M0038], misplaced await
-unsupported.mo:62.39-62.47: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:62.39-62.47: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
+unsupported.mo:72.44-72.47: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:66.1-66.25: type error [M0038], misplaced await
-unsupported.mo:66.1-66.25: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:72.34-72.37: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:73.44-73.47: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version and flag -ref-system-api.)
-unsupported.mo:73.27-73.30: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:4.14-4.50: type error [M0126], a shared function cannot be private
   (This is a limitation of the current version and flag -ref-system-api.)

test/run-drun/ok/unsupported.comp.ok

@@ -1,24 +1,16 @@
-unsupported.mo:2.1-33.2: type error [M0038], misplaced await
-unsupported.mo:2.1-33.2: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:4.14-4.50: type error [M0126], a shared function cannot be private
+unsupported.mo:36.36-36.39: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version.)
-unsupported.mo:36.26-36.29: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:50.11-50.43: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
   (This is a limitation of the current version.)
-unsupported.mo:50.3-50.35: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
+unsupported.mo:54.11-54.50: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
   (This is a limitation of the current version.)
-unsupported.mo:54.3-54.42: type error [M0139], inner actor classes are not supported yet; any actor class must come last in your program
+unsupported.mo:58.53-58.61: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
   (This is a limitation of the current version.)
-unsupported.mo:58.45-58.53: type error [M0038], misplaced await
-unsupported.mo:58.45-58.53: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:58.45-58.53: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
+unsupported.mo:62.47-62.55: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
   (This is a limitation of the current version.)
-unsupported.mo:62.39-62.47: type error [M0038], misplaced await
-unsupported.mo:62.39-62.47: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:62.39-62.47: type error [M0069], non-toplevel actor; an actor can only be declared at the toplevel of a program
+unsupported.mo:72.44-72.47: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version.)
-unsupported.mo:66.1-66.25: type error [M0038], misplaced await
-unsupported.mo:66.1-66.25: type error [M0037], misplaced async expression; try enclosing in an async function
-unsupported.mo:72.34-72.37: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:73.44-73.47: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version.)
-unsupported.mo:73.27-73.30: type error [M0077], a shared function is only allowed as a public field of an actor
+unsupported.mo:4.14-4.50: type error [M0126], a shared function cannot be private
   (This is a limitation of the current version.)