bugfix: repro and fix for issue-4297 (#4306)

repro and (ugly) fix for issue #4297:

Moc let's you compile a sequence of declarations as an implicit actor, which is used by some of our drun tests and was stumbled on by a user. Unfortunately, we failed to set up the initial environment corrrectly, so those declarations could do async/await  at top-level (i.e. in the body of the actor), which should be illegal and rejected (while not being rejected for interpreted code, whose top-level is allowed to async/await).

The hacky fix is to inspect the progs being compiled using `CompUnit.comp_unit_of_prog` and set up the initial capability appropriately. Even better would be to pass the capability down somehow, but this turns out to be trickier than expected.

To avoid clobbering the existing tests too much, we also make typing functions that check the current static capability return local_errors (not errors) on failure, to continue with typechecking and report any other static errors.

Added bonus: setting up the capabilities properly prevents us from doing top-level async/await in the prelude, which would otherwise wreak all sorts of havoc in compile.ml due to unexpected renaming of well-known prelude functions due to cps conversion.

src/mo_frontend/typing.ml

@@ -60,7 +60,7 @@ let env_of_scope msgs scope =
     objs = T.Env.empty;
     labs = T.Env.empty;
     rets = None;
-    async = C.initial_cap();
+    async = Async_cap.NullCap;
     in_actor = false;
     in_prog = true;
     context = [];
@@ -434,10 +434,14 @@ and check_AsyncCap env s at : T.typ * (T.con -> C.async_cap) =
    | C.CompositeCap c -> T.Con(c, []), fun c' -> C.CompositeAwaitCap c'
    | C.QueryCap c -> T.Con(c, []), fun _c' -> C.ErrorCap
    | C.ErrorCap ->
-      error env at "M0037" "misplaced %s; a query cannot contain an %s" s s
-   | C.NullCap -> error env at "M0037" "misplaced %s; try enclosing in an async function" s
+      local_error env at "M0037" "misplaced %s; a query cannot contain an %s" s s;
+      T.Con(C.bogus_cap,[]), fun c -> C.NullCap
+   | C.NullCap ->
+      local_error env at "M0037" "misplaced %s; try enclosing in an async function" s;
+      T.Con(C.bogus_cap,[]), fun c -> C.NullCap
    | C.CompositeAwaitCap _ ->
-      error env at "M0037" "misplaced %s; a composite query cannot contain an %s" s s
+      local_error env at "M0037" "misplaced %s; a composite query cannot contain an %s" s s;
+      T.Con(C.bogus_cap,[]), fun c -> C.NullCap
 
 and check_AwaitCap env s at =
    match env.async with
@@ -447,9 +451,12 @@ and check_AwaitCap env s at =
    | C.QueryCap _
    | C.CompositeCap _
      ->
-     error env at "M0038" "misplaced %s; try enclosing in an async expression" s
+      local_error env at "M0038" "misplaced %s; try enclosing in an async expression" s;
+      T.Con(C.bogus_cap,[])
    | C.ErrorCap
-   | C.NullCap -> error env at "M0038" "misplaced %s" s
+   | C.NullCap ->
+      local_error env at "M0038" "misplaced %s" s;
+      T.Con(C.bogus_cap,[])
 
 and check_ErrorCap env s at =
    match env.async with
@@ -459,8 +466,9 @@ and check_ErrorCap env s at =
    | C.AsyncCap _
    | C.QueryCap _
    | C.CompositeCap _ ->
-     error env at "M0039" "misplaced %s; try enclosing in an async expression or query function" s
-   | C.NullCap -> error env at "M0039" "misplaced %s" s
+     local_error env at "M0039" "misplaced %s; try enclosing in an async expression or query function" s
+   | C.NullCap ->
+     local_error env at "M0039" "misplaced %s" s
 
 and scope_of_env env =
   match env.async with
@@ -2735,12 +2743,13 @@ and infer_dec_valdecs env dec : Scope.t =
 
 (* Programs *)
 
-let infer_prog scope prog : (T.typ * Scope.t) Diag.result =
+let infer_prog scope async_cap prog : (T.typ * Scope.t) Diag.result =
   Diag.with_message_store
     (fun msgs ->
       recover_opt
         (fun prog ->
-          let env = env_of_scope msgs scope in
+          let env0 = env_of_scope msgs scope in
+          let env = { env0 with async = async_cap } in
           let res = infer_block env prog.it prog.at in
           res
         ) prog

src/mo_frontend/typing.mli

@@ -5,7 +5,7 @@ open Type
 open Scope
 
 val initial_scope : scope
-val infer_prog : scope -> Syntax.prog -> (typ * scope) Diag.result
+val infer_prog : scope -> Async_cap.async_cap -> Syntax.prog -> (typ * scope) Diag.result
 
 val check_lib : scope -> Syntax.lib -> scope Diag.result
 val check_actors : scope -> Syntax.prog list -> unit Diag.result

src/mo_types/async_cap.ml

@@ -12,4 +12,6 @@ type async_cap =
 
 let top_cap = Cons.fresh "$top-level" (T.Def([],T.Any))
 
+let bogus_cap = Cons.fresh "$bogus" (T.Def([],T.Non))
+
 let initial_cap () = AwaitCap top_cap

src/pipeline/pipeline.ml

@@ -167,10 +167,23 @@ let print_deps (file : string) : unit =
 
 (* Checking *)
 
-let infer_prog senv prog : (Type.typ * Scope.scope) Diag.result =
+let async_cap_of_prog prog =
+  let open Syntax in
+  let open Source in
+  match (CompUnit.comp_unit_of_prog false prog).it.body.it with
+  | ActorClassU _ -> Async_cap.NullCap
+  | ActorU _ -> Async_cap.initial_cap()
+  | ModuleU _ -> assert false
+  | ProgU _ ->
+     if !Flags.compiled then
+       Async_cap.NullCap
+     else
+       Async_cap.initial_cap()
+
+let infer_prog senv async_cap prog : (Type.typ * Scope.scope) Diag.result =
   let filename = prog.Source.note.Syntax.filename in
   phase "Checking" filename;
-  let r = Typing.infer_prog senv prog in
+  let r = Typing.infer_prog senv async_cap prog in
   if !Flags.trace && !Flags.verbose then begin
     match r with
     | Ok ((_, scope), _) ->
@@ -188,11 +201,12 @@ let infer_prog senv prog : (Type.typ * Scope.scope) Diag.result =
 let rec check_progs senv progs : Scope.scope Diag.result =
   match progs with
   | [] -> Diag.return senv
-  | p::ps ->
+  | prog::progs' ->
     let open Diag.Syntax in
-    let* _t, sscope = infer_prog senv p in
+    let async_cap = async_cap_of_prog prog in
+    let* _t, sscope = infer_prog senv async_cap prog in
     let senv' = Scope.adjoin senv sscope in
-    check_progs senv' ps
+    check_progs senv' progs'
 
 let check_lib senv lib : Scope.scope Diag.result =
   let filename = lib.Source.note.Syntax.filename in
@@ -221,7 +235,7 @@ let check_builtin what src senv0 : Syntax.prog * stat_env =
   match parse_with Lexer.mode_priv lexer parse what with
   | Error es -> builtin_error "parsing" what es
   | Ok (prog, _ws) ->
-    match infer_prog senv0 prog with
+    match infer_prog senv0 Async_cap.NullCap prog with
     | Error es -> builtin_error "checking" what es
     | Ok ((_t, sscope), _ws) ->
       let senv1 = Scope.adjoin senv0 sscope in
@@ -417,7 +431,7 @@ let load_decl parse_one senv : load_decl_result =
   let* parsed = parse_one in
   let* prog, libs = resolve_prog parsed in
   let* libs, senv' = chase_imports parse_file senv libs in
-  let* t, sscope = infer_prog senv' prog in
+  let* t, sscope = infer_prog senv' (Async_cap.(AwaitCap top_cap)) prog in
   let senv'' = Scope.adjoin senv' sscope in
   Diag.return (libs, prog, senv'', t, sscope)
 

test/check-error-codes.py

@@ -32,7 +32,6 @@
     "M0054", # cannot infer type of primitive expression. Could be internal
     "M0068", # mode-specific
     "M0084", # when would the return type be inferred?
-    "M0092", # async scopes
     "M0094", # hard to trigger (check_exp only applies with no type variables, but shared functions have type variables)
     "M0099", # hard to trigger (syntactic checks hit first)
     "M0100", # hard to trigger (syntactic checks hit first)

test/fail/ok/await-in-actor.tc.ok

@@ -1 +1,4 @@
 await-in-actor.mo:3.13-3.30: type error [M0038], misplaced await
+await-in-actor.mo:3.21-3.28: type error [M0037], misplaced async expression; try enclosing in an async function
+await-in-actor.mo:3.13-3.30: type error [M0038], misplaced await
+await-in-actor.mo:3.21-3.28: type error [M0037], misplaced async expression; try enclosing in an async function

test/fail/ok/queries.tc.ok

@@ -4,4 +4,10 @@ queries.mo:17.5-17.13: type error [M0188], send capability required, but not ava
 queries.mo:21.13-21.22: type error [M0188], send capability required, but not available
   (cannot call a `shared` function from a `query` function)
 queries.mo:22.5-22.20: type error [M0038], misplaced await
+queries.mo:22.11-22.20: type error [M0188], send capability required, but not available
+  (cannot call a `shared` function from a `query` function)
 queries.mo:26.5-26.14: type error [M0037], misplaced async expression; a query cannot contain an async expression
+queries.mo:26.5-26.14: type error [M0096], expression of type
+  async<$bogus> ()
+cannot produce expected type
+  ()

test/run-drun/issue-4297.mo

@@ -0,0 +1 @@
+await async {};

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

@@ -1,2 +1,11 @@
 aritybug.mo:13.41-15.2: 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.)
+aritybug.mo:17.25-22.2: type error [M0037], misplaced async expression; try enclosing in an async function
+aritybug.mo:17.25-22.2: type error [M0092], async at scope
+  $bogus
+cannot produce expected scope
+  $top-level
+  scope $top-level is the global scope
+aritybug.mo:18.14-18.27: type error [M0038], misplaced await
+aritybug.mo:18.20-18.27: type error [M0047], send capability required, but not available
+ (need an enclosing async expression or function body)

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

@@ -1,2 +1,11 @@
 aritybug.mo:13.41-15.2: type error [M0077], a shared function is only allowed as a public field of an actor
   (This is a limitation of the current version.)
+aritybug.mo:17.25-22.2: type error [M0037], misplaced async expression; try enclosing in an async function
+aritybug.mo:17.25-22.2: type error [M0092], async at scope
+  $bogus
+cannot produce expected scope
+  $top-level
+  scope $top-level is the global scope
+aritybug.mo:18.14-18.27: type error [M0038], misplaced await
+aritybug.mo:18.20-18.27: type error [M0047], send capability required, but not available
+ (need an enclosing async expression or function body)

test/run-drun/ok/inter-query.tc.ok

@@ -1 +1,3 @@
 inter-query.mo:3.48-3.59: type error [M0038], misplaced await
+inter-query.mo:3.54-3.59: type error [M0188], send capability required, but not available
+  (cannot call a `shared` function from a `query` function)

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

@@ -1,2 +1,2 @@
-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.)
+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

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

@@ -1,2 +1,2 @@
-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.)
+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

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

@@ -1,2 +1,2 @@
-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.)
+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

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

@@ -1,2 +1,2 @@
-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.)
+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

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

@@ -1,2 +1,2 @@
-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.)
+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

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

@@ -1,2 +1,2 @@
-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.)
+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

test/run-drun/ok/issue-4297.comp-ref.ok

@@ -0,0 +1,2 @@
+issue-4297.mo:1.1-1.15: type error [M0038], misplaced await
+issue-4297.mo:1.7-1.15: type error [M0037], misplaced async expression; try enclosing in an async function

test/run-drun/ok/issue-4297.comp-ref.ret.ok

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

test/run-drun/ok/issue-4297.comp.ok

@@ -0,0 +1,2 @@
+issue-4297.mo:1.1-1.15: type error [M0038], misplaced await
+issue-4297.mo:1.7-1.15: type error [M0037], misplaced async expression; try enclosing in an async function

test/run-drun/ok/issue-4297.comp.ret.ok

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

test/run-drun/ok/scope-example-func-implicit.tc.ok

@@ -1 +1,8 @@
 scope-example-func-implicit.mo:7.13-7.22: type error [M0037], misplaced async expression; try enclosing in an async function
+scope-example-func-implicit.mo:7.13-7.22: type error [M0092], async at scope
+  $bogus
+cannot produce expected scope
+  $f
+  scope $f is scope-example-func-implicit.mo:3.43-17.4
+scope-example-func-implicit.mo:3.43: info, start of scope $f mentioned in error at scope-example-func-implicit.mo:7.13-7.22
+scope-example-func-implicit.mo:17.3: info, end of scope $f mentioned in error at scope-example-func-implicit.mo:7.13-7.22

test/run-drun/ok/scope-example-func.tc.ok

@@ -1 +1,8 @@
 scope-example-func.mo:10.13-10.38: type error [M0037], misplaced async expression; try enclosing in an async function
+scope-example-func.mo:10.13-10.38: type error [M0092], async at scope
+  $bogus
+cannot produce expected scope
+  $anon-async-5.60
+  scope $anon-async-5.60 is scope-example-func.mo:5.60-21.4
+scope-example-func.mo:5.60: info, start of scope $anon-async-5.60 mentioned in error at scope-example-func.mo:10.13-10.38
+scope-example-func.mo:21.3: info, end of scope $anon-async-5.60 mentioned in error at scope-example-func.mo:10.13-10.38

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

@@ -1,2 +1,4 @@
-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.)
+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

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

@@ -1,2 +1,4 @@
-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.)
+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

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

@@ -1,3 +1,5 @@
+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
   (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
@@ -6,10 +8,16 @@ unsupported.mo:50.3-50.35: type error [M0139], inner actor classes are not suppo
   (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
   (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
   (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
   (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
   (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

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

@@ -1,3 +1,5 @@
+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
   (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
@@ -6,10 +8,16 @@ unsupported.mo:50.3-50.35: type error [M0139], inner actor classes are not suppo
   (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
   (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
   (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
   (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
   (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