Safe promises

Introduce safe promises, based on #5707

- Add t-first Js.Promise2 with safe bindings
- Remove type check for nested promises
- Add example illustrating a typical example of nested promises, and how it goes away with Js.Promise2

Author: cristianoc

jscomp/ext/warnings.ml

@@ -84,7 +84,6 @@ type t =
   | Bs_integer_literal_overflow (* 107 *)
   | Bs_uninterpreted_delimiters of string (* 108 *)
   | Bs_toplevel_expression_unit (* 109 *)
-  | Bs_nested_promise of string (* 110 *)
 
 (* If you remove a warning, leave a hole in the numbering.  NEVER change
    the numbers of existing warnings.
@@ -150,7 +149,6 @@ let number = function
   | Bs_integer_literal_overflow -> 107
   | Bs_uninterpreted_delimiters _ -> 108
   | Bs_toplevel_expression_unit -> 109
-  | Bs_nested_promise _ -> 110
 
 let last_warning_number = 110
 
@@ -494,8 +492,6 @@ let message = function
   | Bs_uninterpreted_delimiters s -> "Uninterpreted delimiters " ^ s
   | Bs_toplevel_expression_unit ->
       "Toplevel expression is expected to have unit type."
-  | Bs_nested_promise s ->
-      "Expression uses nested promise type " ^ s ^ " which is unsafe."
 
 let sub_locs = function
   | Deprecated (_, def, use) ->

jscomp/ext/warnings.mli

@@ -77,7 +77,6 @@ type t =
   | Bs_integer_literal_overflow (* 107 *)
   | Bs_uninterpreted_delimiters of string (* 108 *)
   | Bs_toplevel_expression_unit (* 109 *)
-  | Bs_nested_promise of string (* 110 *)
 
 val parse_options : bool -> string -> unit
 

jscomp/main/builtin_cmi_datasets.ml

@@ -1865,45 +1865,10 @@ and type_expect ?in_function ?recarg env sexp ty_expected =
          type_expect_ ?in_function ?recarg env sexp ty_expected
       )
   in
-  checkTypeInvariant exp;
   Cmt_format.set_saved_types
   (Cmt_format.Partial_expression exp :: previous_saved_types);
   exp
 
-(* NOTE: the type invariant check should have no side effects and be efficient *)
-and checkTypeInvariant exp : unit =
-  let rec extractPromise t =
-    match t.desc with
-    | Tconstr
-        (Pdot (Pdot (Pident { name = "Js" }, "Promise", _), "t", _), [ t1 ], _)
-    | Tconstr (Pident { name = "promise" }, [ t1 ], _) ->
-      (* Improvement: check for type aliases, if it can be done efficiently *)
-        Some t1
-    | Tlink t1 | Tsubst t1 | Tpoly (t1, []) -> extractPromise t1
-    | _ -> None
-  in
-  (* Only traverse arguments of a type constructors and function types.
-     This should guarantee that the traversal finished quickly. *)
-  let rec findNestedPromise t =
-    match t.desc with
-    | Tlink t1 | Tsubst t1 | Tpoly (t1, []) -> findNestedPromise t1
-    | Tconstr (_, ts, _) -> (
-        match extractPromise t with
-        | Some t1 -> (
-            match extractPromise t1 with
-            | Some _t2 ->
-                let nestedType = Format.asprintf "%a" Printtyp.type_expr t in
-                Location.prerr_warning exp.exp_loc
-                  (Bs_nested_promise nestedType)
-            | None -> ts |> List.iter findNestedPromise)
-        | None -> ts |> List.iter findNestedPromise)
-    | Tarrow (_, t1, t2, _) ->
-        findNestedPromise t1;
-        findNestedPromise t2
-    | _ -> ()
-  in
-  findNestedPromise exp.exp_type
-
 and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
   let loc = sexp.pexp_loc in
   (* Record the expression type before unifying it with the expected type *)

jscomp/main/builtin_cmj_datasets.ml

@@ -249,6 +249,9 @@ module Re = Js_re
 module Promise = Js_promise
 (** Provide bindings to JS Promise *)
 
+module Promise2 = Js_promise2
+(** Provide bindings to JS Promise *)
+
 module Date = Js_date
 (** Provide bindings for JS Date *)
 

jscomp/ml/typecore.ml

@@ -0,0 +1,16 @@
+include Js_promise
+
+let then_ : 'a promise -> ('a -> 'b promise) -> 'b promise =
+  [%raw {|
+  function(p, cont) {
+    Promise.resolve(p).then(cont)
+  }
+  |}]
+
+let catch_ : 'a promise -> (error -> 'a promise) -> 'a promise =
+  [%raw
+    {|
+    function(p, cont) {
+      Promise.resolve(p).catch(cont)
+    }
+    |}]

jscomp/others/js.ml

@@ -47,6 +47,7 @@ o others/js_obj.cmi others/js_obj.cmj : cc others/js_obj.ml | others/belt_intern
 o others/js_option.cmj : cc_cmi others/js_option.ml | others/belt_internals.cmi others/js.cmi others/js_exn.cmj others/js_option.cmi $bsc
 o others/js_option.cmi : cc others/js_option.mli | others/belt_internals.cmi others/js.cmi $bsc
 o others/js_promise.cmi others/js_promise.cmj : cc others/js_promise.ml | others/belt_internals.cmi others/js.cmi $bsc
+o others/js_promise2.cmi others/js_promise2.cmj : cc others/js_promise2.ml | others/belt_internals.cmi others/js.cmi others/js_promise.cmj $bsc
 o others/js_re.cmi others/js_re.cmj : cc others/js_re.ml | others/belt_internals.cmi others/js.cmi others/js.cmj $bsc
 o others/js_result.cmj : cc_cmi others/js_result.ml | others/belt_internals.cmi others/js.cmi others/js_result.cmi $bsc
 o others/js_result.cmi : cc others/js_result.mli | others/belt_internals.cmi others/js.cmi $bsc
@@ -67,7 +68,7 @@ o others/jsx.cmi others/jsx.cmj : cc others/jsx.ml | others/belt_internals.cmi o
 o others/jsxDOM.cmi others/jsxDOM.cmj : cc others/jsxDOM.ml | others/belt_internals.cmi others/js.cmi others/jsx.cmj others/jsxDOMStyle.cmj others/jsxEvent.cmj $bsc
 o others/jsxDOMStyle.cmi others/jsxDOMStyle.cmj : cc others/jsxDOMStyle.ml | others/belt_internals.cmi others/js.cmi $bsc
 o others/jsxEvent.cmi others/jsxEvent.cmj : cc others/jsxEvent.ml | others/belt_internals.cmi others/js.cmi $bsc
-o js_pkg : phony others/js_OO.cmi others/js_OO.cmj others/js_array.cmi others/js_array.cmj others/js_array2.cmi others/js_array2.cmj others/js_bigint.cmi others/js_bigint.cmj others/js_cast.cmi others/js_cast.cmj others/js_console.cmi others/js_console.cmj others/js_date.cmi others/js_date.cmj others/js_dict.cmi others/js_dict.cmj others/js_exn.cmi others/js_exn.cmj others/js_float.cmi others/js_float.cmj others/js_global.cmi others/js_global.cmj others/js_int.cmi others/js_int.cmj others/js_json.cmi others/js_json.cmj others/js_list.cmi others/js_list.cmj others/js_map.cmi others/js_map.cmj others/js_mapperRt.cmi others/js_mapperRt.cmj others/js_math.cmi others/js_math.cmj others/js_null.cmi others/js_null.cmj others/js_null_undefined.cmi others/js_null_undefined.cmj others/js_obj.cmi others/js_obj.cmj others/js_option.cmi others/js_option.cmj others/js_promise.cmi others/js_promise.cmj others/js_re.cmi others/js_re.cmj others/js_result.cmi others/js_result.cmj others/js_set.cmi others/js_set.cmj others/js_string.cmi others/js_string.cmj others/js_string2.cmi others/js_string2.cmj others/js_typed_array.cmi others/js_typed_array.cmj others/js_typed_array2.cmi others/js_typed_array2.cmj others/js_types.cmi others/js_types.cmj others/js_undefined.cmi others/js_undefined.cmj others/js_vector.cmi others/js_vector.cmj others/js_weakmap.cmi others/js_weakmap.cmj others/js_weakset.cmi others/js_weakset.cmj others/jsx.cmi others/jsx.cmj others/jsxDOM.cmi others/jsxDOM.cmj others/jsxDOMStyle.cmi others/jsxDOMStyle.cmj others/jsxEvent.cmi others/jsxEvent.cmj
+o js_pkg : phony others/js_OO.cmi others/js_OO.cmj others/js_array.cmi others/js_array.cmj others/js_array2.cmi others/js_array2.cmj others/js_bigint.cmi others/js_bigint.cmj others/js_cast.cmi others/js_cast.cmj others/js_console.cmi others/js_console.cmj others/js_date.cmi others/js_date.cmj others/js_dict.cmi others/js_dict.cmj others/js_exn.cmi others/js_exn.cmj others/js_float.cmi others/js_float.cmj others/js_global.cmi others/js_global.cmj others/js_int.cmi others/js_int.cmj others/js_json.cmi others/js_json.cmj others/js_list.cmi others/js_list.cmj others/js_map.cmi others/js_map.cmj others/js_mapperRt.cmi others/js_mapperRt.cmj others/js_math.cmi others/js_math.cmj others/js_null.cmi others/js_null.cmj others/js_null_undefined.cmi others/js_null_undefined.cmj others/js_obj.cmi others/js_obj.cmj others/js_option.cmi others/js_option.cmj others/js_promise.cmi others/js_promise.cmj others/js_promise2.cmi others/js_promise2.cmj others/js_re.cmi others/js_re.cmj others/js_result.cmi others/js_result.cmj others/js_set.cmi others/js_set.cmj others/js_string.cmi others/js_string.cmj others/js_string2.cmi others/js_string2.cmj others/js_typed_array.cmi others/js_typed_array.cmj others/js_typed_array2.cmi others/js_typed_array2.cmj others/js_types.cmi others/js_types.cmj others/js_undefined.cmi others/js_undefined.cmj others/js_vector.cmi others/js_vector.cmj others/js_weakmap.cmi others/js_weakmap.cmj others/js_weakset.cmi others/js_weakset.cmj others/jsx.cmi others/jsx.cmj others/jsxDOM.cmi others/jsxDOM.cmj others/jsxDOMStyle.cmi others/jsxDOMStyle.cmj others/jsxEvent.cmi others/jsxEvent.cmj
 o others/belt_Array.cmj : cc_cmi others/belt_Array.ml | others/belt.cmi others/belt_Array.cmi others/belt_internals.cmi others/js.cmi others/js.cmj others/js_math.cmj $bsc js_pkg
 o others/belt_Array.cmi : cc others/belt_Array.mli | others/belt.cmi others/belt_internals.cmi others/js.cmi others/js.cmj $bsc js_pkg
 o others/belt_Float.cmj : cc_cmi others/belt_Float.ml | others/belt.cmi others/belt_Float.cmi others/belt_internals.cmi others/js.cmi $bsc js_pkg

jscomp/others/js_promise2.ml

@@ -258,6 +258,9 @@ module Re = Js_re
 module Promise = Js_promise
 (** Provide bindings to JS promise *)
 
+module Promise2 = Js_promise2
+(** Provide bindings to JS promise *)
+
 module Date = Js_date
 (** Provide bindings for JS Date *)
 

jscomp/others/release.ninja

@@ -0,0 +1,35 @@
+'use strict';
+
+var Js_promise2 = require("../../lib/js/js_promise2.js");
+
+async function nestedPromise(xxx) {
+  var xx = await xxx;
+  Js_promise2.then_(xx, (function (x) {
+          return Promise.resolve((console.log("Promise2.then_", x), undefined));
+        }));
+  Js_promise2.catch_(xx, (function (x) {
+          console.log("Promise2.catch_", x);
+          return Promise.resolve(0);
+        }));
+  var arg1 = function (x) {
+    return Promise.resolve((console.log("Promise.then_", x), undefined));
+  };
+  xx.then(arg1);
+}
+
+async function create(x) {
+  console.log("create", x);
+  return x;
+}
+
+var xx = create(10);
+
+var xxx = create(xx);
+
+nestedPromise(xxx);
+
+exports.nestedPromise = nestedPromise;
+exports.create = create;
+exports.xx = xx;
+exports.xxx = xxx;
+/* xx Not a pure module */

jscomp/runtime/js.ml

@@ -0,0 +1,23 @@
+/*** Problematic example of nested promises is safe with Js.Promise2 */
+
+let nestedPromise = async (xxx: promise<promise<int>>) => {
+  let xx = await xxx
+
+  let _ = xx->Js.Promise2.then_(x => Js.log2("Promise2.then_", x) |> Js.Promise.resolve)
+  let _ = xx->Js.Promise2.catch_(x => {
+    Js.log2("Promise2.catch_", x)
+    0 |> Js.Promise.resolve
+  })
+
+  // This crashes
+  let _ = Js.Promise.then_(x => Js.log2("Promise.then_", x) |> Js.Promise.resolve, xx)
+}
+
+let create = async (x) => {
+  Js.log2("create", x)
+  x
+}
+
+let xx = create(10)
+let xxx = create(xx)
+let _ = nestedPromise(xxx)