Fix issue with async and locally abstract types

To fix the printer, the async internal representation via an attribute needs to be preserved on functions starting with a locally abstract type.
For this reason, annotations cannot be placed individually on the first locally abstract type, if that's how the function starts.

Fixes #5974

Author: cristianoc

CHANGELOG.md

@@ -56,6 +56,7 @@ These are only breaking changes for unformatted code.
 - Fix issue where uncurried functions were incorrectly converting the type of a prop given as a default value to curried https://github.com/rescript-lang/rescript-compiler/pull/5971
 - Fix issue with error messages for uncurried functions where expected and given type were swapped https://github.com/rescript-lang/rescript-compiler/pull/5973
 - Fix issue with nested async functions, where the inner function would be emitted without `async` https://github.com/rescript-lang/rescript-compiler/pull/5983
+- Fix issue with async context check, and printer, for async functions with locally abstract type https://github.com/rescript-lang/rescript-compiler/pull/5982
 
 #### :nail_care: Polish
 

jscomp/frontend/bs_builtin_ppx.ml

@@ -127,6 +127,11 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
       (* Treat @this (. x, y, z) => ... just like @this (x, y, z) => ... *)
       let fun_expr = Ast_uncurried.exprExtractUncurriedFun e in
       self.expr self fun_expr
+  | Pexp_newtype (s, body) ->
+    let async = Ast_attributes.has_async_payload e.pexp_attributes <> None in
+    let body = Ast_async.add_async_attribute ~async body in
+    let res = self.expr self body in
+    {e with pexp_desc = Pexp_newtype(s, res)}
   | Pexp_fun (label, _, pat, body) -> (
       let async = Ast_attributes.has_async_payload e.pexp_attributes <> None in
       match Ast_attributes.process_attributes_rev e.pexp_attributes with

res_syntax/src/res_parsetree_viewer.ml

@@ -182,7 +182,7 @@ let funExpr expr =
     | expr -> (uncurried, attrsBefore, List.rev acc, expr)
   in
   match expr with
-  | {pexp_desc = Pexp_fun _} ->
+  | {pexp_desc = Pexp_fun _ | Pexp_newtype _} ->
     collect ~uncurried:false ~nFun:0 expr.pexp_attributes []
       {expr with pexp_attributes = []}
   | _ when Ast_uncurried.exprIsUncurriedFun expr ->

res_syntax/tests/printer/expr/asyncAwait.res

@@ -120,3 +120,7 @@ let c3 = (. x) => @foo y => x+y
 
 type t1 = (. int) => string => bool
 type t2 = (. int, string) => bool
+
+let f = async (type a, ()) => {
+  await Js.Promise.resolve(())
+}

res_syntax/tests/printer/expr/expected/asyncAwait.res.txt

@@ -142,3 +142,7 @@ let c3 = (. x) => {@foo y => x + y}
 
 type t1 = (. int) => string => bool
 type t2 = (. int, string) => bool
+
+let f = async (type a, ()) => {
+  await Js.Promise.resolve()
+}

res_syntax/tests/printer/expr/expected/newtype.res.txt

@@ -1,19 +1,13 @@
 let f = (type t, xs: list<t>) => ()
-let f = (@attr type t, xs: list<t>) => ()
+let f = @attr (type t, xs: list<t>) => ()
 let f = (type t, xs: list<t>, type s, ys: list<s>) => ()
-let f = (@attr type t, xs: list<t>, @attr2 type s, ys: list<s>) => ()
+let f = @attr (type t, xs: list<t>, @attr2 type s, ys: list<s>) => ()
 let f = (type t u v, xs: list<(t, u, v)>) => ()
-let f = (@attr type t u v, xs: list<(t, u, v)>) => ()
+let f = @attr (type t u v, xs: list<(t, u, v)>) => ()
 let f = (type t u v, xs: list<(t, u, v)>, type s w z, ys: list<(s, w, z)>) => ()
-let f = (@attr type t u v, xs: list<(t, u, v)>, @attr2 type s w z, ys: list<(s, w, z)>) => ()
-let f = (
-  @attr type t,
-  @attr type s,
-  xs: list<(t, s)>,
-  @attr type u,
-  @attr type v w,
-  ys: list<(u, v, w)>,
-) => ()
+let f = @attr (type t u v, xs: list<(t, u, v)>, @attr2 type s w z, ys: list<(s, w, z)>) => ()
+let f = @attr
+(type t, @attr type s, xs: list<(t, s)>, @attr type u, @attr type v w, ys: list<(u, v, w)>) => ()
 
 let mk_formatting_gen:
   type a b c d e f. formatting_gen<a, b, c, d, e, f> => Parsetree.expression =