Fix issue with generating async functions inside loops.

Fixes #6444

Author: cristianoc

jscomp/core/js_dump.ml

@@ -421,12 +421,13 @@ and pp_function ~return_unit ~async ~is_method cxt (f : P.t) ~fn_state
             | No_name _ -> ()
             | Name_non_top name | Name_top name ->
                 ignore (pp_var_assign inner_cxt f name : cxt));
+            if async then P.string f L.await;
             P.string f L.lparen;
             P.string f (L.function_async ~async);
             pp_paren_params inner_cxt f lexical;
             P.brace_vgroup f 0 (fun _ ->
                 return_sp f;
-                P.string f L.function_;
+                P.string f (L.function_async ~async);
                 P.space f;
                 (match fn_state with
                 | Is_return | No_name _ -> ()

jscomp/core/js_dump_lit.ml

@@ -22,6 +22,9 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)
 
+
+let await = "await"
+
 let function_ = "function"
 
 let function_async ~async = if async then "async function" else "function"

jscomp/test/async_inside_loop.js

@@ -0,0 +1,12 @@
+let topLevelAsyncFunction = async () => {
+  for innerScopeVal in 0 to 3 {
+    let asyncClosureAccessingScopedVal = async () => {
+      Js.log2("Accessing scoped var inside loop", innerScopeVal)
+      await Js.Promise.resolve()
+    }
+
+    await asyncClosureAccessingScopedVal()
+  }
+}
+
+let _ = topLevelAsyncFunction()