Fix uncurried arity for primitives.

CHANGELOG.md

@@ -20,7 +20,7 @@
 - Allow free vars in types for type coercion `e :> t`. https://github.com/rescript-lang/rescript-compiler/pull/6828
 - Allow `private` in with constraints. https://github.com/rescript-lang/rescript-compiler/pull/6843
 - Add regex literals as syntax sugar for `@bs.re`. https://github.com/rescript-lang/rescript-compiler/pull/6776
-- Improved mechanism to determine arity of externals, which is consistent however the type is written. https://github.com/rescript-lang/rescript-compiler/pull/6874 https://github.com/rescript-lang/rescript-compiler/pull/6881
+- Improved mechanism to determine arity of externals, which is consistent however the type is written. https://github.com/rescript-lang/rescript-compiler/pull/6874 https://github.com/rescript-lang/rescript-compiler/pull/6881 https://github.com/rescript-lang/rescript-compiler/pull/6883
 
 #### :boom: Breaking Change
 

jscomp/ml/typedecl.ml

@@ -1719,7 +1719,9 @@ let rec arity_from_arrow_type env core_type ty =
 let parse_arity env core_type ty =
   match Ast_uncurried.uncurried_type_get_arity_opt ~env ty with
   | Some arity ->
-    let from_constructor = Ast_uncurried.uncurried_type_get_arity_opt ~env:Env.empty ty = None in
+    let from_constructor = match ty.desc with
+    | Tconstr (_, _, _) -> not (Ast_uncurried_utils.type_is_uncurried_fun ty)
+    | _ -> false in
     (arity, from_constructor)
   | None -> (arity_from_arrow_type env core_type ty, false)