rescript-lang · cristianoc · Jul 18, 2025 · Jul 17, 2025 · Jul 17, 2025 · Jul 17, 2025
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -19,6 +19,7 @@
 #### :nail_care: Polish
 
 - Add missing backtick and spaces to `Belt.Map.map` doc comment. https://github.com/rescript-lang/rescript/pull/7632
+- AST: store the attributes directly on function arguments. https://github.com/rescript-lang/rescript/pull/7660
 
 #### :house: Internal
 

diff --git a/compiler/frontend/ast_core_type.ml b/compiler/frontend/ast_core_type.ml
@@ -95,7 +95,7 @@ let from_labels ~loc arity labels : t =
   in
   let args =
     Ext_list.map2 labels tyvars (fun label tyvar ->
-        {Parsetree.lbl = Asttypes.Labelled label; typ = tyvar})
+        {Parsetree.attrs = []; lbl = Asttypes.Labelled label; typ = tyvar})
   in
   Typ.arrows ~loc args result_type
 
@@ -143,7 +143,8 @@ let mk_fn_type (new_arg_types_ty : param_type list) (result : t) : t =
     Ext_list.fold_right new_arg_types_ty result
       (fun {label; ty; attr; loc} acc ->
         Ast_helper.Typ.arrow ~loc ~attrs:attr ~arity:None
-          {lbl = label; typ = ty} acc)
+          {attrs = []; lbl = label; typ = ty}
+          acc)
   in
   match t.ptyp_desc with
   | Ptyp_arrow arr ->
@@ -156,12 +157,7 @@ let list_of_arrow (ty : t) : t * param_type list =
     match ty.ptyp_desc with
     | Ptyp_arrow {arg; ret; arity} when arity = None || acc = [] ->
       aux ret
-        (({
-            label = arg.lbl;
-            ty = arg.typ;
-            attr = ty.ptyp_attributes;
-            loc = ty.ptyp_loc;
-          }
+        (({label = arg.lbl; ty = arg.typ; attr = arg.attrs; loc = ty.ptyp_loc}
            : param_type)
         :: acc)
     | Ptyp_poly (_, ty) ->

diff --git a/compiler/frontend/ast_derive_abstract.ml b/compiler/frontend/ast_derive_abstract.ml
@@ -84,7 +84,7 @@ let handle_tdcl light (tdcl : Parsetree.type_declaration) :
         ( [],
           (if has_optional_field then
              Ast_helper.Typ.arrow ~loc ~arity:None
-               {lbl = Nolabel; typ = Ast_literal.type_unit ()}
+               {attrs = []; lbl = Nolabel; typ = Ast_literal.type_unit ()}
                core_type
            else core_type),
           [] )
@@ -116,19 +116,19 @@ let handle_tdcl light (tdcl : Parsetree.type_declaration) :
             if is_optional then
               let optional_type = Ast_core_type.lift_option_type pld_type in
               ( Ast_helper.Typ.arrow ~loc:pld_loc ~arity
-                  {lbl = Asttypes.Optional pld_name; typ = pld_type}
+                  {attrs = []; lbl = Asttypes.Optional pld_name; typ = pld_type}
                   maker,
                 Val.mk ~loc:pld_loc
                   (if light then pld_name
                    else {pld_name with txt = pld_name.txt ^ "Get"})
                   ~attrs:get_optional_attrs ~prim
                   (Ast_helper.Typ.arrow ~loc ~arity:(Some 1)
-                     {lbl = Nolabel; typ = core_type}
+                     {attrs = []; lbl = Nolabel; typ = core_type}
                      optional_type)
                 :: acc )
             else
               ( Ast_helper.Typ.arrow ~loc:pld_loc ~arity
-                  {lbl = Asttypes.Labelled pld_name; typ = pld_type}
+                  {attrs = []; lbl = Asttypes.Labelled pld_name; typ = pld_type}
                   maker,
                 Val.mk ~loc:pld_loc
                   (if light then pld_name
@@ -140,7 +140,7 @@ let handle_tdcl light (tdcl : Parsetree.type_declaration) :
                        [External_arg_spec.dummy] Return_identity
                        (Js_get {js_get_name = prim_as_name; js_get_scopes = []}))
                   (Ast_helper.Typ.arrow ~loc ~arity:(Some 1)
-                     {lbl = Nolabel; typ = core_type}
+                     {attrs = []; lbl = Nolabel; typ = core_type}
                      pld_type)
                 :: acc )
           in
@@ -149,9 +149,9 @@ let handle_tdcl light (tdcl : Parsetree.type_declaration) :
             if is_current_field_mutable then
               let setter_type =
                 Ast_helper.Typ.arrow ~arity:(Some 2)
-                  {lbl = Nolabel; typ = core_type}
+                  {attrs = []; lbl = Nolabel; typ = core_type}
                   (Ast_helper.Typ.arrow ~arity:None
-                     {lbl = Nolabel; typ = pld_type} (* setter *)
+                     {attrs = []; lbl = Nolabel; typ = pld_type} (* setter *)
                      (Ast_literal.type_unit ()))
               in
               Val.mk ~loc:pld_loc

diff --git a/compiler/frontend/ast_derive_js_mapper.ml b/compiler/frontend/ast_derive_js_mapper.ml
@@ -69,7 +69,9 @@ let erase_type_str =
   Str.primitive
     (Val.mk ~prim:["%identity"]
        {loc = noloc; txt = erase_type_lit}
-       (Ast_helper.Typ.arrow ~arity:(Some 1) {lbl = Nolabel; typ = any} any))
+       (Ast_helper.Typ.arrow ~arity:(Some 1)
+          {attrs = []; lbl = Nolabel; typ = any}
+          any))
 
 let unsafe_index = "_index"
 
@@ -79,8 +81,11 @@ let unsafe_index_get =
     (Val.mk ~prim:[""]
        {loc = noloc; txt = unsafe_index}
        ~attrs:[Ast_attributes.get_index]
-       (Ast_helper.Typ.arrow ~arity:None {lbl = Nolabel; typ = any}
-          (Ast_helper.Typ.arrow ~arity:None {lbl = Nolabel; typ = any} any)))
+       (Ast_helper.Typ.arrow ~arity:None
+          {attrs = []; lbl = Nolabel; typ = any}
+          (Ast_helper.Typ.arrow ~arity:None
+             {attrs = []; lbl = Nolabel; typ = any}
+             any)))
 
 let unsafe_index_get_exp = Exp.ident {loc = noloc; txt = Lident unsafe_index}
 
@@ -132,7 +137,7 @@ let app1 = Ast_compatible.app1
 let app2 = Ast_compatible.app2
 
 let ( ->~ ) a b =
-  Ast_helper.Typ.arrow ~arity:(Some 1) {lbl = Nolabel; typ = a} b
+  Ast_helper.Typ.arrow ~arity:(Some 1) {attrs = []; lbl = Nolabel; typ = a} b
 
 let raise_when_not_found_ident =
   Longident.Ldot (Lident Primitive_modules.util, "raiseWhenNotFound")
@@ -305,7 +310,7 @@ let init () =
               let to_js_type result =
                 Ast_comb.single_non_rec_val pat_to_js
                   (Ast_helper.Typ.arrow ~arity:(Some 1)
-                     {lbl = Nolabel; typ = core_type}
+                     {attrs = []; lbl = Nolabel; typ = core_type}
                      result)
               in
               let new_type, new_tdcl =

diff --git a/compiler/frontend/ast_derive_projector.ml b/compiler/frontend/ast_derive_projector.ml
@@ -137,7 +137,7 @@ let init () =
                 Ext_list.map label_declarations (fun {pld_name; pld_type} ->
                     Ast_comb.single_non_rec_val ?attrs:gentype_attrs pld_name
                       (Ast_helper.Typ.arrow ~arity:(Some 1)
-                         {lbl = Nolabel; typ = core_type}
+                         {attrs = []; lbl = Nolabel; typ = core_type}
                          pld_type
                          (*arity will alwys be 1 since these are single param functions*)))
               | Ptype_variant constructor_declarations ->
@@ -170,7 +170,8 @@ let init () =
                       {loc; txt = Ext_string.uncapitalize_ascii con_name}
                       (Ext_list.fold_right pcd_args annotate_type (fun x acc ->
                            Ast_helper.Typ.arrow ~arity:None
-                             {lbl = Nolabel; typ = x} acc)
+                             {attrs = []; lbl = Nolabel; typ = x}
+                             acc)
                       |> add_arity ~arity))
               | Ptype_open | Ptype_abstract ->
                 Ast_derive_util.not_applicable tdcl.ptype_loc deriving_name;

diff --git a/compiler/frontend/ast_exp_handle_external.ml b/compiler/frontend/ast_exp_handle_external.ml
@@ -43,7 +43,7 @@ let handle_external loc (x : string) : Parsetree.expression =
         Ast_external_mk.local_external_apply loc ~pval_prim:["#raw_expr"]
           ~pval_type:
             (Ast_helper.Typ.arrow ~arity:(Some 1)
-               {lbl = Nolabel; typ = Ast_helper.Typ.any ()}
+               {attrs = []; lbl = Nolabel; typ = Ast_helper.Typ.any ()}
                (Ast_helper.Typ.any ()))
           [str_exp];
     }
@@ -72,7 +72,7 @@ let handle_debugger loc (payload : Ast_payload.t) =
     Ast_external_mk.local_external_apply loc ~pval_prim:["%debugger"]
       ~pval_type:
         (Ast_helper.Typ.arrow ~arity:(Some 1)
-           {lbl = Nolabel; typ = Ast_helper.Typ.any ()}
+           {attrs = []; lbl = Nolabel; typ = Ast_helper.Typ.any ()}
            (Ast_literal.type_unit ()))
       [Ast_literal.val_unit ~loc ()]
   | _ ->
@@ -99,7 +99,7 @@ let handle_raw ~kind loc payload =
         Ast_external_mk.local_external_apply loc ~pval_prim:["#raw_expr"]
           ~pval_type:
             (Ast_helper.Typ.arrow ~arity:(Some 1)
-               {lbl = Nolabel; typ = Ast_helper.Typ.any ()}
+               {attrs = []; lbl = Nolabel; typ = Ast_helper.Typ.any ()}
                (Ast_helper.Typ.any ()))
           [exp];
       pexp_attributes =
@@ -128,11 +128,16 @@ let handle_ffi ~loc ~payload =
       let unit = Ast_literal.type_unit ~loc () in
       let rec arrow ~arity =
         if arity = 0 then
-          Ast_helper.Typ.arrow ~arity:None ~loc {lbl = Nolabel; typ = unit} any
+          Ast_helper.Typ.arrow ~arity:None ~loc
+            {attrs = []; lbl = Nolabel; typ = unit}
+            any
         else if arity = 1 then
-          Ast_helper.Typ.arrow ~arity:None ~loc {lbl = Nolabel; typ = any} any
+          Ast_helper.Typ.arrow ~arity:None ~loc
+            {attrs = []; lbl = Nolabel; typ = any}
+            any
         else
-          Ast_helper.Typ.arrow ~loc ~arity:None {lbl = Nolabel; typ = any}
+          Ast_helper.Typ.arrow ~loc ~arity:None
+            {attrs = []; lbl = Nolabel; typ = any}
             (arrow ~arity:(arity - 1))
       in
       match !is_function with
@@ -152,7 +157,7 @@ let handle_ffi ~loc ~payload =
           Ast_external_mk.local_external_apply loc ~pval_prim:["#raw_expr"]
             ~pval_type:
               (Ast_helper.Typ.arrow ~arity:(Some 1)
-                 {lbl = Nolabel; typ = Ast_helper.Typ.any ()}
+                 {attrs = []; lbl = Nolabel; typ = Ast_helper.Typ.any ()}
                  (Ast_helper.Typ.any ()))
             [exp];
         pexp_attributes =
@@ -171,7 +176,7 @@ let handle_raw_structure loc payload =
           Ast_external_mk.local_external_apply loc ~pval_prim:["#raw_stmt"]
             ~pval_type:
               (Ast_helper.Typ.arrow ~arity:(Some 1)
-                 {lbl = Nolabel; typ = Ast_helper.Typ.any ()}
+                 {attrs = []; lbl = Nolabel; typ = Ast_helper.Typ.any ()}
                  (Ast_helper.Typ.any ()))
             [exp];
       }

diff --git a/compiler/frontend/ast_typ_uncurry.ml b/compiler/frontend/ast_typ_uncurry.ml
@@ -32,7 +32,9 @@ let to_method_callback_type loc (mapper : Bs_ast_mapper.mapper)
   let first_arg = mapper.typ mapper first_arg in
   let typ = mapper.typ mapper typ in
   let meth_type =
-    Ast_helper.Typ.arrow ~loc ~arity:None {lbl = label; typ = first_arg} typ
+    Ast_helper.Typ.arrow ~loc ~arity:None
+      {attrs = []; lbl = label; typ = first_arg}
+      typ
   in
   let arity = Ast_core_type.get_uncurry_arity meth_type in
   match arity with
@@ -58,7 +60,9 @@ let to_uncurry_type loc (mapper : Bs_ast_mapper.mapper)
   let typ = mapper.typ mapper typ in
 
   let fn_type =
-    Ast_helper.Typ.arrow ~loc ~arity:None {lbl = label; typ = first_arg} typ
+    Ast_helper.Typ.arrow ~loc ~arity:None
+      {attrs = []; lbl = label; typ = first_arg}
+      typ
   in
   let arity = Ast_core_type.get_uncurry_arity fn_type in
   let fn_type =

diff --git a/compiler/ml/ast_mapper_from0.ml b/compiler/ml/ast_mapper_from0.ml
@@ -99,8 +99,8 @@ module T = struct
     | Ptyp_var s -> Typ.var ~loc ~attrs s
     | Ptyp_arrow (lbl, t1, t2) ->
       let lbl = Asttypes.to_arg_label lbl in
-      Typ.arrow ~loc ~attrs ~arity:None
-        {lbl; typ = sub.typ sub t1}
+      Typ.arrow ~loc ~arity:None
+        {attrs; lbl; typ = sub.typ sub t1}
         (sub.typ sub t2)
     | Ptyp_tuple tyl -> Typ.tuple ~loc ~attrs (List.map (sub.typ sub) tyl)
     | Ptyp_constr (lid, tl) -> (

diff --git a/compiler/ml/parsetree.ml b/compiler/ml/parsetree.ml
@@ -73,7 +73,7 @@ and core_type = {
   ptyp_attributes: attributes; (* ... [@id1] [@id2] *)
 }
 
-and arg = {lbl: arg_label; typ: core_type}
+and arg = {attrs: attributes; lbl: arg_label; typ: core_type}
 
 and core_type_desc =
   | Ptyp_any (*  _ *)

diff --git a/compiler/ml/pprintast.ml b/compiler/ml/pprintast.ml
@@ -285,11 +285,15 @@ let tyvar f str = pp f "'%s" str
 let tyvar_loc f str = pp f "'%s" str.txt
 let string_quot f x = pp f "`%s" x
 
-let rec type_with_label ctxt f (label, c) =
-  match label with
-  | Nolabel -> core_type1 ctxt f c (* otherwise parenthesize *)
-  | Labelled {txt = s} -> pp f "%s:%a" s (core_type1 ctxt) c
-  | Optional {txt = s} -> pp f "?%s:%a" s (core_type1 ctxt) c
+let rec type_with_label ctxt f arg =
+  match arg.lbl with
+  | Nolabel ->
+    pp f "%a%a" (core_type1 ctxt) arg.typ (attributes ctxt) arg.attrs
+    (* otherwise parenthesize *)
+  | Labelled {txt = s} ->
+    pp f "%s:%a%a" s (core_type1 ctxt) arg.typ (attributes ctxt) arg.attrs
+  | Optional {txt = s} ->
+    pp f "?%s:%a%a" s (core_type1 ctxt) arg.typ (attributes ctxt) arg.attrs
 
 and core_type ctxt f x =
   if x.ptyp_attributes <> [] then
@@ -300,7 +304,7 @@ and core_type ctxt f x =
     match x.ptyp_desc with
     | Ptyp_arrow {arg; ret; arity} ->
       pp f "@[<2>%a@;->@;%a%s@]" (* FIXME remove parens later *)
-        (type_with_label ctxt) (arg.lbl, arg.typ) (core_type ctxt) ret
+        (type_with_label ctxt) arg (core_type ctxt) ret
         (match arity with
         | None -> ""
         | Some n -> " (a:" ^ string_of_int n ^ ")")

diff --git a/compiler/syntax/src/jsx_v4.ml b/compiler/syntax/src/jsx_v4.ml
@@ -918,20 +918,16 @@ let transform_structure_item ~config item =
         |> Option.map Jsx_common.typ_vars_of_core_type
         |> Option.value ~default:[]
       in
-      let rec get_prop_types types
-          ({ptyp_loc; ptyp_desc; ptyp_attributes} as full_type) =
+      let rec get_prop_types types ({ptyp_loc; ptyp_desc} as full_type) =
         match ptyp_desc with
         | Ptyp_arrow {arg; ret = {ptyp_desc = Ptyp_arrow _} as typ2}
           when is_labelled arg.lbl || is_optional arg.lbl ->
-          get_prop_types
-            ((arg.lbl, ptyp_attributes, ptyp_loc, arg.typ) :: types)
-            typ2
+          get_prop_types ((arg.lbl, arg.attrs, ptyp_loc, arg.typ) :: types) typ2
         | Ptyp_arrow {arg = {lbl = Nolabel}; ret} -> get_prop_types types ret
         | Ptyp_arrow {arg; ret = return_value}
           when is_labelled arg.lbl || is_optional arg.lbl ->
           ( return_value,
-            (arg.lbl, ptyp_attributes, return_value.ptyp_loc, arg.typ) :: types
-          )
+            (arg.lbl, arg.attrs, return_value.ptyp_loc, arg.typ) :: types )
         | _ -> (full_type, types)
       in
       let inner_type, prop_types = get_prop_types [] pval_type in
@@ -1027,9 +1023,7 @@ let transform_signature_item ~config item =
         match ptyp_desc with
         | Ptyp_arrow {arg; ret = {ptyp_desc = Ptyp_arrow _} as rest}
           when is_optional arg.lbl || is_labelled arg.lbl ->
-          get_prop_types
-            ((arg.lbl, arg.typ.ptyp_attributes, ptyp_loc, arg.typ) :: types)
-            rest
+          get_prop_types ((arg.lbl, arg.attrs, ptyp_loc, arg.typ) :: types) rest
         | Ptyp_arrow
             {
               arg =
@@ -1045,8 +1039,7 @@ let transform_signature_item ~config item =
         | Ptyp_arrow {arg; ret = return_value}
           when is_optional arg.lbl || is_labelled arg.lbl ->
           ( return_value,
-            (arg.lbl, arg.typ.ptyp_attributes, return_value.ptyp_loc, arg.typ)
-            :: types )
+            (arg.lbl, arg.attrs, return_value.ptyp_loc, arg.typ) :: types )
         | _ -> (full_type, types)
       in
       let inner_type, prop_types = get_prop_types [] pval_type in

diff --git a/compiler/syntax/src/res_core.ml b/compiler/syntax/src/res_core.ml
@@ -4039,7 +4039,8 @@ and parse_poly_type_expr ?current_type_name_path ?inline_types_context p =
         let typ = Ast_helper.Typ.var ~loc:var.loc var.txt in
         let return_type = parse_typ_expr ~alias:false p in
         let loc = mk_loc typ.Parsetree.ptyp_loc.loc_start p.prev_end_pos in
-        Ast_helper.Typ.arrow ~loc ~arity:(Some 1) {lbl = Nolabel; typ}
+        Ast_helper.Typ.arrow ~loc ~arity:(Some 1)
+          {attrs = []; lbl = Nolabel; typ}
           return_type
       | _ -> Ast_helper.Typ.var ~loc:var.loc var.txt)
     | _ -> assert false)
@@ -4400,7 +4401,7 @@ and parse_es6_arrow_type ~attrs p =
     Parser.expect EqualGreater p;
     let return_type = parse_typ_expr ~alias:false p in
     let loc = mk_loc start_pos p.prev_end_pos in
-    Ast_helper.Typ.arrow ~loc ~attrs ~arity:None {lbl; typ} return_type
+    Ast_helper.Typ.arrow ~loc ~arity:None {attrs; lbl; typ} return_type
   | DocComment _ -> assert false
   | _ ->
     let parameters = parse_type_parameters p in
@@ -4429,7 +4430,7 @@ and parse_es6_arrow_type ~attrs p =
             | _ -> arity
           in
           let t_arg =
-            Ast_helper.Typ.arrow ~loc ~attrs ~arity:None {lbl = arg_lbl; typ} t
+            Ast_helper.Typ.arrow ~loc ~arity:None {attrs; lbl = arg_lbl; typ} t
           in
           if param_num = 1 then
             (param_num - 1, Ast_uncurried.uncurried_type ~arity t_arg, 1)
@@ -4493,7 +4494,9 @@ and parse_arrow_type_rest ~es6_arrow ~start_pos typ p =
     Parser.next p;
     let return_type = parse_typ_expr ~alias:false p in
     let loc = mk_loc start_pos p.prev_end_pos in
-    Ast_helper.Typ.arrow ~loc ~arity:(Some 1) {lbl = Nolabel; typ} return_type
+    Ast_helper.Typ.arrow ~loc ~arity:(Some 1)
+      {attrs = []; lbl = Nolabel; typ}
+      return_type
   | _ -> typ
 
 and parse_typ_expr_region p =
@@ -5151,7 +5154,8 @@ and parse_type_equation_or_constr_decl p =
         let return_type = parse_typ_expr ~alias:false p in
         let loc = mk_loc uident_start_pos p.prev_end_pos in
         let arrow_type =
-          Ast_helper.Typ.arrow ~loc ~arity:(Some 1) {lbl = Nolabel; typ}
+          Ast_helper.Typ.arrow ~loc ~arity:(Some 1)
+            {attrs = []; lbl = Nolabel; typ}
             return_type
         in
         let typ = parse_type_alias p arrow_type in