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
 
@@ -131,39 +131,22 @@ let get_curry_arity (ty : t) =
 
 let is_arity_one ty = get_curry_arity ty = 1
 
-type param_type = {
-  label: Asttypes.arg_label;
-  ty: Parsetree.core_type;
-  attr: Parsetree.attributes;
-  loc: loc;
-}
-
-let mk_fn_type (new_arg_types_ty : param_type list) (result : t) : t =
+let mk_fn_type ~loc (new_arg_types_ty : Parsetree.arg list) (result : t) : t =
   let 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)
+    Ext_list.fold_right new_arg_types_ty result (fun {lbl; typ; attrs} acc ->
+        Ast_helper.Typ.arrow ~loc ~attrs ~arity:None {attrs = []; lbl; typ} acc)
   in
   match t.ptyp_desc with
   | Ptyp_arrow arr ->
     let arity = List.length new_arg_types_ty in
     {t with ptyp_desc = Ptyp_arrow {arr with arity = Some arity}}
   | _ -> t
 
-let list_of_arrow (ty : t) : t * param_type list =
+let list_of_arrow (ty : t) : t * Parsetree.arg list =
   let rec aux (ty : t) acc =
     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;
-          }
-           : param_type)
-        :: acc)
+      aux ret (arg :: acc)
     | Ptyp_poly (_, ty) ->
       (* should not happen? *)
       Bs_syntaxerr.err ty.ptyp_loc Unhandled_poly_type
@@ -173,6 +156,6 @@ let list_of_arrow (ty : t) : t * param_type list =
 
 let add_last_obj (ty : t) (obj : t) =
   let result, params = list_of_arrow ty in
-  mk_fn_type
-    (params @ [{label = Nolabel; ty = obj; attr = []; loc = obj.ptyp_loc}])
+  mk_fn_type ~loc:obj.ptyp_loc
+    (params @ [{lbl = Nolabel; typ = obj; attrs = []}])
     result
diff --git a/compiler/frontend/ast_core_type.mli b/compiler/frontend/ast_core_type.mli
@@ -47,16 +47,9 @@ val get_uncurry_arity : t -> int option
    None -- means not a function
 *)
 
-type param_type = {
-  label: Asttypes.arg_label;
-  ty: t;
-  attr: Parsetree.attributes;
-  loc: Location.t;
-}
+val mk_fn_type : loc:Location.t -> Parsetree.arg list -> t -> t
 
-val mk_fn_type : param_type list -> t -> t
-
-val list_of_arrow : t -> t * param_type list
+val list_of_arrow : t -> t * Parsetree.arg list
 (** fails when Ptyp_poly *)
 
 val add_last_obj : t -> t -> t

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_external_process.ml b/compiler/frontend/ast_external_process.ml
@@ -408,8 +408,7 @@ type response = {
 }
 
 let process_obj (loc : Location.t) (st : external_desc) (prim_name : string)
-    (arg_types_ty : Ast_core_type.param_type list)
-    (result_type : Ast_core_type.t) :
+    (arg_types_ty : Parsetree.arg list) (result_type : Ast_core_type.t) :
     int * Parsetree.core_type * External_ffi_types.t =
   match st with
   | {
@@ -440,11 +439,10 @@ let process_obj (loc : Location.t) (st : external_desc) (prim_name : string)
       Ext_list.fold_right arg_types_ty ([], [], [])
         (fun
           param_type
-          (arg_labels, (arg_types : Ast_core_type.param_type list), result_types)
+          (arg_labels, (arg_types : Parsetree.arg list), result_types)
         ->
-          let arg_label = param_type.label in
-          let loc = param_type.loc in
-          let ty = param_type.ty in
+          let arg_label = param_type.lbl in
+          let ty = param_type.typ in
           let new_arg_label, new_arg_types, output_tys =
             match arg_label with
             | Nolabel -> (
@@ -459,7 +457,7 @@ let process_obj (loc : Location.t) (st : external_desc) (prim_name : string)
             | Labelled {txt = label} -> (
               let field_name =
                 match
-                  Ast_attributes.iter_process_bs_string_as param_type.attr
+                  Ast_attributes.iter_process_bs_string_as param_type.attrs
                 with
                 | Some alias -> alias
                 | None -> label
@@ -518,7 +516,7 @@ let process_obj (loc : Location.t) (st : external_desc) (prim_name : string)
             | Optional {txt = label} -> (
               let field_name =
                 match
-                  Ast_attributes.iter_process_bs_string_as param_type.attr
+                  Ast_attributes.iter_process_bs_string_as param_type.attrs
                 with
                 | Some alias -> alias
                 | None -> label
@@ -594,7 +592,7 @@ let process_obj (loc : Location.t) (st : external_desc) (prim_name : string)
     in
 
     ( List.length new_arg_types_ty,
-      Ast_core_type.mk_fn_type new_arg_types_ty result,
+      Ast_core_type.mk_fn_type ~loc new_arg_types_ty result,
       External_ffi_types.ffi_obj_create arg_kinds )
   | _ -> Location.raise_errorf ~loc "Attribute found that conflicts with %@obj"
 
@@ -942,11 +940,10 @@ let handle_attributes (loc : Bs_loc.t) (type_annotation : Parsetree.core_type)
     let splice = external_desc.splice in
     let arg_type_specs, new_arg_types_ty, arg_type_specs_length =
       Ext_list.fold_right arg_types_ty
-        (([], [], 0)
-          : External_arg_spec.params * Ast_core_type.param_type list * int)
+        (([], [], 0) : External_arg_spec.params * Parsetree.arg list * int)
         (fun param_type (arg_type_specs, arg_types, i) ->
-          let arg_label = param_type.label in
-          let ty = param_type.ty in
+          let arg_label = param_type.lbl in
+          let ty = param_type.typ in
           (if i = 0 && splice then
              match arg_label with
              | Optional _ ->
@@ -1008,7 +1005,7 @@ let handle_attributes (loc : Bs_loc.t) (type_annotation : Parsetree.core_type)
     let return_wrapper =
       check_return_wrapper loc external_desc.return_wrapper result_type
     in
-    let fn_type = Ast_core_type.mk_fn_type new_arg_types_ty result_type in
+    let fn_type = Ast_core_type.mk_fn_type ~loc new_arg_types_ty result_type in
     ( build_uncurried_type ~arity:(List.length new_arg_types_ty) fn_type,
       External_ffi_types.ffi_bs arg_type_specs return_wrapper ffi,
       unused_attrs,

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 (*  _ *)