Object representation cleanup: typed field mutability and structural access

AGENTS.md

@@ -34,7 +34,9 @@ The Makefile’s targets build on each other in this order:
 
 - **We are NOT bound by OCaml compatibility** - The ReScript compiler originated as a fork of the OCaml compiler, but we maintain our own AST and can make breaking changes. Focus on what's best for ReScript's JavaScript compilation target.
 
-- **Never modify `parsetree0.ml`** - Existing PPX (parser extensions) rely on this frozen v0 version. When changing `parsetree.ml`, always update the mapping modules `ast_mapper_from0.ml` and `ast_mapper_to0.ml` to maintain PPX compatibility while allowing the main parsetree to evolve
+- **Never modify `parsetree0.ml`** - Existing PPX (parser extensions) rely on this frozen v0 version. When changing `parsetree.ml`, always update the mapping modules `ast_mapper_from0.ml` and `ast_mapper_to0.ml` to maintain PPX compatibility while allowing the main parsetree to evolve. **Test the bridge with the existing infra** — do not build new harnesses for this:
+  - Add a source fixture exercising the new syntax to `tests/syntax_tests/data/ast-mapping/`. Every file there is run through `res_parser -test-ast-conversion` (which round-trips the parsetree through the frozen v0 AST before printing) as part of `make test-syntax`; the printed output must match the snapshot in its `expected/` directory.
+  - For exact-identity invariants (locations, attributes) or the v0 wire shape itself, add cases to `tests/ounit_tests/ounit_ast_mapper0_tests.ml`, which tests `ast_mapper_to0`/`ast_mapper_from0` directly.
 
 - **Missing test coverage** - Always add tests for syntax, lambda, and end-to-end behavior
 

CHANGELOG.md

@@ -18,6 +18,8 @@
 - Remove the deprecated `Js` namespace and its runtime modules. https://github.com/rescript-lang/rescript/pull/8531
 - Move Belt into the separately installed `@rescript/belt` package. Projects using Belt must install the package and list it in their `rescript.json` dependencies. https://github.com/rescript-lang/rescript/pull/8554
 - Correct the structured function details produced by `rescript-tools doc` and exposed by `RescriptTools.Docgen`: parameters now retain labels and optionality, nested functions, tuples, variables, and generic arguments retain their type structure, return types are identified correctly, and non-function values no longer receive fake function details. This changes the published docgen detail schema. https://github.com/rescript-lang/rescript/pull/8576
+- Make object-field mutability part of the type. A property has one type for reading and writing. Assignment requires `@set`, except on an inferred open row, where assignment makes the field settable. Private rows are not inferred open rows, so a field in `type t = private {.."x": int}` is writable only when annotated with `@set`. Coercions never grant or widen write capability. Previously, getter and setter types were tracked independently, allowing a property to be written at a different type than it was read and allowing writes through a value coerced to a type without `@set`. https://github.com/rescript-lang/rescript/pull/8597
+- Remove the undocumented object-field attribute forms `@get` (bare or with a `null`/`undefined`/`nullable` payload) and `@set({no_get: ...})` on object types. Only bare `@set` marks a field settable; nullable getter types are written directly (`null<t>`, `undefined<t>`, `nullable<t>`). https://github.com/rescript-lang/rescript/pull/8597
 
 #### :eyeglasses: Spec Compliance
 
@@ -30,6 +32,7 @@
 
 #### :bug: Bug fix
 
+- Object typing errors now describe fields directly: assigning to a field without `@set` reports that the field is not settable and suggests the annotation, and missing-property errors name the field instead of a phantom `"x#="` member. https://github.com/rescript-lang/rescript/pull/8597
 - Fix signature inclusion rejecting equivalent object externals after type-alias expansion. https://github.com/rescript-lang/rescript/pull/8581
 - Fix externals whose result type is an alias of `unit` so they use the same unit-return behavior as externals declared to return `unit`. https://github.com/rescript-lang/rescript/pull/8581
 - Fix dynamic imports of external bindings that require FFI argument or result conversions, including `@variadic`, `@unwrap`, polymorphic variant encodings, `@as` phantom arguments, optional labeled arguments, and `@return` wrappers. The imported value now applies the same conversions as a direct external call. https://github.com/rescript-lang/rescript/pull/8582
@@ -57,6 +60,7 @@
 
 #### :house: Internal
 
+- Rework the object-type representation end to end: object rows are plain field chains carrying a per-field mutability state (no phantom setter members), object literals are typed directly and property access and assignment are first-class AST and Lambda nodes shared between the Lambda and JS pipelines, and dead class-system remnants (the field-presence lattice, the class-abbreviation memo on object types, method-send typing) are removed. https://github.com/rescript-lang/rescript/pull/8597
 - Upgrade the development toolchain and primary CI builds to OCaml 5.5 while retaining OCaml 5.0 as the minimum supported version. https://github.com/rescript-lang/rescript/pull/8589
 - Upgrade the vendored Flow parser from 0.267.0 to 0.320.0, the final release of the OCaml implementation. https://github.com/rescript-lang/rescript/pull/8588
 - Vendor the Flow parser 0.267.0 sources used by the compiler, removing the external `flow_parser` dependency and establishing a maintained baseline for future OCaml upgrades. https://github.com/rescript-lang/rescript/pull/8587

analysis/reanalyze/src/arnold.ml

@@ -1003,9 +1003,16 @@ module Compile = struct
     | Texp_for_await_of (_id, _pat, e1, e2) ->
       let open Command in
       expression ~ctx e1 +++ expression ~ctx e2
-    | Texp_send _ ->
-      not_implemented "Texp_send";
-      assert false
+    | Texp_object_literal fields ->
+      (* Fields are emitted and evaluated in source order *)
+      fields
+      |> List.map (fun (_name, e) -> e |> expression ~ctx)
+      |> Command.sequence
+    | Texp_object_get (e, _) -> e |> expression ~ctx
+    | Texp_object_set (e1, _, e2) ->
+      (* Receiver first, then the assigned value *)
+      let open Command in
+      expression ~ctx e1 +++ expression ~ctx e2
     | Texp_letmodule _ ->
       not_implemented "Texp_letmodule";
       assert false

analysis/reanalyze/src/side_effects.ml

@@ -65,7 +65,10 @@ let rec expr_no_side_effects (expr : Typedtree.expression) =
     e1 |> expr_no_side_effects && e2 |> expr_no_side_effects
     && e3 |> expr_no_side_effects
   | Texp_for_of _ | Texp_for_await_of _ -> false
-  | Texp_send _ -> false
+  | Texp_object_literal fields ->
+    fields |> List.for_all (fun (_name, e) -> e |> expr_no_side_effects)
+  | Texp_object_get _ -> false
+  | Texp_object_set _ -> false
   | Texp_letexception (_ec, e) -> e |> expr_no_side_effects
   | Texp_pack _ -> false
   | Texp_extension_constructor _ when true -> true

analysis/src/completion_front_end.ml

@@ -254,7 +254,7 @@ let rec expr_to_context_path_inner ~(in_jsx_context : bool)
            expr_loc = e1.pexp_loc;
            in_jsx = in_jsx_context;
          })
-  | Pexp_send (e1, {txt}) -> (
+  | Pexp_object_get (e1, {txt}) -> (
     match expr_to_context_path ~in_jsx_context e1 with
     | None -> None
     | Some contex_path -> Some (CPObj (contex_path, txt)))
@@ -1230,8 +1230,8 @@ let completion_with_parser1 ~debug ~offset ~pos_cursor ~kind_file
       if expr.pexp_loc |> Loc.has_pos ~pos:pos_no_white && !result = None then (
         set_found ();
         match expr.pexp_desc with
-        | Pexp_extension ({txt = "obj"}, PStr [str_item]) ->
-          Ast_iterator.default_iterator.structure_item iterator str_item
+        | Pexp_object_literal fields ->
+          List.iter (fun (_, e) -> iterator.expr iterator e) fields
         | Pexp_extension ({txt}, _) -> set_result (CextensionNode txt)
         | Pexp_constant _ -> set_result Cnone
         | Pexp_ident lid ->
@@ -1580,7 +1580,8 @@ let completion_with_parser1 ~debug ~offset ~pos_cursor ~kind_file
               |> iterate_fn_arguments ~is_pipe:false ~args ~iterator;
               reset_current_ctx_path old_ctx_path)
           | Some arg_completable -> set_result arg_completable)
-        | Pexp_send (lhs, {txt; loc}) -> (
+        | (Pexp_object_get (lhs, {txt; loc}) as object_access)
+        | (Pexp_object_set (lhs, {txt; loc}, _) as object_access) -> (
           (* e["txt"]
              If the string for txt is not closed, it could go over several lines.
              Only take the first like to represent the label *)
@@ -1596,7 +1597,12 @@ let completion_with_parser1 ~debug ~offset ~pos_cursor ~kind_file
             ((l, c + 1), (l, c + 1 + String.length label))
           in
           if debug then
-            Printf.printf "Pexp_send %s%s e:%s\n" label
+            Printf.printf "%s %s%s e:%s\n"
+              (match object_access with
+              | Pexp_object_get _ -> "Pexp_object_get"
+              | Pexp_object_set _ -> "Pexp_object_set"
+              | _ -> assert false)
+              label
               (Range.to_string label_range)
               (Loc.to_string lhs.pexp_loc);
           if

analysis/src/hint.ml

@@ -62,8 +62,8 @@ let inlay ~source ~kind_file ~pos ~max_length ~full ~state ~debug =
          pexp_desc =
            ( Pexp_constant _ | Pexp_tuple _ | Pexp_record _ | Pexp_variant _
            | Pexp_apply _ | Pexp_match _ | Pexp_construct _ | Pexp_ifthenelse _
-           | Pexp_array _ | Pexp_ident _ | Pexp_try _ | Pexp_send _
-           | Pexp_field _ | Pexp_open _ | Pexp_fun _ );
+           | Pexp_array _ | Pexp_ident _ | Pexp_try _ | Pexp_object_get _
+           | Pexp_object_set _ | Pexp_field _ | Pexp_open _ | Pexp_fun _ );
        };
     } ->
       push vb.pvb_pat.ppat_loc Type

analysis/src/references.ml

@@ -78,21 +78,6 @@ let get_loc_item ~full ~pos ~debug =
        heuristic for: [Props, x], give loc of `x`";
     if debug then Printf.printf "n1:%s n2:%s\n" (name_of li1) (name_of li2);
     Some li2
-  | [
-   ({loc_type = Typed (_, _, LocalReference _)} as li1);
-   ({
-      loc_type = Typed (_, _, GlobalReference ("Js_OO", ["unsafe_downgrade"], _));
-    } as li2);
-   li3;
-  ]
-  (* For older compiler 9.0 or earlier *)
-    when li1.loc = li2.loc && li2.loc = li3.loc ->
-    (* Not currently testable on 9.1.4 *)
-    log 6
-      "heuristic for JSX and compiler combined:\n\
-       ~x becomes Js_OO.unsafe_downgrade(Props)#x\n\
-       heuristic for: [Props, unsafe_downgrade, x], give loc of `x`";
-    Some li3
   | [
    ({loc_type = Typed (_, _, LocalReference (_, Value))} as li1);
    ({loc_type = Typed (_, _, Definition (_, Value))} as li2);

analysis/src/semantic_tokens.ml

@@ -358,6 +358,15 @@ let command ~debug ~emitter ~source ~kind_file =
         Printf.printf "Binary operator %s %s\n" op (Loc.to_string loc);
       emitter |> emit_from_loc ~loc ~type_:Operator;
       Ast_iterator.default_iterator.expr iterator e
+    | Pexp_object_literal fields ->
+      fields
+      |> List.iter (fun ((s : string Asttypes.loc), _) ->
+          if not (Utils.is_first_char_uppercase s.txt) then
+            emitter
+            |> emit_record_label
+                 ~label:{Asttypes.txt = Longident.Lident s.txt; loc = s.loc}
+                 ~debug);
+      Ast_iterator.default_iterator.expr iterator e
     | Pexp_record (cases, _) ->
       Ext_list.filter_map cases (fun {lid} ->
           match lid.txt with

analysis/src/type_utils.ml

@@ -34,8 +34,8 @@ let rec has_tvar (ty : Types.type_expr) : bool =
     List.exists (fun ({typ} : Types.arg) -> has_tvar typ) params || has_tvar ret
   | Ttuple tyl -> List.exists has_tvar tyl
   | Tconstr (_, tyl, _) -> List.exists has_tvar tyl
-  | Tobject (ty, _) -> has_tvar ty
-  | Tfield (_, _, ty1, ty2) -> has_tvar ty1 || has_tvar ty2
+  | Tobject ty -> has_tvar ty
+  | Tfield {typ = ty1; rest = ty2} -> has_tvar ty1 || has_tvar ty2
   | Tnil -> false
   | Tlink ty -> has_tvar ty
   | Tsubst ty -> has_tvar ty
@@ -156,8 +156,9 @@ let instantiate_type ~type_params ~type_args (t : Types.type_expr) =
                 loop ret );
         }
       | Ttuple tl -> {t with desc = Ttuple (tl |> List.map loop)}
-      | Tobject (t, r) -> {t with desc = Tobject (loop t, r)}
-      | Tfield (n, k, t1, t2) -> {t with desc = Tfield (n, k, loop t1, loop t2)}
+      | Tobject t -> {t with desc = Tobject (loop t)}
+      | Tfield f ->
+        {t with desc = Tfield {f with typ = loop f.typ; rest = loop f.rest}}
       | Tpoly (t, []) -> loop t
       | Tpoly (t, tl) -> {t with desc = Tpoly (loop t, tl |> List.map loop)}
       | Tpackage (p, l, tl) ->
@@ -217,8 +218,9 @@ let instantiate_type2 ?(type_arg_context : type_arg_context option)
                 loop ret );
         }
       | Ttuple tl -> {t with desc = Ttuple (tl |> List.map loop)}
-      | Tobject (t, r) -> {t with desc = Tobject (loop t, r)}
-      | Tfield (n, k, t1, t2) -> {t with desc = Tfield (n, k, loop t1, loop t2)}
+      | Tobject t -> {t with desc = Tobject (loop t)}
+      | Tfield f ->
+        {t with desc = Tfield {f with typ = loop f.typ; rest = loop f.rest}}
       | Tpoly (t, []) -> loop t
       | Tpoly (t, tl) -> {t with desc = Tpoly (loop t, tl |> List.map loop)}
       | Tpackage (p, l, tl) ->
@@ -270,7 +272,7 @@ let rec extract_object_type ~state ~env ~package (t : Types.type_expr) =
   match t.desc with
   | Tlink t1 | Tsubst t1 | Tpoly (t1, []) ->
     extract_object_type ~state ~env ~package t1
-  | Tobject (t_obj, _) -> Some (env, t_obj)
+  | Tobject t_obj -> Some (env, t_obj)
   | Tconstr (path, type_args, _) -> (
     match References.dig_constructor ~state ~env ~package path with
     | Some (env, {item = {decl = {type_manifest = Some t1; type_params}}}) ->
@@ -1334,7 +1336,7 @@ let remove_current_module_if_needed ~env_completion_is_made_from completion_path
 
 let rec get_obj_fields (texp : Types.type_expr) =
   match texp.desc with
-  | Tfield (name, _, t1, t2) ->
+  | Tfield {name; typ = t1; rest = t2} ->
     let fields = t2 |> get_obj_fields in
     (name, t1) :: fields
   | Tlink te | Tsubst te | Tpoly (te, []) -> te |> get_obj_fields

analysis/src/utils.ml

@@ -107,7 +107,9 @@ let identify_pexp pexp =
   | Pexp_for_await_of _ -> "Pexp_for_await_of"
   | Pexp_constraint _ -> "Pexp_constraint"
   | Pexp_coerce _ -> "Pexp_coerce"
-  | Pexp_send _ -> "Pexp_send"
+  | Pexp_object_get _ -> "Pexp_object_get"
+  | Pexp_object_set _ -> "Pexp_object_set"
+  | Pexp_object_literal _ -> "Pexp_object_literal"
   | Pexp_letmodule _ -> "Pexp_letmodule"
   | Pexp_letexception _ -> "Pexp_letexception"
   | Pexp_assert _ -> "Pexp_assert"

compiler/core/lam.ml

@@ -107,7 +107,6 @@ module Types = struct
     | Lfor_of of ident * t * t
     | Lfor_await_of of ident * t * t
     | Lassign of ident * t
-  (* | Lsend of Lam_compat.meth_kind * t * t * t list * Location.t *)
 end
 
 include Types

compiler/core/lam.mli

@@ -79,7 +79,6 @@ and t = private
   | Lfor_await_of of ident * t * t
   | Lassign of ident * t
 
-(* | Lsend of Lambda.meth_kind * t * t * t list * Location.t *)
 (* | Levent of t * Lambda.lambda_event
    [Levent] in the branch hurt pattern match,
    we should use record for trivial debugger info

compiler/core/lam_analysis.ml

@@ -93,7 +93,8 @@ let rec no_side_effects (lam : Lam.t) : bool =
     (* A tagged template invokes its tag at runtime, so it always has side
        effects. *)
     | Ptagged_template | Pjs_apply | Pjs_runtime_apply | Pjs_call _ | Pinit_mod
-    | Pupdate_mod | Pjs_unsafe_downgrade _ | Pdebugger | Pjs_fn_method
+    | Pupdate_mod | Pjs_object_get _ | Pjs_object_set _ | Pdebugger
+    | Pjs_fn_method
     (* Await promise *)
     | Pawait
     (* TODO *)
@@ -123,7 +124,6 @@ let rec no_side_effects (lam : Lam.t) : bool =
   | Lfor _ -> false
   | Lfor_of _ | Lfor_await_of _ -> false
   | Lassign _ -> false (* actually it depends ... *)
-  (* | Lsend _ -> false  *)
   | Lapply
       {
         ap_func = Lprim {primitive = Pfield (_, Fld_module {name = "from_fun"})};
@@ -186,7 +186,6 @@ let rec size (lam : Lam.t) =
     | Lfor_of _ | Lfor_await_of _ -> really_big ()
     | Lassign (_, v) -> 1 + size v
     (* This is side effectful,  be careful *)
-    (* | Lsend _  ->  really_big () *)
   with Too_big_to_inline -> 1000
 
 and size_constant x =

compiler/core/lam_compile.ml

@@ -1405,50 +1405,6 @@ let compile output_prefix =
         Js_output.make
           (aux lambda_cxt
              {lambda_cxt with continuation = EffectCall new_return_type})
-  (* Note that in [Texp_apply] for [%sendcache] the cache might not be used
-     see {!CamlinternalOO.send_meth} and {!Translcore.transl_exp0} the branch
-     [Texp_apply] when [public_send ], args are simply dropped
-
-     reference
-     [js_of_ocaml]
-     1. GETPUBMET
-     2. GETDYNMET
-     3. GETMETHOD
-     [ocaml]
-     Lsend (bytegen.ml)
-     For the object layout refer to [camlinternalOO/create_object]
-     {[
-       let create_object table =
-         (* XXX Appel de [obj_block] *)
-         let obj = mark_ocaml_object @@ Obj.new_block Obj.object_tag table.size in
-         (* XXX Appel de [caml_modify] *)
-         Obj.set_field obj 0 (Obj.repr table.methods);
-         Obj.obj (set_id obj)
-
-       let create_object_opt obj_0 table =
-         if (Obj.magic obj_0 : bool) then obj_0 else begin
-           (* XXX Appel de [obj_block] *)
-           let obj = mark_ocaml_object @@ Obj.new_block Obj.object_tag table.size in
-           (* XXX Appel de [caml_modify] *)
-           Obj.set_field obj 0 (Obj.repr table.methods);
-           Obj.obj (set_id obj)
-         end
-     ]}
-     it's a block with tag [248], the first field is [table.methods] which is an array
-     {[
-       type table =
-         { mutable size: int;
-           mutable methods: closure array;
-           mutable methods_by_name: meths;
-           mutable methods_by_label: labs;
-           mutable previous_states:
-             (meths * labs * (label * item) list * vars *
-              label list * string list) list;
-           mutable hidden_meths: (label * item) list;
-           mutable vars: vars;
-           mutable initializers: (obj -> unit) list }
-     ]}
-  *)
   and compile_ifthenelse (predicate : Lam.t) (t_branch : Lam.t)
       (f_branch : Lam.t) (lambda_cxt : Lam_compile_context.t) =
     match
@@ -1765,11 +1721,8 @@ let compile output_prefix =
          check the arity of fn before wrapping it
          we need mark something that such eta-conversion can not be simplified in some cases
       *)
-    | {
-     primitive = Pjs_unsafe_downgrade {name = property; setter = false};
-     args = [obj];
-    } -> (
-      (* getter {[ x #. height ]} *)
+    | {primitive = Pjs_object_get property; args = [obj]} -> (
+      (* property read: obj["height"] *)
       match
         compile_lambda {lambda_cxt with continuation = NeedValue Not_tail} obj
       with
@@ -1785,11 +1738,8 @@ let compile output_prefix =
         in
         Js_output.output_of_block_and_expression lambda_cxt.continuation blocks
           ret)
-    | {
-     primitive = Pjs_unsafe_downgrade {name = property; setter = true};
-     args = [obj; setter_val];
-    } -> (
-      (* setter {[ x ## method_call ]} *)
+    | {primitive = Pjs_object_set property; args = [obj; setter_val]} -> (
+      (* property write: obj["height"] = v *)
       let need_value_no_return_cxt =
         {lambda_cxt with continuation = NeedValue Not_tail}
       in
@@ -1812,7 +1762,7 @@ let compile output_prefix =
         | Some (obj_code, obj) ->
           cont obj_block arg_block (Some obj_code)
             (E.seq (E.assign (E.dot (E.var obj) property) value) E.unit)))
-    | {primitive = Pjs_unsafe_downgrade _; args} -> assert false
+    | {primitive = Pjs_object_get _ | Pjs_object_set _; args} -> assert false
     | {primitive = Pjs_fn_method; args = args_lambda} -> (
       match args_lambda with
       | [Lfunction {params; body; attr = {return_unit; async}; loc}] ->

compiler/core/lam_compile_primitive.ml

@@ -176,7 +176,7 @@ let translate output_prefix loc (cxt : Lam_compile_context.t)
   | Pis_undefined -> E.is_undef (Ext_list.singleton_exn args)
   | Pis_null_undefined -> E.is_null_undefined (Ext_list.singleton_exn args)
   | Ptypeof -> E.typeof (Ext_list.singleton_exn args)
-  | Pjs_unsafe_downgrade _ | Pdebugger | Pjs_fn_method ->
+  | Pjs_object_get _ | Pjs_object_set _ | Pdebugger | Pjs_fn_method ->
     assert false (* already handled by {!Lam_compile} *)
   | Pstringadd -> (
     match args with