a few functions to replace of_yojson dependency

ppx.ml

(*
TODO: If we want to remove the dependency on of_json, we need to implement the json decoder manually.
TODO: Maybe use a custom deriving called "rsc" or similar where it handles the JSON/Promise/React.element. *)

let rec make_of_json ~loc (type_ : core_type) value =
   match type_.ptyp_desc with
   | Ptyp_constr ({ txt = Lident "int"; _ }, _) -> value
   | Ptyp_constr ({ txt = Lident "string"; _ }, _) -> value
   | Ptyp_constr ({ txt = Lident "bool"; _ }, _) -> value
   | Ptyp_constr ({ txt = Lident "float"; _ }, _) -> value
   | Ptyp_constr ({ txt = Lident "unit"; _ }, _) -> value
   | Ptyp_constr ({ txt = Lident "list"; _ }, list) ->
       let inner = List.hd list in
       let mapped = [%expr Stdlib.List.map (fun x -> [%e make_of_json ~loc inner [%expr x]]) [%e value]] in
       pexp_variant ~loc:value.pexp_loc "List" (Some mapped)
   | Ptyp_constr ({ txt = Lident "array"; _ }, array) ->
       let inner = List.hd array in
       let mapped = [%expr Stdlib.Array.map (fun x -> [%e make_of_json ~loc inner [%expr x]]) [%e value]] in
       let as_list = [%expr Stdlib.Array.to_list [%e mapped]] in
       pexp_variant ~loc:value.pexp_loc "List" (Some as_list)
   | Ptyp_constr ({ txt = Lident "option"; _ }, option) ->
       let inner = List.hd option in
       let matched = [%expr match [%e value] with None -> `Null | Some x -> [%e make_of_json ~loc inner [%expr x]]] in
       matched
   (* TODO: Add json/yojson *)
   (* | [%type: Yojson.Basic.t] -> pexp_variant ~loc:value.pexp_loc "Yojson" (Some value) *)
   | Ptyp_constr ({ txt = lident; _ }, _) ->
       let rec make_of_json_fn lident =
         match lident with
         | Lident name when name = "t" -> Lident "of_json"
         | Lident name -> Lident (Printf.sprintf "%s_of_json" name)
         | Ldot (modulePath, name) when name = "t" -> Ldot (modulePath, "of_json")
         | Ldot (modulePath, name) -> Ldot (modulePath, Printf.sprintf "%s_of_json" name)
         | Lapply (apply, longident) -> Lapply (apply, make_of_json_fn longident)
       in
       pexp_apply ~loc:value.pexp_loc (pexp_ident ~loc { txt = make_of_json_fn lident; loc }) [ (Nolabel, value) ]
   | Ptyp_tuple tuple ->
       let item_name index = "x" ^ Int.to_string index in
       let loc = value.pexp_loc in
       let descructuring =
         ppat_tuple ~loc (List.mapi ~f:(fun index _ -> ppat_var ~loc { txt = item_name index; loc }) tuple)
       in
       let list =
         List.mapi
           ~f:(fun index t ->
             let identifier = pexp_ident ~loc { txt = Lident (item_name index); loc } in
             make_of_json ~loc [%type: [%t t]] identifier)
           tuple
       in
       pexp_let ~loc Nonrecursive
         [ value_binding ~loc ~pat:descructuring ~expr:value ]
         [%expr `List [%e pexp_list ~loc list]]
   | Ptyp_var name ->
       let msg = Printf.sprintf "server-reason-react: unsupported type: '%s" name in
       [%expr [%ocaml.error [%e estring ~loc msg]]]
   | Ptyp_arrow _ ->
       [%expr
         [%ocaml.error
           "server-reason-react: callbacks are not supported in client components. Functions can't be serialized to the \
            client."]]
   (* | Ptyp_object _ -> error_cannot_create_json_encoder ~loc ~type_name:"objects"
      | Ptyp_class _ -> error_cannot_create_json_encoder ~loc ~type_name:"classes"
      | Ptyp_variant _ -> error_cannot_create_json_encoder ~loc ~type_name:"polyvariants"
      | Ptyp_alias _ -> error_not_supported ~loc ~type_name:"aliases"
      | Ptyp_extension _ -> error_not_supported ~loc ~type_name:"extensions"
      | Ptyp_package _ -> error_not_supported ~loc ~type_name:"modules"
      | Ptyp_poly _ -> error_not_supported ~loc ~type_name:"polymorphic types"
      | Ptyp_any -> error_not_supported ~loc ~type_name:"'_' annotations" *)
   | _ -> [%expr [%ocaml.error "server-reason-react: unsupported type"]]

(* let error_cannot_create_json_encoder ~loc ~type_name =
  let msg =
    Printf.sprintf
      "server-reason-react: inline types such as %s, need to be a type definition with a json encoder. If the type is \
       named 't' the encoder should be named 't_to_json', if the type is named 'foo' the encoder should be named \
       'foo_to_json'."
      type_name
  in
  [%expr [%ocaml.error [%e estring ~loc msg]]]

let error_not_supported ~loc ~type_name =
  let msg =
    Printf.sprintf
      "server-reason-react: %s aren't supported in client components. Try using a type definition with a json encoder \
       but there's no guarantee that it will work. Open an issue if you need it."
      type_name
  in
  [%expr [%ocaml.error [%e estring ~loc msg]]] *)

let rec make_to_yojson ~loc (type_ : core_type) value =
   match type_.ptyp_desc with
   | Ptyp_constr ({ txt = Lident "int"; _ }, _) -> pexp_variant ~loc:value.pexp_loc "Int" (Some value)
   | Ptyp_constr ({ txt = Lident "string"; _ }, _) -> pexp_variant ~loc:value.pexp_loc "String" (Some value)
   | Ptyp_constr ({ txt = Lident "bool"; _ }, _) -> pexp_variant ~loc:value.pexp_loc "Bool" (Some value)
   | Ptyp_constr ({ txt = Lident "float"; _ }, _) -> pexp_variant ~loc:value.pexp_loc "Float" (Some value)
   | Ptyp_constr ({ txt = Lident "list"; _ }, list) ->
       let inner = List.hd list in
       let mapped = [%expr Stdlib.List.map (fun x -> [%e make_to_yojson ~loc inner [%expr x]]) [%e value]] in
       pexp_variant ~loc:value.pexp_loc "List" (Some mapped)
   | Ptyp_constr ({ txt = Lident "array"; _ }, array) ->
       let inner = List.hd array in
       let mapped = [%expr Stdlib.Array.map (fun x -> [%e make_to_yojson ~loc inner [%expr x]]) [%e value]] in
       let as_list = [%expr Stdlib.Array.to_list [%e mapped]] in
       pexp_variant ~loc:value.pexp_loc "List" (Some as_list)
   | Ptyp_constr ({ txt = Lident "option"; _ }, option) ->
       let inner = List.hd option in
       let matched =
         [%expr match [%e value] with None -> `Null | Some x -> [%e make_to_yojson ~loc inner [%expr x]]]
       in
       matched
   | Ptyp_constr ({ txt = Lident "unit"; _ }, _) -> pexp_variant ~loc:value.pexp_loc "Null" None
   (* TODO: Add json/yojson *)
   (* | [%type: Yojson.Basic.t] -> pexp_variant ~loc:value.pexp_loc "Yojson" (Some value) *)
   | Ptyp_constr ({ txt = lident; _ }, _) ->
       let rec make_to_json_fn lident =
         match lident with
         | Lident name when name = "t" -> Lident "to_json"
         | Lident name -> Lident (Printf.sprintf "%s_to_json" name)
         | Ldot (modulePath, name) when name = "t" -> Ldot (modulePath, "to_json")
         | Ldot (modulePath, name) -> Ldot (modulePath, Printf.sprintf "%s_to_json" name)
         | Lapply (apply, longident) -> Lapply (apply, make_to_json_fn longident)
       in
       pexp_apply ~loc:value.pexp_loc (pexp_ident ~loc { txt = make_to_json_fn lident; loc }) [ (Nolabel, value) ]
   | Ptyp_tuple tuple ->
       let item_name index = "x" ^ Int.to_string index in
       let loc = value.pexp_loc in
       let descructuring =
         ppat_tuple ~loc (List.mapi ~f:(fun index _ -> ppat_var ~loc { txt = item_name index; loc }) tuple)
       in
       let list =
         List.mapi
           ~f:(fun index t ->
             let identifier = pexp_ident ~loc { txt = Lident (item_name index); loc } in
             make_to_yojson ~loc [%type: [%t t]] identifier)
           tuple
       in
       pexp_let ~loc Nonrecursive
         [ value_binding ~loc ~pat:descructuring ~expr:value ]
         [%expr `List [%e pexp_list ~loc list]]
   | Ptyp_var name ->
       let msg = Printf.sprintf "server-reason-react: unsupported type: '%s" name in
       [%expr [%ocaml.error [%e estring ~loc msg]]]
   | Ptyp_arrow _ ->
       [%expr
         [%ocaml.error
           "server-reason-react: callbacks are not supported in client components. Functions can't be serialized to the \
            client."]]
   | Ptyp_object _ -> error_cannot_create_json_encoder ~loc ~type_name:"objects"
   | Ptyp_class _ -> error_cannot_create_json_encoder ~loc ~type_name:"classes"
   | Ptyp_variant _ -> error_cannot_create_json_encoder ~loc ~type_name:"polyvariants"
   | Ptyp_alias _ -> error_not_supported ~loc ~type_name:"aliases"
   | Ptyp_extension _ -> error_not_supported ~loc ~type_name:"extensions"
   | Ptyp_package _ -> error_not_supported ~loc ~type_name:"modules"
   | Ptyp_poly _ -> error_not_supported ~loc ~type_name:"polymorphic types"
   | Ptyp_any -> error_not_supported ~loc ~type_name:"'_' annotations"