Name the reader of an external argument's encoding

iter_process_bs_string_int_unwrap_uncurry advertised uncurry, which it
does not handle, and omitted ignore, which it does. It answers which of
@string, @int, @ignore and @unwrap an external's argument carries, so it
is now arg_encoding.

Signed-off-by: Cristiano Calcagno <ccrisccris@gmail.com>

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W8g8qwBARAcvW9MyuKQq8H

Author: cristianoc

compiler/frontend/ast_attributes.ml

@@ -105,8 +105,10 @@ let process_derive_type (attrs : t) : derive_attr * t =
         | Some _ -> Bs_syntaxerr.err loc Duplicated_bs_deriving)
       | _ -> (st, attr :: acc))
 
-(* duplicated attributes not allowed *)
-let iter_process_bs_string_int_unwrap_uncurry (attrs : t) =
+(* How an external's argument is encoded, from the one of [@string], [@int],
+   [@ignore] and [@unwrap] it carries. They are alternatives, so more than one
+   is a conflict. *)
+let arg_encoding (attrs : t) =
   let attr_name = function
     | `String -> "string"
     | `Int -> "int"

compiler/frontend/ast_attributes.mli

@@ -35,8 +35,9 @@ val has_await_payload : t -> bool
 
 type derive_attr = {bs_deriving: Ast_payload.action list option} [@@unboxed]
 
-val iter_process_bs_string_int_unwrap_uncurry :
-  t -> [`Nothing | `String | `Int | `Ignore | `Unwrap]
+val arg_encoding : t -> [`Nothing | `String | `Int | `Ignore | `Unwrap]
+(** How an external's argument is encoded, from the one of [@string], [@int],
+    [@ignore] and [@unwrap] it carries. *)
 
 val as_string : t -> string option
 

compiler/frontend/ast_external_process.ml

@@ -39,10 +39,7 @@ let variant_unwrap (row_fields : Parsetree.row_field list) : bool =
 let spec_of_ptyp (nolabel : bool) (ptyp : Parsetree.core_type) :
     External_arg_spec.attr =
   let ptyp_desc = ptyp.ptyp_desc in
-  match
-    Ast_attributes.iter_process_bs_string_int_unwrap_uncurry
-      ptyp.ptyp_attributes
-  with
+  match Ast_attributes.arg_encoding ptyp.ptyp_attributes with
   | `String -> (
     match ptyp_desc with
     | Ptyp_variant (row_fields, Closed, None) ->