Remove unreachable case with const extention cases

Author: DZakh

jscomp/ml/matching.ml

@@ -2273,13 +2273,13 @@ let split_variant_cases tag_lambda_list =
  sort_int_lambda_list const,
  sort_int_lambda_list nonconst 
 
-let split_extension_cases tag_lambda_list =
+let get_extension_cases tag_lambda_list =
  let rec split_rec = function
- [] -> ([], [])
+ [] -> []
  | (cstr, act) :: rem ->
- let (consts, nonconsts) = split_rec rem in
+ let nonconsts = split_rec rem in
  match cstr with
- | Cstr_extension(path, _) -> (consts, (path, act) :: nonconsts)
+ | Cstr_extension(path, _) -> ((path, act) :: nonconsts)
  | _ -> assert false in
  split_rec tag_lambda_list
 
@@ -2293,35 +2293,25 @@ let combine_constructor sw_names loc arg ex_pat cstr partial ctx def
  let fail, local_jumps =
  mk_failaction_neg partial ctx def in
  let lambda1 =
- let consts, nonconsts = split_extension_cases tag_lambda_list in
- let default, consts, nonconsts =
+ let extension_cases = get_extension_cases tag_lambda_list in
+ let default, extension_cases =
  match fail with
  | None ->
- begin match consts, nonconsts with
- | _, (_, act)::rem -> act, consts, rem
- | (_, act)::rem, _ -> act, rem, nonconsts
- | _ -> assert false
+ begin match extension_cases with
+ | (_, act)::rem -> act, rem
+ | _ -> failwith "Empty extension case list is not possible"
  end
- | Some fail -> fail, consts, nonconsts in
- let nonconst_lambda =
- match nonconsts with
- [] -> default
+ | Some fail -> fail, extension_cases in
+ match extension_cases with
+ | [] -> default
  | _ ->
  List.fold_right
  (fun (path, act) rem ->
  let ext = transl_extension_path ex_pat.pat_env path in
  Lifthenelse(Lprim(extension_slot_eq , [arg; ext], loc),
  act, rem))
- nonconsts
+ extension_cases
  default 
- in
- List.fold_right
- (fun (path, act) rem ->
- let ext = transl_extension_path ex_pat.pat_env path in
- Lifthenelse(Lprim(extension_slot_eq , [arg; ext], loc),
- act, rem))
- consts
- nonconst_lambda
  in
  lambda1, jumps_union local_jumps total1
  end else begin