ast_bs_open.ml

(* Copyright (C) 2015-2016 Bloomberg Finance L.P.
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * In addition to the permissions granted to you by the LGPL, you may combine
 * or link a "work that uses the Library" with a publicly distributed version
 * of this file to produce a combined library or application, then distribute
 * that combined work under the terms of your choosing, with no requirement
 * to comply with the obligations normally placed on you by section 4 of the
 * LGPL version 3 (or the corresponding section of a later version of the LGPL
 * should you choose to use a later version).
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *)

let isCamlExceptionOrOpenVariant : Longident.t =
  Ldot (Ldot (Lident "Js", "Exn"), "isCamlExceptionOrOpenVariant")

let obj_magic : Longident.t = Lident "__unsafe_cast"

let rec checkCases (cases : Parsetree.case list) = List.iter check_case cases

and check_case case = check_pat case.pc_lhs

and check_pat (pat : Parsetree.pattern) =
  match pat.ppat_desc with
  | Ppat_construct _ -> ()
  | Ppat_or (l, r) ->
      check_pat l;
      check_pat r
  | _ ->
      Location.raise_errorf ~loc:pat.ppat_loc "Unsupported pattern in `bs.open`"

let convertBsErrorFunction loc (self : Bs_ast_mapper.mapper) attrs
    (cases : Parsetree.case list) =
  let open Ast_helper in
  let txt = "match" in
  let txt_expr = Exp.ident ~loc { txt = Lident txt; loc } in
  let none = Exp.construct ~loc { txt = Ast_literal.predef_none; loc } None in
  let () = checkCases cases in
  let cases = self.cases self cases in
  Ast_compatible.fun_ ~attrs ~loc
    (Pat.var ~loc { txt; loc })
    (Exp.ifthenelse ~loc
       (Ast_compatible.app1 ~loc
          (Exp.ident ~loc { txt = isCamlExceptionOrOpenVariant; loc })
          txt_expr)
       (Exp.match_ ~loc
          (Exp.constraint_ ~loc
             (Ast_compatible.app1 ~loc
                (Exp.ident ~loc { txt = obj_magic; loc })
                txt_expr)
             (Ast_literal.type_exn ~loc ()))
          (Ext_list.map_append cases
             [ Exp.case (Pat.any ~loc ()) none ]
             (fun x ->
               let pc_rhs = x.pc_rhs in
               let loc = pc_rhs.pexp_loc in
               {
                 x with
                 pc_rhs =
                   Exp.construct ~loc
                     { txt = Ast_literal.predef_some; loc }
                     (Some pc_rhs);
               })))
       (Some none))