hphp/hack/src/typing/tast_check/string_cast_check.ml

   1 (**
   2  * Copyright (c) 2018, Facebook, Inc.
   3  * All rights reserved.
   4  *
   5  * This source code is licensed under the MIT license found in the
   6  * LICENSE file in the "hack" directory of this source tree.
   7  *
   8 *)
   9
  10 open Tast
  11
  12 module Env = Tast_env
  13 module TCO = TypecheckerOptions
  14 module SN = Naming_special_names
  15
  16 let should_enforce env =
  17   TCO.disallow_stringish_magic (Env.get_tcopt env)
  18
  19 (** Produce an error on (string) casts of objects. Currently it is allowed in HHVM to
  20     cast an object if it is Stringish (i.e., has a __toString() method), but all
  21     (string) casts of objects will be banned in the future. Eventually,
  22     __toString/(string) casts of objects will be removed from HHVM entirely. *)
  23
  24 let check__toString m is_static =
  25   let (pos, name) = m.m_name in
  26   if name = SN.Members.__toString
  27   then begin
  28     if m.m_visibility <> Public || is_static
  29     then Errors.toString_visibility pos;
  30     match m.m_ret with
  31     | Some (_, Hprim Tstring) -> ()
  32     | Some (p, _) -> Errors.toString_returns_string p
  33     | None -> ()
  34   end
  35
  36 let handler = object
  37   inherit Tast_visitor.handler_base
  38
  39   method! at_expr env ((p, _), expr) =
  40     match expr with
  41     | Cast ((_, Hprim Tstring), te) when should_enforce env ->
  42       let ((_, ty), _) = te in
  43       (* Whitelist mixed/nonnull *)
  44       if not (Env.is_stringish env ty ~allow_mixed:true)
  45       then Errors.string_cast p (Env.print_ty env ty)
  46     | _ -> ()
  47
  48   method! at_static_method _ m = check__toString m true
  49
  50   method! at_method_ _ m = check__toString m false
  51
  52   method! at_constructor _ m = check__toString m true
  53 end