Fix readonly check for like arrays

Summary: Readonly is implemented as a Tast_check that does a match over types, so it looks at locl tys which can be like types due to lack of enforcement. Look through likeness when checking if it is a Hack array.

Differential Revision: D45928361

fbshipit-source-id: dfc0309413cc76ac166642d9fd03210a41206fe6

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

@@ -143,6 +143,7 @@ let rec ty_expr env ((_, _, expr_) : Tast.expr) : rty =
 let is_value_collection_ty env ty =
   let mixed = MakeType.mixed Reason.none in
   let env = Tast_env.tast_env_as_typing_env env in
+  let ty = Typing_utils.strip_dynamic env ty in
   let hackarray = MakeType.any_array Reason.none mixed mixed in
   (* Subtype against an empty open shape (shape(...)) *)
   let shape = MakeType.open_shape Reason.none Typing_defs.TShapeMap.empty in