make [%debugger] runtime free, so that we can use it without depending on runtime

Author: bobzhang

jscomp/runtime/js.ml

@@ -52,8 +52,10 @@ type +'a t
     ]}
  *)
 
-[@@@warning "-49"]
-(* internal types for FFI, these types are not used by normal users *)
+[@@@warning "-49"] 
+(* internal types for FFI, these types are not used by normal users 
+    Absent cmi file when looking up module alias.
+*)
 
 (**/**)
 module MapperRt = Js_mapperRt
@@ -65,7 +67,7 @@ module Internal = struct
  (** Js uncurried function *)
 
  external (!)  : 'a t -> 'a = "#unsafe_downgrade"
- external debugger : unit -> unit = "#debugger"
+ 
  external unsafe_downgrade : 'a t -> 'a = "#unsafe_downgrade"
 
  external fn_mk0 : (unit -> 'a0) -> (([`Arity_0], 'a0) fn) = "#fn_mk" "0"

jscomp/syntax/ast_util.ml

@@ -293,9 +293,13 @@ let to_method_callback  =
 let handle_debugger loc (payload : Ast_payload.t) = 
   match payload with 
   | PStr [] -> 
-    Parsetree.Pexp_apply
-      (Exp.ident {txt = Ldot(Ast_literal.Lid.js_internal, Literals.debugger ); loc}, 
-       [ Nolabel, Ast_literal.val_unit ~loc ()])
+    Ast_external_mk.local_external_apply
+    loc 
+    ~pval_prim:["#debugger"]
+    ~pval_type:(Typ.arrow Nolabel (Typ.any ()) 
+      (Ast_literal.type_unit ())
+      )
+    [Ast_literal.val_unit ~loc ()]
   | _ ->  
     Location.raise_errorf ~loc "bs.debugger does not accept payload"