write_compute_value_instructions` doesn't consider Nullable pointers

[ManasJayanth]

Trying to generate bindings for Gstreamer (GstTagList), I get the following on compiling the generated bindings.

File "lib/Tag_list.ml", line 38, characters 34-43:
Error: This expression has type
         GLib.Date.t Ctypes.structure Ctypes_static.ptr option Ctypes.ptr =
           (GLib.Date.t Ctypes.structure Ctypes_static.ptr option, [ `C ])
           Ctypes_static.pointer
       but an expression was expected of type
         GLib.Date.t Ctypes.structure Ctypes_static.ptr Ctypes_static.ptr =
           (GLib.Date.t Ctypes.structure Ctypes_static.ptr, [ `C ])
           Ctypes_static.pointer
       Type GLib.Date.t Ctypes.structure Ctypes_static.ptr option
       is not compatible with type
         GLib.Date.t Ctypes.structure Ctypes_static.ptr =
           (GLib.Date.t Ctypes.structure, [ `C ]) Ctypes_static.pointer

Pointing to a line like this

  let value_ptr = allocate (ptr_opt Date.t_typ) None in                                                                                                                                                            
  let ret = get_date_raw self tag value_ptr in 

I think write_compute_value_instructions must check if the out args (inout args too I'm guessing) could be a Nullable.

I couldn't find the right patch to get this work, if I have any luck, I'll raise a PR.

[ManasJayanth]

Related

  in
  let format_ptr = allocate Format.t_view (Format.t_view.of_value (Unsigned.UInt32.zero)) in
  let processed_ptr = allocate uint64_t Unsigned.UInt64.zero in

Format.t_view doesn't actually have of_value

Format.mli

open Ctypes                                                                                                                                                                                                        
                                                                                                                                                                                                                   
type t = Undefined | Default | Bytes | Time | Buffers | Percent                                                                                                                                                    
                                                                                                                                                                                                                   
val of_value:                                                                                                                                                                                                      
  Unsigned.uint32 -> t                                                                                                                                                                                             
                                                                                                                                                                                                                   
val to_value:                                                                                                                                                                                                      
  t -> Unsigned.uint32                                                                                                                                                                                             
                                                                                                                                                                                                                   
val t_view: t typ