[RFC wayland] scanner: provide convenience defines for NULL handlers

[Pekka Paalanen]

On Thu, 19 Sep 2013 13:54:34 +1000
Peter Hutterer <peter.hutterer at who-t.net> wrote:

> Instead of NULL, a client that doesn't implement all callbacks of a listener
> can use named defines to increase readability of the code. For example:
> 
> const struct wl_pointer_listener pointer_listener = {
> 	WL_POINTER_ENTER_HANDLER_NONE,
> 	WL_POINTER_LEAVE_HANDLER_NONE,
> 	motion_handler,
> 	button_handler,
> 	axis_handler,
> };
> 
> These are defined as typed NULL, so getting the order wrong will yield a
> compiler warning in most cases - at least where neighbouring functions don't
> have the same signature.
> 
>  #define WL_POINTER_ENTER_HANDLER_NONE \
>  ((void(*)(void *, struct wl_pointer *, uint32_t , struct wl_surface *, wl_fixed_t , wl_fixed_t )) NULL)
> ---
> Just gathering interest in this, if we want this I'll polish it up and test
> it a bit more.

Hi,

are you sure a NULL handler function pointer is actually legal?
I thought we segfault if it is NULL and the event comes to dispatch.
Or was there some earlier patch that lifted this restriction?


Thanks,
pq

>  src/scanner.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/src/scanner.c b/src/scanner.c
> index d02d865..a41da11 100644
> --- a/src/scanner.c
> +++ b/src/scanner.c
> @@ -872,6 +872,23 @@ emit_structs(struct wl_list *message_list, struct interface *interface)
>  	printf("};\n\n");
>  
>  	if (!is_interface) {
> +	    wl_list_for_each(m, message_list, link) {
> +	        printf("#define %s_%s_HANDLER_NONE ((void(*)(",
> +		       interface->uppercase_name, m->uppercase_name);
> +			printf("void *, "),
> +			printf("struct %s *", interface->name);
> +		wl_list_for_each(a, &m->arg_list, link) {
> +			printf(", ");
> +			if (a->type == OBJECT && a->interface_name == NULL)
> +				printf("void *");
> +			else if (a->type == NEW_ID)
> +				printf("struct %s *", a->interface_name);
> +			else
> +				emit_type(a);
> +		}
> +		printf(")) NULL)\n");
> +	    }
> +
>  	    printf("static inline int\n"
>  		   "%s_add_listener(struct %s *%s,\n"
>  		   "%sconst struct %s_listener *listener, void *data)\n"