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

[Peter Hutterer]

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.

 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"
-- 
1.8.3.1