[PATCH] wayland-util.h: add forward declaration for wl_object

[Chris Billington]

The definition of wl_argument in wayland-util.h references wl_object,
so wl_object ought to be defined in wayland-util.h. This resolves
gitlab issue #78.
---
 src/wayland-util.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/wayland-util.h b/src/wayland-util.h
index b6cbe0e..2115f5c 100644
--- a/src/wayland-util.h
+++ b/src/wayland-util.h
@@ -68,6 +68,20 @@ extern "C" {
 #define WL_PRINTF(x, y)
 #endif
 
+/** \class wl_object
+ *
+ * \brief A protocol object.
+ *
+ * A `wl_object` is an opaque struct identifying the protocol object
+ * underlying a `wl_proxy` or `wl_resource`.
+ *
+ * \note Functions accessing a `wl_object` are not normally used by client code.
+ * Clients should normally use the higher level interface generated by the
+ * scanner to interact with compositor objects.
+ *
+ */
+struct wl_object;
+
 /**
  * Protocol message signature
  *
-- 
2.21.0