People often call
gst_caps_make_writable (caps);
instead of
caps = gst_caps_make_writable (caps);
and cause a bug. Warning about an unused return value helps here.
See https://bugzilla.gnome.org/show_bug.cgi?id=616541#c2 for an example.
/* reference counting */
GstCaps * gst_caps_ref (GstCaps *caps);
GstCaps * gst_caps_copy (const GstCaps *caps);
-GstCaps * gst_caps_make_writable (GstCaps *caps);
+GstCaps * gst_caps_make_writable (GstCaps *caps) G_GNUC_WARN_UNUSED_RESULT;
void gst_caps_unref (GstCaps *caps);
GType gst_static_caps_get_type (void);