pointer-constraints: add unstable header
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
#ifndef WLR_TYPES_WLR_POINTER_CONSTRAINTS_V1_H
#define WLR_TYPES_WLR_POINTER_CONSTRAINTS_V1_H
