[map] Enable using hashmap with unique_ptr

src/hb-map.hh

@@ -479,4 +479,15 @@ void hb_hashmap_destroy (hb_hashmap_t<K, V>* map)
   hb_free (map);
 }
 
+namespace hb {
+
+template <typename K, typename V>
+struct vtable<hb_hashmap_t<K, V>>
+{
+  static constexpr auto destroy = hb_hashmap_destroy<K,V>;
+};
+
+}
+
+
 #endif /* HB_MAP_HH */

src/test-map.cc

@@ -212,6 +212,12 @@ main (int argc, char **argv)
     m.keys_ref ();
     m.values_ref ();
   }
+  /* Test more complex unique_ptr's. */
+  {
+    hb_hashmap_t<int, hb::unique_ptr<hb_hashmap_t<int, int>>> m;
+
+    m.get (0);
+  }
 
   return 0;
 }