sparse_set/storage: improve emplace(N) with non-sequential entities

src/entt/entity/sparse_set.hpp

@@ -363,7 +363,11 @@ protected:
                 bump(entt);
             }
 
-            swap_at(static_cast<size_type>(traits_type::to_entity(elem)), (pos = static_cast<size_type>(head++)));
+            if(force_back) {
+                pos = static_cast<size_type>(head++);
+                swap_at(static_cast<size_type>(traits_type::to_entity(elem)), pos);
+            }
+
             break;
         }
 
@@ -760,7 +764,7 @@ public:
      * `end()` iterator otherwise.
      */
     iterator push(const entity_type entt, const void *elem = nullptr) {
-        return try_emplace(entt, false, elem);
+        return try_emplace(entt, (mode == deletion_policy::swap_only), elem);
     }
 
     /**

src/entt/entity/storage.hpp

@@ -1091,16 +1091,13 @@ public:
             return emplace();
         } else if(const auto curr = local_traits_type::construct(local_traits_type::to_entity(hint), base_type::current(hint)); curr == tombstone) {
             const auto pos = static_cast<size_type>(local_traits_type::to_entity(hint));
+            const auto entt = *base_type::try_emplace(hint, true);
 
             while(!(pos < base_type::size())) {
-                const auto it = base_type::try_emplace(entity_at(base_type::size()), true);
-                const auto entt = *it;
-
-                base_type::swap_only(it);
-                base_type::bump(entt);
+                base_type::try_emplace(entity_at(base_type::size() - 1u), false);
             }
 
-            return *base_type::try_emplace(hint, true);
+            return entt;
         } else if(const auto idx = base_type::index(curr); idx < base_type::free_list()) {
             return emplace();
         } else {