} while (source->cargo_count > 0 && (dest = dest->next) != NULL);

		dest = v;

	} while ((source = source->next) != NULL);

}

/* Replaces a vehicle (used to be called autorenew)

 * This function is only called from MaybeReplaceVehicle()

 * Must be called with _current_player set to the owner of the vehicle

 * @param w Vehicle to replace

 * @param flags is the flags to use when calling DoCommand(). Mainly DC_EXEC counts

 * @return value is cost of the replacement or CMD_ERROR

 */

static int32 ReplaceVehicle(Vehicle **w, byte flags)

{

	int32 cost;

	Vehicle *old_v = *w;

	const Player *p = GetPlayer(old_v->owner);

	EngineID new_engine_type;

	const UnitID cached_unitnumber = old_v->unitnumber;

	bool new_front = false;

	Vehicle *new_v = NULL;

	char vehicle_name[32];

	if (new_engine_type == INVALID_ENGINE) new_engine_type = old_v->engine_type;

	cost = DoCommand(old_v->x_pos, old_v->y_pos, new_engine_type, 1, flags, CMD_BUILD_VEH(old_v->type));

	if (CmdFailed(cost)) return cost;

	if (flags & DC_EXEC) {

		new_v = GetVehicle(_new_vehicle_id);

		*w = new_v;	//we changed the vehicle, so MaybeReplaceVehicle needs to work on the new one. Now we tell it what the new one is

		/* refit if needed */

		if (new_v->type != VEH_Road) { // road vehicles can't be refitted

			if (old_v->cargo_type != new_v->cargo_type && old_v->cargo_cap != 0 && new_v->cargo_cap != 0) {// some train engines do not have cargo capacity

				DoCommand(0, 0, new_v->index, old_v->cargo_type, DC_EXEC, CMD_REFIT_VEH(new_v->type));

			}

		}

		if (old_v->type == VEH_Train && !IsFrontEngine(old_v)) {

			/* this is a railcar. We need to move the car into the train

			 * We add the new engine after the old one instead of replacing it. It will give the same result anyway when we

			 * sell the old engine in a moment

			 */

			DoCommand(0, 0, (GetPrevVehicleInChain(old_v)->index << 16) | new_v->index, 1, DC_EXEC, CMD_MOVE_RAIL_VEHICLE);

			/* Now we move the old one out of the train */

	assert(v->type == VEH_Train || v->type == VEH_Road || v->type == VEH_Ship || v->type == VEH_Aircraft);

	assert(v->vehstatus & VS_STOPPED);	// the vehicle should have been stopped in VehicleEnteredDepotThisTick() if needed

	if (v->leave_depot_instantly) {

		// we stopped the vehicle to do this, so we have to remember to start it again when we are done

		// we need to store this info as the engine might be replaced and lose this info

		stopped = true;

	}

	for (;;) {

		cost = 0;

		w = v;

		do {

			if (w->type == VEH_Train && IsMultiheaded(w) && !IsTrainEngine(w)) {

				/* we build the rear ends of multiheaded trains with the front ones */

				continue;

			}

			// check if the vehicle should be replaced

			if (!p->engine_renew ||

					w->age - w->max_age < (p->engine_renew_months * 30) || // replace if engine is too old

					w->max_age == 0) { // rail cars got a max age of 0

					continue;

			}

			/* Now replace the vehicle */

			temp_cost = ReplaceVehicle(&w, flags);

			if (flags & DC_EXEC &&

					(w->type != VEH_Train || w->u.rail.first_engine == INVALID_VEHICLE)) {

				/* now we bought a new engine and sold the old one. We need to fix the

				 * pointers in order to avoid pointing to the old one for trains: these

				 * pointers should point to the front engine and not the cars

				 */

				v = w;

			}

			if (CmdFailed(temp_cost)) break;

			cost += temp_cost;

		} while (w->type == VEH_Train && (w = GetNextVehicle(w)) != NULL);

		if (!(flags & DC_EXEC) && (CmdFailed(temp_cost) || p->money64 < (int32)(cost + p->engine_renew_money) || cost == 0)) {

			if (p->money64 < (int32)(cost + p->engine_renew_money) && ( _local_player == v->owner ) && cost != 0) {

				StringID message;

				SetDParam(0, v->unitnumber);