Function CmdConvertRail

src/rail_cmd.cpp:1539–1756

* Convert one rail type to the other. You can convert normal rail to * monorail/maglev easily or vice-versa. * @param flags operation to perform * @param tile end tile of rail conversion drag * @param area_start start tile of drag * @param totype new railtype to convert to. * @param diagonal build diagonally or not. * @return the cost of this operation or an error */

 * @return the cost of this operation or an error
 */
CommandCost CmdConvertRail(DoCommandFlags flags, TileIndex tile, TileIndex area_start, RailType totype, bool diagonal)
{
	TileIndex area_end = tile;

	if (!ValParamRailType(totype)) return CMD_ERROR;
	if (area_start >= Map::Size()) return CMD_ERROR;

	TrainList affected_trains;

	CommandCost cost(EXPENSES_CONSTRUCTION);
	CommandCost error = CommandCost(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK); // by default, there is no track to convert.
	bool found_convertible_track = false; // whether we actually did convert some track (see bug #7633)

	std::unique_ptr<TileIterator> iter = TileIterator::Create(area_start, area_end, diagonal);
	for (; (tile = *iter) != INVALID_TILE; ++(*iter)) {
		TileType tt = GetTileType(tile);

		/* Check if there is any track on tile */
		switch (tt) {
			case MP_RAILWAY:
				break;
			case MP_STATION:
				if (!HasStationRail(tile)) continue;
				break;
			case MP_ROAD:
				if (!IsLevelCrossing(tile)) continue;
				if (RailNoLevelCrossings(totype)) {
					error.MakeError(STR_ERROR_CROSSING_DISALLOWED_RAIL);
					continue;
				}
				break;
			case MP_TUNNELBRIDGE:
				if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) continue;
				break;
			default: continue;
		}

		/* Original railtype we are converting from */
		RailType type = GetRailType(tile);

		/* Converting to the same type or converting 'hidden' elrail -> rail */
		if (type == totype || (_settings_game.vehicle.disable_elrails && totype == RAILTYPE_RAIL && type == RAILTYPE_ELECTRIC)) continue;

		/* Trying to convert other's rail */
		CommandCost ret = CheckTileOwnership(tile);
		if (ret.Failed()) {
			error = std::move(ret);
			continue;
		}

		std::vector<Train *> vehicles_affected;

		/* Vehicle on the tile when not converting Rail <-> ElRail
		 * Tunnels and bridges have special check later */
		if (tt != MP_TUNNELBRIDGE) {
			if (!IsCompatibleRail(type, totype)) {
				ret = IsPlainRailTile(tile) ? EnsureNoTrainOnTrackBits(tile, GetTrackBits(tile)) : EnsureNoVehicleOnGround(tile);
				if (ret.Failed()) {