Codechange: use INVALID_TOWN instead of 0 to denote 'not applicable'

src/road_cmd.cpp

@@ -604,7 +604,7 @@ static CommandCost CheckRoadSlope(Slope tileh, RoadBits *pieces, RoadBits existi
  * @param pieces road pieces to build (RoadBits)
  * @param rt road type
  * @param toggle_drd disallowed directions to toggle
- * @param town_id the town that is building the road (0 if not applicable)
+ * @param town_id the town that is building the road (INVALID_TOWN if not applicable)
  * @return the cost of this operation or an error
  */
 CommandCost CmdBuildRoad(DoCommandFlag flags, TileIndex tile, RoadBits pieces, RoadType rt, DisallowedRoadDirections toggle_drd, TownID town_id)
@@ -617,7 +617,7 @@ CommandCost CmdBuildRoad(DoCommandFlag flags, TileIndex tile, RoadBits pieces, R
 
 	/* Road pieces are max 4 bitset values (NE, NW, SE, SW) and town can only be non-zero
 	 * if a non-company is building the road */
-	if ((Company::IsValidID(company) && town_id != 0) || (company == OWNER_TOWN && !Town::IsValidID(town_id)) || (company == OWNER_DEITY && town_id != 0)) return CMD_ERROR;
+	if ((Company::IsValidID(company) && town_id != INVALID_TOWN) || (company == OWNER_TOWN && !Town::IsValidID(town_id)) || (company == OWNER_DEITY && town_id != INVALID_TOWN)) return CMD_ERROR;
 	if (company != OWNER_TOWN) {
 		const Town *town = CalcClosestTownFromTile(tile);
 		town_id = (town != nullptr) ? town->index : INVALID_TOWN;
@@ -1026,7 +1026,7 @@ CommandCost CmdBuildLongRoad(DoCommandFlag flags, TileIndex end_tile, TileIndex
 			if (tile == start_tile && start_half) bits &= DiagDirToRoadBits(dir);
 		}
 
-		CommandCost ret = Command<CMD_BUILD_ROAD>::Do(flags, tile, bits, rt, drd, 0);
+		CommandCost ret = Command<CMD_BUILD_ROAD>::Do(flags, tile, bits, rt, drd, INVALID_TOWN);
 		if (ret.Failed()) {
 			last_error = ret;
 			if (last_error.GetErrorMessage() != STR_ERROR_ALREADY_BUILT) {

src/road_gui.cpp

@@ -165,7 +165,7 @@ void ConnectRoadToStructure(TileIndex tile, DiagDirection direction)
 	/* if there is a roadpiece just outside of the station entrance, build a connecting route */
 	if (IsNormalRoadTile(tile)) {
 		if (GetRoadBits(tile, GetRoadTramType(_cur_roadtype)) != ROAD_NONE) {
-			Command<CMD_BUILD_ROAD>::Post(tile, DiagDirToRoadBits(ReverseDiagDir(direction)), _cur_roadtype, DRD_NONE, 0);
+			Command<CMD_BUILD_ROAD>::Post(tile, DiagDirToRoadBits(ReverseDiagDir(direction)), _cur_roadtype, DRD_NONE, INVALID_TOWN);
 		}
 	}
 }

src/roadveh_cmd.cpp

@@ -1126,7 +1126,7 @@ static bool CanBuildTramTrackOnTile(CompanyID c, TileIndex t, RoadType rt, RoadB
 	/* The 'current' company is not necessarily the owner of the vehicle. */
 	Backup<CompanyID> cur_company(_current_company, c);
 
-	CommandCost ret = Command<CMD_BUILD_ROAD>::Do(DC_NO_WATER, t, r, rt, DRD_NONE, 0);
+	CommandCost ret = Command<CMD_BUILD_ROAD>::Do(DC_NO_WATER, t, r, rt, DRD_NONE, INVALID_TOWN);
 
 	cur_company.Restore();
 	return ret.Succeeded();

src/script/api/script_bridge.cpp

@@ -105,7 +105,7 @@ static void _DoCommandReturnBuildBridge1(class ScriptInstance *instance)
 	DiagDirection dir_1 = ::DiagdirBetweenTiles(end, start);
 	DiagDirection dir_2 = ::ReverseDiagDir(dir_1);
 
-	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(&::_DoCommandReturnBuildBridge2, start + ::TileOffsByDiagDir(dir_1), ::DiagDirToRoadBits(dir_2), (::RoadType)ScriptRoad::GetCurrentRoadType(), DRD_NONE, 0);
+	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(&::_DoCommandReturnBuildBridge2, start + ::TileOffsByDiagDir(dir_1), ::DiagDirToRoadBits(dir_2), (::RoadType)ScriptRoad::GetCurrentRoadType(), DRD_NONE, INVALID_TOWN);
 }
 
 /* static */ bool ScriptBridge::_BuildBridgeRoad2()
@@ -119,7 +119,7 @@ static void _DoCommandReturnBuildBridge1(class ScriptInstance *instance)
 	DiagDirection dir_1 = ::DiagdirBetweenTiles(end, start);
 	DiagDirection dir_2 = ::ReverseDiagDir(dir_1);
 
-	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(end + ::TileOffsByDiagDir(dir_2), ::DiagDirToRoadBits(dir_1), (::RoadType)ScriptRoad::GetCurrentRoadType(), DRD_NONE, 0);
+	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(end + ::TileOffsByDiagDir(dir_2), ::DiagDirToRoadBits(dir_1), (::RoadType)ScriptRoad::GetCurrentRoadType(), DRD_NONE, INVALID_TOWN);
 }
 
 /* static */ bool ScriptBridge::RemoveBridge(TileIndex tile)

src/script/api/script_tunnel.cpp

@@ -108,7 +108,7 @@ static void _DoCommandReturnBuildTunnel1(class ScriptInstance *instance)
 	DiagDirection dir_1 = ::DiagdirBetweenTiles(end, start);
 	DiagDirection dir_2 = ::ReverseDiagDir(dir_1);
 
-	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(&::_DoCommandReturnBuildTunnel2, start + ::TileOffsByDiagDir(dir_1), ::DiagDirToRoadBits(dir_2), ScriptRoad::GetRoadType(), DRD_NONE, 0);
+	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(&::_DoCommandReturnBuildTunnel2, start + ::TileOffsByDiagDir(dir_1), ::DiagDirToRoadBits(dir_2), ScriptRoad::GetRoadType(), DRD_NONE, INVALID_TOWN);
 }
 
 /* static */ bool ScriptTunnel::_BuildTunnelRoad2()
@@ -122,7 +122,7 @@ static void _DoCommandReturnBuildTunnel1(class ScriptInstance *instance)
 	DiagDirection dir_1 = ::DiagdirBetweenTiles(end, start);
 	DiagDirection dir_2 = ::ReverseDiagDir(dir_1);
 
-	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(end + ::TileOffsByDiagDir(dir_2), ::DiagDirToRoadBits(dir_1), ScriptRoad::GetRoadType(), DRD_NONE, 0);
+	return ScriptObject::Command<CMD_BUILD_ROAD>::Do(end + ::TileOffsByDiagDir(dir_2), ::DiagDirToRoadBits(dir_1), ScriptRoad::GetRoadType(), DRD_NONE, INVALID_TOWN);
 }
 
 /* static */ bool ScriptTunnel::RemoveTunnel(TileIndex tile)

src/town.h

@@ -28,8 +28,6 @@ struct BuildingCounts {
 static const uint CUSTOM_TOWN_NUMBER_DIFFICULTY  = 4; ///< value for custom town number in difficulty settings
 static const uint CUSTOM_TOWN_MAX_NUMBER = 5000;  ///< this is the maximum number of towns a user can specify in customisation
 
-static const TownID INVALID_TOWN = 0xFFFF;
-
 static const uint TOWN_GROWTH_WINTER = 0xFFFFFFFE; ///< The town only needs this cargo in the winter (any amount)
 static const uint TOWN_GROWTH_DESERT = 0xFFFFFFFF; ///< The town needs the cargo for growth when on desert (any amount)
 static const uint16_t TOWN_GROWTH_RATE_NONE = 0xFFFF; ///< Special value for Town::growth_rate to disable town growth.

src/town_cmd.cpp

@@ -1077,7 +1077,7 @@ static bool IsRoadAllowedHere(Town *t, TileIndex tile, DiagDirection dir)
 		 * If that fails clear the land, and if that fails exit.
 		 * This is to make sure that we can build a road here later. */
 		RoadType rt = GetTownRoadType();
-		if (Command<CMD_BUILD_ROAD>::Do(DC_AUTO | DC_NO_WATER, tile, (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? ROAD_Y : ROAD_X, rt, DRD_NONE, 0).Failed() &&
+		if (Command<CMD_BUILD_ROAD>::Do(DC_AUTO | DC_NO_WATER, tile, (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? ROAD_Y : ROAD_X, rt, DRD_NONE, INVALID_TOWN).Failed() &&
 				Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, tile).Failed()) {
 			return false;
 		}

src/town_type.h

@@ -13,6 +13,8 @@
 #include "core/enum_type.hpp"
 
 typedef uint16_t TownID;
+static const TownID INVALID_TOWN = 0xFFFF;
+
 struct Town;
 
 /** Supported initial town sizes */