Fix adjacent level crossings left barred after removing middle of crossing

See: #517

src/rail_cmd.cpp

@@ -848,7 +848,7 @@ CommandCost CmdBuildSingleRail(TileIndex tile, DoCommandFlag flags, uint32 p1, u
 					if (flags & DC_EXEC) {
 						MakeRoadCrossing(tile, road_owner, tram_owner, _current_company, (track == TRACK_X ? AXIS_Y : AXIS_X), railtype, roadtype_road, roadtype_tram, GetTownIndex(tile));
 						UpdateLevelCrossing(tile, false);
-						MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(tile, GetCrossingRoadAxis(tile));
+						MarkDirtyAdjacentLevelCrossingTilesOnAdd(tile, GetCrossingRoadAxis(tile));
 						Company::Get(_current_company)->infrastructure.rail[railtype] += LEVELCROSSING_TRACKBIT_FACTOR;
 						DirtyCompanyInfrastructureWindows(_current_company);
 						if (num_new_road_pieces > 0 && Company::IsValidID(road_owner)) {
@@ -968,7 +968,7 @@ CommandCost CmdRemoveSingleRail(TileIndex tile, DoCommandFlag flags, uint32 p1,
 			}
 
 			if (flags & DC_EXEC) {
-				MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(tile, GetCrossingRoadAxis(tile));
+				UpdateAdjacentLevelCrossingTilesOnRemove(tile, GetCrossingRoadAxis(tile));
 				if (v != nullptr) FreeTrainTrackReservation(v);
 
 				owner = GetTileOwner(tile);

src/road_cmd.cpp

@@ -853,7 +853,7 @@ static CommandCost RemoveRoad(TileIndex tile, DoCommandFlag flags, RoadBits piec
 			}
 
 			if (flags & DC_EXEC) {
-				MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(tile, GetCrossingRoadAxis(tile));
+				UpdateAdjacentLevelCrossingTilesOnRemove(tile, GetCrossingRoadAxis(tile));
 
 				/* A full diagonal road tile has two road bits. */
 				UpdateCompanyRoadInfrastructure(existing_rt, GetRoadOwner(tile, rtt), -2);
@@ -1158,7 +1158,7 @@ CommandCost CmdBuildRoad(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32
 				MakeRoadCrossing(tile, company, company, GetTileOwner(tile), roaddir, GetRailType(tile), rtt == RTT_ROAD ? rt : INVALID_ROADTYPE, (rtt == RTT_TRAM) ? rt : INVALID_ROADTYPE, p2);
 				SetCrossingReservation(tile, reserved);
 				UpdateLevelCrossing(tile, false);
-				MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(tile, GetCrossingRoadAxis(tile));
+				MarkDirtyAdjacentLevelCrossingTilesOnAdd(tile, GetCrossingRoadAxis(tile));
 				if (RoadLayoutChangeNotificationEnabled(true)) NotifyRoadLayoutChangedIfTileNonLeaf(tile, rtt, GetCrossingRoadBits(tile));
 				if (rtt == RTT_ROAD) {
 					UpdateRoadCachedOneWayStatesAroundTile(tile);

src/road_func.h

@@ -155,7 +155,8 @@ RoadTypes GetRoadTypes(bool introduces);
 RoadTypes AddDateIntroducedRoadTypes(RoadTypes current, Date date);
 
 void UpdateLevelCrossing(TileIndex tile, bool sound = true, bool force_close = false);
-void MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(TileIndex tile, Axis road_axis);
+void MarkDirtyAdjacentLevelCrossingTilesOnAdd(TileIndex tile, Axis road_axis);
+void UpdateAdjacentLevelCrossingTilesOnRemove(TileIndex tile, Axis road_axis);
 bool IsCrossingOccupiedByRoadVehicle(TileIndex t);
 
 void UpdateRoadCachedOneWayStatesAroundTile(TileIndex tile);

src/train_cmd.cpp

@@ -2724,7 +2724,7 @@ void UpdateLevelCrossing(TileIndex tile, bool sound, bool force_close)
 	}
 }
 
-void MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(TileIndex tile, Axis road_axis)
+void MarkDirtyAdjacentLevelCrossingTilesOnAdd(TileIndex tile, Axis road_axis)
 {
 	if (!_settings_game.vehicle.adjacent_crossings) return;
 
@@ -2738,6 +2738,29 @@ void MarkDirtyAdjacentLevelCrossingTilesOnAddRemove(TileIndex tile, Axis road_ax
 	}
 }
 
+void UpdateAdjacentLevelCrossingTilesOnRemove(TileIndex tile, Axis road_axis)
+{
+	const DiagDirection dir1 = AxisToDiagDir(road_axis);
+	const DiagDirection dir2 = ReverseDiagDir(dir1);
+	for (DiagDirection dir : { dir1, dir2 }) {
+		const TileIndexDiff diff = TileOffsByDiagDir(dir);
+		bool occupied = false;
+		for (TileIndex t = tile + diff; IsValidTile(t) && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
+			occupied |= CheckLevelCrossing(t);
+		}
+		if (!occupied) {
+			for (TileIndex t = tile + diff; IsValidTile(t) && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
+				UpdateLevelCrossingTile(t, false, true, false);
+			}
+		} else {
+			const TileIndex t = tile + diff;
+			if (IsValidTile(t) && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis) {
+				MarkTileDirtyByTile(t, VMDF_NOT_MAP_MODE);
+			}
+		}
+	}
+}
+
 /**
  * Check if the level crossing is occupied by road vehicle(s).
  * @param t The tile to query.