From a2c0e6aa1863db1a7b1b32b6834f240bd44c5cf7 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Sat, 3 Jun 2023 22:04:24 +0100
Subject: [PATCH] Fix #10831: Level crossing parts left barred after crossing
 tile removal (#10874)

---
 src/rail_cmd.cpp  |  2 +-
 src/road_cmd.cpp  |  2 +-
 src/road_func.h   |  1 +
 src/train_cmd.cpp | 41 ++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index 1f44022211..eee3856a24 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -651,7 +651,7 @@ CommandCost CmdRemoveSingleRail(DoCommandFlag flags, TileIndex tile, Track track
 			cost.AddCost(RailClearCost(GetRailType(tile)));
 
 			if (flags & DC_EXEC) {
-				MarkDirtyAdjacentLevelCrossingTiles(tile, GetCrossingRoadAxis(tile));
+				UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(tile, GetCrossingRoadAxis(tile));
 
 				if (HasReservedTracks(tile, trackbit)) {
 					v = GetTrainForReservation(tile, track);
diff --git a/src/road_cmd.cpp b/src/road_cmd.cpp
index 0f112dc0a7..c29fef09e7 100644
--- a/src/road_cmd.cpp
+++ b/src/road_cmd.cpp
@@ -504,7 +504,7 @@ static CommandCost RemoveRoad(TileIndex tile, DoCommandFlag flags, RoadBits piec
 			}
 
 			if (flags & DC_EXEC) {
-				MarkDirtyAdjacentLevelCrossingTiles(tile, GetCrossingRoadAxis(tile));
+				UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(tile, GetCrossingRoadAxis(tile));
 
 				/* A full diagonal road tile has two road bits. */
 				UpdateCompanyRoadInfrastructure(existing_rt, GetRoadOwner(tile, rtt), -2);
diff --git a/src/road_func.h b/src/road_func.h
index 3c770a9de1..9b66fcc85b 100644
--- a/src/road_func.h
+++ b/src/road_func.h
@@ -155,6 +155,7 @@ RoadTypes AddDateIntroducedRoadTypes(RoadTypes current, TimerGameCalendar::Date
 
 void UpdateLevelCrossing(TileIndex tile, bool sound = true, bool force_bar = false);
 void MarkDirtyAdjacentLevelCrossingTiles(TileIndex tile, Axis road_axis);
+void UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(TileIndex tile, Axis road_axis);
 void UpdateCompanyRoadInfrastructure(RoadType rt, Owner o, int count);
 
 struct TileInfo;
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 13c241f4e9..6a0243d26c 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -1790,7 +1790,8 @@ void UpdateLevelCrossing(TileIndex tile, bool sound, bool force_bar)
 
 /**
  * Find adjacent level crossing tiles in this multi-track crossing and mark them dirty.
- * @param The tile which causes the update.
+ * @param tile The tile which causes the update.
+ * @param road_axis The road axis.
  */
 void MarkDirtyAdjacentLevelCrossingTiles(TileIndex tile, Axis road_axis)
 {
@@ -1804,6 +1805,44 @@ void MarkDirtyAdjacentLevelCrossingTiles(TileIndex tile, Axis road_axis)
 	}
 }
 
+/**
+ * Update adjacent level crossing tiles in this multi-track crossing, due to removal of a level crossing tile.
+ * @param tile The crossing tile which has been or is about to be removed, and which caused the update.
+ * @param road_axis The road axis.
+ */
+void UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(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; t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
+			occupied |= CheckLevelCrossing(t);
+		}
+		if (occupied) {
+			/* Mark the immediately adjacent tile dirty */
+			const TileIndex t = tile + diff;
+			if (t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis) {
+				MarkTileDirtyByTile(t);
+			}
+		} else {
+			/* Unbar the crossing tiles in this direction as necessary */
+			for (TileIndex t = tile + diff; t < Map::Size() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == road_axis; t += diff) {
+				if (IsCrossingBarred(t)) {
+					/* The crossing tile is barred, unbar it and continue to check the next tile */
+					SetCrossingBarred(t, false);
+					MarkTileDirtyByTile(t);
+				} else {
+					/* The crossing tile is already unbarred, mark the tile dirty and stop checking */
+					MarkTileDirtyByTile(t);
+					break;
+				}
+			}
+		}
+	}
+}
+
 /**
  * Bars crossing and plays ding-ding sound if not barred already
  * @param tile tile with crossing