Preserve signal simulation/reservation data when upgrading bridges.

Based on commit 301925f948c9b36966c9c668e1476c2485425338

src/bridge_map.h

@@ -163,10 +163,24 @@ static inline void MakeRoadBridgeRamp(TileIndex t, Owner o, Owner owner_road, Ow
  * @param bridgetype the type of bridge this bridge ramp belongs to
  * @param d          the direction this ramp must be facing
  * @param r          the rail type of the bridge
+ * @param upgrade    whether the bridge is an upgrade instead of a totally new bridge
  */
-static inline void MakeRailBridgeRamp(TileIndex t, Owner o, BridgeType bridgetype, DiagDirection d, RailType r)
+static inline void MakeRailBridgeRamp(TileIndex t, Owner o, BridgeType bridgetype, DiagDirection d, RailType r, bool upgrade)
 {
+	// Backup bridge signal data.
+	auto m2_backup = _m[t].m2;
+	auto m5_backup = _m[t].m5;
+	auto m6_backup = _me[t].m6;
+
 	MakeBridgeRamp(t, o, bridgetype, d, TRANSPORT_RAIL, r);
+
+	// Restore bridge signal data if we're upgrading an existing bridge.
+	if (upgrade) {
+		_m[t].m2 = m2_backup;
+		SB(_m[t].m5, 4, 3, GB(m5_backup, 4, 3));
+		SB(_me[t].m6, 0, 2, GB(m6_backup, 0, 2));
+		SB(_me[t].m6, 6, 1, GB(m6_backup, 6, 1));
+	}
 }
 
 /**

src/tunnelbridge_cmd.cpp

@@ -339,7 +339,6 @@ CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, u
 	int z_end;
 	Slope tileh_start = GetTileSlope(tile_start, &z_start);
 	Slope tileh_end = GetTileSlope(tile_end, &z_end);
-	bool pbs_reservation = false;
 
 	CommandCost terraform_cost_north = CheckBridgeSlopeNorth(direction, &tileh_start, &z_start);
 	CommandCost terraform_cost_south = CheckBridgeSlopeSouth(direction, &tileh_end,   &z_end);
@@ -351,6 +350,7 @@ CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, u
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 	Owner owner;
 	bool is_new_owner;
+	bool is_upgrade = false;
 	if (IsBridgeTile(tile_start) && IsBridgeTile(tile_end) &&
 			GetOtherBridgeEnd(tile_start) == tile_end &&
 			GetTunnelBridgeTransportType(tile_start) == transport_type) {
@@ -393,11 +393,6 @@ CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, u
 		if (is_new_owner) owner = company;
 
 		switch (transport_type) {
-			case TRANSPORT_RAIL:
-				/* Keep the reservation, the path stays valid. */
-				pbs_reservation = HasTunnelBridgeReservation(tile_start);
-				break;
-
 			case TRANSPORT_ROAD:
 				/* Do not remove road types when upgrading a bridge */
 				roadtypes |= GetRoadTypes(tile_start);
@@ -405,6 +400,8 @@ CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, u
 
 			default: break;
 		}
+
+		is_upgrade = true;
 	} else {
 		/* Build a new bridge. */
 
@@ -518,10 +515,8 @@ CommandCost CmdBuildBridge(TileIndex end_tile, DoCommandFlag flags, uint32 p1, u
 			case TRANSPORT_RAIL:
 				/* Add to company infrastructure count if required. */
 				if (is_new_owner && c != NULL) c->infrastructure.rail[railtype] += (bridge_len + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR;
-				MakeRailBridgeRamp(tile_start, owner, bridge_type, dir,                 railtype);
-				MakeRailBridgeRamp(tile_end,   owner, bridge_type, ReverseDiagDir(dir), railtype);
-				SetTunnelBridgeReservation(tile_start, pbs_reservation);
-				SetTunnelBridgeReservation(tile_end,   pbs_reservation);
+				MakeRailBridgeRamp(tile_start, owner, bridge_type, dir,                 railtype, is_upgrade);
+				MakeRailBridgeRamp(tile_end,   owner, bridge_type, ReverseDiagDir(dir), railtype, is_upgrade);
 				break;
 
 			case TRANSPORT_ROAD: {