(svn r17460) -Feature: allow building rail stations over existing rail without signals but will upgrade normal rail to electrified rail if necessary (based on patch by laurijh)

src/station_cmd.cpp

@@ -662,7 +662,7 @@ CommandCost ClearTile_Station(TileIndex tile, DoCommandFlag flags);
  * @param check_clear if clearing tile should be performed (in wich case, cost will be added)
  * @return the cost in case of success, or an error code if it failed.
  */
-CommandCost CheckFlatLandBelow(TileIndex tile, uint w, uint h, DoCommandFlag flags, uint invalid_dirs, StationID *station, bool check_clear = true)
+CommandCost CheckFlatLandBelow(TileIndex tile, uint w, uint h, DoCommandFlag flags, uint invalid_dirs, StationID *station, bool check_clear = true, RailType rt = INVALID_RAILTYPE)
 {
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 	int allowed_z = -1;
@@ -723,6 +723,29 @@ CommandCost CheckFlatLandBelow(TileIndex tile, uint w, uint h, DoCommandFlag fla
 				}
 			}
 		} else if (check_clear) {
+			/* Rail type is only valid when building a railway station; in station to
+			 * build isn't a rail station it's INVALID_RAILTYPE. */
+			if (rt != INVALID_RAILTYPE &&
+					IsPlainRailTile(tile_cur) && !HasSignals(tile_cur) &&
+					HasPowerOnRail(GetRailType(tile), rt)) {
+				/* Allow overbuilding if the tile:
+				 *  - has rail, but no signals
+				 *  - it has exactly one track
+				 *  - the track is in line with the station
+				 *  - the current rail type has power on the to-be-built type (e.g. convert normal rail to el rail)
+				 */
+				TrackBits tracks = GetTrackBits(tile_cur);
+				Track track = RemoveFirstTrack(&tracks);
+				Track expected_track = HasBit(invalid_dirs, DIAGDIR_NE) ? TRACK_X : TRACK_Y;
+
+				if (tracks == TRACK_BIT_NONE && track == expected_track) {
+					CommandCost ret = DoCommand(tile_cur, 0, track, flags, CMD_REMOVE_SINGLE_RAIL);
+					if (CmdFailed(ret)) return ret;
+					cost.AddCost(ret);
+					/* With flags & ~DC_EXEC CmdLandscapeClear would fail since the rail still exists */
+					continue;
+				}
+			}
 			CommandCost ret = DoCommand(tile_cur, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
 			if (CmdFailed(ret)) return ret;
 			cost.AddCost(ret);
@@ -975,7 +998,7 @@ CommandCost CmdBuildRailStation(TileIndex tile_org, DoCommandFlag flags, uint32
 	/* If DC_EXEC is in flag, do not want to pass it to CheckFlatLandBelow, because of a nice bug
 	 * for detail info, see:
 	 * https://sourceforge.net/tracker/index.php?func=detail&aid=1029064&group_id=103924&atid=636365 */
-	CommandCost ret = CheckFlatLandBelow(tile_org, w_org, h_org, flags & ~DC_EXEC, 5 << axis, _settings_game.station.nonuniform_stations ? &est : NULL);
+	CommandCost ret = CheckFlatLandBelow(tile_org, w_org, h_org, flags & ~DC_EXEC, 5 << axis, _settings_game.station.nonuniform_stations ? &est : NULL, true, rt);
 	if (CmdFailed(ret)) return ret;
 	CommandCost cost(EXPENSES_CONSTRUCTION, ret.GetCost() + (numtracks * _price.train_station_track + _price.train_station_length) * plat_len);
 
@@ -1045,7 +1068,7 @@ CommandCost CmdBuildRailStation(TileIndex tile_org, DoCommandFlag flags, uint32
 		/* Now really clear the land below the station
 		 * It should never return CMD_ERROR.. but you never know ;)
 		 * (a bit strange function name for it, but it really does clear the land, when DC_EXEC is in flags) */
-		ret = CheckFlatLandBelow(tile_org, w_org, h_org, flags, 5 << axis, _settings_game.station.nonuniform_stations ? &est : NULL);
+		ret = CheckFlatLandBelow(tile_org, w_org, h_org, flags, 5 << axis, _settings_game.station.nonuniform_stations ? &est : NULL, true, rt);
 		if (CmdFailed(ret)) return ret;
 
 		st->train_station = new_location;

src/unmovable_cmd.cpp

@@ -99,7 +99,7 @@ void UpdateCompanyHQ(Company *c, uint score)
 	MarkTileDirtyByTile(tile + TileDiffXY(1, 1));
 }
 
-extern CommandCost CheckFlatLandBelow(TileIndex tile, uint w, uint h, DoCommandFlag flags, uint invalid_dirs, StationID *station, bool check_clear = true);
+extern CommandCost CheckFlatLandBelow(TileIndex tile, uint w, uint h, DoCommandFlag flags, uint invalid_dirs, StationID *station, bool check_clear = true, RailType rt = INVALID_RAILTYPE);
 
 /** Build or relocate the HQ. This depends if the HQ is already built or not
  * @param tile tile where the HQ will be built or relocated to