From 67506e3781c0c1a19eeac875e87868e1905d3499 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Tue, 27 Oct 2020 17:36:53 +0000
Subject: [PATCH] Return error when upgrading airport to an identical
 configuration

See: #200
---
 src/station_cmd.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index cbf533cdec..307deedf98 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -2467,6 +2467,10 @@ CommandCost CmdBuildAirport(TileIndex tile, DoCommandFlag flags, uint32 p1, uint
 		return_cmd_error(STR_ERROR_TOO_CLOSE_TO_ANOTHER_AIRPORT);
 	}
 
+	if (action == AIRPORT_UPGRADE && airport_type == st->airport.type && layout == st->airport.layout && st->airport.tile == tile) {
+		return_cmd_error(STR_ERROR_ALREADY_BUILT);
+	}
+
 	/* The noise level is the noise from the airport and reduce it to account for the distance to the town center. */
 	uint dist;
 	Town *nearest = AirportGetNearestTown(as, iter, dist);