Feature: Draw infinite water when all borders are water (#13289)

src/object_cmd.cpp

@@ -253,6 +253,11 @@ CommandCost CmdBuildObject(DoCommandFlags flags, TileIndex tile, ObjectType type
 					Owner o = GetTileOwner(t);
 					if (o != OWNER_NONE && o != OWNER_WATER) cost.AddCost(CheckOwnership(o, t));
 
+					/* If freeform edges are disabled, don't allow building on edge tiles. */
+					if (!_settings_game.construction.freeform_edges && (!IsInsideMM(TileX(t), 1, Map::MaxX() - 1) || !IsInsideMM(TileY(t), 1, Map::MaxY() - 1))) {
+						return CommandCost(STR_ERROR_TOO_CLOSE_TO_EDGE_OF_MAP);
+					}
+
 					/* However, the tile has to be clear of vehicles. */
 					cost.AddCost(EnsureNoVehicleOnGround(t));
 				}