Chunnel: Add setting to enable construction, default off.

src/lang/english.txt

@@ -1267,6 +1267,9 @@ STR_CONFIG_SETTING_INFRASTRUCTURE_MAINTENANCE_HELPTEXT          :When enabled, i
 STR_CONFIG_SETTING_SHIP_COLLISION_AVOIDANCE                     :Ships avoid collisions: {STRING2}
 STR_CONFIG_SETTING_SHIP_COLLISION_AVOIDANCE_HELPTEXT            :When enabled, ships try to avoid passing through each other. Requires 90° turns to be forbidden.
 
+STR_CONFIG_SETTING_CHUNNEL                                      :Allow construction of tunnels under water: {STRING2}
+STR_CONFIG_SETTING_CHUNNEL_HELPTEXT                             :When enabled, tunnels can be constructed under bodies of water at sea level. This requires the tunnel ends to be least 3 tiles away from the shore.
+
 STR_CONFIG_SETTING_NO_TRAIN_CRASH_OTHER_COMPANY                 :Trains from different companies may not crash into each other: {STRING2}
 STR_CONFIG_SETTING_NO_TRAIN_CRASH_OTHER_COMPANY_HELPTEXT        :This setting is primarily to prevent untrusted players deliberately causing crashes involving other companies' trains in multi-player rail infrastructure sharing games.
 

src/settings_gui.cpp

@@ -1701,6 +1701,7 @@ static SettingsContainer &GetSettingsTree()
 			limitations->Add(new SettingEntry("construction.max_bridge_length"));
 			limitations->Add(new SettingEntry("construction.max_bridge_height"));
 			limitations->Add(new SettingEntry("construction.max_tunnel_length"));
+			limitations->Add(new SettingEntry("construction.chunnel"));
 			limitations->Add(new SettingEntry("station.never_expire_airports"));
 			limitations->Add(new SettingEntry("vehicle.never_expire_vehicles"));
 			limitations->Add(new SettingEntry("vehicle.max_trains"));

src/settings_type.h

@@ -355,6 +355,7 @@ struct ConstructionSettings {
 	byte   simulated_wormhole_signals;       ///< simulate signals in tunnel
 	bool   enable_build_river;               ///< enable building rivers in-game
 	uint8  road_custom_bridge_heads;         ///< allow construction of road custom bridge heads
+	bool   chunnel;                          ///< allow construction of tunnels under water
 
 	uint32 terraform_per_64k_frames;         ///< how many tile heights may, over a long period, be terraformed per 65536 frames?
 	uint16 terraform_frame_burst;            ///< how many tile heights may, over a short period, be terraformed?

src/table/settings.ini

@@ -597,6 +597,16 @@ str      = STR_CONFIG_SETTING_MAX_TUNNEL_LENGTH
 strhelp  = STR_CONFIG_SETTING_MAX_TUNNEL_LENGTH_HELPTEXT
 strval   = STR_CONFIG_SETTING_TILE_LENGTH
 
+[SDT_BOOL]
+base     = GameSettings
+var      = construction.chunnel
+def      = false
+str      = STR_CONFIG_SETTING_CHUNNEL
+strhelp  = STR_CONFIG_SETTING_CHUNNEL_HELPTEXT
+from     = 0
+cat      = SC_BASIC
+patxname = ""chunnel.construction.chunnel""
+
 [SDT_VAR]
 base     = GameSettings
 var      = construction.simulated_wormhole_signals

src/tunnelbridge_cmd.cpp

@@ -692,7 +692,7 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 			_build_tunnel_endtile = found_tunnel_tile != INVALID_TILE ? found_tunnel_tile : end_tile;
 
 			/* Test if we are on a shore. */
-			if (end_z == 0 &&
+			if (end_z == 0 && _settings_game.construction.chunnel &&
 					(IsCoastTile(end_tile) ||
 					(IsValidTile(end_tile + delta) && HasTileWaterGround(end_tile + delta)) ||
 					(IsValidTile(end_tile + delta * 2) && HasTileWaterGround(end_tile + delta * 2)))) {