Feature: Engine expiry setting to keep owned engines available for purchase

src/engine.cpp

@@ -24,6 +24,7 @@
 #include "engine_gui.h"
 #include "engine_func.h"
 #include "engine_base.h"
+#include "engine_type.h"
 #include "company_base.h"
 #include "vehicle_func.h"
 #include "articulated_vehicles.h"
@@ -604,6 +605,32 @@ static void ClearLastVariant(EngineID engine_id, VehicleType type)
 	}
 }
 
+/**
+ * Is a given engine allowed to expire?
+ * @note This does not age or retire the engine, just check if expiry is allowed.
+ * @param e The engine in question.
+ * @return True iff the engine can be checked for retirement.
+ */
+static bool AllowEngineExpiry(Engine *e)
+{
+	/* The vehicle is set to never expire. */
+	if (e->info.base_life == 0xFF) return false;
+
+	/* The player will not allow any vehicle to expire. */
+	if (_settings_game.vehicle.engine_expiry == EngineExpiryMode::Never) return false;
+
+	/* The player wants to keep buying vehicles someone already owns. */
+	if (_settings_game.vehicle.engine_expiry == EngineExpiryMode::Owned) {
+		for (const Company *c : Company::Iterate()) {
+			if (c == nullptr) continue;
+			if (GetGroupNumEngines(c->index, ALL_GROUP, e->index) > 0) return false;
+		}
+	}
+
+	/* Vehicles expire normally. */
+	return true;
+}
+
 /**
  * Update #Engine::reliability and (if needed) update the engine GUIs.
  * @param e %Engine to update.
@@ -620,7 +647,7 @@ void CalcEngineReliability(Engine *e, bool new_month)
 	if (new_month && re->index > e->index && age != INT32_MAX) age++; /* parent variant's age has not yet updated. */
 
 	/* Check for early retirement */
-	if (e->company_avail != 0 && !_settings_game.vehicle.never_expire_vehicles && e->info.base_life != 0xFF) {
+	if (e->company_avail != 0 && AllowEngineExpiry(e)) {
 		int retire_early = e->info.retire_early;
 		uint retire_early_max_age = std::max(0, e->duration_phase_1 + e->duration_phase_2 - retire_early * 12);
 		if (retire_early != 0 && age >= retire_early_max_age) {
@@ -634,7 +661,7 @@ void CalcEngineReliability(Engine *e, bool new_month)
 	if (age < e->duration_phase_1) {
 		uint start = e->reliability_start;
 		e->reliability = age * (e->reliability_max - start) / e->duration_phase_1 + start;
-	} else if ((age -= e->duration_phase_1) < e->duration_phase_2 || _settings_game.vehicle.never_expire_vehicles || e->info.base_life == 0xFF) {
+	} else if ((age -= e->duration_phase_1) < e->duration_phase_2 || !AllowEngineExpiry(e)) {
 		/* We are at the peak of this engines life. It will have max reliability.
 		 * This is also true if the engines never expire. They will not go bad over time */
 		e->reliability = e->reliability_max;

src/engine_type.h

@@ -195,6 +195,15 @@ enum EngineNameContext : uint8_t {
 	AutoreplaceVehicleInUse = 0x22, ///< Name is show in the autoreplace window 'Vehicles in use' panel.
 };
 
+/**
+ * Possible values of the "engine_expiry" setting.
+ */
+enum EngineExpiryMode : uint8_t {
+	Off = 0,   ///< Engines expire normally.
+	Never = 1, ///< Engines never expire.
+	Owned = 2, ///< Engines which are currently owned by any company never expire. Unowned vehicles expire normally.
+};
+
 /** Combine an engine ID and a name context to an engine name dparam. */
 inline uint64_t PackEngineNameDParam(EngineID engine_id, EngineNameContext context, uint32_t extra_data = 0)
 {

src/lang/english.txt

@@ -1492,7 +1492,12 @@ STR_CONFIG_SETTING_WARN_INCOME_LESS_HELPTEXT                    :When enabled, a
 STR_CONFIG_SETTING_WARN_INCOME_LESS_HELPTEXT_PERIOD             :When enabled, a news message gets sent when a vehicle has not made any profit within a period
 
 STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES                        :Vehicles never expire: {STRING2}
-STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_HELPTEXT               :When enabled, all vehicle models remain available forever after their introduction
+STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_HELPTEXT               :Choose if vehicle models remain available forever after their introduction
+
+###length 3
+STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_OFF                    :Off
+STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_NEVER                  :All available forever
+STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_OWNED                  :Owned vehicles available forever
 
 STR_CONFIG_SETTING_TIMEKEEPING_UNITS                            :Timekeeping: {STRING2}
 STR_CONFIG_SETTING_TIMEKEEPING_UNITS_HELPTEXT                   :Select the timekeeping units of the game. This cannot be changed later.{}{}Calendar-based is the classic OpenTTD experience, with a year consisting of 12 months, and each month having 28-31 days.{}{}In Wallclock-based time, cargo production and financials are instead based on one-minute increments, which is about as long as a 30 day month takes in Calendar-based mode. These are grouped into 12-minute periods, equivalent to a year in Calendar-based mode.{}{}In either mode there is always a classic calendar, which is used for introduction dates of vehicles, houses, and other infrastructure

src/saveload/afterload.cpp

@@ -795,6 +795,11 @@ bool AfterLoadGame()
 		_settings_game.linkgraph.recalc_time     *= CalendarTime::SECONDS_PER_DAY;
 	}
 
+	/* Convert old engine expiry setting. */
+	if (IsSavegameVersionBefore(SLV_ENGINE_EXPIRY_OWNED)) {
+		_settings_game.vehicle.engine_expiry = _settings_game.vehicle.never_expire_vehicles ? EngineExpiryMode::Never : EngineExpiryMode::Off;
+	}
+
 	/* Load the sprites */
 	GfxLoadSprites();
 	LoadStringWidthTable();

src/saveload/saveload.h

@@ -379,6 +379,8 @@ enum SaveLoadVersion : uint16_t {
 	SLV_SCRIPT_RANDOMIZER,                  ///< 333  PR#12063 v14.0-RC1 Save script randomizers.
 	SLV_VEHICLE_ECONOMY_AGE,                ///< 334  PR#12141 v14.0 Add vehicle age in economy year, for profit stats minimum age
 
+	SLV_ENGINE_EXPIRY_OWNED,                ///< 335  PR#12598 Add engine expiry mode to keep owned engines available for purchase.
+
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };
 

src/settings_gui.cpp

@@ -2144,7 +2144,7 @@ static SettingsContainer &GetSettingsTree()
 			limitations->Add(new SettingEntry("construction.max_bridge_height"));
 			limitations->Add(new SettingEntry("construction.max_tunnel_length"));
 			limitations->Add(new SettingEntry("station.never_expire_airports"));
-			limitations->Add(new SettingEntry("vehicle.never_expire_vehicles"));
+			limitations->Add(new SettingEntry("vehicle.engine_expiry"));
 			limitations->Add(new SettingEntry("vehicle.max_trains"));
 			limitations->Add(new SettingEntry("vehicle.max_roadveh"));
 			limitations->Add(new SettingEntry("vehicle.max_aircraft"));

src/settings_type.h

@@ -14,6 +14,7 @@
 #include "economy_type.h"
 #include "town_type.h"
 #include "transport_type.h"
+#include "engine_type.h"
 #include "network/network_type.h"
 #include "company_type.h"
 #include "cargotype.h"
@@ -516,6 +517,8 @@ struct OrderSettings {
 
 /** Settings related to vehicles. */
 struct VehicleSettings {
+	bool never_expire_vehicles;              ///< Unused value, used to load old savegames.
+
 	uint8_t  max_train_length;                 ///< maximum length for trains
 	uint8_t  smoke_amount;                     ///< amount of smoke/sparks locomotives produce
 	uint8_t  train_acceleration_model;         ///< realistic acceleration for trains
@@ -531,7 +534,7 @@ struct VehicleSettings {
 	uint8_t  plane_speed;                      ///< divisor for speed of aircraft
 	uint8_t  freight_trains;                   ///< value to multiply the weight of cargo by
 	bool   dynamic_engines;                  ///< enable dynamic allocation of engine data
-	bool   never_expire_vehicles;            ///< never expire vehicles
+	EngineExpiryMode engine_expiry;           ///< engine expiry
 	uint8_t extend_vehicle_life;              ///< extend vehicle life by this many years
 	uint8_t road_side;                        ///< the side of the road vehicles drive on
 	uint8_t  plane_crashes;                    ///< number of plane crashes, 0 = none, 1 = reduced, 2 = normal

src/table/settings/game_settings.ini

@@ -10,6 +10,7 @@
 
 [pre-amble]
 static constexpr std::initializer_list<const char*> _roadsides{"left", "right"};
+static constexpr std::initializer_list<const char*> _engine_expiry_modes{"off", "never", "owned"};
 
 static void StationSpreadChanged(int32_t new_value);
 static void UpdateConsists(int32_t new_value);
@@ -243,8 +244,21 @@ strval   = STR_CONFIG_SETTING_NONE
 var      = vehicle.never_expire_vehicles
 flags    = SF_NO_NETWORK
 def      = false
+to       = SLV_ENGINE_EXPIRY_OWNED
+
+[SDT_OMANY]
+var      = vehicle.engine_expiry
+type     = SLE_UINT8
+from     = SLV_ENGINE_EXPIRY_OWNED
+flags    = SF_GUI_DROPDOWN | SF_NO_NETWORK
+def      = EngineExpiryMode::Off
+min      = EngineExpiryMode::Off
+max      = EngineExpiryMode::Owned
+full     = _engine_expiry_modes
 str      = STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES
 strhelp  = STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_HELPTEXT
+strval   = STR_CONFIG_SETTING_NEVER_EXPIRE_VEHICLES_OFF
+cat      = SC_BASIC
 
 [SDT_VAR]
 var      = vehicle.max_trains