Add setting to control whether trains can crash with other companies'.

src/lang/english.txt

@@ -1254,6 +1254,9 @@ STR_CONFIG_SETTING_DYNAMIC_ENGINES_EXISTING_VEHICLES            :{WHITE}Changing
 STR_CONFIG_SETTING_INFRASTRUCTURE_MAINTENANCE                   :Infrastructure maintenance: {STRING2}
 STR_CONFIG_SETTING_INFRASTRUCTURE_MAINTENANCE_HELPTEXT          :When enabled, infrastructure causes maintenance costs. The cost grows over-proportional with the network size, thus affecting bigger companies more than smaller ones
 
+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.
+
 STR_CONFIG_SETTING_NEVER_EXPIRE_AIRPORTS                        :Airports never expire: {STRING2}
 STR_CONFIG_SETTING_NEVER_EXPIRE_AIRPORTS_HELPTEXT               :Enabling this setting makes each airport type stay available forever after its introduction
 

src/settings_gui.cpp

@@ -1661,6 +1661,7 @@ static SettingsContainer &GetSettingsTree()
 			disasters->Add(new SettingEntry("difficulty.economy"));
 			disasters->Add(new SettingEntry("difficulty.vehicle_breakdowns"));
 			disasters->Add(new SettingEntry("vehicle.plane_crashes"));
+			disasters->Add(new SettingEntry("vehicle.no_train_crash_other_company"));
 		}
 
 		SettingsPage *genworld = main->Add(new SettingsPage(STR_CONFIG_SETTING_GENWORLD));

src/settings_type.h

@@ -462,6 +462,7 @@ struct VehicleSettings {
 	byte   extend_vehicle_life;              ///< extend vehicle life by this many years
 	byte   road_side;                        ///< the side of the road vehicles drive on
 	uint8  plane_crashes;                    ///< number of plane crashes, 0 = none, 1 = reduced, 2 = normal
+	bool   no_train_crash_other_company;     ///< trains cannot crash with trains from other companies
 };
 
 /** Settings related to the economy. */

src/table/settings.ini

@@ -1142,6 +1142,15 @@ strhelp  = STR_CONFIG_SETTING_PLANE_CRASHES_HELPTEXT
 strval   = STR_CONFIG_SETTING_PLANE_CRASHES_NONE
 cat      = SC_BASIC
 
+[SDT_BOOL]
+base     = GameSettings
+var      = vehicle.no_train_crash_other_company
+def      = false
+str      = STR_CONFIG_SETTING_NO_TRAIN_CRASH_OTHER_COMPANY
+strhelp  = STR_CONFIG_SETTING_NO_TRAIN_CRASH_OTHER_COMPANY_HELPTEXT
+extver   = SlXvFeatureTest(XSLFTO_AND, XSLFI_INFRA_SHARING)
+patxname = ""infra_sharing.vehicle.no_train_crash_other_company""
+
 ; station.join_stations
 [SDT_NULL]
 length   = 1

src/train_cmd.cpp

@@ -3011,6 +3011,11 @@ static Vehicle *FindTrainCollideEnum(Vehicle *v, void *data)
 	/* not a train or in depot */
 	if (v->type != VEH_TRAIN || Train::From(v)->track == TRACK_BIT_DEPOT) return NULL;
 
+	if (_settings_game.vehicle.no_train_crash_other_company) {
+		/* do not crash into trains of another company. */
+		if (v->owner != tcc->v->owner) return NULL;
+	}
+
 	/* get first vehicle now to make most usual checks faster */
 	Train *coll = Train::From(v)->First();