Fix: Update last servicing dates when using the date cheat (#9694)

src/cheat_gui.cpp

@@ -14,6 +14,7 @@
 #include "company_func.h"
 #include "date_func.h"
 #include "saveload/saveload.h"
+#include "vehicle_base.h"
 #include "textbuf_gui.h"
 #include "window_gui.h"
 #include "string_func.h"
@@ -106,6 +107,7 @@ static int32 ClickChangeDateCheat(int32 p1, int32 p2)
 	if (p1 == _cur_year) return _cur_year;
 
 	Date new_date = ConvertYMDToDate(p1, ymd.month, ymd.day);
+	for (auto v : Vehicle::Iterate()) v->ShiftDates(new_date - _date);
 	LinkGraphSchedule::instance.ShiftDates(new_date - _date);
 	SetDate(new_date, _date_fract);
 	EnginesMonthlyLoop();

src/date.cpp

@@ -211,7 +211,7 @@ static void OnNewYear()
 		_cur_year--;
 		days_this_year = IsLeapYear(_cur_year) ? DAYS_IN_LEAP_YEAR : DAYS_IN_YEAR;
 		_date -= days_this_year;
-		for (Vehicle *v : Vehicle::Iterate()) v->date_of_last_service -= days_this_year;
+		for (Vehicle *v : Vehicle::Iterate()) v->ShiftDates(-days_this_year);
 		for (LinkGraph *lg : LinkGraph::Iterate()) lg->ShiftDates(-days_this_year);
 
 		/* Because the _date wraps here, and text-messages expire by game-days, we have to clean out

src/vehicle.cpp

@@ -763,6 +763,16 @@ uint32 Vehicle::GetGRFID() const
 	return this->GetEngine()->GetGRFID();
 }
 
+/**
+ * Shift all dates by given interval.
+ * This is useful if the date has been modified with the cheat menu.
+ * @param interval Number of days to be added or substracted.
+ */
+void Vehicle::ShiftDates(int interval)
+{
+	this->date_of_last_service += interval;
+}
+
 /**
  * Handle the pathfinding result, especially the lost status.
  * If the vehicle is now lost and wasn't previously fire an

src/vehicle_base.h

@@ -545,6 +545,8 @@ public:
 	 */
 	virtual void OnNewDay() {};
 
+	void ShiftDates(int interval);
+
 	/**
 	 * Crash the (whole) vehicle chain.
 	 * @param flooded whether the cause of the crash is flooding or not.