Scheduled dispatch: Fixup start dates when changing game date

src/cheat_gui.cpp

@@ -28,6 +28,7 @@
 #include "newgrf.h"
 #include "error.h"
 #include "network/network.h"
+#include "order_base.h"
 
 #include "widgets/cheat_widget.h"
 
@@ -108,6 +109,7 @@ static int32 ClickChangeDateCheat(int32 p1, int32 p2)
 
 	Date new_date = ConvertYMDToDate(p1, ymd.month, ymd.day);
 	LinkGraphSchedule::instance.ShiftDates(new_date - _date);
+	ShiftOrderDates(new_date - _date);
 	SetDate(new_date, _date_fract);
 	EnginesMonthlyLoop();
 	SetWindowDirty(WC_STATUS_BAR, 0);

src/date.cpp

@@ -231,6 +231,7 @@ static void OnNewYear()
 		_date -= days_this_year;
 		for (Vehicle *v : Vehicle::Iterate()) v->date_of_last_service -= days_this_year;
 		for (LinkGraph *lg : LinkGraph::Iterate()) lg->ShiftDates(-days_this_year);
+		ShiftOrderDates(-days_this_year);
 
 		/* Because the _date wraps here, and text-messages expire by game-days, we have to clean out
 		 *  all of them if the date is set back, else those messages will hang for ever */

src/order_base.h

@@ -809,6 +809,8 @@ public:
 
 };
 
+void ShiftOrderDates(int interval);
+
 #define FOR_VEHICLE_ORDERS(v, order) for (order = (v->orders.list == nullptr) ? nullptr : v->orders.list->GetFirstOrder(); order != nullptr; order = order->next)
 
 #endif /* ORDER_BASE_H */

src/order_cmd.cpp

@@ -3004,3 +3004,12 @@ CommandCost CmdMassChangeOrder(TileIndex tile, DoCommandFlag flags, uint32 p1, u
 	}
 	return CommandCost();
 }
+
+void ShiftOrderDates(int interval)
+{
+	for (OrderList *orderlist : OrderList::Iterate()) {
+		if (orderlist->GetScheduledDispatchStartDatePart() >= 0) {
+			orderlist->SetScheduledDispatchStartDate(orderlist->GetScheduledDispatchStartDatePart() + interval, orderlist->GetScheduledDispatchStartDateFractPart());
+		}
+	}
+}

src/toolbar_gui.cpp

@@ -1159,6 +1159,7 @@ void SetStartingYear(Year year)
 	Date new_date = ConvertYMDToDate(_settings_game.game_creation.starting_year, 0, 1);
 	/* If you open a savegame as scenario there may already be link graphs.*/
 	LinkGraphSchedule::instance.ShiftDates(new_date - _date);
+	ShiftOrderDates(new_date - _date);
 	SetDate(new_date, 0);
 }