Tracerestrict: Add flag for whether reserve through is always set

src/pbs.cpp

@@ -1262,6 +1262,7 @@ bool IsSafeWaitingPosition(const Train *v, TileIndex tile, Trackdir trackdir, bo
 			if (IsRestrictedSignal(ft.m_new_tile)) {
 				const TraceRestrictProgram *prog = GetExistingTraceRestrictProgram(ft.m_new_tile, TrackdirToTrack(td));
 				if (prog && prog->actions_used_flags & TRPAUF_RESERVE_THROUGH) {
+					if (prog->actions_used_flags & TRPAUF_RESERVE_THROUGH_ALWAYS) return false;
 					TraceRestrictProgramResult out;
 					prog->Execute(v, TraceRestrictProgramInput(ft.m_new_tile, td, &VehiclePosTraceRestrictPreviousSignalCallback, nullptr), out);
 					if (out.flags & TRPRF_RESERVE_THROUGH) {

src/tracerestrict.cpp

@@ -931,6 +931,11 @@ CommandCost TraceRestrictProgram::Validate(const std::vector<TraceRestrictItem>
 
 				case TRIT_RESERVE_THROUGH:
 					actions_used_flags |= TRPAUF_RESERVE_THROUGH;
+					if (GetTraceRestrictValue(item)) {
+						actions_used_flags &= ~TRPAUF_RESERVE_THROUGH_ALWAYS;
+					} else if (condstack.empty()) {
+						actions_used_flags |= TRPAUF_RESERVE_THROUGH_ALWAYS;
+					}
 					break;
 
 				case TRIT_LONG_RESERVE:

src/tracerestrict.h

@@ -422,6 +422,7 @@ enum TraceRestrictProgramActionsUsedFlags {
 	TRPAUF_SLOT_ACQUIRE_ON_RES    = 1 << 14, ///< Slot acquire (on reserve) action is present
 	TRPAUF_SPEED_ADAPTATION       = 1 << 15, ///< Speed adaptation control
 	TRPAUF_PBS_RES_END_SIMULATE   = 1 << 16, ///< PBS reservations ending at this signal slot changes must be fully simulated in dry run mode
+	TRPAUF_RESERVE_THROUGH_ALWAYS = 1 << 17, ///< Reserve through action is unconditionally set
 };
 DECLARE_ENUM_AS_BIT_SET(TraceRestrictProgramActionsUsedFlags)