Do not unnecessarily extend train reservations when passing signal

When the signal is a next-only or non-aspect-incrementing type, and
its maximum lookahead is not beyond the current end of the reservation

src/pbs.cpp

@@ -1099,14 +1099,13 @@ void TryCreateLookAheadForTrainInTunnelBridge(Train *t)
 	}
 }
 
-void SetTrainReservationLookaheadEnd(Train *v)
+int AdvanceTrainReservationLookaheadEnd(const Train *v, int lookahead_end_position)
 {
 	if (_settings_game.vehicle.realistic_braking_aspect_limited != TRBALM_ON || _extra_aspects == 0) {
-		v->lookahead->lookahead_end_position = v->lookahead->reservation_end_position + 1;
-		return;
+		return v->lookahead->reservation_end_position + 1;
 	}
 
-	if (v->lookahead->lookahead_end_position > v->lookahead->reservation_end_position) return;
+	if (lookahead_end_position > v->lookahead->reservation_end_position) return lookahead_end_position;
 
 	int32 threshold = v->lookahead->current_position + 24;
 	uint8 known_signals_ahead = 1;
@@ -1125,8 +1124,8 @@ void SetTrainReservationLookaheadEnd(Train *v)
 					known_signals_ahead = 1;
 					continue;
 				} else {
-					if (item.start > v->lookahead->lookahead_end_position) v->lookahead->lookahead_end_position = item.start;
-					return;
+					if (item.start > lookahead_end_position) lookahead_end_position = item.start;
+					return lookahead_end_position;
 				}
 			}
 
@@ -1141,18 +1140,24 @@ void SetTrainReservationLookaheadEnd(Train *v)
 			if (!HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC) || !allow_skip_no_aspect_inc) {
 				known_signals_ahead--;
 				if (known_signals_ahead == 0) {
-					if (item.start > v->lookahead->lookahead_end_position) v->lookahead->lookahead_end_position = item.start;
-					return;
+					if (item.start > lookahead_end_position) lookahead_end_position = item.start;
+					return lookahead_end_position;
 				}
 			}
 		}
 	}
 
 	/* Didn't need to stop at a signal along the reservation */
-	if (v->lookahead->reservation_end_position >= v->lookahead->lookahead_end_position) {
-		v->lookahead->lookahead_end_position = v->lookahead->reservation_end_position;
-		if (known_signals_ahead > 1) v->lookahead->lookahead_end_position++;
+	if (v->lookahead->reservation_end_position >= lookahead_end_position) {
+		lookahead_end_position = v->lookahead->reservation_end_position;
+		if (known_signals_ahead > 1) lookahead_end_position++;
 	}
+	return lookahead_end_position;
+}
+
+void SetTrainReservationLookaheadEnd(Train *v)
+{
+	v->lookahead->lookahead_end_position = AdvanceTrainReservationLookaheadEnd(v, v->lookahead->lookahead_end_position);
 }
 
 void FillTrainReservationLookAhead(Train *v)

src/pbs.h

@@ -164,6 +164,7 @@ bool ValidateLookAhead(const Train *v);
 PBSTileInfo FollowTrainReservation(const Train *v, Vehicle **train_on_res = nullptr, FollowTrainReservationFlags flags = FTRF_NONE);
 void ApplyAvailableFreeTunnelBridgeTiles(TrainReservationLookAhead *lookahead, int free_tiles, TileIndex tile, TileIndex end);
 void TryCreateLookAheadForTrainInTunnelBridge(Train *t);
+int AdvanceTrainReservationLookaheadEnd(const Train *v, int lookahead_end_position);
 void SetTrainReservationLookaheadEnd(Train *v);
 void FillTrainReservationLookAhead(Train *v);
 bool TrainReservationPassesThroughTile(const Train *v, TileIndex search_tile);

src/train_cmd.cpp

@@ -4120,6 +4120,7 @@ static bool IsReservationLookAheadLongEnough(const Train *v, const ChooseTrainTr
 	int signal_speed = 0;
 	int signal_position = 0;
 	int signal_z = 0;
+	bool signal_limited_lookahead_check = false;
 
 	for (const TrainReservationLookAheadItem &item : v->lookahead->items) {
 		if (item.type == TRLIT_REVERSE) {
@@ -4139,6 +4140,21 @@ static bool IsReservationLookAheadLongEnough(const Train *v, const ChooseTrainTr
 			signal_z = item.z_pos;
 			found_signal = true;
 		}
+
+		if (item.type == TRLIT_SIGNAL && _settings_game.vehicle.realistic_braking_aspect_limited == TRBALM_ON && item.start <= v->lookahead->current_position + 24) {
+			if (HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC) || HasBit(item.data_aux, TRSLAI_NEXT_ONLY) || HasBit(item.data_aux, TRSLAI_COMBINED_SHUNT)) {
+				signal_limited_lookahead_check = true;
+			}
+		}
+	}
+
+	if (signal_limited_lookahead_check) {
+		/* Do not unnecessarily extend the reservation when passing a signal within the reservation which could not display an aspect
+		 * beyond the current end of the reservation, e.g. banner repeaters and shunt signals */
+		if (AdvanceTrainReservationLookaheadEnd(v, v->lookahead->current_position + 24) <= v->lookahead->reservation_end_position &&
+				v->lookahead->reservation_end_position > v->lookahead->current_position + 24) {
+			return true;
+		}
 	}
 
 	if (found_signal) {