Add reserve through action to trace restrict programs.

This only changes the behaviour of PBS reservations which
would otherwise terminate at a PBS signal.
If the signal restriction sets the reserve through state,
the reservation continues through the signal, and the signal
is set to green.

src/lang/english.txt

@@ -2413,6 +2413,8 @@ STR_TRACE_RESTRICT_END                                          :End
 STR_TRACE_RESTRICT_PF_DENY                                      :Deny
 STR_TRACE_RESTRICT_PF_ALLOW                                     :Allow
 STR_TRACE_RESTRICT_PF_ALLOW_LONG                                :Allow (cancel previous Deny)
+STR_TRACE_RESTRICT_RESERVE_THROUGH                              :Reserve through
+STR_TRACE_RESTRICT_RESERVE_THROUGH_CANCEL                       :Cancel reserve through
 STR_TRACE_RESTRICT_PF_PENALTY                                   :Penalty
 STR_TRACE_RESTRICT_PF_VALUE_SMALL                               :small
 STR_TRACE_RESTRICT_PF_VALUE_MEDIUM                              :medium

src/pathfinder/yapf/yapf_rail.cpp

@@ -97,7 +97,7 @@ private:
 				m_res_fail_td = td;
 			}
 		} else {
-			if (!TryReserveRailTrack(tile, TrackdirToTrack(td))) {
+			if (!TryReserveRailTrackdir(tile, td)) {
 				/* Tile couldn't be reserved, undo. */
 				m_res_fail_tile = tile;
 				m_res_fail_td = td;

src/pbs.cpp

@@ -14,6 +14,7 @@
 #include "vehicle_func.h"
 #include "newgrf_station.h"
 #include "pathfinder/follow_track.hpp"
+#include "tracerestrict.h"
 
 #include "safeguards.h"
 
@@ -71,6 +72,24 @@ void SetRailStationPlatformReservation(TileIndex start, DiagDirection dir, bool
 	} while (IsCompatibleTrainStationTile(tile, start));
 }
 
+/**
+ * Try to reserve a specific track on a tile
+ * This also sets PBS signals to green if reserving through the facing track direction
+ * @param tile the tile
+ * @param t the track
+ * @param trigger_stations whether to call station randomisation trigger
+ * @return \c true if reservation was successful, i.e. the track was
+ *     free and didn't cross any other reserved tracks.
+ */
+bool TryReserveRailTrackdir(TileIndex tile, Trackdir td, bool trigger_stations)
+{
+	bool success = TryReserveRailTrack(tile, TrackdirToTrack(td), trigger_stations);
+	if (success && HasPbsSignalOnTrackdir(tile, td)) {
+		SetSignalStateByTrackdir(tile, td, SIGNAL_STATE_GREEN);
+	}
+	return success;
+}
+
 /**
  * Try to reserve a specific track on a tile
  * @param tile the tile
@@ -370,6 +389,46 @@ Train *GetTrainForReservation(TileIndex tile, Track track)
 	return NULL;
 }
 
+/**
+ * This is called to retrieve the previous signal, as required
+ * This is not run all the time as it is somewhat expensive and most restrictions will not test for the previous signal
+ */
+static TileIndex IsSafeWaitingPositionTraceRestrictPreviousSignalCallback(const Train *v, const void *)
+{
+	// scan forwards from vehicle position, for the case that train is waiting at/approaching PBS signal
+
+	TileIndex tile = v->tile;
+	Trackdir  trackdir = v->GetVehicleTrackdir();
+
+	CFollowTrackRail ft(v);
+
+	for (;;) {
+		if (IsTileType(tile, MP_RAILWAY) && HasSignalOnTrackdir(tile, trackdir)) {
+			if (HasPbsSignalOnTrackdir(tile, trackdir)) {
+				// found PBS signal
+				return tile;
+			} else {
+				// wrong type of signal
+				return INVALID_TILE;
+			}
+		}
+
+		// advance to next tile
+		if (!ft.Follow(tile, trackdir)) {
+			// ran out of track
+			return INVALID_TILE;
+		}
+
+		if (KillFirstBit(ft.m_new_td_bits) != TRACKDIR_BIT_NONE) {
+			// reached a junction tile
+			return INVALID_TILE;
+		}
+
+		tile = ft.m_new_tile;
+		trackdir = FindFirstTrackdir(ft.m_new_td_bits);
+	}
+}
+
 /**
  * Determine whether a certain track on a tile is a safe position to end a path.
  *
@@ -405,8 +464,20 @@ bool IsSafeWaitingPosition(const Train *v, TileIndex tile, Trackdir trackdir, bo
 
 	if (ft.m_new_td_bits != TRACKDIR_BIT_NONE && KillFirstBit(ft.m_new_td_bits) == TRACKDIR_BIT_NONE) {
 		Trackdir td = FindFirstTrackdir(ft.m_new_td_bits);
-		/* PBS signal on next trackdir? Safe position. */
+		/* PBS signal on next trackdir? Conditionally safe position. */
-		if (HasPbsSignalOnTrackdir(ft.m_new_tile, td)) return true;
+		if (HasPbsSignalOnTrackdir(ft.m_new_tile, td)) {
+			if (IsRestrictedSignal(ft.m_new_tile)) {
+				const TraceRestrictProgram *prog = GetExistingTraceRestrictProgram(ft.m_new_tile, TrackdirToTrack(td));
+				if (prog) {
+					TraceRestrictProgramResult out;
+					prog->Execute(v, TraceRestrictProgramInput(tile, trackdir, &IsSafeWaitingPositionTraceRestrictPreviousSignalCallback, nullptr), out);
+					if (out.flags & TRPRF_RESERVE_THROUGH) {
+						return false;
+					}
+				}
+			}
+			return true;
+		}
 		/* One-way PBS signal against us? Safe if end-of-line is allowed. */
 		if (IsTileType(ft.m_new_tile, MP_RAILWAY) && HasSignalOnTrackdir(ft.m_new_tile, ReverseTrackdir(td)) &&
 				GetSignalType(ft.m_new_tile, TrackdirToTrack(td)) == SIGTYPE_PBS_ONEWAY) {

src/pbs.h

@@ -22,6 +22,7 @@ TrackBits GetReservedTrackbits(TileIndex t);
 void SetRailStationPlatformReservation(TileIndex start, DiagDirection dir, bool b);
 
 bool TryReserveRailTrack(TileIndex tile, Track t, bool trigger_stations = true);
+bool TryReserveRailTrackdir(TileIndex tile, Trackdir td, bool trigger_stations = true);
 void UnreserveRailTrack(TileIndex tile, Track t);
 
 /** This struct contains information about the end of a reserved path. */

src/tracerestrict.cpp

@@ -382,6 +382,14 @@ void TraceRestrictProgram::Execute(const Train* v, const TraceRestrictProgramInp
 						}
 						break;
 
+					case TRIT_RESERVE_THROUGH:
+						if (GetTraceRestrictValue(item)) {
+							out.flags &= ~TRPRF_RESERVE_THROUGH;
+						} else {
+							out.flags |= TRPRF_RESERVE_THROUGH;
+						}
+						break;
+
 					default:
 						NOT_REACHED();
 				}
@@ -502,6 +510,7 @@ void SetTraceRestrictValueDefault(TraceRestrictItem &item, TraceRestrictValueTyp
 		case TRVT_DENY:
 		case TRVT_SPEED:
 		case TRVT_TILE_INDEX:
+		case TRVT_RESERVE_THROUGH:
 			SetTraceRestrictValue(item, 0);
 			SetTraceRestrictAuxField(item, 0);
 			break;

src/tracerestrict.h

@@ -97,6 +97,7 @@ enum TraceRestrictItemType {
 	TRIT_NULL                     = 0,    ///< Null-type, not in programs and not valid for execution, mainly used with TraceRestrictNullTypeSpecialValue for start/end
 	TRIT_PF_DENY                  = 1,    ///< Pathfinder deny/allow
 	TRIT_PF_PENALTY               = 2,    ///< Add to pathfinder penalty
+	TRIT_RESERVE_THROUGH          = 3,    ///< Reserve through PBS signal
 
 	TRIT_COND_BEGIN               = 8,    ///< Start of conditional item types, note that this has the save value as TRIT_COND_ENDIF
 	TRIT_COND_ENDIF               = 8,    ///< This is an endif block or an else block
@@ -192,6 +193,7 @@ enum TraceRestrictPathfinderPenaltyPresetIndex {
  */
 enum TraceRestrictProgramResultFlags {
 	TRPRF_DENY                    = 1 << 0,  ///< Pathfinder deny is set
+	TRPRF_RESERVE_THROUGH         = 1 << 1,  ///< Reserve through is set
 };
 DECLARE_ENUM_AS_BIT_SET(TraceRestrictProgramResultFlags)
 
@@ -392,6 +394,7 @@ enum TraceRestrictValueType {
 	TRVT_DIRECTION                = 7, ///< takes a TraceRestrictDirectionTypeSpecialValue
 	TRVT_TILE_INDEX               = 8, ///< takes a TileIndex in the next item slot
 	TRVT_PF_PENALTY               = 9, ///< takes a pathfinder penalty value or preset index, as per the auxiliary field as type: TraceRestrictPathfinderPenaltyAuxField
+	TRVT_RESERVE_THROUGH          = 10,///< takes a value 0 = reserve through, 1 = cancel previous reserve through
 };
 
 /**
@@ -463,6 +466,8 @@ static inline TraceRestrictTypePropertySet GetTraceRestrictTypeProperties(TraceR
 			out.value_type = TRVT_PF_PENALTY;
 		} else if (GetTraceRestrictType(item) == TRIT_PF_DENY) {
 			out.value_type = TRVT_DENY;
+		} else if (GetTraceRestrictType(item) == TRIT_RESERVE_THROUGH) {
+			out.value_type = TRVT_RESERVE_THROUGH;
 		} else {
 			out.value_type = TRVT_NONE;
 		}

src/tracerestrict_gui.cpp

@@ -119,6 +119,7 @@ static const StringID _program_insert_str[] = {
 	STR_TRACE_RESTRICT_CONDITIONAL_ELSE,
 	STR_TRACE_RESTRICT_PF_DENY,
 	STR_TRACE_RESTRICT_PF_PENALTY,
+	STR_TRACE_RESTRICT_RESERVE_THROUGH,
 	INVALID_STRING_ID
 };
 static const uint32 _program_insert_else_hide_mask    = 8;     ///< disable bitmask for else
@@ -131,6 +132,7 @@ static const uint _program_insert_val[] = {
 	TRIT_COND_ENDIF | (TRCF_ELSE << 16),               // else block
 	TRIT_PF_DENY,                                      // deny
 	TRIT_PF_PENALTY,                                   // penalty
+	TRIT_RESERVE_THROUGH,                              // reserve through
 };
 
 /** insert drop down list strings and values */
@@ -153,6 +155,21 @@ static const TraceRestrictDropDownListSet _deny_value = {
 	_deny_value_str, _deny_value_val,
 };
 
+static const StringID _reserve_through_value_str[] = {
+	STR_TRACE_RESTRICT_RESERVE_THROUGH,
+	STR_TRACE_RESTRICT_RESERVE_THROUGH_CANCEL,
+	INVALID_STRING_ID
+};
+static const uint _reserve_through_value_val[] = {
+	0,
+	1,
+};
+
+/** value drop down list for deny types strings and values */
+static const TraceRestrictDropDownListSet _reserve_through_value = {
+	_reserve_through_value_str, _reserve_through_value_val,
+};
+
 static const StringID _direction_value_str[] = {
 	STR_TRACE_RESTRICT_DIRECTION_FRONT,
 	STR_TRACE_RESTRICT_DIRECTION_BACK,
@@ -211,11 +228,13 @@ static const TraceRestrictDropDownListSet *GetTypeDropDownListSet(TraceRestrictI
 	static const StringID str_action[] = {
 		STR_TRACE_RESTRICT_PF_DENY,
 		STR_TRACE_RESTRICT_PF_PENALTY,
+		STR_TRACE_RESTRICT_RESERVE_THROUGH,
 		INVALID_STRING_ID,
 	};
 	static const uint val_action[] = {
 		TRIT_PF_DENY,
 		TRIT_PF_PENALTY,
+		TRIT_RESERVE_THROUGH,
 	};
 	static const TraceRestrictDropDownListSet set_action = {
 		str_action, val_action,
@@ -642,6 +661,10 @@ static void DrawInstructionString(const TraceRestrictProgram *prog, TraceRestric
 				}
 				break;
 
+			case TRIT_RESERVE_THROUGH:
+				instruction_string = GetTraceRestrictValue(item) ? STR_TRACE_RESTRICT_RESERVE_THROUGH_CANCEL : STR_TRACE_RESTRICT_RESERVE_THROUGH;
+				break;
+
 			default:
 				NOT_REACHED();
 				break;
@@ -843,6 +866,10 @@ public:
 						this->ShowDropDownListWithValue(&_pf_penalty_dropdown, GetPathfinderPenaltyDropdownIndex(item), false, TR_WIDGET_VALUE_DROPDOWN, 0, 0, 0);
 						break;
 
+					case TRVT_RESERVE_THROUGH:
+						this->ShowDropDownListWithValue(&_reserve_through_value, GetTraceRestrictValue(item), false, TR_WIDGET_VALUE_DROPDOWN, 0, 0, 0);
+						break;
+
 					default:
 						break;
 				}
@@ -1581,6 +1608,13 @@ private:
 							}
 							break;
 
+						case TRVT_RESERVE_THROUGH:
+							right_sel->SetDisplayedPlane(DPR_VALUE_DROPDOWN);
+							this->EnableWidget(TR_WIDGET_VALUE_DROPDOWN);
+							this->GetWidget<NWidgetCore>(TR_WIDGET_VALUE_DROPDOWN)->widget_data =
+									GetTraceRestrictValue(item) ? STR_TRACE_RESTRICT_RESERVE_THROUGH_CANCEL : STR_TRACE_RESTRICT_RESERVE_THROUGH;
+							break;
+
 						default:
 							break;
 					}

src/train_cmd.cpp

@@ -2386,7 +2386,7 @@ static PBSTileInfo ExtendTrainReservation(const Train *v, TrackBits *new_tracks,
 			return PBSTileInfo(tile, cur_td, true);
 		}
 
-		if (!TryReserveRailTrack(tile, TrackdirToTrack(cur_td))) break;
+		if (!TryReserveRailTrackdir(tile, cur_td)) break;
 	}
 
 	if (ft.m_err == CFollowTrackRail::EC_OWNER || ft.m_err == CFollowTrackRail::EC_NO_WAY) {