Add trace restrict slot membership conditional.

src/lang/english.txt

@@ -2403,6 +2403,7 @@ STR_TRACE_RESTRICT_VARIABLE_ENTRY_DIRECTION                     :entry direction
 STR_TRACE_RESTRICT_VARIABLE_PBS_ENTRY_SIGNAL                    :PBS entry signal
 STR_TRACE_RESTRICT_VARIABLE_PBS_ENTRY_SIGNAL_LONG               :entered signal of PBS block
 STR_TRACE_RESTRICT_VARIABLE_TRAIN_GROUP                         :train group
+STR_TRACE_RESTRICT_VARIABLE_TRAIN_SLOT                          :slot
 STR_TRACE_RESTRICT_VARIABLE_TRAIN_WEIGHT                        :weight
 STR_TRACE_RESTRICT_VARIABLE_TRAIN_POWER                         :power
 STR_TRACE_RESTRICT_VARIABLE_TRAIN_MAX_TE                        :max T.E.
@@ -2426,6 +2427,8 @@ STR_TRACE_RESTRICT_CONDITIONAL_ENTRY_SIGNAL_FACE                :{STRING} train
 STR_TRACE_RESTRICT_CONDITIONAL_TILE_INDEX                       :{STRING} {STRING} {STRING} at {NUM} x {NUM} then
 STR_TRACE_RESTRICT_CONDITIONAL_GROUP                            :{STRING} train {STRING} in group: {GROUP} then
 STR_TRACE_RESTRICT_CONDITIONAL_GROUP_STR                        :{STRING} train {STRING} in group: {STRING} {BLACK}{STRING}then
+STR_TRACE_RESTRICT_CONDITIONAL_SLOT                             :{STRING} train {STRING} in slot: {TRSLOT} then
+STR_TRACE_RESTRICT_CONDITIONAL_SLOT_STR                         :{STRING} train {STRING} in slot: {STRING} {BLACK}{STRING}then
 STR_TRACE_RESTRICT_CONDITIONAL_UNDEFINED                        :{STRING} {STRING} {STRING} {RED}undefined {BLACK}{STRING}then
 STR_TRACE_RESTRICT_CONDITIONAL_COMPARE_UNDEFINED                :{STRING} {RED}undefined {BLACK}{STRING}then
 STR_TRACE_RESTRICT_PF_PENALTY_ITEM                              :Add pathfinder penalty: {COMMA}

src/tracerestrict.cpp

@@ -354,6 +354,12 @@ void TraceRestrictProgram::Execute(const Train* v, const TraceRestrictProgramInp
 						break;
 					}
 
+					case TRIT_COND_SLOT: {
+						const TraceRestrictSlot *slot = TraceRestrictSlot::GetIfValid(GetTraceRestrictValue(item));
+						result = TestBinaryConditionCommon(item, slot != NULL && slot->IsOccupant(v->index));
+						break;
+					}
+
 					case TRIT_COND_PHYS_PROP: {
 						switch (static_cast<TraceRestrictPhysPropCondAuxField>(GetTraceRestrictAuxField(item))) {
 							case TRPPCAF_WEIGHT:
@@ -563,6 +569,7 @@ CommandCost TraceRestrictProgram::Validate(const std::vector<TraceRestrictItem>
 				case TRIT_COND_ENTRY_DIRECTION:
 				case TRIT_COND_PBS_ENTRY_SIGNAL:
 				case TRIT_COND_TRAIN_GROUP:
+				case TRIT_COND_SLOT:
 				case TRIT_COND_PHYS_PROP:
 				case TRIT_COND_PHYS_RATIO:
 					break;
@@ -1482,7 +1489,7 @@ void TraceRestrictRemoveSlotID(TraceRestrictSlotID index)
 	FOR_ALL_TRACE_RESTRICT_PROGRAMS(prog) {
 		for (size_t i = 0; i < prog->items.size(); i++) {
 			TraceRestrictItem &item = prog->items[i]; // note this is a reference,
-			if (GetTraceRestrictType(item) == TRIT_SLOT && GetTraceRestrictValue(item) == index) {
+			if ((GetTraceRestrictType(item) == TRIT_SLOT || GetTraceRestrictType(item) == TRIT_COND_SLOT) && GetTraceRestrictValue(item) == index) {
 				SetTraceRestrictValueDefault(item, TRVT_SLOT_INDEX); // this updates the instruction in-place
 			}
 			if (IsTraceRestrictDoubleItem(item)) i++;

src/tracerestrict.h

@@ -133,6 +133,7 @@ enum TraceRestrictItemType {
 	TRIT_COND_TRAIN_GROUP         = 18,   ///< Test train group membership
 	TRIT_COND_PHYS_PROP           = 19,   ///< Test train physical property
 	TRIT_COND_PHYS_RATIO          = 20,   ///< Test train physical property ratio
+	TRIT_COND_SLOT                = 21,   ///< Test train slot membership
 	//TRIT_COND_TRAIN_OWNER       = 24,   ///< Test train owner: reserved for future use
 	/* space up to 31 */
 };
@@ -551,6 +552,11 @@ static inline TraceRestrictTypePropertySet GetTraceRestrictTypeProperties(TraceR
 				out.cond_type = TRCOT_BINARY;
 				break;
 
+			case TRIT_COND_SLOT:
+				out.value_type = TRVT_SLOT_INDEX;
+				out.cond_type = TRCOT_BINARY;
+				break;
+
 			case TRIT_COND_PHYS_PROP:
 				switch (static_cast<TraceRestrictPhysPropCondAuxField>(GetTraceRestrictAuxField(item))) {
 					case TRPPCAF_WEIGHT:

src/tracerestrict_gui.cpp

@@ -327,6 +327,7 @@ static const TraceRestrictDropDownListSet *GetTypeDropDownListSet(TraceRestrictG
 		STR_TRACE_RESTRICT_VARIABLE_TRAIN_MAX_TE,
 		STR_TRACE_RESTRICT_VARIABLE_TRAIN_POWER_WEIGHT_RATIO,
 		STR_TRACE_RESTRICT_VARIABLE_TRAIN_MAX_TE_WEIGHT_RATIO,
+		STR_TRACE_RESTRICT_VARIABLE_TRAIN_SLOT,
 		STR_TRACE_RESTRICT_VARIABLE_UNDEFINED,
 		INVALID_STRING_ID,
 	};
@@ -345,6 +346,7 @@ static const TraceRestrictDropDownListSet *GetTypeDropDownListSet(TraceRestrictG
 		TRIT_COND_PHYS_PROP | (TRPPCAF_MAX_TE << 16),
 		TRIT_COND_PHYS_RATIO | (TRPPRCAF_POWER_WEIGHT << 16),
 		TRIT_COND_PHYS_RATIO | (TRPPRCAF_MAX_TE_WEIGHT << 16),
+		TRIT_COND_SLOT,
 		TRIT_COND_UNDEFINED,
 	};
 	static const TraceRestrictDropDownListSet set_cond = {
@@ -912,6 +914,19 @@ static void DrawInstructionString(const TraceRestrictProgram *prog, TraceRestric
 					DrawInstructionStringConditionalIntegerCommon(item, properties);
 					break;
 
+				case TRVT_SLOT_INDEX:
+					SetDParam(0, _program_cond_type[GetTraceRestrictCondFlags(item)]);
+					SetDParam(1, GetDropDownStringByValue(GetCondOpDropDownListSet(properties), GetTraceRestrictCondOp(item)));
+					if (GetTraceRestrictValue(item) == INVALID_TRACE_RESTRICT_SLOT_ID) {
+						instruction_string = STR_TRACE_RESTRICT_CONDITIONAL_SLOT_STR;
+						SetDParam(2, STR_TRACE_RESTRICT_VARIABLE_UNDEFINED_RED);
+						SetDParam(3, selected ? STR_TRACE_RESTRICT_WHITE : STR_EMPTY);
+					} else {
+						instruction_string = STR_TRACE_RESTRICT_CONDITIONAL_SLOT;
+						SetDParam(2, GetTraceRestrictValue(item));
+					}
+					break;
+
 				default:
 					NOT_REACHED();
 					break;
@@ -2132,9 +2147,11 @@ private:
 							break;
 
 						case TRVT_SLOT_INDEX:
-							middle_sel->SetDisplayedPlane(DPM_SLOT_OP);
 							right_sel->SetDisplayedPlane(DPR_VALUE_DROPDOWN);
+							if (!IsTraceRestrictConditional(item)) {
+								middle_sel->SetDisplayedPlane(DPM_SLOT_OP);
 								this->EnableWidget(TR_WIDGET_SLOT_OP);
+							}
 
 							const TraceRestrictSlot *slot;
 							FOR_ALL_TRACE_RESTRICT_SLOTS(slot) {