Add release slot train order

src/order_gui.cpp

@@ -621,6 +621,7 @@ static const StringID _order_goto_dropdown[] = {
 	STR_ORDER_GO_TO_NEAREST_DEPOT,
 	STR_ORDER_CONDITIONAL,
 	STR_ORDER_SHARE,
+	STR_ORDER_RELEASE_SLOT_BUTTON,
 	INVALID_STRING_ID
 };
 
@@ -629,6 +630,7 @@ static const StringID _order_goto_dropdown_aircraft[] = {
 	STR_ORDER_GO_TO_NEAREST_HANGAR,
 	STR_ORDER_CONDITIONAL,
 	STR_ORDER_SHARE,
+	STR_ORDER_RELEASE_SLOT_BUTTON,
 	INVALID_STRING_ID
 };
 
@@ -1023,6 +1025,16 @@ void DrawOrderString(const Vehicle *v, const Order *order, int order_index, int
 			break;
 		}
 
+		case OT_RELEASE_SLOT:
+			SetDParam(0, STR_ORDER_RELEASE_SLOT);
+			if (order->GetDestination() == INVALID_TRACE_RESTRICT_SLOT_ID) {
+				SetDParam(1, STR_TRACE_RESTRICT_VARIABLE_UNDEFINED_RED);
+			} else {
+				SetDParam(1, STR_TRACE_RESTRICT_SLOT_NAME);
+				SetDParam(2, order->GetDestination());
+			}
+			break;
+
 		default: NOT_REACHED();
 	}
 
@@ -1200,6 +1212,7 @@ private:
 		/* WID_O_SEL_TOP_ROW_GROUNDVEHICLE */
 		DP_GROUNDVEHICLE_ROW_NORMAL      = 0, ///< Display the row for normal/depot orders in the top row of the train/rv order window.
 		DP_GROUNDVEHICLE_ROW_CONDITIONAL = 1, ///< Display the row for conditional orders in the top row of the train/rv order window.
+		DP_GROUNDVEHICLE_ROW_SLOT        = 2, ///< Display the row for release slot orders in the top row of the train/rv order window.
 
 		/* WID_O_SEL_TOP_LEFT */
 		DP_LEFT_LOAD       = 0, ///< Display 'load' in the left button of the top row of the train/rv order window.
@@ -1404,6 +1417,19 @@ private:
 		this->InsertNewOrder(order.Pack());
 	}
 
+	/**
+	 * Handle the click on the release slot button.
+	 */
+	void OrderClick_ReleaseSlot()
+	{
+		Order order;
+		order.next = nullptr;
+		order.index = 0;
+		order.MakeReleaseSlot();
+
+		this->InsertNewOrder(order.Pack());
+	}
+
 	/**
 	 * Handle the click on the unload button.
 	 */
@@ -1947,6 +1973,19 @@ public:
 					break;
 				}
 
+				case OT_RELEASE_SLOT: {
+					if (row_sel != nullptr) {
+						NOT_REACHED();
+					} else {
+						train_row_sel->SetDisplayedPlane(DP_GROUNDVEHICLE_ROW_SLOT);
+					}
+
+					TraceRestrictSlotID slot_id = (order != nullptr && TraceRestrictSlot::IsValidID(order->GetDestination()) ? order->GetDestination() : INVALID_TRACE_RESTRICT_SLOT_ID);
+
+					this->GetWidget<NWidgetCore>(WID_O_RELEASE_SLOT)->widget_data = (slot_id != INVALID_TRACE_RESTRICT_SLOT_ID) ? STR_TRACE_RESTRICT_SLOT_NAME : STR_TRACE_RESTRICT_VARIABLE_UNDEFINED;
+					break;
+				}
+
 				default: // every other order
 					if (row_sel != nullptr) {
 						row_sel->SetDisplayedPlane(DP_ROW_LOAD);
@@ -2145,6 +2184,17 @@ public:
 					SetDParam(1, 0);
 				}
 				break;
+
+			case WID_O_RELEASE_SLOT: {
+				VehicleOrderID sel = this->OrderGetSel();
+				const Order *order = this->vehicle->GetOrder(sel);
+
+				if (order != nullptr && order->IsType(OT_RELEASE_SLOT)) {
+					TraceRestrictSlotID value = order->GetDestination();
+					SetDParam(0, value);
+				}
+				break;
+			}
 		}
 	}
 
@@ -2264,7 +2314,8 @@ public:
 						case OPOS_SHARE:       sel =  3; break;
 						default: NOT_REACHED();
 					}
-					ShowDropDownMenu(this, this->vehicle->type == VEH_AIRCRAFT ? _order_goto_dropdown_aircraft : _order_goto_dropdown, sel, WID_O_GOTO, 0, 0, 0, DDSF_LOST_FOCUS);
+					ShowDropDownMenu(this, this->vehicle->type == VEH_AIRCRAFT ? _order_goto_dropdown_aircraft : _order_goto_dropdown, sel, WID_O_GOTO,
+							0, (this->vehicle->type == VEH_TRAIN &&_settings_client.gui.show_adv_tracerestrict_features ? 0 : 0x10), 0, DDSF_LOST_FOCUS);
 				}
 				break;
 
@@ -2449,6 +2500,14 @@ public:
 				this->UpdateButtonState();
 				this->ReInit();
 				break;
+
+			case WID_O_RELEASE_SLOT: {
+				int selected;
+				TraceRestrictSlotID value = this->vehicle->GetOrder(this->OrderGetSel())->GetDestination();
+				DropDownList list = GetSlotDropDownList(this->vehicle->owner, value, selected);
+				if (!list.empty()) ShowDropDownList(this, std::move(list), selected, WID_O_RELEASE_SLOT, 0, true);
+				break;
+			}
 		}
 	}
 
@@ -2512,6 +2571,7 @@ public:
 					case 1: this->OrderClick_NearestDepot(); break;
 					case 2: this->OrderClick_Goto(OPOS_CONDITIONAL); break;
 					case 3: this->OrderClick_Goto(OPOS_SHARE); break;
+					case 4: this->OrderClick_ReleaseSlot(); break;
 					default: NOT_REACHED();
 				}
 				break;
@@ -2552,6 +2612,10 @@ public:
 				this->ModifyOrder(this->OrderGetSel(), MOF_COND_VALUE_2 | index << 4);
 				break;
 
+			case WID_O_RELEASE_SLOT:
+				this->ModifyOrder(this->OrderGetSel(), MOF_SLOT | index << 4);
+				break;
+
 			case WID_O_MANAGE_LIST:
 				switch (index) {
 					case 0: this->OrderClick_ReverseOrderList(0); break;
@@ -2822,6 +2886,12 @@ static const NWidgetPart _nested_orders_train_widgets[] = {
 															SetDataTip(STR_NULL, STR_ORDER_CONDITIONAL_SLOT_TOOLTIP), SetResize(1, 0),
 				EndContainer(),
 			EndContainer(),
+			NWidget(NWID_HORIZONTAL, NC_EQUALSIZE),
+				NWidget(WWT_PANEL, COLOUR_GREY), EndContainer(),
+				NWidget(WWT_PANEL, COLOUR_GREY), EndContainer(),
+				NWidget(WWT_DROPDOWN, COLOUR_GREY, WID_O_RELEASE_SLOT), SetMinimalSize(124, 12), SetFill(1, 0),
+														SetDataTip(STR_NULL, STR_ORDER_RELEASE_SLOT_TOOLTIP), SetResize(1, 0),
+			EndContainer(),
 		EndContainer(),
 		NWidget(WWT_TEXTBTN, COLOUR_GREY, WID_O_OCCUPANCY_TOGGLE), SetMinimalSize(36, 12), SetDataTip(STR_ORDERS_OCCUPANCY_BUTTON, STR_ORDERS_OCCUPANCY_BUTTON_TOOLTIP),
 		NWidget(NWID_SELECTION, INVALID_COLOUR, WID_O_SEL_SHARED),