1168 			/* Back up and clear the first_engine data to avoid using wagon override group */

  1168 			/* Don't check callback for articulated or rear dual headed parts */

  1169 			EngineID first_engine = next_to_attach->u.rail.first_engine;

  1169 			if (!IsArticulatedPart(next_to_attach) && !IsRearDualheaded(next_to_attach)) {

  1170 			next_to_attach->u.rail.first_engine = INVALID_ENGINE;

  1170 				/* Back up and clear the first_engine data to avoid using wagon override group */

  1171 

  1171 				EngineID first_engine = next_to_attach->u.rail.first_engine;

  1172 			uint16 callback = GetVehicleCallbackParent(CBID_TRAIN_ALLOW_WAGON_ATTACH, 0, 0, dst_head->engine_type, next_to_attach, dst_head);

  1172 				next_to_attach->u.rail.first_engine = INVALID_ENGINE;

  1173 

  1173 

  1174 			/* Restore original first_engine data */

  1174 				uint16 callback = GetVehicleCallbackParent(CBID_TRAIN_ALLOW_WAGON_ATTACH, 0, 0, dst_head->engine_type, next_to_attach, dst_head);

  1175 			next_to_attach->u.rail.first_engine = first_engine;

  1175 

  1176 

  1176 				/* Restore original first_engine data */

  1177 			if (callback != CALLBACK_FAILED) {

  1177 				next_to_attach->u.rail.first_engine = first_engine;

  1178 				StringID error = STR_NULL;

  1178 

  1179 

  1179 				if (callback != CALLBACK_FAILED) {

  1180 				if (callback == 0xFD) error = STR_INCOMPATIBLE_RAIL_TYPES;

  1180 					StringID error = STR_NULL;

  1181 				if (callback < 0xFD) error = GetGRFStringID(GetEngineGRFID(dst_head->engine_type), 0xD000 + callback);

  1181 

  1182 

  1182 					if (callback == 0xFD) error = STR_INCOMPATIBLE_RAIL_TYPES;

  1183 				if (error != STR_NULL) {

  1183 					if (callback < 0xFD) error = GetGRFStringID(GetEngineGRFID(dst_head->engine_type), 0xD000 + callback);

  1184 					/*

  1184 

  1185 					 * The attaching is not allowed. In this case 'next_to_attach'

  1185 					if (error != STR_NULL) {

  1186 					 * can contain some vehicles of the 'source' and the destination

  1186 						/*

  1187 					 * train can have some too. We 'just' add the to-be added wagons

  1187 						 * The attaching is not allowed. In this case 'next_to_attach'

  1188 					 * to the chain and then split it where it was previously

  1188 						 * can contain some vehicles of the 'source' and the destination

  1189 					 * separated, i.e. the tail of the original destination train.

  1189 						 * train can have some too. We 'just' add the to-be added wagons

  1190 					 * Furthermore the 'previous' link of the original source vehicle needs

  1190 						 * to the chain and then split it where it was previously

  1191 					 * to be restored, otherwise the train goes missing in the depot.

  1191 						 * separated, i.e. the tail of the original destination train.

  1192 					 */

  1192 						 * Furthermore the 'previous' link of the original source vehicle needs

  1193 					dst_tail->SetNext(next_to_attach);

  1193 						 * to be restored, otherwise the train goes missing in the depot.

  1194 					orig_tail->SetNext(NULL);

  1194 						 */

  1195 					if (src_previous != NULL) src_previous->SetNext(src);

  1195 						dst_tail->SetNext(next_to_attach);

  1196 

  1196 						orig_tail->SetNext(NULL);

  1197 					return_cmd_error(error);

  1197 						if (src_previous != NULL) src_previous->SetNext(src);

  1198 

  1199 						return_cmd_error(error);

  1200 					}