Add NoOp stage (moveit#534)

This stage can be used to add arbitrary user-defined properties w/o modifying the PlanningScene state or adding a trajectory.

Co-authored-by: Robert Haschke <[email protected]>

Author: captain-yoshi

core/include/moveit/task_constructor/stages/noop.h

@@ -0,0 +1,64 @@
+/*********************************************************************
+ * Software License Agreement (BSD License)
+ *
+ *  Copyright (c) 2024, Sherbrooke University
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
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+/* Authors: Captain Yoshi */
+
+#pragma once
+
+#include <moveit/task_constructor/stage.h>
+#include <moveit/planning_scene/planning_scene.h>
+
+namespace moveit {
+namespace task_constructor {
+namespace stages {
+
+/** no-op stage, which doesn't modify the interface state nor adds a trajectory.
+ *  However, it can be used to store custom stage properties,
+ *  which in turn can be queried post-planning to steer the execution.
+ */
+
+class NoOp : public PropagatingEitherWay
+{
+public:
+	NoOp(const std::string& name = "no-op") : PropagatingEitherWay(name){};
+
+private:
+	bool compute(const InterfaceState& state, planning_scene::PlanningScenePtr& scene, SubTrajectory& /*trajectory*/,
+	             Interface::Direction /*dir*/) override {
+		scene = state.scene()->diff();
+		return true;
+	};
+};
+}  // namespace stages
+}  // namespace task_constructor
+}  // namespace moveit

core/src/stages/CMakeLists.txt

@@ -11,6 +11,7 @@ add_library(${PROJECT_NAME}_stages
 	${PROJECT_INCLUDE}/stages/generate_place_pose.h
 	${PROJECT_INCLUDE}/stages/compute_ik.h
 	${PROJECT_INCLUDE}/stages/passthrough.h
+	${PROJECT_INCLUDE}/stages/noop.h
 	${PROJECT_INCLUDE}/stages/predicate_filter.h
 
 	${PROJECT_INCLUDE}/stages/connect.h