fix: behaviour when transitioning from a child to a parent state

fixes #3

CHANGES.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.1.1] - 2023-04-12
+### Fixed
+- Transitioning from a child to a parent state should no longer throw an error when the parent is the root node ([#3](https://github.com/derkork/godot-statecharts/issues/3)).
+- Transitioning from a child to a parent compound / parallel state now properly counts as [self transition](https://statecharts.dev/glossary/self-transition.html), so that the parent node is exited and re-entered.
+
+
 ## [0.1.0] - 2023-04-06
 ### Breaking changes
 - The state chart debugger now is no longer a single node  but a full scene. This allows to have more complex UI in the debugger. Please replace the old debugger node with the new scene which is located at `addons/godot-statecharts/utilities/state_chart_debugger.tscn`. The debugger will no longer appear in the node list. You can quickly add it using the "Instatiate child scene" button in the scene inspector.

addons/godot_state_charts/compound_state.gd

@@ -125,6 +125,8 @@ func _handle_transition(transition:Transition, source:State):
 		return
 
 	# the target state can be
+	# 0. this state. in this case exit this state and re-enter it. This can happen when
+	#    a child state transfers to its parent state.
 	# 1. a direct child of this state. this is the easy case in which
 	#    we will deactivate the current _active_state and activate the target
 	# 2. a descendant of this state. in this case we find the direct child which
@@ -133,6 +135,12 @@ func _handle_transition(transition:Transition, source:State):
 	# 3. no descendant of this state. in this case, we ask our parent state to
 	#    perform the transition
 
+	if target == self:
+		# exit this state and re-enter it
+		_state_exit()
+		_state_enter(false)
+		return
+
 	if target in get_children():
 		# all good, now first deactivate the current state
 		if is_instance_valid(_active_state):

addons/godot_state_charts/parallel_state.gd

@@ -28,6 +28,8 @@ func _handle_transition(transition:Transition, source:State):
 		return
 
 	# the target state can be
+	# 0. this state. in this case just activate the state and all its children.
+	#    this can happen when a child state transfers back to its parent state.
 	# 1. a direct child of this state. this is the easy case in which
 	#    we will do nothing, because our direct children are always active.
 	# 2. a descendant of this state. in this case we find the direct child which
@@ -36,6 +38,13 @@ func _handle_transition(transition:Transition, source:State):
 	# 3. no descendant of this state. in this case, we ask our parent state to
 	#    perform the transition
 
+	if target == self:
+		# exit this state
+		_state_exit()
+		# then re-enter it
+		_state_enter(false)
+		return
+
 	if target in get_children():
 		# all good, nothing to do.
 		return