Stack Underflow (Engine Bug) when using yield completed

[muchitto]

Godot version:
3.2-dev (fb5e8b5)

OS/device including version:
Windows 10 x64

Issue description:
I was implementing a kind of state machine and ran into the Stack Underflow (Engine Bug) problem, which has been mentioned in issue #30269. It seems to occur at specific times when using the yield(gdfunctionstate, "completed") kind of code.

Steps to reproduce:
Open the project, run and press space (or any of the default "ui_accept" action keys).
All the code in the minimal reproduction project is in the Main.gd file:

extends Node2D

class Runner:
	signal ContinueExecution()
	
	func continue_excution ():
		emit_signal("ContinueExecution")
	
	func run_data ():
		var run_state = run_branch()
		
		if run_state is GDScriptFunctionState:
			yield(run_state, "completed")
			
		return run_state
	
	func run_branch ():
		yield(self, "ContinueExecution")
	
var data_intpr := Runner.new()

func _ready():
	data_intpr.run_data()

func _process(delta):
	if Input.is_action_just_pressed("ui_accept"):
		data_intpr.continue_excution()

Minimal reproduction project:
Stack Underflow Yield problem.zip

[muchitto]

Ok, if you comment out the return line from the run_data() function, it doesn't show the underflow error...

[bojidar-bg]

Probably related to this comment on the PR which change yield: https://github.com/godotengine/godot/pull/28884/files/9df1a2442b480f9ed8a8d4ec8992ea5046b98719#r284189443