How to hunt and solve bugs efficiently ?

TwistedMind

Hello everyone,

I try to debug my strategy game and sometimes, I have got randoms errors about list's index out of range. I know it's because the list may be changed dynamically for any reasons (push away, new move, ...) but it's impossible to found exactly which unit and why exactly that error appears, because the game is in "breakpoint state".

One exemple:

if faceToFace:
	actionToDo = 'faceToface'
else:
	for neighbors in unitCore.unitCroisement:
		if not neighbors.pathUnit.empty():
-----> during the "for" checking, possible there are modifications but I'm not sure <----
			if unitCore.Map.world_to_map(neighbors.pathUnit[neighbors.step]) == unitCore.Map.world_to_map(unitCore.position):
				actionToDo = 'conturn'
				break
			else:
				actionToDo = 'wait'

Sometimes too, I see some units pass trough an unpassable square but it's so quick than I don't have the time to see, because too many units move at the same time. Even when I record with OBS, I can't found an explanation...

I can do a breakpoint when it reach this unpassable square but that's all... I'm stuck by the fault of my inexperience...

How can I do to hunt and solve all of this ?

Toxe

TwistedMind You could always just do a lot of helpful print() statements and the check the console output. Or add some debug UI overlay to your game and show some helpful information there.

Now, I don't know if this is deliberate or if you just copied part of the code but...

	for neighbors in unitCore.unitCroisement:
		if not neighbors.pathUnit.empty():
			if unitCore.Map.world_to_map(neighbors.pathUnit[neighbors.step]) == unitCore.Map.world_to_map(unitCore.position):
				actionToDo = 'conturn'
				break
			else:
				actionToDo = 'wait'

...there is no break in your else branch. So you will always run through the whole loop. No idea if that is what you actually want or not.

xyz

TwistedMind Which array?

MikeCL

TwistedMind Having quite a hard time following this discussion. Reading the title of the thread, I'm assuming you're more asking for different concepts and debugging strategies rather than help solving specific problems? Then I see some code examples, but I'm not sure what the question is.

But if asking for some strategies, here's what helped me for many years:

Rubber ducking, a very underestimated technique. Can't tell you how many times this has solved issues for me even before finishing that email, tapping a peer on the back for help, posting the question online, etc.
This might be controversial for some, but asking AI to help you debug. Not write any code, but just analyze the code, see if it can spot anything you missed, and give explanations to any findings. But be careful with this one, as AI tends to be "confidently wrong". So you need to be good enough to spot when you are given an answer that is incorrect/wrong.
Including asserts in the codebase has also been proven to increase code quality in my projects. If something is wrong in the code, you would want to know it asap.
Include testing in the project.
Keep the code modular and have functions small and readable.

Then, in general, just read up on some good foundations and principles. Best practices in how to keep the code readable and maintainable. Knowing about design patterns, I would say, will be increasingly important as the project grows in complexity.

When you have a new feature working, don't be afraid to refactor it with a cleaner structure to reduce tech debt.

In some instances, drawing out the flow of something can also help visualize it. Also, when testing the flow, use the debugger to confirm the code behaves as you expect.

With this said. I'm not sure if this discussion is meant to cover debugging concepts or has morphed into seeking specific help for a project. If you're looking for specific help, I think it would be better served in a separate thread. It would be easier to follow, help out, and stay on-topic.

TwistedMind

Toxe , Yes, I do. But it's difficult when you have got a bunch of vehicles...

I deliberately copied a part of my code. Let me explain the situation:
unitCore.unitCroisement = an array where the unit detect his neighbors, distance = 1.

What this code do:

One unit goes from A to B, there are 5 checkpoints between.
When it reachs a checkpoint, this code is called.
If a neighbor is detected and he has got a path (it moves), the unit must check if this neighbor's position is the next chekpoint to reach. If yes, he must conturn it, if not, he must wait. That's means we can break the loop.

Why it must wait: because the neighbor can be on the way. No need to break the loop, because not necessary.

list's index out of range error, I suspect it's because one neighbor on the way has reachs his final point, but the unit in move doesn't know it.

Here the complete code:

# for loop...
# if...
# elif...
elif myCurrentPath == hisPosMap: # if neighbor on the way
	# if neighbor out of fuel or stuck by other unit out of fuel, conturn
	if reasonListWait.has(unit.waitReason):
		actionToDo = 'conturn'
		breakLoop = true
	else: # if neighbor not out of fuel but still on the way
		var faceToFace = false
		
		for dir in dirOpposite:
			if ((myVelo == dir[0] and hisVelo == dir[1]) or\
			(myVelo == dir[1] and hisVelo == dir[0])):
				faceToFace = true
				break
		
		if faceToFace:
			actionToDo = 'faceToface'
		else:
			for neighbor in unitCore.unitCrossed:
				if not neighbor.unitPath.empty():
					if unitCore.Map.world_to_map(neighbor.unitPath[neighbor.step]) == unitCore.Map.world_to_map(unitCore.position):
						actionToDo = 'conturn'
						break
					else:
						actionToDo = 'wait'
		
		breakLoop = true
else:
	actionToDo = 'move'

Toxe

TwistedMind At how many positions in your code do you manipulate the list that you iterate while iterating it? I mean, if you change that list while iterating it then that is something that you just shouldn't do at all.

TwistedMind

Not in this code: the array is in another script and it is changed by a signal.
When an neighbor is detected by the sensors of a unit, the neighbor is added to the array.

Example:
Unit 1 -> unitCrossed = [Unit 2]
Unit 2 -> unitCrossed = [Unit 1]

But if unit 2 reachs his final destination before unit 1, it clears his own path array, that can explain the out of range error, because the code I shared update the state... but if it is the case... why if not neighbor.unitPath.empty(): pass as true ?

Here the stop move function:

func stop_move():
	unitCore.set_physics_process(false)
	unitCore.unitPath = PoolVector2Array([])
	unitCore.step = 0

xyz

TwistedMind The whole thing looks like it may require rethinking and re-arrangement of data structures you use.

But as a short term band aid, simply check if the index is valid every time before you use it. If if's out of bounds - skip the part of code that uses it.

TwistedMind

xyz Yes, it should works.

What do you need, if I must re-arrange and re-think the structure ?

xyz

TwistedMind What do you need, if I must re-arrange and re-think the structure ?

Well redo it in a way that makes it impossible for out of bounds indexing to happen. That's all I can conclude given the limited info and context you provided.

Toxe

Consider all your lists to be immutable.

TwistedMind

@Toxe, I have to check that but I need time to have got the required conditions...

But... in my case... it's not the list, it's the unit's variables ? The list contain only the node of each units... ?

@xyz, I will explain later how I build the system...

Toxe

TwistedMind Does it means I should collect units found first and then execute the code ?

Probably, yes. I still don't understand your exact problems because that has too much to do with your program logic but this is basically what I meant by "immutable lists". Don't modify your units in place but instead collect them and then execute on all of them later in one go.

TwistedMind

Ok, adding the condition about the path index and the out of range context avoid any bugs, it's a good thing.

The problem: find why I have got some bugs, where and how to show them.

The bugs:

Some units go to invalid square when they conturn another units;
Find why sometimes I have got array's errors "out of range" (solved).

<--- in practice.

Let me explain how my system works. First, the unit's script.

unitCross is a local array variable where a unit "remind" who is close to him as ally.

func _on_areaNeigbor_area_entered(area):
	if is_instance_valid(area.get_parent()) and area.get_parent() != self:
		unitCross.append(area.get_parent())

func _on_areaNeigbor_area_exited(area):
	unitCross.erase(area.get_parent())

Script "moveManager" linked to units:

var myCurrentPath = unitCore.Map.world_to_map(unitCore.UnitPath[unitCore.etape])
var breakLoop = false

for unit in unitCore.unitCross:
	if breakLoop:
		break
		
	var hisPosMap = unitCore.Map.world_to_map(unit.position)
	
	if unit.nationCol == unitCore.nationCol:
		if unit.UnitPath.empty(): # pushed
			if myCurrentPath == hisPosMap:
				if unit.refuelTarget == null:
					pushAway(unit)
					actionToDo = 'wait'
				else:
					if unit.dropFuel.playing:
						actionToDo = 'conturn'
					else:
						actionToDo = 'wait'
				
				breakLoop = true
			
			else:
				actionToDo = 'move'
		else:
			if unit.step < unit.UnitPath.size():
				var hisCurrentPath = unitCore.Map.world_to_map(unit.UnitPath[unit.step])
				var myVelo = unitCore.velocity.normalized().round()
				var hisVelo = unit.velocity.normalized().round()
				
				if myCurrentPath == hisCurrentPath:
					if unit.waitReason == 'brokenDown':
						actionToDo = 'move'
					else:
						var faceToFace = false
						
						for dir in dirOpposite:
							if ((myVelo == dir[0] and hisVelo == dir[1]) or\
							(myVelo == dir[1] and hisVelo == dir[0])):
								faceToFace = true
								break
						
						if faceToFace:
							actionToDo = 'faceAface'
							breakLoop = true
						
						else:
							if unitCore.id > unit.id:
								
								if unit.is_physics_processing():
									actionToDo = 'wait'
									breakLoop= true
								else:
									actionToDo = 'move'
									
							else:
								if unit.waitReason == '':
									actionToDo = 'wait'
									breakLoop = true
				
				elif myCurrentPath == hisPosMap: 
					
					if reasonListWait.has(unit.waitReason):
						actionToDo = 'conturn'
						breakLoop = true
					else:
						var faceToFace = false
						
						for dir in dirOpposite:
							if ((myVelo == dir[0] and hisVelo == dir[1]) or\
							(myVelo == dir[1] and hisVelo == dir[0])):
								faceToFace = true
								break
						
						if faceToFace:
							actionToDo = 'faceAface'
						else:
							for neigbor in unitCore.unitCross:
								if not neigbor.UnitPath.empty() and neigbor.UnitPath.size() > voisin.step:
									if unitCore.Map.world_to_map(neigbor.UnitPath[neigbor.step]) == unitCore.Map.world_to_map(unitCore.position):
										actionToDo = 'conturn'
										break
									else:
										actionToDo = 'wait'
						
						breakLoop = true
				else:
					actionToDo = 'move'
	else:
		if unit.UnitPath.empty():
			if myCurrentPath == hisPosMap:
				actionToDo = 'wait'
				breakLoop = true
			else:
				actionToDo = 'move'
		else:
			var hisCurrentPath = unitCore.Map.world_to_map(unit.UnitPath[unit.step])
			
			if myCurrentPath == hisPosMap or myCurrentPath == hisCurrentPath:
				actionToDo = 'wait'
				breakLoop = true
			else:
				actionToDo = 'move'

if actionToDo == 'faceAface':

elif actionToDo == 'conturn':

elif actionToDo == 'wait':

elif actionToDo == 'move':

xyz

TwistedMind You've explained hardly anything. Just copy pasted a bunch of code. Very unlikely that anyone will go and debug some random heap of non-runnable code for you. Well some copilot gemini bullshit might 🙂.

You need to explain your code and your system architecture primarily to yourself, and then proceed to determine if there is something there that is not done properly (thus causing bugs/malfunction), either in system design or in implementation.

Toxe

To add to this: if your architecture is too complex to explain chances are that it's, well, too complex. Try to break it down a bit. Looking at your code that function is way too long and there are far too many ifs and elses. If I need to scroll to read your function then it's too long. A good indicator is indentation depth. Break your code down into smaller functions (that ideally are reusable) and give them good names.

And while we are talking about names: I know that this is your code and you didn't expect anyone else to read it at this point but still, "faceAface" doesn't really convey meaning and as far as I am aware there is no word like "conturn" in the English dictionary. Makes it a lot harder to understand your code.

Also: Never use string identifiers like "move", "wait" etc. Use either const values or (preferably) Enums.

xyz You need to explain your code and your system architecture primarily to yourself

Rubber Duck Debugging. Sounds silly but works surprisingly well.

I know that this sucks and these aren't the answers you are hoping for but I can assure you that every single programmer went through this at some point.

TwistedMind

I understand, but when I explain in text, it's complicated too, so I paste the code to be efficient, to prevent the question "Can you share us a code ? I don't understand".

It's not about any form of disrespect.

By this way or another, If no one understand, no one may move on, I know that.

I don't expect you solve the problem in my place, but I expect you understand the situation and explain what I can do to solve it.
I do my best to explain the more clearly I can.
If it's not clear, you can tell me what you need, and I will do my best to answer you.

That's why, in the start, I said "What do you need ?".

xyz

TwistedMind That's why, in the start, I said "What do you need ?".

For the best chance to get your code debugged, post a Minimal Reproducible Project, as small as possible that clearly reproduces the problem.

In any case, your original question was "how to hunt bugs". The answer is - using standard debugging techniques; print everything, use breakpoints and debugger watches, reduce code to isolate buggy behavior, mentally follow what your code is doing. You can ask ai to elaborate on those and other techniques, and then apply them until you find your bugs.

DaveTheCoder

xyz You can ask ai

😮

xyz

Toxe Rubber Duck Debugging

Yeah I'm a big fan of it. Sadly, many people, beginners especially, think they're "smarter than that" and that they fully understand what they are doing, otherwise they won't be doing it that way, right? Like, what's the point of explaining to themselves something they already know 🙂

Oh how wrong they are. The thing is; the more experience you attain, the more respect you'll have for talking to the duck.

Tomcat

Toxe Rubber Duck Debugging. Sounds silly but works surprisingly well.

A Сat who will listen and can be consulted is much more effective.

Toxe

Tomcat A Сat who will listen and can be consulted is much more effective.

I'm not sure if I would trust the advice of cats. At least half of them seem to be selfish pricks who are only in it for themselves.