How can Squeak Through 2 be configured to enable going through Merged Chests?

You can put "container" into the "remove collision types" setting, enable the checkbox and you will be able to walk through all chests

Tnx, but unfortunately I don't think it works. Is there a way to find out the object type under the cursor?

Before we try alternatives, I just want to make sure: Did you check the "Use remove collision lists" setting? They won't work if you didn't check that.

If you mean this:
https://i.ibb.co/vBnnxPZ/image.png
then yes.

And, the setting is not overwritten by the previous value in my save.

There's a checkbox right above the textbox you need to check to enable the remove collision settings, it's the one with the "WARNING: Affects biters!".
You should only need "tree, container" once you have that checkbox ticked.

If enabled, I get this:
https://i.ibb.co/VmSGkX9/image.png
even with default mod settings.

Hmm, looks like I forgot to update just that one part of the code, Fixed in 0.1.1

OK, no error at the start, but I still cannot go through merged chests (while I can through plain ones)...

Alright, I think I might have to add a dependency on Merging Chests then, because it's either doing something really wacky with compound entities which I doubt, or it's generating the chests after my mod runs and therefore isn't getting modified. I'll do that in a couple minutes when I get home, and that should finally solve the problem. Sorry it took so long to get this working!

I just tried it on my end, and I'm able to walk through the containers with no issues.
I didn't have to add a dependency, I just installed the mod and used these settings below:
https://imgur.com/a/Sb6gnAO

This was the mod I installed, just to be sure:
https://mods.factorio.com/mod/WideChests

I'm not really sure what else the problem could be, so I can't really help you much further without more information.
Are you using any other mods that could be messing with collision masks after squeak through?
Feel free to post the whole mod list and I might be able to narrow it down if that is the problem.

OK, I figured out what breaks Squeak Through - I also have installed https://mods.factorio.com/mod/WideChestsAllTypes

If enabled, Squeak Through stops working. I've seen that WideChests internally names things a bit differently when this mod is present, but I haven't spotted in your sources that you rely on its strings...

Okay, I did some digging and found out why it wasn't working - it was a very obscure bug in my code, I'm not sure if it was introduced from migrating to 2.0 or if it's been there the whole time, but regardless it's been fixed in 0.1.2. Thanks for being so patient with me.

I confirm it works now!

You've been very helpful, thank you! :)