Question - Game mods and UIDs

[pietru2004]

I want to ask. What will happen if for example game mod, patch or dlc get's released as separate pck?

In mind https://docs.godotengine.org/en/stable/tutorials/export/exporting_pcks.html

Like if modder's that makes mod in folder say filepath res://mods/mod_id/mod_files
and RNG strikes they get the same UID as one of game assets UIDs ?

What is math chance 2 files get the same UID ?
Also what if resource is loaded after compiling from filesystem(like if dev implements modding other than via PCK files), does it get UID assigned or is it only filepath based in this case?

Note

(Asking in Engine Core cause last time I seen UID stuff it was in Engine Core)

[theraot]

If I recall correctly, the UIDs when created for the first time are path based, and so different paths should not have collisions. However, the whole point of UIDs is that you can move them around and keep them. I imagine the resources in the pck come with their UIDs, after all, internal references that use UIDs would not work otherwise. This also means a mod author could intentionally cause an UID collision.

[pietru2004]

Still I think it would be valid to assume non 0 chance of UID being generated as dupe unintentionally... right ?
So I wonder what is chance of that occurring, like what is a chance that UID can be dupe
Also if UID was path based wouldn't it mean if you move original file to another path (along with any additional sub files like .import) and create copy of file with exactly same name shouldn't that generate the same UID and make dupe UID ?

[theraot]

Still I think it would be valid to assume non 0 chance of UID being generated as dupe unintentionally... right ?

Yes, there should not be, there might be collisions, due to good old pigeon hole principle.

Also if UID was path based wouldn't it mean if you move original file to another path (along with any additional sub files like .import) and create copy of file with exactly same name shouldn't that generate the same UID and make dupe UID ?

Makes sense.

I have now done an experiment: if I remove a uid and reload the project Godot will assign the same uid from cache, but if I remove the uid and remove the cache Godot will generate a different one.

I also found code to generate the uid using random with simple collision resolution: https://github.com/godotengine/godot/blob/a8598cd8e261716fa3addb6f10bb57c03a061be9/core/io/resource_uid.cpp#L110

That means that - at least locally - there would not be collisions.

Also that I might have been wrong on thinking it was path based, and instead it is just that Godot keeps a cache.