ResourceSaver.save deletes UID from resource when not running inside the Editor

[Rubonnek]

Godot version

master branch at ee118e7

System information

Arch Linux

Issue description

ResourceSaver.save removes the UID when present in a resource.

I was expecting it to either keep the current UID or generate a new one.

Steps to reproduce

1. Open the attached MRP and note that resource_with_uid.tres has an UID:

[gd_resource type="Resource" format=3 uid="uid://cm483l5h4cwi2"]

2. Run the attached project which will run: ResourceSaver.save(load("res://resource_with_uid.tres"))
3. The UID is now gone:

[gd_resource type="Resource" format=3]

Minimal reproduction project

ResourceSaverUIDNukeBug.zip

[KoBeWi]

Works correctly when run inside the editor.

[jsjtxietian]

The uid is set by ResourceUID::ID uid = ResourceSaver::get_resource_id_for_path(local_path, true); which will return -1 as uid when save_get_id_for_path is null. save_get_id_for_path is set in EditorFileSystem's constructor. So it's fine in editor but breaks when running.

[AThousandShips]

I'm not sure how this should be solved, or even treated, UID is an editor specific feature when assigning, and needs to be in editor to be handled correctly

I think this isn't so much a bug as it is a limitation, the one bug would be IMO that you can edit files in the project from a running project, and that this limitation should be documented or you shouldn't be allowed to modify the files this way

[jsjtxietian]

IMHO I do agree that we should not edit files (or edit resources) from a running project, tool script is built for that purpose. But the uid loss is a limition as it might make the user confuse. Although I think it still works well because the path is not lost so user can still reference the resource, just the uid is missing.

Also it seems hard to detect this problem as load and save are common operations.

[AThousandShips]

Yeah, could be done when editing in the res file scope, but I think this is more a documentation thing, unless we can find a clear way to error about this