v4.5.beta1 `ConfigFile` is breaking compatibility

[jinyangcruise]

Tested versions

• Reproducible in v4.5.beta1
• Not reproducible in v4.5.dev5

System information

Godot v4.5.beta1 - Windows 11 (build 26100) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 Ti (NVIDIA; 32.0.15.6636) - 13th Gen Intel(R) Core(TM) i5-13600KF (20 threads) - 47.84 GiB memory

Issue description

When saving resources to ConfigFile, the data structure changes and makes this file unable to be opened by the old version of Godot. Can this be avoided somehow?

Steps to reproduce

NA

Minimal reproduction project (MRP)

NA

[jinyangcruise]

related: #106902

[lyuma]

Hi, @jinyangcruise
Thank you for opening this issue to track the forward compatibility issue. Let us continue the discussion here.

As for why the change, We discussed this in two core meetings, and we agreed that the current course of action (breaking forward compatibility) would lead to more maintainable code. Godot's version policy technically only guarantees backward compatibility.

As a result of this change, any .import or other config file with a hard external resource reference cannot be read by an old version of Godot. As a workaround, it is possible to embed the resource (make local) if you intend to share the files with an older version.

Just to lay everything on the table, I do have code to enable forward and backward compatibility by using lines starting with =, which are currently ignored in ConfigFile, but it leads to more code and hence more technical debt and hence the consensus at the meeting was not to do this version of the change. You can see it in the PR history if you are curious.

[jinyangcruise]

OK, that's sounds reasonable.

Do you know how to embed a resource into a ConfigFile?

[lyuma]

If you create a new object of some type, for example, on the Skeleton3D node of the advanced importer, creating a new BoneMap and SkeletonProfileHumanoid will be embedded ising the Resource( ... ) or Object( ... ) syntax in the .import file.

For files you load, for example a T-Pose rest animation for skeleton retargeting, after loading the animation file in the advanced importer dialog inspector, you should be able to open the dropdown and choose Make Local just like the normal godot inspector. This will embed the whole resource in text form, so it is not good for a very large animation, texture or mesh data but otherwise could be a viable workflow.

[jinyangcruise]

Thanks, do you know how to embed a resource not relying on the engine's UI but code?

[jinyangcruise]

Btw, I find it's not good that once a resource is missing, the ConfigFile is totally broken. If it's not encrypted, it's fine, because we can still modify it manually. But if it's encrypted, then it becomes tricky.

[aaronfranke]

My recommended mitigation is to backport the ability to read this to supported branches: #107798

This way, even if you can't downgrade from Godot 4.5 to 4.4.1, you could do it with 4.4.2... or at least, this change won't prevent you from doing that downgrade.

[jinyangcruise]

@aaronfranke Appreciate your work, it's a good idea.