GDScript does not update cached singleton references when GDExtension is reloaded

[DmitriySalnikov]

Godot version

v4.2.rc.mono.custom_build [ad72de5]

System information

Windows 10

Issue description

As I pointed out several times earlier in #80284, the references to singletons in GDScript are still not updated after the GDExtension reload.

Code_X5GbuGGVab.1.1.mp4

Singletons themselves are updated and work correctly, but references to these singletons are not updated in @tool scripts. That is, Engine.get_singleton returns the actual working reference, but using the singleton directly through its name causes errors.

Steps to reproduce

• Clone 4.2.reload_singleton branch from the MRP repository https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton
• Build as usual
• Open the project from the project/ folder
• Add one character to the source code and rebuild
• Focus on the editor to reload extension
• Watch for error spam when calling by singleton name

Minimal reproduction project

https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton

[dsnopek]

Thanks for creating this issue!

I'm still not sure how to fix this - I think we'll need some help from the GDScript team to figure out how (or if it's even possible) to refresh those references.