For v4.3+, switch #[class(tool)] to use Godot's native "runtime class" feature

[Bromeon]

For Godot 4.0, 4.1 and 4.2, gdext emulates a mode where classes' lifecycle methods are not executed in the editor, unless #[class(tool)] is specified or the global editor_run_behavior() is configured.

Starting from Godot 4.3, GDExtension provides this feature natively, dubbed "runtime classes" (formerly "gameplay classes").
This has been implemented in godotengine/godot#82554 and merged a few hours ago.

This PR thus conditionally switches to the native implementation, when API 4.3 is targeted.

I briefly tested the functionality with dodge-the-creeps, but it might be that there are still some bugs, as it's hard to write automated tests for this. Let us know in case things don't work as expected.

[GodotRust]

API docs are being generated and will be shortly available at: https://godot-rust.github.io/docs/gdext/pr-619

[kang-sw]

Hello, sorry for commenting on closed PR. I'm experiencing panics on any access to singletons (checked from DisplayServer, RenderingServer) from tool classes, after hot reloading in editor. Is this known issue and being fixed from this PR(and from Godot 4.3), otherwise should I rather to open separate issue with MRP?

• Currently working with Godot 4.2
• Latest master branch (Feb 25, 2024)

---

Usually this assertion is hit:

#[inline(always)]
pub unsafe fn class_servers_api() -> &'static ClassServersMethodTable {
    // SAFETY: `get_binding` has the same preconditions as this function.
    let binding = unsafe { get_binding() };

    debug_assert!(
        binding.class_server_method_table.is_initialized(), // <<< THIS ONE!
        "cannot fetch classes; init level 'Servers' not yet loaded"
    );

    // SAFETY: `initialize_class_server_method_table` has been called.
    unsafe { binding.class_server_method_table.get_unchecked() }
}

[Bromeon]

That problem has been reported on Discord before, but I don't see the relation to this PR?

[kang-sw]

Aha, I was curious if the bug was related to tool class behavior. Thanks for checking it out! I think #582 issue is simillar situation with me where crashing on engine resource access after hot reloading, however, I'm not sure if it's exactly the same issue.

I've just tested another PR which targets to resolve broken hot reloading by reverting some commit(#628, revert UnsafeOnceCell to static mut), it still triggers similar assertion at similar code point.

#[inline(always)]
pub unsafe fn class_servers_api() -> &'static ClassServersMethodTable {
    let table = &unwrap_ref_unchecked(&BINDING).class_server_method_table;
    debug_assert!(
        table.is_some(), // <<< Only method name changed ...
        "cannot fetch classes; init level 'Servers' not yet loaded"
    );

    table.as_ref().unwrap_unchecked()
}

May I create a separate issue about this? This is pretty big blocker for me developing egui plugin for editor plugin purpose. 😢

[Bromeon]

Yes sure, feel free to open an issue :)

Maybe also comment on #628. But in its current form I can't merge that one, we should isolate the issue.