Static methods and custom constructors on custom types

[HenryWConklin]

Question/Feature Request

Is there a way to define methods on your custom types in Rust which do not take a self parameter?

A minimal example of how I would expect it to work:

use godot::prelude::*;

#[derive(GodotClass)]
#[class(base=Object)]
pub struct MyType {
    pub foo: f32,
}

#[godot_api]
impl MyType {
    #[func]
    pub fn from_foo(foo: f32) -> Gd<MyType> {
        Gd::new(MyType { foo })
    }
}

But, I currently get a somewhat cryptic error from the macro:

error: no rules expected the token `foo`
   --> mycrate/src/lib.rs:125:21
    |
125 |     pub fn from_foo(foo: f32) -> Gd<MyType> {
    |                     ^^^ no rules expected this token in macro call

error: could not compile `mycrate` due to previous error

Use case for this would be static methods and constructors that actually take arguments.
This would ideally be called from GdScript like MyType.from_foo(foo) which constructs a MyType from a foo.

There is godotengine/godot#61963 which seems to suggest it's supported by gdextension, but I haven't found a way to do it in Rust using this repo.

There's also #43 which looks like the other direction, exposing static methods on Godot types in Rust.

[ttencate]

I have a PR (#210) that will make this compile, but it's blocked behind some other work (#204) that will actually make it useful. Right now it would probably either crash or leak if you tried anything nontrivial like returning a Gd type.