get_host.rs

// Example generated bindings
mod bindings {
    pub trait Host {
        fn host_func(&mut self);
    }

    pub trait GetHost<T>: Send + Sync + 'static {
        fn get_host<'a>(&self, data: &'a mut T) -> impl Host;
    }

    pub fn add_to_linker_get_host<T>(
        linker: &mut wasmtime::component::Linker<T>,
        host_getter: impl GetHost<T>,
    ) -> wasmtime::Result<()> {
        let mut inst = linker.instance("foo")?;
        inst.func_wrap(
            "bar",
            move |mut caller: wasmtime::StoreContextMut<'_, T>, (): ()| {
                let mut host = host_getter.get_host(caller.data_mut());
                host.host_func();
                Ok(())
            },
        )
    }

    impl<T, U, F> GetHost<T> for F
    where
        U: Host,
        F: Fn(&mut T) -> &mut U + Send + Sync + 'static,
    {
        fn get_host<'a>(&self, data: &'a mut T) -> impl Host {
            self(data)
        }
    }

    impl<T: Host + ?Sized> Host for &mut T {
        fn host_func(&mut self) {
            (*self).host_func()
        }
    }

    pub fn add_to_linker<T, U>(
        linker: &mut wasmtime::component::Linker<T>,
        get: impl Fn(&mut T) -> &mut U + Send + Sync + Copy + 'static,
    ) -> wasmtime::Result<()>
    where
        U: Host,
    {
        add_to_linker_get_host(linker, get)
    }
}

// Example usage

struct HostImpl;

impl bindings::Host for HostImpl {
    fn host_func(&mut self) {}
}

struct HostWrapper<'a> {
    host: &'a mut HostImpl,
}

impl<'a> bindings::Host for HostWrapper<'a> {
    fn host_func(&mut self) {
        self.host.host_func()
    }
}

struct HostWrapperGetter;

impl bindings::GetHost<Data> for HostWrapperGetter {
    fn get_host<'a>(&self, data: &'a mut Data) -> impl bindings::Host + 'a {
        HostWrapper {
            host: &mut data.host,
        }
    }
}

pub struct Data {
    host: HostImpl,
}

#[allow(unused)]
pub fn setup(linker: &mut wasmtime::component::Linker<Data>) {
    bindings::add_to_linker(linker, |data| &mut data.host).unwrap();
    bindings::add_to_linker_get_host(linker, HostWrapperGetter).unwrap();
}