Richard Backhouse (Jan 21 2025 at 13:30): Richard Backhouse (Jan 21 2025 at 13:30):I'm trying to migrate my app to wasmtime 29.0.0 and am hitting a compile error for the Host implementations I have.
For one of them I have a wit that looks like this
interface evt {
enum event-type {
info,
warning,
error,
debug,
}
emit-event: func(et: event-type, event-name: string, event-data: list<u8>);
}
world event {
import evt;
}
And the Host code using the bindgen macro looks like this
wasmtime::component::bindgen!({
path: "../../wit/event",
world: "event",
async: true,
});
pub enum EventType {
Info,
Warning,
Error,
Debug,
}
pub struct EventManagerCtx {
eventmanager: Box<dyn EventManager + std::marker::Send>
}
impl EventManagerCtx {
pub fn new(eventmanager: Box<dyn EventManager + std::marker::Send>) -> anyhow::Result<Self> {
Ok(EventManagerCtx {
eventmanager: eventmanager
})
}
}
#[async_trait::async_trait]
pub trait EventManager {
async fn emit_event(&mut self, et: EventType, event_name: String, event_data: Vec<u8>) -> ();
}
#[async_trait::async_trait]
impl airedale::event::evt::Host for EventManagerCtx {
async fn emit_event(&mut self, et:airedale::event::evt::EventType, event_name:String, event_data:Vec<u8>,) -> () {
let event_type: EventType;
match et {
airedale::event::evt::EventType::Info => event_type = EventType::Info,
airedale::event::evt::EventType::Warning => event_type = EventType::Warning,
airedale::event::evt::EventType::Debug => event_type = EventType::Debug,
airedale::event::evt::EventType::Error => event_type = EventType::Error,
}
self.eventmanager.emit_event(event_type, event_name, event_data).await;
}
}
pub trait EventManagerFactory {
fn new_eventmanager(&mut self) -> Box<dyn EventManager + std::marker::Send>;
}
With 29.0.0 I'm now getting an error on the emit_event function
error[E0195]: lifetime parameters or bounds on method `emit_event` do not match the trait declaration
--> crates/airedale-container/src/event.rs:33:14
|
5 | });
| - lifetimes in impl do not match this method in trait
...
31 | #[async_trait::async_trait]
| --------------------------- this `where` clause might not match the one in the trait
32 | impl airedale::event::evt::Host for EventManagerCtx {
33 | async fn emit_event(&mut self, et:airedale::event::evt::EventType, event_name:String, event_data:Vec<u8>,) -> () {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetimes do not match method in trait
I took a look at comparing the generated code and see that
#[wasmtime::component::__internal::async_trait]
was removed in the 29.0.0 version and replaced with
#[wasmtime::component::__internal::trait_variant_make(::core::marker::Send)]
Any thoughts on how to fix this ?
Thanks
Victor Adossi (Jan 21 2025 at 14:03):Just a guess but I think this is coming from a vendored version of the trait-variant crate that is now in use by wasmtime to ensure that the Send bound is present on the Self in question.
In your example the EventManagerCtx contains a Box<T> which is only Send when the internal type (dyn T in this case) is Send, and that's not the case by default -- You likely need to change to using a Box<dyn T + Send> to restrict what can be put in the Box to be Send (which should then then trigger the auto-implementation of Send for Box<T>).
Richard Backhouse (Jan 21 2025 at 15:31):I guess I'm not following. The EventManagerCtx already has the Box<dyn T + Send>.
pub struct EventManagerCtx {
eventmanager: Box<dyn EventManager + std::marker::Send>
}
It looks like this pr removed async_trait from bindgen
https://github.com/bytecodealliance/wasmtime/issues/9823
Victor Adossi (Jan 21 2025 at 15:51):Ah sorry I could have sworn it only said Box<dyn EventManager>...
Did you try removing the async_trait annotation and using the built in async w/ return position impl Trait? This is where the trait_variant recommendation comes from (at least that's where I saw it)
Last updated: Jan 24 2025 at 00:11 UTC