wasmtime: list<u8> types do not work in async mode

[tailhook]

I'm using the following:

wit_bindgen_wasmtime::import!({
    paths: ["./wit/my_module.wit"],
    async: *,
});

And wit contains something along the lines of:

record response {
    body: string,
}
handle_request: function() -> response

This fails in runtime with the following:

thread 'tokio-runtime-worker' panicked at 'must use `call_async` with async stores', /work/target/.cargo/registry/src/github.zerozr99.workers.dev-1ecc6299db9ec823/wasmtime-0.33
.0/src/func/typed.rs:75:9
stack backtrace:
   0: std::panicking::begin_panic
             at /rustc/02072b482a8b5357f7fb5e5637444ae30e423c40/library/std/src/panicking.rs:525:12
   1: wasmtime::func::typed::TypedFunc<Params,Results>::call
             at ./target/.cargo/registry/src/github.zerozr99.workers.dev-1ecc6299db9ec823/wasmtime-0.33.0/src/func/typed.rs:75:9
   2: wit_bindgen_wasmtime::rt::copy_slice
             at ./target/.cargo/git/checkouts/wit-bindgen-f98ccff846621481/8fdf702/crates/wasmtime/src/lib.rs:154:9
   3: edgedb_wasm_server::abi::http_server_v1::edgedb_http_server_v1::EdgedbHttpServerV1<T>::handle_request::{{closure}}
             at ./server/src/abi/http_server_v1.rs:1:1

The issue is, copy_slice function which also accepts destructor:

    pub fn copy_slice<T: Endian>(
        store: impl AsContextMut,
        memory: &Memory,
        free: &TypedFunc<(i32, i32, i32), ()>,
        base: i32,
        len: i32,
        align: i32,
    ) -> Result<Vec<T>, Trap> {
        let size = (len as u32)
            .checked_mul(mem::size_of::<T>() as u32)
            .ok_or_else(|| Trap::new("array too large to fit in wasm memory"))?;
        let slice = memory
            .data(&store)
            .get(base as usize..)
            .and_then(|s| s.get(..size as usize))
            .ok_or_else(|| Trap::new("out of bounds read"))?;
        let result = Le::from_slice(slice).iter().map(|s| s.get()).collect();
        free.call(store, (base, size as i32, align))?;   // <<< this line should be async!
        Ok(result)
    }

Seems easy enough to fix. What fix do you prefer, having copy_slice_async function? Or just moving the free call out of the function into the generated code? (or maybe a boolean flag argument?).

[alexcrichton]

Thanks for the report, and indeed this looks like a bug! I think the best fix here is probably to move the free operation out of copy_slice and do it in the caller so the caller can appropriately choose call vs call_async