Components without WASI

[kvcache]

I'm attempting to compile guest functions using wasm32-unknown-unknown, but I'd like to use the Component model. Trying to parse a guest function as a Component does not work without wasm32-wasip2.

I don't want to use wasm32-wasip2 because I need to define all of my host interfaces.

Client:

wit_bindgen::generate!({
    world: "function",
});

struct Function;

impl exports::momento::functions::function_invoke_post::Guest for Function {
    fn post(payload: Vec::<u8>,) -> Vec::<u8> {
        todo!()
    }
}

export!(Function);

Host fails when parsing wasm byte array:

let component = wasmtime::component::Component::new(&engine, wasm_bytes).map_err(|e| FunctionError::InvalidWasm(e))?;

When I compile with wasm32-unknown-unknown, it says "attempted to parse a wasm module with a component parser".

When I compile with wasm32-wasip2, it fails on WASI interfaces I'm not adding to the linker.

[pchickey]

When compiling with wasm32-unknown-unknown rustc emits a WebAssembly Module. You can convert that to a WebAssembly Component with the wasm-tools component new command line tool, or using https://docs.rs/wit-component/latest/wit_component/struct.ComponentEncoder.html directly.

The wasm32-wasip2 target passes the Module emitted by rustc to wasm-component-ld which wraps up the Component conversion performed above, plus some details to adapt wasip1 interfaces to wasip2, which you don't care about.

[kvcache]

@pchickey Thank you, this is what I needed! I now see an example does this too.