fib.rs

fn main() {
    let n = 42;
    println!("fib({}) = {}", n, fib(n));
}

fn fib(n: u32) -> u32 {
    if n <= 2 {
        1
    } else {
        fib(n - 1) + fib(n - 2)
    }
}

wasmtime.rs

use wasmtime::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut config = Config::new();
    config.profiler(ProfilingStrategy::JitDump)?;
    let engine = Engine::new(&config);
    let store = Store::new(&engine);
    let module = Module::from_file(&engine, "./fib.wasm")?;
    let instance = Instance::new(&store, &module, &[])?;
    let start = instance.get_func("main").unwrap();
    let start = start.get2::<i32, i32, i32>()?;
    let f = if false {
        Func::wrap(&store, move || {
            start(0, 0)?;
            Ok(())
        })
    } else {
        let ty = FuncType::new(Box::new([]), Box::new([]));
        Func::new(&store, ty, move |_, _, _| {
            start(0, 0)?;
            Ok(())
        })
    };
    f.call(&[]).unwrap();

    Ok(())
}