tokio::main problem minimal example

Cargo.toml

[package]
name = "tokio-main"
version = "0.1.0"
authors = ["Fenhl <[email protected]>"]
edition = "2018"

[[bin]]
name = "tokio-main"
path = "src/main.rs"

[dependencies.futures-preview]
version = "0.3.0-alpha.16"

[dependencies.tokio]
git = "https://github.com/tokio-rs/tokio"
rev = "22918231814fb5591a4c0c6d5aa0c5ba8172c9c1"

main.rs

#![feature(async_await)]

use {
    std::pin::Pin,
    futures::prelude::*
};

fn stream() -> Pin<Box<dyn Stream<Item = ()>>> {
    stream::repeat(()).boxed()
}

#[tokio::main]
async fn main() {
    let mut stream = stream();
    stream.next().await;
}