问错误:无法在tokio中找到main或io，无效的返回类型“`impl Future”

EN

use hyper::{body::HttpBody as _, Client};
use tokio::io::{self, AsyncWriteExt as _};

type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;

#[tokio::main]
async fn main() -> Result<()> {
    // ...
    fetch_url(url).await
}


async fn fetch_url(url: hyper::Uri) -> Result<()> {
    // ...
    Ok(())
}

[package]
name = "projectname"
version = "0.1.0"
authors = ["username"]
edition = "2018"
    
[dependencies]
hyper = "0.14.4"
tokio = "1.2.0"

error[E0433]: failed to resolve: could not find `main` in `tokio`
 --> src/main.rs:9:10
  |
9 | #[tokio::main]
  |          ^^^^ could not find `main` in `tokio`

error[E0277]: `main` has invalid return type `impl Future`
  --> src/main.rs:10:20
   |
10 | async fn main() -> Result<()> {
   |                    ^^^^^^^^^^ `main` can only return types that implement `Termination`

error[E0432]: unresolved import `hyper::Client`
 --> src/main.rs:3:34
  |
3 | use hyper::{body::HttpBody as _, Client};
  |                                  ^^^^^^ no `Client` in the root

error[E0425]: cannot find function `stdout` in module `io`
  --> src/main.rs:45:13
   |
45 |         io::stdout().write_all(&chunk).await?;
   |             ^^^^^^ not found in `io`
   |

error[E0432]: unresolved import `tokio::io::AsyncWriteExt`
 --> src/main.rs:4:23
  |
4 | use tokio::io::{self, AsyncWriteExt as _};
  |                       -------------^^^^^
  |                       |
  |                       no `AsyncWriteExt` in `io`
  |                       help: a similar name exists in the module: `AsyncWrite`