How to ? different Error type in the same async block

[CGQAQ]

according to this article
Using ? with different Error type in the same async block seems unachievable

async fn a() -> Result<(), reqwest::Error> {Ok(())}
async fn b() -> Result<(), std::io::Error> {Ok(())}

fn c() {
    async {
        a().await?;
        b().await?;
        Ok(())    // error msg 1
        // Ok::<(), impl std::error::Error>(())  // error msg 2
    };
}

async fn d() -> Result<(), impl std::error::Error> {
    a().await?;
    b().await?;
    Ok(())
}

1

 --> src/x.rs:6:9
  |
6 |         a().await?;
  |         ^^^^^^^^^^ cannot infer type

2

error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
 --> src/x.rs:8:18
  |
8 |         Ok::<(), impl std::error::Error>(())
  | 

Maybe add something like this? Unify closure and block

async || -> Result<(), impl std::error::Error> {
        a().await?;
        b().await?;
        Ok(())
};

[csmoe]

async closure is already there with #![feature(async_closure)].