Cannot use async fn with rustfmt

[SushiWaUmai]

The async fn keyword is not valid in the 2015 version of rustfmt.

Therefore I suggest that we should add a --edition 2021 argument to the rustfmt by default .

[regexPattern]

I got the same error here. Here is the full mesage when I just try to run :Format on a project that uses tokio (the message is from rustfmt itself):

Failed to run formatter rustfmt. error[E0670]: `async fn` is not permitted in Rust 2015  --> <stdin>:36:1   |36 | async fn main() {   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
   |   = help: pass `--edition 2021` to `rustc`   = note: for more on editions, read https://doc.rust-lang.org/edition-guideerror: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an 
operator, found keyword `move`  --> <stdin>:64:37   |64 |                 (tokio::spawn(async move {   |                                     ^^^^ expected one of 8 possible tokens

[nerosnm]

One possible workaround is to add a rustfmt.toml file to your project with the contents edition = "2021" or edition = "2018" (see rust-lang/rustfmt#4454). But I agree that we should add an --edition 2021 argument by default.