Use cargo to run rustfmt

[jtdowney]

While attempting to format Rust code that uses async functions and new syntax, apheleia runs rustfmt without an edition specified, which causes an error. This change uses cargo fmt instead, which uses the configured Rust edition from the Cargo.toml file to invoke rustfmt.

This is the error I was getting before the change:

$ rustfmt --quiet --emit stdout

error[E0670]: `async fn` is not permitted in Rust 2015
 --> <stdin>:5:1
  |
5 | async fn main() -> Result<(), Box<dyn std::error::Error>> {
  | ^^^^^ 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-guide

error: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an operator, found keyword `move`
  --> <stdin>:11:21
   |
11 |     tokio::spawn(async move {
   |                        ^^^^ expected one of 8 possible tokens

Command failed with exit code 1.

[jtdowney]

I'll get the tests fixed and push another commit when I get some time.

[jtdowney]

After digging into this, it appears I was mistaken, and cargo fmt can't be used because it formats everything, not a single file. However, as a workaround, you can tell rustfmt about the edition in rustfmt.toml as well, and that works with apheleia as is.

[raxod502]

Ah gotcha. Cool, thanks!

[dallagi]

FYI you can also set the rust edition within your emacs config as an argument to rustfmt instead of an external rustfmt.toml file, like this:

(add-to-list 'apheleia-formatters '(rustfmt . ("rustfmt" "--quiet" "--emit" "stdout" "--edition" "2021")))