Format buffer fails due to running in 2015

[nicrosengren]

Hi,

I recently updated rust-mode and looking through the recent changes i see rustfmt is now invoked without the --edition flag.

I'm not getting errors when running rust-format-buffer.

I created a new project with edition = 2024 in Cargo.toml using $ cargo new proj.

Added an async function and ran rust-format-buffer and received the error:

error[E0670]: `async fn` is not permitted in Rust 2015
 --> main.rs:6:1
  |
6 | async fn give() -> String {
  | ^^^^^ to use `async fn`, switch to Rust 2018 or later
  |
  = help: pass `--edition 2024` to `rustc`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

All configuration I have for rustmode is:

(use-package rust-mode
  :ensure t
  :init
  (setq rust-format-on-save t)
  :hook (rust-mode . eglot-ensure))

Is this the intended behavior?

[spacekookie]

I have this same issue. This definitely feels like a regression; I didn't see this behaviour even a few days ago (I don't update my system super often).

I'm wondering if something in emacs changed that causes this (I didn't update rust-mode, only emacs)

Edit 1: Kinda looks like f2c0802 is to blame, but I understand why it was done. I also didn't see any mention in the docs as to having to configure something new.

Edit 2: I found a work-around for now: create a rustfmt.toml in your project (or your home directory) and set edition = "2024". I feel that if rust-mode calls rustfmt for me then it should also accept configuration as for the edition I want to use... it's fundamental to having a working text editor and changing this behaviour without even documenting why it was done or how to work around it seems not very nice)

[LatencyIndex]

Probably the most correct thing to do would be to invoke rustfmt with cargo fmt instead, which is what rustfmt recommends.

[ramsayleung]

I have this same issue, but I don't want to create a rustfmt.toml for my project, it's kind of tedious.

By taking a close look at this f2c0802, I figured out the solution for this problem:

  (setq rust-rustfmt-switches '("--edition" "2024"))

However, I do agree the most correct way is to instruct rust-format-buffer to use cargo fmt, so it could respect the edition defined in cargo.toml, but couldn't figure out the way to set cargo fmt as binary.

[sp1ff]

Not sure what changed, but I started experiencing the same behavior after updating Oh, I see it now (this commit-- h/t @spacekookie).

The problem with invoking it as cargo fmt is that that will reformat your entire crate. The same recommendation linked above (by @LatencyIndex) also notes "To format individual files..., the rustfmt binary should be used."

I wound-up setting the edition configuration item to "2021" in my rustfmt.toml.