Order of `use` items disagrees with rustfmt on beta

[jonhoo]

rust.vim version: 889b9a7

rustc version: rustc 1.90.0-beta.1 (788da80fc 2025-08-04)

editor or extension: NVIM v0.11.3

code snippet to reproduce:

use std::collections::{hash_map, HashMap};

rust.vim's format-on-save insists that this should be formatted as above, but cargo fmt on both beta and stable rewrites it to:

use std::collections::{HashMap, hash_map};

[jonhoo]

This is with edition = "2024" in case it's relevant.

[jonhoo]

Digging some more, I think this is because the order changed with the 2024 edition, and rust.vim will fall back to 2018 edition formatting if there's no rustfmt.toml:

rust.vim/autoload/rustfmt.vim

Line 75 in 889b9a7

return '--edition 2018'

[jonhoo]

Indeed, creating a rustfmt.toml with

edition = "2024"

fixes the issue.

Ideally though, we should auto-detect which Rust edition the workspace uses by looking at Cargo.toml. Unclear what to do if there are multiple sub-crates though.