vim.lsp.formatOnSave doesn't work when rust has an async function

[JamyGolden]

⚠️ Please verify that this bug has NOT been reported before.

• I checked all existing issues and didn't find a similar issue

Description

vim.lsp.formatOnSave doesn't work when there is an async function in the file.

👟 Reproduction steps

1. Create example.rs

   pub(crate) async fn example_fn(
   ) -> Result<(), Box<(dyn std::error::Error + 'static)>> {
   println!("hello world");
   
       Ok(())
   }

   Saving this file doesn't run vim.lsp.buf.format() (lua). When i run that manually :lua vim.lsp.buf.format() it formats correctly.

2. Removing the async keyword enables the formatting:

   pub(crate) fn example_fn(
   ) -> Result<(), Box<(dyn std::error::Error + 'static)>> {
   println!("hello world");
   
       Ok(())
   }

   Saving this file formats correctly indenting the println!("hello world"); line.

👀 Expected behavior

Format correctly with async keyword present in file.

😓 Actual Behavior

Only formats when async keyword doesn't exist in file.

💻 Metadata

• system: "x86_64-linux" - host os: Linux 6.9.3-76060903-generic, Pop!_OS, 22.04 LTS, nobuild - multi-user?: no - sandbox: yes - version: nix-env (Nix) 2.25.2 - nixpkgs: /home/user/.nix-defexpr/channels/nixpkgs

📝 Relevant log output

n/a

[NotAShelf]

Okay I can certainly reproduce this, but I'm not exactly sure where this comes from. I'll need to look into this further, but I currently lack the time.

I'll try to bump plugin inputs tomorrow and see if that helps, my guess would be that rustaceanvim screwed up somewhere (since it provides LSP formatting capabilities) or none-ls is overriding something, incorrectly.

[NotAShelf]

I've updated rustaceanvim in a recent commit, could you see if it resolves the issue?

  'github:mrcjkb/rustaceanvim/51c097ebfb65d83baa71f48000b1e5c0a8dcc4fb' (2024-12-29)
  → 'github:mrcjkb/rustaceanvim/4a2f2d2cc04f5b0aa0981f98bb7d002c898318ad' (2025-01-29)

does not inspire much confidence, but since I have not noticed breakage with async before chances are it's an issue with Neovim 0.10.3 >

[JamyGolden]

I've tested and still getting the same issue. I don't get this bug with rustaceanvim on my dotfiles setup (with neovim 0.10.3), but I use lsp-zero and formatOnSave set to rust-analyzer. If the issue is with null-ls, I'm guessing the issue is here to stay since it was deprecated in 2023.

[NotAShelf]

We've since switched to the maintained fork, none-ls, but I not entirely conviced that it is where the issue resides.

Regardless, we'll be dropping none-ls in favor of conform and nvim-lint very soon.

[cramt]

i also seem to be having this issue in rust

[NotAShelf]

Yes, I've confirmed the issue but have not been able to determine the root cause yet. My two guesses are

1. nixpkgs & rustfmt
2. none-ls doing something weird (more likely)

Progress is being made in #593, which introduces a new formatter framework. It's halted for the time, but I'll try to complete it over this week.

[cramt]

when i come home i'll try out the branch and see if solves it for me