set nixfmt as the default formatter for nix

[notnmeyer]

sets the default formatter for nix to nixfmt and enables auto-formatting.

closes https://github.com/helix-editor/helix/issues/10803

[poliorcetics]

Is it stable yet ? I agree that using what is going to be the official formatter is nice but it's still in < 1.0 so I'm afraid they'll do breaking changes yet and we'll get issues with people complaining helix is changing all the formatting because of two different versions of nixfmt on two machines

[notnmeyer]

could they... use nix to avoid that? joking aside, if this a concern a practical solution would just be disable auto-format as a default. i think the scenario where different tooling versions "fight" over the correct formatting style can apply to a lot of tools and different configuration settings. personally, i don't think its that big of deal.

[poliorcetics]

could they... use nix to avoid that

I must admit I laughed 😁

And really my comment was a question for you. I settled on "nixpkgs-fmt" a long time ago for nix formatting because I didn't want to depend on something that, at the time, was still only a project and not actual working code, but if the situation has changed and stabilized, adding out of the box support in helix is certainly something I'll agree with.

I have not followed evolutions though, so I genuinely don't know 😅

[notnmeyer]

the current RFC style is packaged in nixfmt-rfc-style (which still installs a nixfmt binary) and i believe the intention is to eventually just have the nixfmt package be the source of truth. i cant comment on how "stable" the formatter is, but ive been using it myself and it works fine.

the main points here:

1. the style rfc has been adopted
2. the formatter is packaged and available

• https://github.com/NixOS/rfcs/pull/166
• https://github.com/NixOS/rfcs/blob/master/rfcs/0166-nix-formatting.md
• https://github.com/NixOS/nixfmt/pull/118

[the-mikedavis]

Yeah let's keep auto-format off for now by default. We should only enable auto-format for languages where formatting is ubiquitous like Rust - otherwise it can unexpectedly reformat older code. Eventually if formatting becomes very popular for Nix we can enable it but where the RFC was accepted recently I think it's too soon.

Super ideally though we wouldn't need to set up a formatter binary for this. Ideally the language servers would depend-on/use nixfmt. External formatters are fairly wasteful since we need to spawn them and send the whole document through them and figure out the diff ourself per-save while with language servers we have incremental document sync and text edits to describe the changes. Maybe for now we could just recommend formatter.command = "nixfmt" in the documentation since I assume language servers will follow the RFC in the (near?) future.

[notnmeyer]

or now we could just recommend formatter.command = "nixfmt" in the documentation

works for me, thanks