Comment directive to disable nixfmt

[PAI5REECHO]

Description

It'd be nice to have a way to disable formatting with a comment directive such as nix-community/nixpkgs-fmt#265. If this were added I'd probably switch from using nixpkgs-fmt.

Small example input

# nixfmt: off
{
  "asd" = 123; "abc" = 321;
}
# nixfmt: on

Expected output

# nixfmt: off
{
  "asd" = 123; "abc" = 321;
}
# nixfmt: on

Actual output

# nixfmt: off
{
  "asd" = 123;
  "abc" = 321;
}
# nixfmt: on

[spikespaz]

Needed especially for this file:
https://github.com/spikespaz/dotfiles/blob/bb736ba0cb12f96024c638df443c623d2e6a1997/packages/ttf-ms-win11/hashes.nix

This is a very top-priority feature for me. I've been wanting it for quite some time.

[piegamesde]

I think this would be incredibly difficult to implement. You are probably better off simply adding that file to your treefmt ignore list.

Edit: Y'all can dislike this comment all you want, this isn't going to make implementing it any easier, and someone skilled and motivated needs to step up to the task

[spikespaz]

simply adding that file to your treefmt ignore list.

I don't know what treefmt is nor do I use Neovim.

[yorickvP]

It would be hard for us to not format certain sections, it would be easy to skip formatting the entire file.

However, there are already ways to achieve this:
treefmt is a formatter runner, that calls the correct formatter for every file in your project. It supports specifying files to keep unformatted.

[spikespaz]

What about when I use

formatter = eachSystem (system: inputs.nixfmt.packages.${system}.default);

Is there a way to exclude a file then?

[spikespaz]

Perhaps a directive to disable a file would work well.

# @nixfmt off

For a whole file, not section.

[mbekkomo]

Any update to this?

[piegamesde]

Functionally the implementation issue is the same as in #223. To quote my comment from there:

Nixfmt works by pretty-printing parsed AST nodes. How should it deal with partial nodes, especially at the line boundaries? Also, how does it know the base indentation to use? It could calculate that from the global AST but it may differ from the unformatted parts