Document how to use `treefmt.toml` instead of `treefmt.nix` with treefmt-nix so that `nix fmt` & `nix flake check` can share configuration with treefmt-vscode

[vorburger]

I've added treefmt-nix to this example project, with a treefmt.nix as documented on the README of this project.

Then I've discovered https://github.com/isbecker/treefmt-vscode and want to use it. But that apparently doesn't dig treefmt.nix, but needs treefmt.toml.

I'm a new Nix user, and it's not clear to me if these 2 ways of configuring formatters can be combined, without duplication?

In a perfect world, this project would document a bit more clearly how to do set-up this combination.

[jfly]

@voFrederick, this is an area we need to work on (sort of tracked by numtide/treefmt#583).

I believe that in order to use isbecker/treefmt-vscode you would have to "eject" from treefmt-nix to a plain treefmt.toml.

I personally would like to see someone build a vscode plugin that runs (the equivalent of) nix fmt on whatever file you're editing. I added support for this to neovim by creating none-ls's nix_flake_fmt builtin. That ended up quite messy (see the implementation), but the latest version of nix (2.29+) has some tooling to make this simpler to build.

[hackardoX]

Hi @vorburger, I partially succeed to make it work with vscode, without using any treefmt.toml.

Premise: I use snowfall to organize my flake, and I am using nix-darwin and home-manager to configure my machine, you can have a look here: https://github.com/andrea11/nix.

TLDR, here what I did:

1. Create a package to wrap the treefmt-nix:

{
  channels,
  inputs,
  writeShellApplication,
  ...
}:
let
  treefmtWrapper = inputs.treefmt-nix.lib.mkWrapper channels.nixpkgs ../../treefmt.nix;
in
writeShellApplication {
  name = "treefmt-nix";

  meta = {
    mainProgram = "treefmt-nix";
  };

  text = ''
    exec ${treefmtWrapper}/bin/treefmt "$@"
  '';
}

2. Install this created package using home-manager (or nixos/darwin):

home = {
      packages =
        with pkgs;
        [
          ...
          treefmt
          pkgs.${namespace}.treefmt-nix
          ...
        ];

3. Configure vscode to use treefmt-nix as binary for treefmt:

Now, in my case it works, but I see that when I open a project I first need to force vscode to "run treefmt" once (provided by treefmt-vscode) in order to make it work.
Hope to see better solutions