Allow customising format command

[TheColorman]

⚠️ Please verify that this feature request has NOT been suggested before.

• I checked and didn't find a similar feature request

🏷️ Feature Type

API Additions

🔖 Feature description

A lot of formatters come with options and configuration, but NVF does not support configuring any of them.

✔️ Solution

A simple vim.languages.<lang>.format.command would suffice, as it's standard practice for formatters to support configuration either through CLI arguments or by passing a configuration file.
This option would override vim.languages.<lang>.format.{package, type} as you would effectively need to specify a path in the nix store to the formatter.

Usage example:

{ pkgs, lib, ...}: {
  vim.languages.nix.format.command =
    "${lib.getExe pkgs.alejandra} --experimental-config ${./alejandra.toml}";
}

❓ Alternatives

A lot of formatters read configuration files automatically relative to their execution directory, but I'd like to set defaults for all files of a specific language.

📝 Additional Context

#382 will completely change how language configuration works, so I'd like to take a shot at implementing this myself with a bit of guidance if given the go-ahead, to prevent needlessly increasing your workload.

[NotAShelf]

#382 somewhat abandoned. I was very unsure of the design, and because of a mistake in a merge some changes got into main prematurely

#643 supersedes the PR, conform and nvim-lint features are already in main. I'd like to finish formatter changes after LSP configs are done- which is sure to change with Neovim 0.11 but I do, in fact, want to support formatter options. I'll be creating a discussion in the discussions tab soon.

[NotAShelf]

I've closed #382 because honestly I don't think I'll be tackling it soon. Although, I would appreciate your feedback/thoughts in #748 to discuss this further. Language rewrite is a large task, probably best that we take it slow.

[TheColorman]

Ah, didn't see the conform options. I've made it work with

{
  lib,
  pkgs,
  parentInputs,
  ...
}: {
  vim = {
    formatter.conform-nvim = {
      enable = true;
      setupOpts = {
        formatters_by_ft.nix = ["alejandra"];
        formatters.alejandra = {
          command = lib.getExe parentInputs.alejandra.defaultPackage.${pkgs.stdenv.hostPlatform.system};
          args = ["--experimental-config" ../alejandra.toml];
        };
      };
    };
    languages.enableFormat = true;
  };
}

Note for anyone looking to copy this: as of time of writing, the latest version of Alejandra is 3.1.0, which doesn't support the --experimental-config flag, so I've pulled it in directly as a flake input.