Add Nix Flake Check and Nix Fmt to Devenv Hooks

[shikanime]

Automatically integrate standard nix flake check and nix fmt. Specifically, when treefmt or git-hooks are configured in a project.

[domenkozar]

We won't add nix flake check as it takes too long, commit hooks should be fast!

We should be able to add nix fmt.

[shikanime]

Sorry, yes it was meant to devenv.

[domenkozar]

I don't understand.

[shikanime]

This issue was intended to be opened in cachix/devenv, since the git-hooks.nix and treefmt-nix Flake modules already add the formatters and checks individually. However, problems arise when they are defined at the devenv level such as:

{
  inputs = {
    devenv.url = "github:cachix/devenv";
    flake-parts.url = "github:hercules-ci/flake-parts";
    git-hooks.url = "github:cachix/git-hooks.nix";
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    treefmt-nix.url = "github:numtide/treefmt-nix";
  };

  outputs =
    inputs@{
      self,
      devenv,
      git-hooks,
      flake-parts,
      treefmt-nix,
      ...
    }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        devenv.flakeModule
        treefmt-nix.flakeModule
        git-hooks.flakeModule
      ];
      perSystem =
        {
          config,
          pkgs,
          system,
          ...
        }:
          {
            # We need to set the treefmt wrapper to the one from the devenv shell
            treefmt.build.wrapper = config.devenv.shells.default.treefmt.config.build.wrapper;
            devenv.shells.default.treefmt.enable = true;
          };
    };
}

[shikanime]

Here's an example of how I fixed it on my side: https://github.com/shikanime-studio/devlib/blob/cc2d111e461b4fa4b413f3d14ddffa50de65e007/modules/flake/default.nix