treefmt is a CLI tool to format all files in a repository. It recurses through a directory and calls the right formatter based on the type of file it finds.

treefmt requires a configuration file that tells it what to execute for each file type. It doesn't include this configuration by default, so it takes some time to get the configuration right and requires knowledge of the different kinds of formatters that you'd like the use. Knowledge like which CLI flags to use.

treefmt-nix is a Nix module system to build a treefmt configuration. It includes options for most of the different formatters and allows just enabling them. The same kind of module system devenv uses.

For instance:

treefmt-nix.mkWrapper nixpkgs {
  # Used to find the project root
  projectRootFile = ".git/config";
  # Enable the terraform formatter
  programs.terraform.enable = true;
  # Override the default package
  programs.terraform.package = nixpkgs.terraform_1;
  # Override the default settings generated by the above option
  settings.formatter.terraform.excludes = [ "hello.tf" ];
}

It would be nice if this could be integrated into devenv, so that you could have options in devenv like:

services.treefmt.enable = true;
services.treefmt.programs.terraform.enable = true;

This probably requires adding treefmt-nix as a Nix flake input to devenv. Is this something we'd want?