{
  description = "A flake for building Object Introspection.";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";

    flake-utils.url = "github:numtide/flake-utils";

    treefmt-nix.url = "github:numtide/treefmt-nix";
    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = { self, nixpkgs, flake-utils, treefmt-nix, ... }@inputs:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        treefmtEval = treefmt-nix.lib.evalModule pkgs (pkgs: {
          projectRootFile = "flake.nix";
          settings.global.excludes = [ "./extern/**" ];

          programs.nixfmt.enable = true;
          programs.clang-format.enable = true;
          programs.black.enable = true;
          programs.isort.enable = true;
        });
      in {
        formatter = treefmtEval.config.build.wrapper;
        checks.formatting = treefmtEval.config.build.check self;
      });
}