Is there a reason, that the ./. argument is separate from the following attributeset?

Why this:

  outputs = inputs:
    inputs.flakelight ./. {
      inherit inputs;

And not this:

  outputs = inputs:
    inputs.flakelight {
      inherit inputs;
      src = ./.;

I guess the first is a little shorter, but are there any other reason?

Yeah, it only seems to work with nixDir and flakelight.editorconfig disabled:

{
  inputs = flakelight.url = "github:accelbread/flakelight";

  outputs =
    inputs@{
      flakelight,
      self,
      ...
    }:

    flakelight self {
      inherit inputs;

      nixDir = null;
      flakelight.editorconfig = false;

      packages.hello = pkgs: pkgs.hello;
    };
}

Yeah, it only seems to work with nixDir and flakelight.editorconfig disabled:

{
  inputs.flakelight.url = "github:accelbread/flakelight";

  outputs =
    inputs@{
      flakelight,
      self,
      ...
    }:

    flakelight self {
      inherit inputs;

      nixDir = null;
      flakelight.editorconfig = false;

      packages.hello = pkgs: pkgs.hello;
    };
}

Fair, but it would be nice if Flakelight has a opinionated way to add helper functions, that will be made available everywhere like with packages.

It does not have to be by modifying lib, but I'm not sure what the alternative could be.

I have noticed that devShells evaluates all nixosConfigurations, if you refer to checks from outputs:

# devShell.nix
pkgs: pkgs.mkShell {
  packages = [
    outputs.checks.${pkgs.system}.pre-commit-check.enabledPackages
  ];
}

# checks.nix
{
  checks.pre-commit-check = {
    inputs,
    system,
    ...
  }:
    inputs.git-hooks.lib.${system}.run {
      src = ./.;
      hooks = {
        alejandra.enable = true;
        statix.enable = true;
        ruff-format.enable = true;
      };
    };
}

I have noticed that devShells evaluates all nixosConfigurations, if you refer to checks from outputs:

# devShell.nix
pkgs: pkgs.mkShell {
  packages = [
    outputs.checks.${pkgs.system}.pre-commit-check.enabledPackages
  ];
}

# checks.nix
{
  checks.pre-commit-check = {
    inputs,
    system,
    ...
  }:
    inputs.git-hooks.lib.${system}.run {
      src = ./.;
      hooks = {
        alejandra.enable = true;
        statix.enable = true;
        ruff-format.enable = true;
      };
    };
}

The offending code is in builtinModules/nixosConfigurations.nix:

      checks = foldl recursiveUpdate { } (mapAttrsToList
        (n: v: {
          # Wrapping the drv is needed as computing its name is expensive
          # If not wrapped, it slows down `nix flake show` significantly
          ${v.config.nixpkgs.system}."nixos-${n}" = v.pkgs.runCommand
            "check-nixos-${n}"
            { } "echo ${v.config.system.build.toplevel} > $out";
        })

The offending code is in builtinModules/nixosConfigurations.nix:

      checks = foldl recursiveUpdate { } (mapAttrsToList
        (n: v: {
          # Wrapping the drv is needed as computing its name is expensive
          # If not wrapped, it slows down `nix flake show` significantly
          ${v.config.nixpkgs.system}."nixos-${n}" = v.pkgs.runCommand
            "check-nixos-${n}"
            { } "echo ${v.config.system.build.toplevel} > $out";
        })
        configs);