I'd like to float an idea.

If you just want flakelight to provide you a recent nixpkgs (the default), you dont have to do anything:

{
  inputs.flakelight.url = "github:nix-community/flakelight";
  outputs = { flakelight, ... }:
    flakelight ./. {
    };
}

If you want to bring your own nixpkgs, you have to pass it to flakelight:

{
  inputs = {
    nixpkgs.url = "nixpkgs/nixos-unstable";
    flakelight.url = "github:nix-community/flakelight";
  };
  outputs = { flakelight, ... }@inputs:
    flakelight ./. {
      inherit inputs;
    };
}

But what if you didn't have to pass it and flakelight would use your input?

Like this:

{
  inputs = {
    nixpkgs.url = "nixpkgs/nixos-unstable";
    flakelight.url = "github:nix-community/flakelight";
  };
  outputs = { flakelight, ... }:
    flakelight ./. {
    };
}

Currently, that is having a nixpkgs input, but having flakelight still use its
default.

With this proposal, that becomes using your nixpkgs input for flakelight as well.

Upsides:

• Easier to just override inputs
• current behavior might confuse people?
• Less boilerplate

Downsides:

• Someone might intentionally want to have a nixpkgs input but still have
  flakelight use the default (seems unlikely).
• Maybe small perf impact as have to read flake lock?

Passing inputs explicitly may still be preferred for performance or unusual circumstances,
so of course passed inputs override detected ones. It would also need to be
passed if one wishes to pass inputs and the path passed is not ./..

(The autodetection would work by reading ./flake.lock, which is why if the
path passed is not the usual ./., it can't autodetect.)

Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
    };
}

Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
      devShell = { pkgs, inputs, ... }: devenv.lib.mkShell { 
        inherit inputs pkgs;
        ...
      };
    };
}

Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
      devShell = { pkgs, inputs, ... }: devenv.lib.mkShell { 
        inherit inputs pkgs;
        modules = [
        ];
      };
    };
}

Something like:

{
  inputs = {
    flakelight.url = "github:nix-community/flakelight";
    devenv.url = "github:cachix/devenv";
  };
  outputs = { flakelight, devenv, ... }:
    flakelight ./. {
      devShell = { pkgs, inputs, ... }: devenv.lib.mkShell { 
        inherit inputs pkgs;
        modules = [
          # Your stuff here
        ];
      };
    };
}

for autoloading could have:

{ pkgs, inputs, ... }:
  inputs.devenv.lib.mkShell { 
    inherit inputs pkgs;
    modules = [
      # Your stuff here
    ];
  };

and put that in nix/devShell.nix or nix/devShells/devenv.nix or such

any idea why a package definition in nix/packages/example/default.nix, looking like this would complain lib.customisation.callPackageWith: Function called without required argument "buildPythonPackage" at /nix/store/... ?

{ buildPythonPackage }:

buildPythonPackage rec {
  pname = "example"....

haven't run into this with other packages I've defined wherein I use a bunch of build inputs from nixpkgs.
sorry for all the questions 😅