flake-parts module breaks nix flake show

[zarelit]

Describe the bug

When imported, nix flake show throws an error like: error: The option `perSystem.x86_64-linux.treefmt' is used but not defined.
Running nix flake show again says error: 'checks.x86_64-linux' is not an attribute set

To Reproduce

This is a minimal flake.nix triggering the issue

{
  description = "Description for the project";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    treefmt-nix.url = "github:numtide/treefmt-nix";
  };

  outputs = inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        inputs.treefmt-nix.flakeModule
      ];
      systems = ["x86_64-linux"];
    };
}

Error is encountered by running nix flake show or also by running nix fmt

Expected behavior

If there's a mandatory option to set in order to not have errors, have it printed in the error message or documented in the flake-parts website

System information

These are the commits in the lockfile at the moment of writing as obtained with nix flake metadata

treefmt-nix: github:numtide/treefmt-nix/42045102f90cfd23ca44ae4ef8362180fefcd7fd
flake-parts: github:hercules-ci/flake-parts/006c75898cf814ef9497252b022e91c946ba8e17

Running on x86_64-linux

[zimbatm]

I think this was fixed. At least I couldn't repro.

I'll close the issue but let me know if you still have that problem.

[zarelit]

@zimbatm this is still happening with these inputs:

Inputs:
├───flake-parts: github:hercules-ci/flake-parts/8e8d955c22df93dbe24f19ea04f47a74adbdc5ec
│   └───nixpkgs-lib: github:NixOS/nixpkgs/4bc72cae107788bf3f24f30db2e2f685c9298dc9?dir=lib
├───nixpkgs: github:NixOS/nixpkgs/6cee3b5893090b0f5f0a06b4cf42ca4e60e5d222
└───treefmt-nix: github:numtide/treefmt-nix/719c2977f958c41fa60a928e2fbc50af14844114
    └───nixpkgs: github:nixos/nixpkgs/d9f759f2ea8d265d974a6e1259bd510ac5844c5d

The weird thing it that some nix caching is involved because it returns two different errors if I run nix flake show twice:

[zarel@playa:~/code/nix examples/linting]$ nix flake show
path:/home/zarel/code/nix examples/linting?lastModified=1689771602&narHash=sha256-l2k02g4W%2fh0c2MdgBYRwDxYqVk4Xq2%2fQjX1sP2ab%2fWc=
├───apps
│   └───x86_64-linux
├───checks
│   └───x86_64-linux
error: The option `perSystem.x86_64-linux.treefmt' is used but not defined.
(use '--show-trace' to show detailed location information)

[zarel@playa:~/code/nix examples/linting]$ nix flake show
path:/home/zarel/code/nix examples/linting?lastModified=1689771602&narHash=sha256-l2k02g4W%2fh0c2MdgBYRwDxYqVk4Xq2%2fQjX1sP2ab%2fWc=
├───apps
│   └───x86_64-linux
├───checks
│   └───x86_64-linux
error: 'checks.x86_64-linux' is not an attribute set

I'm going to open a repository for you to try this out, if it's not reproducible then I don't know what's happening since I don't have any special configuration (it's Nix 2.13.3 with sandbox and flakes enabled) and that's it

[zarelit]

This is the minimal example that breaks the show for me
https://github.com/zarelit/repro-treefmt-issue-78

[zimbatm]

I'm getting a different error on your repo:

$ nix flake show
git+file:///home/zimbatm/go/src/github.com/zarelit/repro-treefmt-issue-78?ref=refs/heads/main&rev=c4f05b1b50f3b7376169f5e91dd79626a0881a76
├───checks
│   └───x86_64-linux
error: 'checks.x86_64-linux' is not an attribute set