Improve support for Nix

[BCVerdouw]

Tell us more.

After a few days of trying (and failing) to get Renovate working the way I expected on my Nix projects I decided to take a look at the source code.

While doing so I identified two issues worth addressing.
I'm already working on a pull-request addressing these issues, this discussion is mostly meant as additional context to describe, and explain the changes I'm making.

Misinterpretation of the flake.lock nodes.root entry:

In lib/modules/manager/nix/extract.ts, on line 66, there's a check intended to skip inputs that are not defined in nodes.root.
While that seems to be a good idea to skip transitive dependencies, the current implementation does not account for the fact that the entries in nodes.root.inputs map input names to lockfile node names (inputs.<input name>: <lockfile node name>).
To explain, assuming the following flake.nix and flake.lock:

flake.nix

{
  description = "A minimal flake";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
    home-manager.url = "github:nix-community/home-manager/release-25.11";
  };

  outputs = { self, nixpkgs, ... }: let
    # Define supported systems (e.g., Linux or macOS)
    system = "x86_64-linux";
    pkgs = import nixpkgs { inherit system; };
  in {
    # Define the default development shell environment
    devShells.${system}.default = pkgs.mkShell {
      buildInputs = [
        pkgs.hello
        pkgs.git
      ];
    };
  };
}

flake.lock

{
  "nodes": {
    "home-manager": {
      "inputs": {
        "nixpkgs": "nixpkgs"
      },
      "locked": {
        "lastModified": 1779506708,
        "narHash": "sha256-QOD/CNm196nCJRheux/URi4/HE66fthdOMqCJoPP1Y0=",
        "owner": "nix-community",
        "repo": "home-manager",
        "rev": "3ee51fbdac8c8bdfe1e7e1fcaba6520a563f394f",
        "type": "github"
      },
      "original": {
        "owner": "nix-community",
        "ref": "release-25.11",
        "repo": "home-manager",
        "type": "github"
      }
    },
    "nixpkgs": {
      "locked": {
        "lastModified": 1779102034,
        "narHash": "sha256-vZJZjLo513IeI8hjzHFc6TDezUd4uCE2Eq4SNO3DNNg=",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "687f05a9184cad4eaf905c48b63649e3a86f5433",
        "type": "github"
      },
      "original": {
        "owner": "NixOS",
        "ref": "nixos-25.11",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1779796641,
        "narHash": "sha256-ZsIrKmhp4vbBXoXXmR/tBXA/UCsAQiJL9vsgZEduhVY=",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "25f538306313eae3927264466c70d7001dcea1df",
        "type": "github"
      },
      "original": {
        "owner": "NixOS",
        "ref": "nixos-25.11",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "home-manager": "home-manager",
        "nixpkgs": "nixpkgs_2"
      }
    }
  },
  "root": "root",
  "version": 7
}

The problem is that nixpkgs_2 is the lockfile representation of inputs.nixpkgs, yet it will be skipped. Potentially even worse, nixpkgs, which is a transitive dependency, will be parsed as if it were the canonical representation of inputs.nixpkgs.

In this simplified example the issue is not a major concern because both entries happen to follow nixos-25.11, however, that is not always the case.

Hardcoded usage of nixpkgs versioning only in nixos/nixpkgs

Within lib/modules/manager/nix/extract.ts, on lines 151-154 there is a hardcoded check that enables the nixpkgs versioning scheme only for nixpkgs, sourced specifically from https://github.com/NixOS/nixpkgs. As a result, other projects that follow the same versioning scheme, such as home-manager and aagl-gtk-on-nix, are currently excluded from this versioning logic.

AI Assistance Notice:

• I've used AI (Google's built-in one) to generate the minimal flake.nix shown here, the resulting flake.lock is part of the test set in my local changes.
• I've used ChatGPT to check the readability of this discussion starter.

[BCVerdouw]

After a month of silence on both this discussion, and the related PR, I'm curious. is the lack of engagement due to the manager I've worked on being too niche, or just due to the high volume of activity on Renovate as a whole?

[RahulGautamSingh]

The latter. Too much activity, sorry for that, I will look into it when time allows.

I see you have a PR open I will review that shortly.