`nix flake check` fails when nix-unit is used in a flake-parts partitioned module without network

[folliehiyuki]

I'm using nix-unit in a partitioned flake, following https://flake.parts/options/flake-parts-partitions. When executing nix flake check, nix-unit still tries to fetch unknown inputs even when perSystem.nix-input.inputs is defined. The check command refers to the top-level flake, where no partitioned inputs exist.

nix-unit/lib/modules/flake/system.nix

Line 124 in 388045c

--flake ${self}#tests.systems.${system} \

The flake module works when flake-parts' partition module is not used.

Reproduced setup

flake.nix

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

    # Use https://github.com/hercules-ci/flake-parts/pull/273 to eliminate any other networking factors.
    flake-parts = {
      url = "github:MattSturgeon/flake-parts/override-flake-compat";
      inputs.nixpkgs-lib.follows = "nixpkgs";
    };

    flake-compat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };
  };

  outputs =
    inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        flake-parts.flakeModules.partitions
      ];

      systems = [
        "x86_64-linux"
        "aarch64-linux"
        "x86_64-darwin"
        "aarch64-darwin"
      ];

      flakeCompatSrc = inputs.flake-compat;

      partitionedAttrs.checks = "dev";
      partitionedAttrs.tests = "dev";
      partitions.dev.extraInputsFlake = ./dev;
      partitions.dev.module =
        { inputs, ... }:
        {
          imports = [
            inputs.nix-unit.modules.flake.default
          ];

          perSystem = _: {
            nix-unit.inputs = {
              inherit (inputs) nixpkgs flake-parts nix-unit flake-compat;
            };

            nix-unit.allowNetwork = false;
          };

          flake.tests."test example" = {
            expr = {
              x = 1;
            };
            expected = {
              y = 1;
            };
          };
        };
    };
}

dev/flake.nix

{
  outputs = _: { };

  inputs = {
    treefmt-nix.url = "github:numtide/treefmt-nix";

    nix-unit = {
      url = "github:nix-community/nix-unit";
      inputs.treefmt-nix.follows = "treefmt-nix";
    };
  };
}

Error output

The command doesn't know about nix-unit input, which is only defined in the partitioned flake, so the override doesn't work.

out=/nix/store/4jmf3610h9cwniw29bjhd23inpbq5h1r-nix-unit-check
Running tests for  x86_64-linux
warning: `--gc-roots-dir' not specified
warning: input '' has an override for a non-existent input 'nix-unit'
warning: the flag '--override-input nix-unit path:/nix/store/b6mpyyfj2lkxhz92nb1yyc0zkay6d6ff-source' does not match any input
warning: not writing modified lock file of flake 'path:/nix/store/rsp82k7fcp2aybicikh44kwlsp3xkayl-source':
• Updated input 'flake-compat':
    'github:edolstra/flake-compat/9100a0f413b0c601e0533d1d94ffd501ce2e7885?narHash=sha256-CIVLLkVgvHYbgI2UpXvIIBJ12HWgX%2BfjA8Xf8PUmqCY%3D' (2025-05-12)
  → 'path:/nix/store/b0my5vy8pzfzjqrr3g58j0w6md9jf3ch-source?lastModified=1&narHash=sha256-CIVLLkVgvHYbgI2UpXvIIBJ12HWgX%2BfjA8Xf8PUmqCY%3D' (1970-01-01)
• Updated input 'flake-parts':
    'github:MattSturgeon/flake-parts/ebfbd32548b4bd19a5315ec08e489c01ef0978e2?narHash=sha256-xg5ssb8T8t28umxjtpLmSJusKUdAb0r%2BZ2DJRHh0cD0%3D' (2025-02-24)
  → 'path:/nix/store/ym4gk90zcjrsq9anrvybjvsghcis5j5w-source?lastModified=1&narHash=sha256-xg5ssb8T8t28umxjtpLmSJusKUdAb0r%2BZ2DJRHh0cD0%3D' (1970-01-01)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/3b9f00d7a7bf68acd4c4abb9d43695afb04e03a5?narHash=sha256-XexyKZpf46cMiO5Vbj%2BdWSAXOnr285GHsMch8FBoHbc%3D' (2025-08-25)
  → 'path:/nix/store/r33xw4w5nmpmfac4g47h1lmrcl4qlz7k-source?lastModified=0&narHash=sha256-XexyKZpf46cMiO5Vbj%2BdWSAXOnr285GHsMch8FBoHbc%3D' (1970-01-01)
unpacking 'github:nix-community/nix-unit/388045c7bee5a2617cca8e94444bea1862df19ac?narHash=sha256-OLaoMtlNL5AvYuaQ5P4p7riy7M9J8XpFdWKpD5RzQfU%3D' into the Git cache...
warning: error: unable to download 'https://github.com/nix-community/nix-unit/archive/388045c7bee5a2617cca8e94444bea1862df19ac.tar.gz': Could not resolve hostname (6) Could not resolve host: github.com; retrying in 325 ms

Maintainers ping

cc @roberth

[Endermanbugzjfc]

I think I get the same problem. Imma just allow internet, see if this can workaround the problem.

error: builder for '/nix/store/hlw5kr7x9brh2fjvqnb6pd1z2jvxji96-nix-unit-check.drv' failed with exit code 1;
       last 25 log lines:
       >          at «flakes-internal»/call-flake.nix:96:18:
       >            95|         if node.flake or true then
       >            96|           assert builtins.isFunction flake.outputs;
       >              |                  ^
       >            97|           result
       >
       >        … while calling the 'import' builtin
       >          at «flakes-internal»/call-flake.nix:66:15:
       >            65|
       >            66|       flake = import (outPath + "/flake.nix");
       >              |               ^
       >            67|
       >
       >        … while realising the context of a path
       >
       >        … while calling the 'fetchFinalTree' builtin
       >          at «flakes-internal»/call-flake.nix:56:11:
       >            55|           # Note: lock file entries are always final.
       >            56|           fetchTreeFinal (node.info or { } // removeAttrs node.locked [ "dir" ]);
       >              |           ^
       >            57|
       >
       >        … while fetching the input 'github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e?narHash=sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768%3D'
       >
       >        error: Failed to open archive (Source threw exception: error: unable to download 'https://github.com/nix-systems/default/archive/da67096a3b9bf56a91d16901293e51ba5b49a27e.tar.gz': Could not resolve hostname (6) Could not resolve host: github.com)
       For full logs, run:
         nix log /nix/store/hlw5kr7x9brh2fjvqnb6pd1z2jvxji96-nix-unit-check.drv

[Endermanbugzjfc]

Nvm I fixed it without enabling internet: I missed some flake inputs in nix-unit.inputs.

[mightyiam]

This seems to be specifically due to the partitions module fetching flake-compat.

[roberth]

@mightyiam Can happen due to any fetchTree/fetchGit/getFlake/{FOD+IFD} input.
Been thinking about this. Unusual, but right for flake-parts:

• Update and vendor flake-compat hercules-ci/flake-parts#315

[folliehiyuki]

The issue still occurs if the needed inputs for nix-unit are defined in the partitioned flake and not in the top-level one (as shown in the issue description).

[roberth]

Right, the linked PR only fixes the case where you're testing non-partitioned attributes of a partitioned flake.
This issue includes partitions.dev.extraInputsFlake = ./dev; which loads a hardcoded lockfile.
This lockfile needs to be overridden somehow.
Maybe this nix-unit module / derivation should make a local copy of the flake in the sandbox so that it can easily replace any file, including this lock file.
Alternatively, I imagine support for file-level overrides could be added to Nix (somewhat hard, not sure if desirable), or perhaps arbitrary overriding / configuration in a (this?) flake-parts module so that the ./dev definition can be removed and individual inputs (from the non-sandbox evaluation) added.