Run a single flake check

[9999years]

There's currently (Nix 2.17.0) no way to run a single flake check.

For example, with the given flake.nix:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = {
    self,
    nixpkgs,
    flake-utils,
  }:
    flake-utils.lib.eachDefaultSystem (
      system: let
        pkgs = import nixpkgs {
          inherit system;
        };
      in {
        checks = {
          my-check = pkgs.runCommand "my-check" {} "echo hello > $out";
        };
      }
    );
}

The only way to build the check my-check is with nix flake check, which builds every check (and packages, and other stuff).

Unlike nix build, nix shell, and nix develop, nix flake check doesn't allow specifying a check:

$ nix flake check .#my-check
error: unexpected fragment 'my-check' in flake reference '.#my-check'

As a workaround, nix build can be used, but it requires specifying the full attribute path, including the current architecture: nix build .#checks.aarch64-darwin.my-check.

Describe the solution you'd like
nix flake check could gain a mode to run individual checks with fragments, like nix flake check .#my-check. Alternatively, to match nix build, nix shell, and nix develop, we could introduce a nix check command.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nix-flake-check-for-current-system-only/18366/4

[tmplt]

Anecdotally, nix run .#checks.<arch>.my-check.driver works for pkgs.testers.runNixOSTest, but only if they are trivial.

I have a multi-node Slurm test (i.e. performs intra-node network operations) that passes in a nix flake check but fails in the nix run approach above.

---

This feature is rather necessary for complex CI projects. I'd love to see it implemented.