Use new packages.${system}.default convention

[thkoch2001]

The switch from defaultPackage to packages.${system}.default happened in NixOS/nix#5532.

Additionally I removed one layer:
self.nixosConfigurations.my-microvm.config.microvm.declaredRunner; self.nixosConfiguration.config.microvm.declaredRunner;

The latter should be easier to understand for new users.

[thkoch2001]

Sorry, while waiting for the checks to pass I learned that nixosConfigurations is a predefined output for flakes and thus it might actually be confusing to have a nixosConfiguration (without plural s). On the other hand I don't believe that a microvm in nixosConfigurations is ever useful outside of the context of microvm?

The diff view can be simplified by surpressing whitespace diff.

[astro]

Happy to catch up with packages.${system}.default.

There is no nixosConfiguration in the Flakes schema, only nixosConfigurations, sorry.

[mikatammi]

Is this right? Shouldn't it be nixosConfigurations.my-microvm = ?

[astro]

No, yes. This PR needs changes.

@thkoch2001 Are you going to do that?

[thkoch2001]

Sorry for the double-push. I reduced the commit now to the trivial one-line change.

In my own local flake however I removed nixosConfigurations entirely from the flake:

  outputs = { self, nixpkgs, microvm }:
    let
      system = "x86_64-linux";
      nixosConfiguration = nixpkgs.lib.nixosSystem {
          inherit system;
          modules = [
            microvm.nixosModules.microvm
[...]
        };
    in {
      packages.${system}.default = nixosConfiguration.config.microvm.declaredRunner;
    };

[astro]

Thank you!