implement nixos-rebuild list-generations

[NotAShelf]

I've recently noticed the list-generations option for nixos-rebuild that outputs a neat table of available generations. Maybe we could implement a nh os generations command as a replacement, that returns similar table of data (+ any other data that we might want) as a formatted table or JSON for parsing purposes.

For reference, here's the example output:

Generation    Build-date           NixOS version                                 Kernel         Configuration Revision  Specialisation
1689 current  2024-06-02 00:20:26  graphical-workstation-24.11.20240527.9ca3f64  6.9.1-xanmod1  dirty                   *
1688          2024-05-31 07:53:58  graphical-workstation-24.11.20240527.9ca3f64  6.9.1-xanmod1  dirty                   *
1687          2024-05-31 07:49:22  graphical-workstation-24.11.20240527.9ca3f64  6.9.1-xanmod1  dirty                   *
1686          2024-05-29 23:45:01  graphical-workstation-24.11.20240527.9ca3f64  6.9.1-xanmod1  dirty                   *

[viperML]

Some time ago I planned a nh os info subcommand, perhaps we could show more useful info

[NotAShelf]

What else would you like to display? I was going to pick apart the list-generations subcommand, so we can definitely add more data

[viperML]

I don't know, that's why I didn't write the command in the end 🤣

Though perhaps closure size (nix path-info -Sh) and nixpkgs commit

[Vortriz]

commenting to refloat this

[NotAShelf]

I was working on this :(

[NotAShelf]

:)

[Vortriz]

i have some suggestions on what all can be shown upon nh os info:

• size of nix store (if thats useful)
• space saved by hardlinking

[NotAShelf]

Nix itself (as per my knowledge) does not report either of those stats. I can calculate the size of the Nix store, but there are already better tools (du, dust, etc.) which I am not sure if we should bother wrapping.