flake/nix-command based eval?

[GenericNerdyUsername]

would it be possible to use nix eval, so that the evaluation is cached? I feel it would speed up usage a fair bit

[Mic92]

I don't think that would work. nixpkgs currently does not expose all packages in the flake and legacyPackages is not cached afaik. Also as far as I know it might also slow down the first evaluation since for every attribute it would needs to create entries in the eval cache sqlite databases.

[GenericNerdyUsername]

This is the first ive heard of not all packages being exposed

[Mic92]

If you do $ nix flake show --legacy you see that it won't include any nested package sets such as python packages. It's probably possible to have an eval script that iterates over all packages in the same way nix-env does, but it likely also slower. And I don't think you will be able to use the eval cache in this case.

[GenericNerdyUsername]

What would be the problem with writing a small expression that gives you all of the packages?

[Mic92]

Than you won't benefit from any cache and just reimplement nix-env in a slower way. Also there are some exceptions thrown in nixpkgs every once in a while that you cannot catch from nix.
This is the script that I used before to go over all of nixpkgs. https://gist.github.com/Mic92/0a30fa6babd3eb9c8445fd877ae8781f

[GenericNerdyUsername]

Why not put that script in a flake and modify the nixpkgs input?

[Mic92]

I'd say it would be easier to just cache the nixpkgs package list that nix-env generates:

nixpkgs-review/nixpkgs_review/review.py

Line 344 in 30a6655

def list_packages(

and less error prone than those terrible nix expressions that has to use tons of tryEval.