nix repl repl-flake behaves differently than :lf

[sg-qwt]

Not sure of this is a bug or desired behavior of the new experimental repl-flake.

With repl-flake enabled and entered my nixos flake, when I run nix repl .#, only 5 variables added. In my previous workflow with :lf inside repl, I can see more variables added. Things like input etc are missing by nix repl .#

> nix repl .#
Welcome to Nix 2.13.3. Type :? for help.

Loading installable 'git+file:///home/me/nixos#'...
Added 5 variables.
nix-repl> :lf .#
Added 17 variables

[asymmetric]

Slightly related: is there a way to print defined variables?

[mvnetbiz]

what's added by nix repl .#

diff nothing.txt replflake.txt | grep \>
> devShells
> legacyPackages
> nixosConfigurations
> overlays
> packages

what's additionally loaded by :lf

diff replflake.txt lf.txt | grep \>
> _type
> inputs
> lastModified
> lastModifiedDate
> narHash
> outPath
> outputs
> sourceInfo
> submodules

The nix <flake>#<attribute> argument apparently only supports the output attributes, so maybe it would make sense to make all nix commands support these attributes too, not just the output attributes. For example, then you could run
nix build .#inputs.nixpkgs.hello to build hello from the nixpkgs input of the flake.

[mvnetbiz]

This workaround loads all the same attributes as :lf with nix repl .#, but some commands show the "unknown" attributes

{
  outputs = { self, ... }: {
    inherit (self) _type inputs lastModified lastModifiedDate narHash outPath outputs sourceInfo submodules;
  };
}

[thufschmitt]

Discussed during the Nix maintainers meeting on 2024-02-26.

• Agreement that we should fix the discrepancy by making nix repl <flakeref> align with :lf.
• Potentially, this should be extended to all the commands (tracked on Expose the flake inputs to the flakes installables #10114).

[nixos-discourse]

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

https://discourse.nixos.org/t/2024-02-28-nix-team-meeting-129/40499/1

[KiaraGrouwstra]

@asymmetric:

Slightly related: is there a way to print defined variables?

you can use functions like trace (from builtins/lib).

@mvnetbiz:

what's additionally loaded by :lf

actually, lib differs between the two as well - for :lf it seems to also have stuff like lib.nixosSystem

[thufschmitt]

actually, lib differs between the two as well - for :lf it seems to also have stuff like lib.nixosSystem

Do you mean that nix repl nixpkgs doesn't give you lib.nixosSystem?

$ nix repl nixpkgs
Nix 2.21.0pre20240304_4388559
Type :? for help.
Loading installable 'flake:nixpkgs#'...
Added 5 variables.
nix-repl> lib.nixosSystem 
«lambda nixosSystem @ /nix/store/3i3rncs75fid9hwai5p2nvwc4ngdnia7-source/flake.nix:21:23»