Nix repl does not work with flakes

[Mic92]

Describe the bug

Before it was possible to use to use nix repl <nixpkgs/nixos> to get nixos in a repl.

This seems not possible anymore with flakes nix repl ".#":

Welcome to Nix version 2.4pre20200622_334e26b. Type :? for help.

Loading '.#'...
error: --- SysError ----------------------------------------------------------- nix
getting status of '/home/joerg/.homesick/repos/dotfiles/.#': No such file or directory

How do I load flakes in a nix repl?

[Mic92]

Current workaround:

cat > ./nixos-config.nix <<EOF
(builtins.getFlake (toString ./.)).nixosConfigurations.turingmachine
EOF
nix repl ./nixos-config.nix

[Ma27]

FWIW, if a snippet like this in your flake.nix you can also do nix run .#repl:

{
  outputs = { flake-utils, ... }: {
      apps.repl = flake-utils.lib.mkApp {
        drv = pkgs.writeShellScriptBin "repl" ''
          confnix=$(mktemp)
          echo "builtins.getFlake (toString $(git rev-parse --show-toplevel))" >$confnix
          trap "rm $confnix" EXIT
          nix repl $confnix
        '';
      };
  };
}

[FlorianFranzen]

Another issue I have in this regard is that getFlakes does not seem to ever provide self.rev or self.lastModified.

[edrex]

How can :lf be used to load a particular output in a flake-based NixOS config?

> nix repl
Welcome to Nix 2.6.1. Type :? for help.

nix-repl> :lf /etc/nixos#myhost
error: unexpected fragment 'myhost' in flake reference '/etc/nixos#myhost'

[srid]

@edrex

[edrex]

thanks @srid, I swear I tried that but it's working now.

[RuRo]

For anyone coming to this issue from google, I found that the most "elegant" solution is to set

nix.nixPath = [ "nixpkgs=${inputs.nixpkgs}" ];

in your system config, where inputs are the system flake inputs passed via specialArgs.

After that you can refer to the system version of nixpkgs as <nixpkgs> even without any channels configured. Also, legacy package stuff like the ability to do nix-shell -p netcat just works.

[anka-213]

Could we also allow nix repl . or nix repl .#foo or something similar to work with flakes, so we don't need to manually type :lf . each time? I know it's a minor thing, but it would be nice to have.

If it's implemented it should hopefully be without removing the ability for nix repl . to work on non flake-based things with default.nix.

[thufschmitt]

It is actually possible, but hidden behind the repl-flake experimental feature:

$ nix --extra-experimental-features repl-flake repl nixpkgs
Welcome to Nix 2.12.0pre20221025_899878f. Type :? for help.

Loading installable 'flake:nixpkgs#'...
Added 5 variables.
nix-repl>  legacyPackages.x86_64-linux.hello
«derivation /nix/store/c7jrxqjhdda93lhbkanqfs07x2bzazbm-hello-2.12.drv»

[andir]

It is actually possible, but hidden behind the repl-flake experimental feature:

$ nix --extra-experimental-features repl-flake repl nixpkgs
Welcome to Nix 2.12.0pre20221025_899878f. Type :? for help.

Loading installable 'flake:nixpkgs#'...
Added 5 variables.
nix-repl>  legacyPackages.x86_64-linux.hello
«derivation /nix/store/c7jrxqjhdda93lhbkanqfs07x2bzazbm-hello-2.12.drv»

This doesn't seem to work with local flakes (nix repl .#) is that right or am I just unable to figure the syntax out?

[thufschmitt]

This doesn't seem to work with local flakes (nix repl .#) is that right or am I just unable to figure the syntax out?

Strange, it seems to work for me:

$ nix repl --extra-experimental-features repl-flake .#
Welcome to Nix 2.12.0pre20221102_dd1970c. Type :? for help.

warning: Git tree '/home/thufschmitt/Repos/nixos/nix/work' is dirty
Loading installable 'git+file:///home/thufschmitt/Repos/nixos/nix/work#'...
Added 5 variables.
nix-repl> packages.x86_64-linux.nix
«derivation /nix/store/88cq60szkf0rg9a0ph6bgymqqi759rks-nix-2.12.0pre20221102_dirty.drv»

[andir]

Yeah, I used flake-repl as feature and not repl-flake... It works now. I've grown blind to Nix throwing "warnings" at me (there are always some :/)

[charles-dyfis-net]

Absent that, one can use builtins.getFlake "git+file://${builtins.toString ./.}"

[sg-qwt]

I'm not sure if that's the intended behavior of repl-flake. When I run nix repl .#, only 5 variables added. I can get nixosCongirations etc. But when I run :lf .# inside repl of same repo, I get 17 variables added. Things like input are added only with :lf.

> 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

[thufschmitt]

@sg-qwt I don't think it is, indeed. Do you mind opening a specific issue for this?

[sg-qwt]

@sg-qwt I don't think it is, indeed. Do you mind opening a specific issue for this?

done. #8059