nix run should not remove arguments after the first positional one

[lheckemann]

Describe the bug

nix run -f '<nixpkgs>' nix flake show --allow-import-from-derivation does not pass --allow-import-from-derivation to the child nix process as expected.

Workaround: nix run -f '<nixpkgs>' -- nix flake show --no-eval-cache (adding --).

nix-env --version output

Tested on both nix (Nix) 2.8.1 and nix (Nix) 2.10.0pre20220812_78bd377 (current lazy-trees).

[Kha]

Previous discussion: https://discourse.nixos.org/t/proposal-simpler-nix-run-syntax/16281

[lheckemann]

I'm fine with not supporting this use without --, but then IMHO it shouldn't pass any args that aren't preceded by -- on to the child. Allowing mixing Nix args and child process args is very confusing.

[fricklerhandwerk]

Triaged in Nix team meeting:

• @edolstra: this is consistent behavior that might not be intuitive
  • there is no special handling for positional parameters after the flake attribute
  • we could add that special handling
  • @fricklerhandwerk: what about the alternative of enforcing -- to separate the nested command?
    • @thufschmitt: probably wouldn't make the situation much better
• needs discussion

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-04-28-nix-team-meeting-minutes-50/27698/1

[fricklerhandwerk]

Discussed in Nix team meeting:

• @roberth: most "higher order bash" commands that do exec separate the nested command line with --
  • @thufschmitt: ssh is a counterexample (that is hell to work with, admittedly)
• @thufschmitt: plugin files handling is another precedence
  • @edolstra: yes, there is a special hack for that
• @edolstra: we could have a special setting in the argument parsing
  • could also say that positional arguments must always be at the end
    • that would break a lot of stuff
  • @thufschmitt: a special case only for nix run would be less trouble
• @roberth: two viable options (everything else is really verbose):
  1. separator (explicit)
  2. taking everything following the installable as arguments (implicit, "Docker style")
• @thufschmitt: could also have --arg flags, would keep the parsing simple
  • @roberth: we should follow existing conventions and not try to be clever
• decision: use everything after the installable parameter as the nested command line, but only for nix run and nix develop

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-05-05-nix-team-meeting-minutes-52/27893/1

[emilazy]

As I just got frustrated by this for the nth time enough to open #8537 before seeing this issue with an approved label, I thought I should ask whether there are any particular nuances that will make implementing this difficult or if it'd be good for me to pick up for a PR?

[roberth]

Personally I haven't made changes to the argument parsing yet; perhaps @Ericson2314 or @edolstra have some insights into how to approach the implementation of this?

As far as the problem statement goes

use everything after the installable parameter as the nested command line, but only for nix run and nix develop

I think this captures it pretty well.

[emilazy]

I'll take a crack at it once I pop a few yaks off the shaving stack (hacking.md → NixOS/nixpkgs#238531 → NixOS/nixpkgs#236656 (comment) → NixOS/nixpkgs#238791...). I expect it shouldn't be too difficult as nix shell -c ... already works correctly.

[nixos-discourse]

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

https://discourse.nixos.org/t/equivalent-of-nix-shell-run-with-nix-shell-or-nix-develop/34712/6