NIX_PATH not honored

[zhaofengli]

On 8802412, NIX_PATH does not appear to have an effect:

$ NIX_PATH=meow=/dev/null ./build/src/nix-eval-jobs -E 'toString <meow>'
...
              error: file 'meow' was not found in the Nix search path (add it using $NIX_PATH or -I)

[Mic92]

This is a "feature" that inherited from the original hydra-eval-jobs:

nix-eval-jobs/src/nix-eval-jobs.cc

Line 348 in 8802412

unsetenv("NIX_PATH");

[zhaofengli]

Oh wow, my grep-foo failed and it worked before. CI relying on <nixpkgs> only started to fail in Colmena since the last bump.

I guess NIX_PATH previously working should be considered unintentional despite the error message?

[Mic92]

Maybe NIX_PATH was interpreted before that line of code?
What should still work is nix-eval-jobs -I nixpkgs= etc?
Not sure what the best course of action here is. I would like to use nix-eval-jobs in hydra again at some point.

[zhaofengli]

Yeah, it was interpreted when constructing the global evalSettings. IMO nix-eval-jobs should act as "normal Nix" and accept the variable and let the user (e.g., Hydra) clear it as needed. The user can opt to use flakes/pure-eval/restrict-eval if they care about hermeticity.

[Mic92]

Feel free to make a pull request removing unsetenv and updating a documentation on how to get hermetic evaluation.