Ability to pass arguments to a shell file

[Unisay]

I use "stock" nix support in direnv like this:

use nix --arg buildAll false

(which is equivalent to nix-shell --arg buildAll false)

it looks like its not possible to pass ARGs to use_nix_gcrooted

use_nix_gcrooted --arg buildAll false
direnv: too many positional arguments

It would be really helpful if this is supported, thanks!

[shajra]

Hi!

I wish this were easier. Here's a copy/paste of the call that does all the magic.

    IN_NIX_SHELL=1 \
        nix-build \
        --show-trace \
        --verbose --verbose \
        --no-out-link \
        --arg src "$shell_file" \
        --expr "((import ${buildSource} {}).build.lorri-eval-$auto_watch_eval)"

This is where I just delegate to Lorri. As you can see, I'm passing the user's Nix file to a build of a Lorri Nix expression. So at this point either:

• I can see if I can get changes into Lorri
• See if I can patch Lorri as part of Lorelei
• Maybe consider if Lorelei and Lorri should combine forces? I feel there's merit to having a daemonless option for Lorri.

Maybe @ProfPatsch has thoughts there? Lorelei is mostly a single file shell script, cooked up by Nix. Because it's cooked up by Nix, it just makes calling out to Lorri easy. But Lorri is really doing all the work.

So I think your request is reasonable. I'm hoping the workarounds Nix gives us are workable. You can have a separate file, just for Lorelei/Direnv. And that way, your normal shell.nix script can be fully parameterized, and your shell.direnv.nix script can be hard-coded with the arguments you are otherwise asking to put in .envrc in the call to use_nix_gcrooted. So I think that solves the problem, but with the worsened ergonomics of yet-another-file you never really wanted.

I'll see if I can stare at Lorri code later to see if it's easier than I think it is at this point.

[Unisay]

Thanks @shajra for a detailed explanation! Fun fact: I evaluated Lorri first, lacked that feature and decided to give a try to Lorelei hoping that it can pass arguments and not realizing it uses Lorri under the hood for this :)

The solution with multiple files that you described was on my mind too (as a backup plan in case if passing args directly doesn't work :) At this point I am leaning towards using it as a workaround.

Thanks for the evaluation!

[shajra]

@Unisay that's good that the workaround might hold you over. I really think the Lorri way of getting references to GC root is the right (or at least the best) algorithm I've seen. Other approaches have problems with FFI. So I really recommend people use either Lorri or Lorelei for Direnv/Nix integration.

In other news, I did look at Lorri code to remind myself how things connect. And here's a relevant line of code: https://github.com/nix-community/lorri/blob/canon/src/logged-evaluation.nix#L41-L42.

This is the point where you'd like your arguments passed in. So... the amount of patching it would take to get this to thread through is not so much. I do have to build a Nix attr set from Bash CLI arguments, though. But that's on par with the kind of complexity that makes up Lorelei as it stands.

Though... I shouldn't dismiss too quickly the trickiness of delimiting strings.

[shajra]

Yeah, quoting with Nix is a wild beast: nixos/nixpkgs#86021

Everything in Nix has this potential to feel like a hack. Some hacks just have more limitations than others. Maybe normal double quotes are counter-intutively the easier ones to use internally.