Use flake --impure example is wrong

[scvalex]

The README says to use echo "use flake . --impure" > .envrc.

Experimentally, that doesn't work, but removing the dot does. So, having use flake --impure in my .envrc works. "Works" here means I was able to start a devShell with nixGL in it. I don't understand how nix-direnv works exactly, so I don't know if the README was always wrong, if if became wrong with some nix version, or if I'm mistaken about what I'm seeing.

nix --version
nix (Nix) 2.5.0pre20211206_d1aaa7e

[bbenne10]

What doesn't work for you? Can you share the flake you're trying to get working?

I can attest to it working locally. We have a flake that simply aborts execution if it is missing a particular environment variable (so --impure is necessary) and this flake works just fine.

[scvalex]

Here's a demo: https://gitlab.com/scvalex/direnv-flake-impure-demo

The .envrc is currently use flake. If you direnv allow that, it will fail with this error:

error: attribute 'currentTime' missing

       at /nix/store/b379mn551mj4cx3dsf94vrxj4j12yx3a-source/nixGL.nix:202:18:

          201|           # Add an impure parameter to force the rebuild on each access.
          202|           time = builtins.currentTime;
             |                  ^
          203|           preferLocalBuild = true;
(use '--show-trace' to show detailed location information)

If you change the .envrc to use flake --impure, then it works and nixGL is available to run.

If you change the .envrc to use flake . --impure it fails with the error again.

[scvalex]

What I was trying to get working was nixGL in a flake. Basically this: nix-community/nixGL#90

[bbenne10]

Thank you for a test case! I'll have to test this on a different machine than is my default macOS testbed, but I will get back to you on this this evening.

[scvalex]

It turns out I don't actually need nixGL for what I'm doing, so I'm not in any rush. I'm just reporting the thing that confused me.

[bbenne10]

So I tested this out this morning (making promises to open source projects when I have a 2.5 year old at home is always a mistake...), and it all seems working with a fresh checkout of nix-direnv and a checkout of the demo repo you sent across.

My process:

1. Clone nix-direnv locally (or fast-forward to master)
2. Clone your test repository as a direct subdirectory of that nix-direnv clone
3. modify the nix-direnv clone to echo when it is being sourced as follows:

  # shellcheck shell=bash

+ echo "sourcing correct nix-direnv"
  REQUIRED_DIRENV_VERSION="2.21.3"

4. Modify the .envrc in the direnv-flake-impure-demo repository to contain only the following

source ../direnvrc
use flake . --impure

5. Run direnv allow and watch. Notably, this does not throw the error about builtins.currentTime for me, whereas a vanilla use flake does.

Unfortunately, I don't have the time to debug old versions of this tool to see how it might be broken in older revisions.
I am running a newer version of nix than you (2.6pre), but I don't suspect that will change much.

If you're interested, I might suggest the inclusion of a set -x in your .envrc so that you can find out exactly what the nix invocation looks like. You may find that you are running an older version of nix-direnv than you believe, or that there's some other issue with your nix version? I'm not sure what else to do, as I cannot replicate.

[scvalex]

Thanks for looking into it.

I updated to NixOS-22.05 with Nix 2.8.1, and I can no longer reproduce this. I guess it must've been something with the old nix version, or something with my 21.11 install.

Closing.