Environment variable equivalent for --nix

[CMCDragonkai]

Just a feature suggestion.

I know there's the --nix flag and the nix setting on the stack.yaml. However I'd prefer there to be a sort of environment variable to utilise instead. Something like STACK_USE_NIX=1.

The reason is that I don't want to force nix onto non-nix users by setting it on the stack.yaml and using an alias doesn't get inherited by shell scripts: alias stack='\stack --nix'.

[chris-martin]

You can also put this into ~/.stack/config.yaml:

nix:
  enable: true

[CMCDragonkai]

That's what I'd like to avoid.

…

On 3 May 2018 14:05:44 GMT+10:00, Chris Martin ***@***.***> wrote: You can also put this into `~/.stack/config.yaml`: ```yaml nix: enable: true ``` -- You are receiving this because you authored the thread. Reply to this email directly or view it on GitHub: #3980 (comment)

-- Sent from my Android device with K-9 Mail. Please excuse my brevity.

[CMCDragonkai]

This is now available inside Nix 2.0. Stack just needs to check this variable:

nix-shell now sets the IN_NIX_SHELL environment variable during evaluation and in the shell itself. This can be used to perform different actions depending on whether you’re in a Nix shell or in a regular build. Nixpkgs provides lib.inNixShell to check this variable during evaluation.

[enolan]

That's set when you're inside nix-shell, not just any shell on NixOS. I think a reasonable default is to check whether the host OS is NixOS by checking whether /run/current-system/nixos-version exists. Overridden by config.yaml and the command line --nix/--no-nix.

Alternatively, it could check whether /nix exists, which would include people running MacOS and other Linux distros that have installed Nix as well. I think the default expectation of those people is Stack works the same whether you install Nix or not, so my preference would be to not do that.

[CMCDragonkai]

I thought this PR #3938 would bring in automatic nix integration without the explicit --nix flag. But I tried the recent 1.7.1 release, and it still required --nix to work. Or maybe that PR did not make it into 1.7.1? I'm not how to check.

Actually I checked the commit: a88aa5a

It indicates that the commit did make it into 1.7.1, so how come I still need --nix when using stack inside nix-shell. Here's my shell.nix:

{
  pkgs ? import (fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/be1461fc0ab29c45c69e7b2c2097c887750e4fe0.tar.gz) {}
}:
  with pkgs;
  haskell.lib.buildStackProject {
    name = "stack-test";
  }

Then run stack --version and try using stack ghci on a simple project. It will say:

> stack ghci
/nix/store/szdi35clpzj13c8dhfzh55fj6hk0z8j6-glibc-2.27-bin/bin/ldconfig: Can't open cache file /nix/store/83lrbvbmxrgv7iz49mgd42yvhi473xp6-glibc-2.27/etc/ld.so.cache
: No such file or directory
I don't know how to install GHC on your system configuration, please install manually

Then stack --nix ghci ends up working.

[snoyberg]

What are the contents of your /etc/os-release file?

[CMCDragonkai]

I'm not currently using stack anymore because Nix + Cabal is sufficient for now.

[snoyberg]

Understood closing