Using editablePackageSources with flakes

[yrd]

When using poetry2nix in a flake-based project, editablePackageSources doesn't seem to work as documented:

pkgs.poetry2nix.mkPoetryEnv {
  projectDir = ./.;
  python = pkgs.python39;
  editablePackageSources = {
    myProject = ./.;
  };
}

In this case, the ./. always references the flake's source that was copied into the store (something like /nix/store/p68s64y2g86wb02rj0am4q4wp4cj8mgs-source). I found a workaround by doing something like this:

editablePackageSources = {
  myProject = builtins.getEnv "PWD";
}

This seems to work when running with --impure, but is there a better way to do this without relying on the environment variable?

[hhoeflin]

I guess fundamentally an editable package will never work with a pure flake, as the whole concept of pureness means it is not editable.

Your pointer helped me. One note, the "PWD" only works when the shell is invoked from the root of the project, so this is a bit of a tripwire. The alternative is to hardcode the path in your home folder into the flake ... also not nice but works as well, so for example

myproject = "${builtins.getEnv "HOME"}/projects/myproject";

[adisbladis]

This isn't actually an issue in poetry2nix, so I'm gonna close this.

[hhoeflin]

I agree that this may not be something that can be fixed in poetry2nix but as flakes are supposedly the new standard, some documentation on the README pointing out this issue would be helpful.

[adisbladis]

Flakes are not the new standard, they are an experimental feature.

With that in mind any sharp edges are up to the user of that experimental feature to deal with.

[hhoeflin]

sorry, sure - it is an experimental feature. I am new to this, so I try to use it almost exclusively. As the flakes are mentioned on the README, I thought it would be good to at least point to some pitfalls. I certainly spent quite a bit of time with this issue as things didn't work as I hoped.

[hhoeflin]

Wanted to add my current workaround as a solution.

pkgs.poetry2nix.mkPoetryEnv {
  projectDir = ./.;
  python = pkgs.python39;
  editablePackageSources = {
    myProject = if builtins.getEnv "PROJECT_DIR" == "" then ./. else builtins.getEnv "PROJECT_DIR";
  };
}

This way, if the flake is pure, the flake directory is used and copied to the store (being reproducible as flakes intended). If --impure, then it uses the variable PROJECT_DIR if present. nix doesn't pass information as to where on the file system the flake is (and it may be on github etc anyway). But we can work around it, as bash gives this information when invoked. So write a short bash-script named e.g. activate_env.sh:

#! /usr/bin/env bash
export PROJECT_DIR=$(dirname "$(realpath -s "${BASH_SOURCE[0]}")")
nix shell --impure $PROJECT_DIR

When sourced, it will drop you into the shell environment with editable sources. The bash script assumes your project dir is your flake directory as well and the package is set as the default.

[yrd]

@hhoeflin Thanks! I think that's a nice solution which causes less friction than only PWD while still using flakes (which, yeah, aren't pure anymore but I guess an in-development environment will never be so I think that's okay).

[nixos-discourse]

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

https://discourse.nixos.org/t/editable-python-environment-with-poetry2nix/44520/2