R: install packages from DESCRIPTION file

[pchabros]

PR works but I need some help:

1. I've created r/ subdirectory to split code into separate files, but it broke generated docs - can I fix it somehow or I should not create subdirectory?
2. I wanted descriptionFile.path to be relative path (./DESCRIPTION) or just a string ("./DESCRIPTION") but after concatenating it with config.devenv.root I got error: access to absolute path '/home' is forbidden in pure evaluation mode - how can I move absolute path to nix-store? Or somehow evaluate relative path in context of devenv.nix instead of modules/languages/r.nix?
3. I've created utils/strings.nix with some generic functions. Should I put it somewhere else?

[b-rodrigues]

Sorry, I’m very new to devenv, but am involved quite a bit with the R ecosystem in Nix. Could you explain what this would achieve? My understanding was that devenv provides the right build dependencies to build any R package, so wouldn’t trying to install an R packages using devenv result in its dependencies also be pulled from CRAN, as they’re listed in "depends"?

[pchabros]

No, it doesn't pull anything from CRAN. It just automatically adds all packages listed in DESCRIPTION file to packages. So, let's assume that you have the following DESCRIPTION file, than instead of copying and pasting dependencies to devenv.nix:

{
  languages.r.enable = true;
  packages = with pkgs.rPackages; [
    readr
    stringr
    data_table
    yaml
    testthat
  ];
}

you can just enable this option:

{
  languages.r = {
    enable = true;
    descriptionFile = {
      path = "${./DESCRIPTION}";
      installPackages.enable = true;
    };
  };
}