A faster, persistent implementation of direnv
's use_nix
, to replace the built-in one.
Prominent features:
- significantly faster after the first run by caching the
nix-shell
environment - prevents garbage collection of build dependencies by symlinking the resulting
shell derivation in the user's
gcroots
(Life is too short to lose your project's build cache if you are on a flight with no internet connection)
Since 20.03 you can install nix-direnv
via nix:
In /etc/nixos/configuration.nix
:
{ pkgs, ... }: {
environment.systemPackages = with pkgs; [ nix-direnv ];
# nix options for derivations to persist garbage collection
nix.extraOptions = ''
keep-outputs = true
keep-derivations = true
'';
environment.pathsToLink = [
"/share/nix-direnv"
];
}
Then source the direnvrc
from this repository in your own .direnvrc
# put this in ~/.direnvrc
source $HOME/.nix-direnv/direnvrc
if [ -f /run/current-system/sw/share/nix-direnv/direnvrc ]; then
source /run/current-system/sw/share/nix-direnv/direnvrc
fi
In $HOME/.config/nixpkgs/home.nix
add
{ pkgs, ... }:
{
# ...other config, other config...
programs.direnv.enable = true;
programs.direnv.enableNixDirenvIntegration = true;
}
Optional: To protect your nix-shell against garbage collection you also need to add these options to your Nix configuration.
If you are on NixOS also add the following lines to your /etc/nixos/configuration.nix
:
{ pkgs, ... }: {
nix.extraOptions = ''
keep-outputs = true
keep-derivations = true
'';
}
On other systems with Nix add the following configuration to your /etc/nix/nix.conf
:
keep-derivations = true
keep-outputs = true
As non-root user do the following:
nix-env -f '<nixpkgs>' -iA nix-direnv
Than follow the home-manager installation except for the $HOME/.config/nixpkgs/home.nix
changes.
Clone the repository to some directory
$ git clone https://github.com/nix-community/nix-direnv $HOME/nix-direnv
Then source the direnvrc from this repository in your own .direnvrc
# put this in ~/.direnvrc
source $HOME/nix-direnv/direnvrc
Either add shell.nix
or a default.nix
to the same directory:
# save this as shell.nix
{ pkgs ? with import <nixpkgs> {}}:
pkgs.mkShell {
nativeBuildInputs = [ pkgs.hello ];
}
Then add the line use nix
to your envrc:
$ echo "use nix" >> .envrc
$ direnv allow
nix-direnv also comes with a flake alternative. The code is tested and works however since future nix versions might change their api regarding this feature we cannot guarantee stability after an nix upgrade.
Save this file as flake.nix
:
{
description = "A very basic flake";
# Provides abstraction to boiler-code when specifying multi-platform outputs.
inputs.flake-utils.url = "github:numtide/flake-utils";
outputs = { self, nixpkgs, flake-utils }:
flake-utils.lib.eachDefaultSystem (system: let
pkgs = nixpkgs.legacyPackages.${system};
in {
devShell = pkgs.mkShell {
nativeBuildInputs = [ pkgs.hello ];
};
});
}
Then add use flake
to your .envrc
:
$ echo "use flake" >> .envrc
$ direnv allow
A .direnv
directory will be created in each use_nix
project, which might
interact badly with backups (e.g. Dropbox) or IDEs.
Therefore it's possible to override a variable called $direnv_layout_dir
in
$HOME/.config/direnv/direnvrc
or in each project's .envrc
.
The following example will create a unique directory name per project
in $HOME/.cache/direnv/layouts/
:
# $HOME/.config/direnv/direnvrc
: ${XDG_CACHE_HOME:=$HOME/.cache}
pwd_hash=$(echo -n $PWD | shasum | cut -d ' ' -f 1)
direnv_layout_dir=$XDG_CACHE_HOME/direnv/layouts/$pwd_hash
In some case nix-direnv does not detect if imported file has changed and still provides
the old cached values. An evaluation can be triggered by updating your .envrc
:
$ touch .envrc
At the moment nix-direnv
depends on GNU Grep and a modern Bash version.
This might lead to problems on macOS.
As a work-around we suggest that macOS users install direnv
/grep
via Nix or Homebrew.
- nix-direnv has flakes support.
- High CPU load/resource usage in some cases: When nixpkgs in
NIX_PATH
is pointed to a directory, i.e. a git checkout, Lorri will try to evaluate nixpkgs everytime something changes causing high cpu load. Nix-direnv compromises between performance and correctness, and only re-evaluates direnv if either the project-specificdefault.nix
/shell.nix
changes, or if there is a new commit added tonixpkgs
. A re-evaluation can be also triggered by usingtouch .envrc
in the same project. - No additional daemon or services required: The codesize is small enough that it can be vendored into a project itself.