A faster, persistent implementation of direnv
's use_nix
and use_flake
, to replace the built-in one.
Prominent features:
nix-shell
environmentgcroots
(Life is too short to lose your project's build cache if you are on a flight with no internet connection)lorri
instead?
Compared to lorri, nix-direnv is simpler (and requires no external daemon). Additionally, lorri can sometimes re-evaluate the entirety of nixpkgs on every change (leading to perpetual high CPU load).
Requirements:
Warning
We assume that direnv is installed properly because nix-direnv IS NOT a replacement for regular direnv (only some of its functionality).
Note
nix-direnv requires a modern Bash. MacOS ships with bash 3.2 from 2007. As a work-around we suggest that macOS users install direnv
via Nix or Homebrew. There are different ways to install nix-direnv, pick your favourite:
Note that while the home-manager integration is recommended, some use cases require the use of features only present in some versions of nix-direnv. It is much harder to control the version of nix-direnv installed with this method. If you require such specific control, please use another method of installing nix-direnv.
In $HOME/.config/home-manager/home.nix
add
{ # ...other config, other config... programs = { direnv = { enable = true; enableBashIntegration = true; # see note on other shells below nix-direnv.enable = true; }; bash.enable = true; # see note on other shells below }; }
Check the current Home Manager Options for integration with shells other than Bash. Be sure to also allow home-manager
to manage your shell with programs.<your_shell>.enable = true
.
Put the following lines in your .envrc
:
if ! has nix_direnv_version || ! nix_direnv_version 3.1.0; then source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.1.0/direnvrc" "sha256-yMJ2OVMzrFaDPn7q8nCBZFRYpL/f0RcHzhmw/i6btJM=" fiVia system configuration on NixOS Via system configuration on NixOS
For NixOS 23.05+ all that's required is
{ programs.direnv.enable = true; }
other available options are:
{ pkgs, ... }: { #set to default values programs.direnv = { package = pkgs.direnv; silent = false; loadInNixShell = true; direnvrcExtra = ""; nix-direnv = { enable = true; package = pkgs.nix-direnv; }; }With `nix profile`
As non-root user do the following:
nix profile install nixpkgs#nix-direnv
Then add nix-direnv to $HOME/.config/direnv/direnvrc
:
source $HOME/.nix-profile/share/nix-direnv/direnvrcFrom source
Clone the repository to some directory and then source the direnvrc from this repository in your own ~/.config/direnv/direnvrc
:
# put this in ~/.config/direnv/direnvrc source $HOME/nix-direnv/direnvrc
Either add shell.nix
or a default.nix
to the project directory:
# save this as shell.nix { pkgs ? import <nixpkgs> {}}: pkgs.mkShell { packages = [ pkgs.hello ]; }
Then add the line use nix
to your envrc:
echo "use nix" >> .envrc direnv allow
If you haven't used direnv before, make sure to hook it into your shell first.
Using a non-standard file nameYou may use a different file name than shell.nix
or default.nix
by passing the file name in .envrc
, e.g.:
echo "use nix foo.nix" >> .envrc
nix-direnv also comes with an alternative use_flake
implementation. The code is tested and does work but the upstream flake api is not finalized, so we cannot guarantee stability after a nix upgrade.
Like use_nix
, our use_flake
will prevent garbage collection of downloaded packages, including flake inputs.
This repository ships with a flake template. which provides a basic flake with devShell integration and a basic .envrc
.
To make use of this template, you may issue the following command:
nix flake new -t github:nix-community/nix-direnv <desired output path>Integrating with a existing flake
echo "use flake" >> .envrc && direnv allow
The use flake
line also takes an additional arbitrary flake parameter, so you can point at external flakes as follows:
use flake ~/myflakes#project
Under the covers, use_flake
calls nix print-dev-env
. The first argument to the use_flake
function is the flake expression to use, and all other arguments are proxied along to the call to print-dev-env
. You may make use of this fact for some more arcane invocations.
For instance, if you have a flake that needs to be called impurely under some conditions, you may wish to pass --impure
to the print-dev-env
invocation so that the environment of the calling shell is passed in.
You can do that as follows:
echo "use flake . --impure" > .envrc direnv allow
Like use flake
, use nix
now uses nix print-dev-env
. Due to historical reasons, the argument parsing emulates nix shell
.
This leads to some limitations in what we can reasonably parse.
Currently, all single-word arguments and some well-known double arguments will be interpreted or passed along.
Manual reload of the nix environmentTo avoid delays and time consuming rebuilds at unexpected times, you can use nix-direnv in the "manual reload" mode. nix-direnv will then tell you when the nix environment is no longer up to date. You can then decide yourself when you want to reload the nix environment.
To activate manual mode, use nix_direnv_manual_reload
in your .envrc
like this:
nix_direnv_manual_reload use nix # or use flake
To reload your nix environment, use the nix-direnv-reload
command:
-p
: Starts a list of packages to install; consumes all remaining arguments--include
/ -I
: Add the following path to the list of lookup locations for <...>
file names--attr
/ -A
: Specify the output attribute to utilize--command
, --run
, --exclude
, --pure
, -i
, and --keep
are explicitly ignored.
All single word arguments (-j4
, --impure
etc) are passed to the underlying nix invocation.
As a convenience, nix-direnv
adds common files to direnv's watched file list automatically.
The list of additionally tracked files is as follows:
for use nix
:
~/.direnvrc
~/.config/direnv/direnvrc
.envrc
,use nix
default.nix
if it existsshell.nix
if it existsfor use flake
:
~/.direnvrc
~/.config/direnv/direnvrc
.envrc
flake.nix
flake.lock
devshell.toml
if it existsUsers are free to use direnv's builtin watch_file
function to track additional files. watch_file
must be invoked before either use flake
or use nix
to take effect.
nix-direnv sets the following environment variables for user consumption. All other environment variables are either a product of the underlying nix invocation or are purely incidental and should not be relied upon.
NIX_DIRENV_DID_FALLBACK
: Set when the current revision of your nix shell or flake's devShell are invalid and nix-direnv has loaded the last known working shell.nix-direnv also respects the following environment variables for configuration.
NIX_DIRENV_FALLBACK_NIX
: Can be set to a fallback Nix binary location, to be used when a compatible one isn't available in PATH
. Defaults to config.nix.package
if installed via the NixOS module, otherwise needs to be set manually. Leave unset or empty to fail immediately when a Nix implementation can't be found on PATH
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