Inputs

Inputs allow you to refer to Nix code outside of your project while preserving reproducibility.

Think of inputs as dependency management for your developer environment.

If you omit devenv.yaml, it defaults to:

devenv.yaml

inputs:
  nixpkgs:
    url: github:cachix/devenv-nixpkgs/rolling
  pre-commit-hooks:
    url: github:cachix/pre-commit-hooks.nix

The dependencies you mention as inputs are passed as an argument to the function.

For example, if you have a devenv.yaml file like:

devenv.yaml

inputs:
  nixpkgs-stable:
    url: github:NixOS/nixpkgs/nixos-23.11

You can access the stable packages via the inputs field:

devenv.nix

{ inputs, pkgs, ... }:

let
  pkgs-stable = import inputs.nixpkgs-stable { system = pkgs.stdenv.system; };
in {
  packages = [ pkgs-stable.git ];

  enterShell = ''
    git --version
  ''
}

See basics for more about devenv.nix.

There are a few special inputs passed into devenv.nix:

devenv.nix

{ pkgs, lib, config, ... }:

{
  env.GREET = "hello";

  enterShell = ''
    echo ${config.env.GREET}
  '';
}

• pkgs is a nixpkgs input containing all of the available packages for your system.
• lib is a collection of functions for working with Nix data structures. You can use noogle to search for a function.
• config is the final resolved configuration for your developer environment, which you can use to reference any other options set in devenv.nix. Since Nix supports lazy evaluation, you can reference any option you define in the same file as long as it doesn't reference itself!

Note

... is a catch-all pattern for any additional inputs, so you can safely omit the inputs you're not using.

See devenv.yaml reference for all supported inputs.

Locking and updating inputs

When you run any of the commands, devenv resolves inputs like github:NixOS/nixpkgs/nixpkgs-unstable into a commit revision and writes them to devenv.lock. This ensures that your environment is reproducible.

To update an input to a newer commit, run devenv update or read the devenv.yaml reference to learn how to pin down the revision/branch at the input level.